0001708055-21-000014 | 10-K | XBRL Viewer | Ribbon Communications INC

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Cover - USD ($) $ in Thousands	12 Months Ended
Cover - USD ($) $ in Thousands	Dec. 31, 2020	Feb. 22, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-38267
Entity Registrant Name	RIBBON COMMUNICATIONS INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	82-1669692
Entity Address, Address Line One	6500 Chase Oaks Boulevard, Suite 100
Entity Address, City or Town	Plano
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	75023
City Area Code	978
Local Phone Number	614-8100
Title of 12(b) Security	Common Stock, par value $0.0001
Trading Symbol	RBBN
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 266,209
Entity Common Stock, Shares Outstanding		145,556,939
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the definitive Proxy Statement to be delivered to stockholders in connection with the Registrant's 2021 Annual Meeting of Stockholders are incorporated by reference into Part III of this report.
Entity Central Index Key	0001708055
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 128,428	$ 44,643
Restricted cash	7,269	0
Accounts receivable, net	237,738	192,706
Inventory	45,750	14,800
Other current assets	28,461	27,146
Total current assets	447,646	279,295
Property and equipment, net	48,888	28,976
Intangible assets, net	417,356	213,366
Goodwill	416,892	224,896
Investments	115,183	0
Deferred income taxes	10,651	4,959
Operating lease right-of-use assets	69,757	36,654
Other assets	20,892	26,762
Total assets	1,547,265	814,908
Current liabilities:
Current portion of term debt	15,531	2,500
Revolving credit facility	0	8,000
Accounts payable	63,387	31,412
Accrued expenses and other	134,865	56,700
Operating lease liabilities	17,023	7,719
Deferred revenue	96,824	100,406
Total current liabilities	327,630	206,737
Long-term debt, net of current	369,035	45,995
Operating lease liabilities, net of current	72,614	37,202
Deferred revenue, net of current	26,010	20,482
Deferred income taxes	16,842	4,648
Other long-term liabilities	48,281	16,589
Total liabilities	860,412	331,653
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.01 par value; 10,000,000 shares authorized; none issued and outstanding	0	0
Common stock, 240,000,000 shares authorized, $0.0001 par value, 145,425,248 shares issued and outstanding at December 31, 2020; 110,471,995 shares issued and outstanding at December 31, 2019	15	11
Additional paid-in capital	1,870,256	1,747,784
Accumulated deficit	(1,178,476)	(1,267,067)
Accumulated other comprehensive (loss) income	(4,942)	2,527
Total stockholders' equity	686,853	483,255
Total liabilities and stockholders' equity	$ 1,547,265	$ 814,908

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	240,000,000	240,000,000
Common stock, shares issued (in shares)	145,425,248	110,471,995
Common stock, shares outstanding (in shares)	145,425,248	110,471,995

Consolidated Statements of Operations - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue:
Total revenue	$ 843,795,000	$ 563,111,000	$ 577,905,000
Cost of revenue:
Total cost of revenue	350,688,000	208,454,000	230,597,000
Gross profit	493,107,000	354,657,000	347,308,000
Operating expenses:
Research and development	194,525,000	141,060,000	145,462,000
Sales and marketing	139,318,000	106,310,000	117,529,000
General and administrative	63,286,000	53,870,000	66,036,000
Amortization of acquired intangible assets	60,910,000	49,225,000	49,723,000
Impairment of goodwill	0	164,300,000	0
Acquisition-, disposal- and integration-related	17,164,000	12,953,000	16,951,000
Restructuring and related	16,235,000	16,399,000	17,015,000
Total operating expenses	491,438,000	544,117,000	412,716,000
Income (loss) from operations	1,669,000	(189,460,000)	(65,408,000)
Interest expense, net	(21,042,000)	(3,877,000)	(4,230,000)
Other income (expense), net	112,690,000	70,444,000	(3,772,000)
Income (loss) before income taxes	93,317,000	(122,893,000)	(73,410,000)
Income tax provision	(4,726,000)	(7,182,000)	(3,400,000)
Net income (loss)	$ 88,591,000	$ (130,075,000)	$ (76,810,000)
Earnings (loss) per share:
Basic (in dollars per share)	$ 0.64	$ (1.19)	$ (0.74)
Diluted (in dollars per share)	$ 0.61	$ (1.19)	$ (0.74)
Shares used to compute earnings (loss) per share:
Basic (in shares)	138,967	109,734	103,916
Diluted (in shares)	144,650	109,734	103,916
Product revenue
Revenue:
Total revenue	$ 467,912,000	$ 262,030,000	$ 279,014,000
Cost of revenue:
Total cost of revenue	204,772,000	95,774,000	103,209,000
Service
Revenue:
Total revenue	375,883,000	301,081,000	298,891,000
Cost of revenue:
Total cost of revenue	$ 145,916,000	$ 112,680,000	$ 127,388,000

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 88,591	$ (130,075)	$ (76,810)
Other comprehensive income (loss), net of tax:
Unrealized loss on interest rate swap, net of reclassifications	(10,948)	0	0
Foreign currency translation adjustments	894	194	220
Unrealized gain on available-for-sale marketable securities, net of reclassification adjustments for realized amounts	0	590	45
Employee retirement benefits	2,585	(1,960)	369
Other comprehensive (loss) income, net of tax	(7,469)	(1,176)	634
Comprehensive income (loss), net of tax	$ 81,122	$ (131,251)	$ (76,176)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated deficit	Accumulated other comprehensive income (loss)	Edgewater Networks, Inc.	Edgewater Networks, Inc. Common stock	Edgewater Networks, Inc. Additional paid-in capital	Anova Data, Inc.	Anova Data, Inc. Common stock	Anova Data, Inc. Additional paid-in capital	Cumulative Effect, Period of Adoption, Adjustment	Cumulative Effect, Period of Adoption, Adjustment Accumulated deficit
Balance (in shares) at Dec. 31, 2017		101,752,856
Balance at Dec. 31, 2017	$ 615,421	$ 10	$ 1,684,768	$ (1,072,426)	$ 3,069							$ 12,244	$ 12,244
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)		15,935
Exercise of stock options	73		73
Vesting of restricted stock awards and units (in shares)		1,278,062
Vesting of performance-based stock awards and units (in shares)		57,768
Shares of restricted stock returned to the Company under net share settlements to satisfy tax withholding obligations (in shares)		(524,516)
Shares of restricted stock returned to the Company under net share settlements to satisfy tax withholding obligations	(2,024)		(2,024)
Shares issued as consideration in connection with acquisition (in shares)							4,235,531
Shares issued as consideration in connection with acquisition						$ 30,000	$ 1	$ 29,999
Assumption of equity awards in connection with acquisition of Edgewater Networks, Inc.	747		747
Stock-based compensation expense	10,013		10,013
Other comprehensive income (loss)	634				634
Net loss	(76,810)			(76,810)
Balance (in shares) at Dec. 31, 2018		106,815,636
Balance at Dec. 31, 2018	590,298	$ 11	1,723,576	(1,136,992)	3,703
Increase (Decrease) in Stockholders' Equity
Issuance of common stock in connection with employee stock purchase plan (in shares)		282,646
Issuance of common stock in connection with employee stock purchase plan	863		863
Exercise of stock options (in shares)		127,334
Exercise of stock options	235		235
Vesting of restricted stock awards and units (in shares)		1,504,707
Vesting of performance-based stock awards and units (in shares)		9,466
Shares of restricted stock returned to the Company under net share settlements to satisfy tax withholding obligations (in shares)		(240,673)
Shares of restricted stock returned to the Company under net share settlements to satisfy tax withholding obligations	(1,193)		(1,193)
Shares issued as consideration in connection with acquisition (in shares)										2,948,793
Shares issued as consideration in connection with acquisition									$ 15,186		$ 15,186
Repurchase and retirement of common stock (in shares)		(975,914)
Repurchase and retirement of common stock	(4,536)		(4,536)
Reclassification of liability to equity for bonuses converted to stock awards	1,052		1,052
Stock-based compensation expense	12,601		12,601
Other comprehensive income (loss)	(1,176)				(1,176)
Net loss	$ (130,075)			(130,075)
Balance (in shares) at Dec. 31, 2019	110,471,995	110,471,995
Balance at Dec. 31, 2019	$ 483,255	$ 11	1,747,784	(1,267,067)	2,527
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)		38,288
Exercise of stock options	70		70
Vesting of restricted stock awards and units (in shares)		2,246,690
Vesting of restricted stock awards and units	1	$ 1
Vesting of performance-based stock awards and units (in shares)		323,752
Shares of restricted stock returned to the Company under net share settlements to satisfy tax withholding obligations (in shares)		(472,028)
Shares of restricted stock returned to the Company under net share settlements to satisfy tax withholding obligations	(1,674)		(1,674)
Shares issued as consideration in connection with acquisition (in shares)		32,500,000								316,551
Shares issued as consideration in connection with acquisition	108,550	$ 3	108,547						$ 1,630		$ 1,630
Stock-based compensation expense	13,899		13,899
Other comprehensive income (loss)	(7,469)				(7,469)
Net loss	$ 88,591			88,591
Balance (in shares) at Dec. 31, 2020	145,425,248	145,425,248
Balance at Dec. 31, 2020	$ 686,853	$ 15	$ 1,870,256	$ (1,178,476)	$ (4,942)

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income (loss)	$ 88,591	$ (130,075)	$ (76,810)
Adjustments to reconcile net income (loss) to cash flows provided by (used in) operating activities:
Depreciation and amortization of property and equipment	17,188	11,949	11,200
Amortization of intangible assets	60,910	49,225	49,723
Amortization of debt issuance costs	5,673	360	204
Stock-based compensation	13,899	12,601	11,072
Impairment of goodwill	0	164,300	0
Deferred income taxes	(4,616)	5,299	513
Gain on sale of business	(83,552)	0	0
Increase in fair value of investments	(30,296)	0	0
Reduction to deferred purchase consideration	(70)	(8,124)	0
Foreign currency exchange losses	2,961	1,090	4,611
Changes in operating assets and liabilities:
Accounts receivable	9,578	(3,936)	(13,017)
Inventory	11,842	7,776	993
Other operating assets	44,343	(17,849)	4,832
Accounts payable	(49,561)	(16,282)	(6,057)
Accrued expenses and other long-term liabilities	20,629	(18,538)	(13,422)
Deferred revenue	(5,955)	(2,111)	16,563
Net cash provided by (used in) operating activities	101,564	55,685	(9,595)
Cash flows from investing activities:
Purchases of property and equipment	(26,721)	(10,824)	(7,907)
Business acquisitions, net of cash acquired	(346,852)	0	(46,389)
Sales/maturities of marketable securities	0	7,295	18,919
Proceeds from the sale of fixed assets	43,500	0	0
Net cash used in investing activities	(330,073)	(3,529)	(35,377)
Cash flows from financing activities:
Borrowings under revolving line of credit	615	117,000	197,500
Principal payments on revolving line of credit	(8,615)	(164,000)	(162,500)
Proceeds from issuance of long-term debt	478,500	50,000	0
Principal payment of debt, related party	0	(24,716)	0
Principal payments of term debt	(134,188)	(1,250)	0
Payment of deferred purchase consideration	0	(21,876)	0
Principal payments of finance leases	(1,258)	(913)	(652)
Payment of debt issuance costs	(14,147)	(891)	(624)
Proceeds from the sale of common stock in connection with employee stock purchase plan	0	863	0
Proceeds from the exercise of stock options	70	235	73
Payment of tax withholding obligations related to net share settlements of restricted stock awards	(1,674)	(1,193)	(2,024)
Repurchase of common stock	0	(4,536)	0
Net cash provided by (used in) financing activities	319,303	(51,277)	31,773
Effect of exchange rate changes on cash and cash equivalents	260	70	(180)
Net increase (decrease) in cash and cash equivalents	91,054	949	(13,379)
Cash and cash equivalents, beginning of year	44,643	43,694	57,073
Cash, cash equivalents and restricted cash, end of year	135,697	44,643	43,694
Supplemental disclosure of cash flow information:
Interest paid	15,546	4,072	2,367
Income taxes paid	9,293	4,665	5,505
Income tax refunds received	1,163	1,757	537
Supplemental disclosure of non-cash investing activities:
Capital expenditures incurred, but not yet paid	3,749	2,566	1,127
Property and equipment acquired under finance leases	0	1,442	2,178
Business acquisition purchase consideration - common stock issued	108,550	15,186	30,000
Business acquisition purchase consideration - deferred payments	1,630	1,700	30,000
Business acquisition purchase consideration - assumed equity awards	0	0	747
Supplemental disclosure of non-cash financing activities:
Total fair value of restricted stock awards, restricted stock units, performance-based stock awards and performance-based stock units on date vested	$ 7,927	$ 7,422	$ 8,312

NATURE OF THE BUSINESS	12 Months Ended
NATURE OF THE BUSINESS	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
NATURE OF THE BUSINESS	NATURE OF THE BUSINESSRibbon Communications Inc. ("Ribbon" or the "Company") is a leading global provider of communications technology to service providers and enterprises. The Company provides a broad range of software and high-performance hardware products, solutions and services that enable the secure delivery of data and voice communications for residential consumers and for small, medium, and large enterprises and industry verticals such as finance, education, government, utilities, and transportation. Ribbon's mission is to create a recognized global technology leader providing cloud-centric solutions that enable the secure exchange of information, with unparalleled scale, performance, and elasticity. The Company is headquartered in Plano, Texas, and has a global presence with research and development, or sales and support locations in over thirty-five countries around the world.

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Basis of Presentation

The consolidated financial statements have been prepared in United States dollars, in accordance with accounting principles generally accepted in the United States ("GAAP").

On December 1, 2020 (the "Kandy Sale Date"), American Virtual Cloud Technologies, Inc. ("AVCT") completed the purchase of the Company's cloud-based enterprise service business (the "Kandy Communications Business"). The revenue and expenses of the Kandy Communications Business are not included in the Company's consolidated financial statements for the period subsequent to the Kandy Sale Date.

On March 3, 2020 (the "ECI Acquisition Date"), the Company merged with ECI Telecom Group Ltd ("ECI") (the "ECI Acquisition"). The financial results of ECI are included in the Company's consolidated financial statements for the period subsequent to the ECI Acquisition Date.

On February 28, 2019 (the "Anova Acquisition Date"), the Company acquired the business and technology assets of Anova Data, Inc. ("Anova"). The financial results of Anova are included in the Company's consolidated financial statements for the period subsequent to the Anova Acquisition Date.

On August 3, 2018 (the "Edgewater Acquisition Date"), the Company completed the acquisition of Edgewater Networks, Inc. ("Edgewater" and such acquisition, the "Edgewater Acquisition"). The financial results of Edgewater are included in the Company's consolidated financial statements for the period subsequent to the Edgewater Acquisition Date.

Significant Accounting Policies

Principles of Consolidation

The accompanying consolidated financial statements include the accounts of Ribbon and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation.

Use of Estimates and Judgments

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and judgments relied upon in preparing these consolidated financial statements include accounting for business combinations, revenue recognition for multiple element arrangements, inventory valuations, assumptions used to determine the fair value of stock-based compensation, intangible assets, goodwill, debentures and warrants, legal contingencies and recoverability of Ribbon's net deferred tax assets and the related valuation allowances. Ribbon regularly assesses these estimates and records changes in estimates in the period in which they become known. Ribbon bases its estimates on historical experience and various other assumptions that it believes to be reasonable under the circumstances. Actual results could differ from those

estimates.

Reclassifications

In the fourth quarter of 2020, the Company reclassified amounts recorded for amortization of acquired intangible assets in prior presentations from Cost of revenue - product and Sales and marketing to a separate line included in operating expenses in the consolidated statements of operations, as management believes this presentation enhances the comparability of the Company's financial statements with industry peers. These reclassifications did not impact operating loss, net loss or loss per share for any historical periods. These reclassifications also did not impact the consolidated balance sheets or statements of cash flows for any historical periods. The Company did not reclassify depreciation of property and equipment related to production activities from cost of revenue to other accounts.

These reclassifications for the years ended December 31, 2019 and 2018 were as follows (in thousands):


	Year ended December 31, 2019						Year ended December 31, 2018
	Prior presentation		Amounts reclassified		Revised presentation		Prior presentation		Amounts reclassified		Revised presentation
Product revenue	$	262,030	$	—	$	262,030	$	279,014	$	—	$	279,014
Service revenue	301,081		—		301,081		298,891		—		298,891
Total revenue	563,111		—		563,111		577,905		—		577,905
Cost of revenue - product	133,347		(37,573)		95,774		142,185		(38,976)		103,209
Cost of revenue - service	112,680		—		112,680		127,388		—		127,388
Total cost of revenue	246,027		(37,573)		208,454		269,573		(38,976)		230,597
Total gross profit	317,084		37,573		354,657		308,332		38,976		347,308
Research and development	141,060		—		141,060		145,462		—		145,462
Sales and marketing	117,962		(11,652)		106,310		128,276		(10,747)		117,529
General and administrative	53,870		—		53,870		66,036		—		66,036
Amortization of acquired intangible assets	—		49,225		49,225		—		49,723		49,723
Impairment of goodwill	164,300		—		164,300		—		—		—
Acquisition-, disposal- and integration-related	12,953		—		12,953		16,951		—		16,951
Restructuring and related	16,399		—		16,399		17,015		—		17,015
Total operating expenses	506,544		37,573		544,117		373,740		38,976		412,716
Operating loss	$	(189,460)	$	—	$	(189,460)	$	(65,408)	$	—	$	(65,408)

In addition, certain other reclassifications, not affecting previously reported net loss, have been made to the previously issued financial statements to conform to the current year presentation.

Business Combinations

The Company recognizes identifiable assets acquired and liabilities assumed at their acquisition date fair values. Goodwill as of the acquisition date is measured as the excess of consideration transferred over the net of the acquisition date fair values of the assets acquired and the liabilities assumed and represents the expected future economic benefits arising from other assets acquired in the business combination that are not individually identified and separately recognized. While the Company uses its best estimates and assumptions as part of the purchase price allocation process to accurately value assets acquired and liabilities assumed at the acquisition date, its estimates are inherently uncertain and subject to refinement. As a result, during the measurement period, which may be up to one year from the acquisition date, the Company records adjustments to the assets acquired and liabilities assumed with the corresponding offset to goodwill to the extent that it identifies adjustments to the preliminary purchase price allocation. Upon the conclusion of the measurement period or final determination of the values of assets acquired and liabilities assumed, whichever comes first, any subsequent adjustments are recorded to the consolidated statements of operations.

Revenue Recognition

The Company derives revenue from two primary sources: products and services. Product revenue includes the Company's hardware and software that function together to deliver the products' essential functionality. Software and hardware are also sold on a standalone basis. Services include customer support (software updates, upgrades and technical support), consulting, design services, installation services and training. Generally, contracts with customers contain multiple performance obligations, consisting of products and services. For these contracts, the Company accounts for individual performance obligations separately if they are considered distinct.

When an arrangement contains more than one performance obligation, the Company will allocate the transaction price to each performance obligation on a relative standalone selling price basis. The Company utilizes the observable price of goods and services when they are sold separately to similar customers in order to estimate standalone selling price.

The Company's software licenses typically provide a perpetual right to use the Company's software. The Company also sells term-based software licenses that expire and Software-as-a-Service ("SaaS")-based software which are referred to as subscription arrangements. The Company does not customize its software nor are installation services required, as the customer has a right to utilize internal resources or a third-party service company. The software and hardware are delivered before related services are provided and are functional without professional services or customer support. The Company has concluded that its software licenses are functional intellectual property that are distinct, as the user can benefit from the software on its own. Product revenue is typically recognized upon transfer of control or when the software is made available for download, as this is the point the user of the software can direct the use of, and obtain substantially all of the remaining benefits from, the functional intellectual property. The Company begins to recognize software revenue related to the renewal of subscription software licenses at the start of the subscription period.

The Company offers warranties on its products. Certain of the Company's warranties are considered to be assurance-type in nature, ensuring the product is functioning as intended. Assurance-type warranties do not represent separate performance obligations. The Company also sells separately-priced maintenance service contracts which qualify as service-type warranties and represent separate performance obligations. The Company does not allow and has no history of accepting product returns.

Services revenue includes revenue from customer support and other professional services. Customer support includes software updates on a when-and-if-available basis, telephone support, integrated web-based support and bug fixes or patches. The Company sells its customer support contracts at a percentage of list or net product price. Customer support revenue is recognized ratably over the term of the customer support agreement, which is typically one year.

The Company's professional services include consulting, technical support, resident engineer services, design services and installation services. Because control transfers over time, revenue is recognized based on progress toward completion of the performance obligation. The method to measure progress toward completion requires judgment and is based on the nature of the products or services to be provided. The Company generally uses the input method to measure progress for its contracts because it believes such method best depicts the transfer of assets to the customer, which occurs as the Company incurs costs for the contracts. However, in some instances, the Company uses the output method because it best depicts the transfer of asset to the customer. Under the cost-to-cost measure of progress, the progress toward completion is measured based on the ratio of costs incurred to date to the total estimated costs at completion of the performance obligation. When the measure of progress is based upon expended labor, progress toward completion is measured as the ratio of labor time expended to date versus the total estimated labor time required to complete the performance obligation. Revenue is recorded proportionally as costs are incurred or as labor is expended. Costs to fulfill these obligations include internal labor as well as subcontractor costs.

Customer training includes courses offered by the Company. The related revenue is typically recognized as the training services are performed.

Operating Segments

The Company's chief operating decision maker (the "CODM") is its president and chief executive officer. Effective in the fourth quarter of 2020 and in connection with the ECI Acquisition, the CODM began to assess the Company's performance based on the performance of two separate organizations within Ribbon: the Cloud and Edge segment ("Cloud and Edge") and the IP Optical Networks segment ("IP Optical Networks"). Financial information for the IP Optical Networks segment is not

presented for any years prior to 2020, as this segment arose from the ECI Acquisition, and accordingly is not included in the Company's consolidated financial statements for the years ended December 31, 2019 and 2018.

Financial Instruments

The carrying amounts of Ribbon's financial instruments approximate their fair values and include accounts receivable, convertible debentures and warrants received as sale consideration, borrowings under a revolving credit facility, accounts payable and term debt.

Investments in marketable securities are reported at fair value, with unrealized gains and losses excluded from earnings and reported, net of tax, in Accumulated other comprehensive income (loss), which is a component of stockholders' equity. Unrealized losses that are determined to be other-than-temporary, based on current and expected market conditions, are recognized in earnings. Declines in fair value determined to be credit-related are charged to earnings. The cost of marketable securities sold is determined by the specific identification method.

Changes in fair value of investments classified as trading securities, such as the convertible debentures and warrants received as sale consideration, are recognized in earnings as components of Other income (expense), net.

Financial instruments with remaining maturities or that are due within one year from the balance sheet date are classified as current. Financial instruments with maturities or that are payable more than one year from the balance sheet date are classified as noncurrent.

Restricted Cash

The Company classifies as restricted cash all cash pledged as collateral to secure long-term obligations and all cash whose use is otherwise limited by contractual provisions. At December 31, 2020, the Company had $7.3 million of restricted cash, comprised of $4.6 million restricted in connection with a tax payment on certain fixed assets formerly held by ECI that were sold in connection with the ECI Acquisition, and $2.7 million of restricted short-term bank deposits pledged to secure certain performance and financial bonds as security for the Company's obligations under tenders, contracts and to one of its main subcontractors.

Transfers of Financial Assets

The Company's IP Optical Networks segment maintains customer receivables factoring agreements with a number of financial institutions. Under the terms of these agreements, the Company may transfer receivables to the financial institutions, on a non-recourse basis, provided that the financial institutions approve the receivables in advance. The Company maintains credit insurance policies from major insurance providers or obtains letters of credit from the customers for a majority of its factored trade receivables. The Company accounts for the factoring of its financial assets as a sale of the assets and records the factoring fees, when incurred, as a component of interest expense in the consolidated statements of operations, and the proceeds from the sales of receivables are included in cash from operating activities in the consolidated statements of cash flows. During the year ended December 31, 2020, the Company received $119.8 million of cash from the sale of certain accounts receivable and recorded $0.9 million of interest expense in connection with these transactions.

Foreign Currency Translation

For foreign subsidiaries where the functional currency is the local currency, assets and liabilities are translated into U.S. dollars at the current exchange rate on the balance sheet date. Revenue and expenses are translated at average rates of exchange prevailing during each period. Translation adjustments for these subsidiaries are included in Accumulated other comprehensive income.

For foreign subsidiaries where the functional currency is the U.S. dollar, monetary assets and liabilities are translated into U.S. dollars at the current exchange rate on the balance sheet date. Nonmonetary assets and liabilities are remeasured into U.S. dollars at historical exchange rates. Revenue and expense items are translated at average rates of exchange prevailing during each period. Translation adjustments for these subsidiaries are included in Other income (expense), net.

Realized and unrealized foreign currency exchange gains and losses arising from transactions denominated in currencies other than the subsidiary's functional currency are reflected in earnings.

The Company records its foreign currency gains (losses) as a component of Other income (expense), net. The Company recognized net foreign currency losses of $3.0 million for the year ended December 31, 2020, $1.1 million for the year ended December 31, 2019 and $4.6 million for the year ended December 31, 2018.

Inventory

Inventory is recorded at the lower of cost or market value using the first-in, first-out convention. The Company reduces the carrying value of inventory for those items that are potentially excess, obsolete or slow-moving based on changes in customer demand, technology developments or other economic factors.

Ribbon writes down evaluation equipment (equipment at customer sites for testing and evaluation) at the time of shipment to its customers, as it is probable that the inventory value will not be realized.

Deferred product costs represent deferred cost of revenue for product shipments to customers prior to satisfaction of Ribbon's revenue recognition criteria. The Company classifies inventory that is not expected to be consumed within one year from the balance sheet date as noncurrent and includes such inventory as a component of Other assets.

Debentures and Warrants.

The Company has Debentures and Warrants that it received as sale consideration in connection with the sale of the Kandy Communications Business (see Note 4), which Ribbon accounts for in accordance with Accounting Standards Codification ("ASC") 820, Fair Value Measurement ("ASC 820)".

The Company calculates the fair value of the Debentures using a Lattice-based valuation approach, which utilizes a binomial tree to model the different paths the price of AVCT's common stock might take over the Debentures' life by using assumptions regarding the stock price volatility and risk-free interest rate. These results are then used to calculate the fair value of the Debentures at each measurement date. The Company uses the Black-Scholes valuation model for estimating the fair value of the Warrants at each measurement date. The fair value of the Warrants is affected by AVCT's stock price as well as valuation assumptions, including the volatility of AVCT's stock price, expected term of the option, risk-free interest rate and expected dividends. Both the Lattice and Black-Scholes valuation models are based on available market data, giving consideration to all of the rights and obligations of each instrument and precluding the use of "blockage" discounts or premiums in determining the fair value of a large lock of financial instruments.

The Company is calculating the fair value of the Debentures and Warrants at each quarter-end and recording any adjustments to the fair values in Other income (expense), net. The fair values of the Debentures and Warrants are reported as Investments in the Company's consolidated balance sheet at December 31, 2020.

Property and Equipment

Property and equipment are stated at cost, net of accumulated depreciation. Expenditures for maintenance and repairs are charged to expense as incurred. Depreciation is computed using the straight-line method over the estimated useful lives of the related assets, which range from two to five years. Leasehold improvements are amortized over the lesser of the lease term or five years. When an asset is sold or retired, the cost and related accumulated depreciation or amortization are eliminated, and the resulting gain or loss, if any, is recognized in income (loss) from operations in the consolidated statement of operations. The Company reviews property and equipment for impairment in the same manner as intangible assets discussed below.

Software development costs associated with internal use software are incurred in three stages of development: the preliminary project stage, the application development stage and the post-implementation stage. Costs incurred during the preliminary project and post-implementation stages are expensed as incurred. Certain qualifying costs incurred during the application development stage are capitalized as property and equipment. Internal use software is amortized on a straight-line basis over its estimated useful life of three years, beginning when the software is ready for its intended use.

Intangible Assets and Goodwill

The Company's intangible assets are comprised of in-process research and development, developed technology, customer relationships, trade names, and internal use software. Intangible assets are reviewed for impairment when events or changes in circumstances indicate that their carrying amounts may not be recoverable based upon the estimated undiscounted cash flows. Recoverability of intangible assets with estimated lives and other long-lived assets is measured by a comparison of the carrying amount of an asset or asset group to future net undiscounted cash flows expected to be generated by the asset or asset group. If these comparisons indicate that an asset is not recoverable, the Company will recognize an impairment loss for the amount by which the carrying value of the asset or asset group exceeds the related estimated fair value. Estimated fair value is based on either discounted future operating cash flows or appraised values, depending on the nature of the asset. The Company amortizes its intangible assets over their respective useful lives, with the exception of in-process research and development, which has an indefinite life until the product is generally available, at which time such asset is typically reclassified to developed technology, and the Company begins to amortize this asset. See Note 10 for additional information regarding the Company's intangible assets.

Goodwill is recorded when the consideration for an acquisition exceeds the fair value of net tangible and identifiable intangible assets acquired. Goodwill is not amortized, but instead is tested for impairment at least annually, or more frequently if indicators of potential impairment exist, by comparing the fair value of the Company's reporting unit to its carrying value.

Prior to 2020, the Company's annual test for impairment of goodwill was completed as of November 30. Effective in 2020, the Company changed its annual goodwill impairment test date from November 30 to October 1. This change did not have a material impact on the Company's consolidated financial statements.

As described above, effective in the fourth quarter of 2020, the Company determined that it has two operating segments: Cloud and Edge, and IP Optical Networks. For the purpose of testing goodwill for impairment, all goodwill is assigned to a reporting unit, which may be either an operating segment or a portion of an operating segment. The Company's reporting units are its operating segments. The Company performs a fair value analysis using both an income and market approach, which encompasses a discounted cash flow analysis and a guideline public company analysis using selected multiples. The Company assesses each valuation methodology based upon the relevance and availability of the data at the time the valuation is performed and the methodologies are weighted appropriately. Any impairment charges are reported separately in the Company's consolidated statements of operations.

Stock-Based Compensation

The Company's stock-based compensation cost is measured at the grant date based on the fair value of the award and is recognized as expense over the requisite service period, which generally represents the vesting period, and includes an estimate of the awards that will be forfeited.

The Company uses the Black-Scholes valuation model for estimating the fair value on the date of grant of stock options. The fair value of stock option awards is affected by the Company's stock price as well as valuation assumptions, including the volatility of Ribbon's stock price, expected term of the option, risk-free interest rate and expected dividends.

The Company may grant performance-based stock units ("PSUs") that include a market condition to certain of its executives. The Company uses a Monte Carlo simulation approach to model future stock price movements based upon the risk-free rate of return, the volatility of each entity and the pair-wise covariance between each entity. These results are then used to calculate the grant date fair values of the PSUs.

Concentration of Risk

The financial instruments that potentially subject Ribbon to concentrations of credit risk are cash, restricted cash and accounts receivable. The Company's cash equivalents and investments were managed by one financial institution at December 31, 2020. Historically, the Company has not experienced significant losses due to such bank depository concentration. The Company's investments at December 31, 2020 consisted of securities of AVCT (see Note 4). The Company did not hold any investments at December 31, 2019.

Certain components and software licenses from third parties used in Ribbon's products are procured from single sources of supply. The failure of a supplier, including a subcontractor, to deliver on schedule could delay or interrupt Ribbon's delivery of products and thereby materially adversely affect Ribbon's revenue and operating results.

Advertising Costs

Advertising costs are expensed as incurred and included as a component of Sales and marketing expense in the Company's consolidated statements of operations. Advertising expenses were $0.8 million for the year ended December 31, 2020, $0.5 million for the year ended December 31, 2019 and $0.5 million for the year ended December 31, 2018.

Loss Contingencies and Reserves

Ribbon is subject to ongoing business risks arising in the ordinary course of business, including legal claims, that affect the estimation process of the carrying value of assets, the recording of liabilities and the possibility of various loss contingencies. An estimated loss contingency is accrued when it is probable that a liability has been incurred or an asset has been impaired and the amount of loss can be reasonably estimated. Ribbon regularly evaluates current information available to determine whether such amounts should be adjusted and records changes in estimates in the period they become known.

An allowance for doubtful accounts is estimated based on the Company's assessment of the collectability of specific customer accounts.

Ribbon accrues for royalties for technology that it licenses from vendors based on established royalty rates and usage. Ribbon is periodically contacted by third parties who claim that Ribbon's products infringe on certain intellectual property of a third party. Ribbon evaluates these claims and accrues amounts when it is probable that the obligation has been incurred and the amounts are reasonably estimable.

Warranty

The Company records warranty liabilities for estimated costs of fulfilling its obligations under standard limited hardware and software warranties at the time of sale. The specific warranty terms and conditions vary depending upon the country in which the Company does business, but generally includes material costs, technical support, labor and associated overhead over a period ranging from one to three years. The Company assumed ECI's warranty liability in connection with the ECI Acquisition. At December 31, 2020, the Company's liability for product warranties was $14.9 million, of which $6.5 million was current and included in Accrued expenses and other and $8.4 million was long-term and included in Other long-term liabilities in the Company's consolidated balance sheet. The Company did not have a warranty accrual at December 31, 2019.

Research and Development Grants

The Company records grants received from the Office of the Innovation Authority of the Israeli Ministry of Economics (the "IIA") as a reduction to Research and development expense. Royalties payable to the IIA are recognized pursuant to sales of related products and are included in Cost of revenue - product.

Accounting for Leases

The Company accounts for its leases in accordance with Accounting Standards Codification ("ASC") 842, Leases ("ASC 842"), which was adopted effective January 1, 2019 using the alternative transition method, which allowed entities to initially apply ASC 842 at the adoption date with no adjustments to prior period lease costs for comparability (see Note 22). The Company has operating and finance leases for corporate offices, research and development facilities, and certain equipment. Operating leases are reported separately in the Company's consolidated balance sheets at December 31, 2020 and 2019. Assets acquired under finance leases are included in Property and equipment, net, in the consolidated balance sheets at December 31, 2020 and 2019.

non-lease components but rather, accounts for the entire arrangement under leasing guidance. Leases with an initial term of 12 months or less are not recorded on the balance sheet and lease expense for these leases is recognized on a straight-line basis over the lease term.

For operating leases, lease expense for minimum fixed lease payments is recognized on a straight-line basis over the lease term. The expense for finance leases includes both interest and amortization expense components, with the interest component calculated based on the effective interest method and the amortization component calculated based on straight-line amortization of the right-of-use asset over the lease term. Lease contracts may contain variable lease costs, such as common area maintenance, utilities and tax reimbursements that vary over the term of the contract. Variable lease costs are not included in minimum fixed lease payments and as a result, are excluded from the measurement of the right-of-use assets and lease liabilities. The Company expenses all variable lease costs as incurred.

Accounting for Income Taxes

Deferred tax assets and liabilities are recognized for the expected future consequences of events that have been reflected in the consolidated financial statements. Deferred tax assets and liabilities are determined based on the differences between the financial reporting and tax basis of assets and liabilities and operating loss carryforwards, using tax rates expected to be in effect for the years in which the differences are expected to reverse. The Company records valuation allowances to reduce deferred income tax assets to the amount that is more likely than not to be realized.

The Company has provided for income taxes on the undistributed earnings of its non-U.S. subsidiaries as of December 31, 2020, excluding Ireland and Israel. These subsidiaries, excluding Ireland and Israel, are cost-plus or limited risk distributors that are not anticipated to need to use excess funds locally. Accordingly, the Company is required to recognize and record deferred taxes in 2020. The deferred taxes are recorded on the entire outside basis differences related to the foreign subsidiaries, the largest of these differences being undistributed earnings. At December 31, 2020, the Company had a deferred tax liability of $15.7 million related to withholding taxes in various countries.

The Company determines whether it is more likely than not that a tax position will be sustained upon examination. If it is not more likely than not that a position will be sustained, no amount of the benefit attributable to the position is recognized. The tax benefit to be recognized of any tax position that meets the more likely than not recognition threshold is calculated as the largest amount that is more than 50% likely of being realized upon resolution of the contingency. The Company accounts for interest and penalties related to uncertain tax positions as part of its provision for income taxes.

Defined Benefit Plans

The Company has defined benefit plans for some of its employees at various international locations. The Company recognizes retirement benefit assets or liabilities in the consolidated balance sheets reflecting the funded status of pension and other retirement benefit plans. Retirement benefit assets and liabilities are adjusted for the difference between the benefit obligations and the plan assets at fair value (measured at year-end), with the offset recorded directly to stockholders' equity through accumulated other comprehensive income (loss), net of tax. The amount recorded in stockholders' equity represents the after-tax unamortized actuarial gains or losses, unamortized transition obligations and unamortized prior service costs.

Recent Accounting Pronouncements

The Financial Accounting Standards Board ("FASB") has issued the following accounting pronouncements, all of which became effective for the Company in 2020 and none of which had a material impact on the Company's consolidated financial statements:

In March 2020, the FASB issued Accounting Standards Update ("ASU") 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting ("ASU 2020-04"), which provides optional expedients and exceptions for applying generally accepted accounting principles to contract modifications and hedging relationships, subject to meeting certain criteria that reference LIBOR or another reference rate expected to be discontinued.

In March 2020, the FASB issued ASU 2020-03, Codification Improvements to Financial Instruments ("ASU 2020-03"), which makes narrow-scope amendments related to topics regarding fair value option disclosures, applicability of the portfolio

exception in Accounting Standards Codification ("ASC") 820 to nonfinancial items, disclosures for depository and lending institutions, cross reference to guidance in ASC 470-50 on line of credit or revolving debt arrangements, cross reference to net asset value practical expedient in ASC 820-10, interaction between ASC 842 and ASC 326 and between ASC 326 and ASC 860-20.

In August 2018, the FASB issued ASU 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”), which provides guidance on implementation costs incurred in a cloud computing arrangement (“CCA”) that is a service contract. ASU 2018-15 amends ASC 350, Intangibles - Goodwill and Other (“ASC 350”) to include in its scope implementation costs of a CCA that is a service contract and clarifies that a customer should apply the guidance in ASC 350-40 to determine which implementation costs should be capitalized in such a CCA.

In August 2018, the FASB issued ASU 2018-14, Compensation - Retirement Benefits - Defined Benefit Plans - General (Subtopic 715-20): Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans (“ASU 2018-14”), which amends ASC 715, Compensation - Retirement Benefits, to add, remove and clarify disclosure requirements related to defined benefit pension and other postretirement plans.

In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”), which changes the fair value measurement requirements of ASC 820, Fair Value Measurement.

In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ("ASU 2016-13"), which adds an impairment model that is based on expected losses rather than incurred losses. Under ASU 2016-13, an entity recognizes as an allowance its estimate of expected credit losses, which the FASB believes will result in more timely recognition of such losses. In April and May 2019, the FASB issued ASU 2019-04, Codification Improvements to Topic 326, Financial Instruments - Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments ("ASU 2019-04") and ASU 2019-05 Financial Instruments - Credit Losses (Topic 326): Targeted Transition Relief ("ASU 2019-05"), respectively. ASU 2019-04 provides transition relief for entities adopting ASU 2016-13 and ASU 2019-05 clarifies certain aspects of the accounting for credit losses, hedging activities and financial instruments in connection with the adoption of ASU 2016-13.

The FASB has issued the following accounting pronouncement which became effective for the Company in 2021, which the Company does not believe will have a material impact on its consolidated financial statements upon adoption:

In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes ("ASU 2019-12"), which modifies ASC 740 to simplify the accounting for income taxes. ASU 2019-12 addresses the accounting for hybrid tax regimes, tax basis step-up in goodwill obtained in a transaction that is not a business combination, separate financial statements of legal entities not subject to tax, intraperiod tax allocation exception to incremental approach, ownership changes in investments - changes from a subsidiary to an equity method investment, ownership changes in investments - changes from an equity method investment to a subsidiary, interim period accounting for enacted changes in tax law and year-to-date loss limitation in interim period tax accounting.

BUSINESS ACQUISITONS

12 Months Ended

Dec. 31, 2020

Business Combinations [Abstract]

BUSINESS ACQUISITIONS

ECI

On the ECI Acquisition Date, Ribbon completed its merger transaction with ECI in accordance with the terms of the Agreement and Plan of Merger, dated as of November 14, 2019, by and among Ribbon, ECI, an indirect wholly-owned subsidiary of Ribbon ("Merger Sub"), Ribbon Communications Israel Ltd. and ECI Holding (Hungary) kft pursuant to which Merger Sub merged with and into ECI, with ECI surviving such merger as a wholly-owned subsidiary of Ribbon. Prior to the ECI Acquisition Date, ECI was a privately-held global provider of end-to-end packet optical transport and software-defined networking ("SDN") and network function virtualization ("NFV") solutions for service providers, enterprises and data center operators. Ribbon acquired ECI because it believed the ECI Acquisition would position the Company for growth and enhance

its competitive strengths by expanding its product portfolio beyond solutions primarily supporting voice applications to include data applications and optical networking.

As consideration for the ECI Acquisition, Ribbon issued the ECI shareholders and certain others 32.5 million shares of Ribbon common stock with a fair value of $108.6 million (the "Stock Consideration") and paid $322.5 million of cash (the "Cash Consideration"), comprised of $183.3 million to repay ECI's outstanding debt, including both principal and interest, and $139.2 million paid to ECI's selling shareholders. In addition, ECI shareholders received $33.4 million from the sale of certain of ECI's real estate assets. Cash Consideration was financed through cash on hand and committed debt financing consisting of a new $400 million term loan facility and $100 million revolving credit facility, which was undrawn at the ECI Acquisition Date.

The ECI Acquisition has been accounted for as a business combination and the financial results of ECI have been included in the Company's consolidated financial statements for the period subsequent to the ECI Acquisition. The Company's financial results for the year ended December 31, 2020 include $260.5 million of revenue and $52.9 million of net loss attributable to ECI.

As of December 31, 2020, the valuation of acquired assets, identifiable intangible assets and certain assumed liabilities had been finalized. During the fourth quarter of 2020, the Company reclassified the acquired assets held for employee' severance benefits of $13.2 million from other assets to other long-term liabilities. This reclassification was recorded to conform to the Company's presentation and resulted in a net long-term liability for severance benefits of $4.7 million in the Company's consolidated balance sheet at December 31, 2020. This amount reflects the net unfunded liability for the defined benefit plans assumed. This reclassification did not impact purchase consideration or goodwill. During the second quarter of 2020, the Company recorded changes to the initial preliminary purchase price allocation, including reductions of $10.4 million and $7.0 million to current and noncurrent inventory respectively, and increases to identifiable intangible assets aggregating $11.0 million, comprised of $3.0 million to in-process research and development, $5.0 million to developed technology, $2.0 million to customer relationships and $1.0 million to trade names. These adjustments, as well as other immaterial adjustments to other balance sheet accounts, resulted in a net increase to goodwill of $2.5 million. The allocation of purchase consideration to the fair value of assets acquired and liabilities assumed includes a noncurrent asset of $5.7 million that represents an indemnification receivable from ECI's selling shareholders for certain liabilities for uncertain tax positions in accordance with the Agreement and Plan of Merger.

A summary of the allocation of the purchase consideration for ECI is as follows (in thousands):


Fair value of consideration transferred:
Cash consideration:
Repayment of ECI outstanding debt obligations	$	183,266


Cash paid to selling shareholders	139,244
Payment to selling shareholders from sale of ECI real estate assets	33,400
Less cash and restricted cash acquired	(9,058)
Net cash consideration	346,852

Fair value of Ribbon stock issued	108,550

Fair value of total consideration	$	455,402

Fair value of assets acquired and liabilities assumed:
Current assets, net of cash and restricted cash acquired	$	120,203
Property and equipment	54,913
Intangible assets:
In-process research and development	34,000
Developed technology	111,900
Customer relationships	116,000
Trade names	3,000
Goodwill	191,996


Other noncurrent assets	37,528

Deferred revenue	(4,369)
Other current liabilities	(146,618)

Deferred revenue, net of current	(3,726)
Deferred tax liability	(13,308)
Other long-term liabilities	(46,117)
	$	455,402

The valuation of the acquired intangible assets is inherently subjective and relies on significant unobservable inputs. The Company used an income approach to value the acquired in-process research and development, developed technology, customer relationships and trade name intangible assets. The valuation for each of these intangible assets was based on estimated projections of expected cash flows to be generated by the assets, discounted to the present value at discount rates commensurate with perceived risk. The valuation assumptions take into consideration the Company's estimates of customer attrition, technology obsolescence and revenue growth projections. The Company is amortizing the identifiable intangible assets arising from the ECI Acquisition in relation to the expected cash flows from the individual intangible assets over their respective useful lives, which have a weighted average life of 12.38 years (see Note 10). Goodwill results from assets that are not separately identifiable as part of the transaction and is not deductible for tax purposes.

Pro Forma Results

The following unaudited pro forma information presents the combined results of operations of Ribbon and ECI for the years ended December 31, 2020 and 2019 as if the ECI Acquisition had been completed on January 1, 2019, with adjustments to give effect to pro forma events that are directly attributable to the ECI Acquisition. These pro forma adjustments include an increase in research and development expense related to the conformance of ECI's cost capitalization policy to Ribbon's, additional amortization expense for the acquired identifiable intangible assets, a decrease in historical ECI interest expense reflecting the extinguishment of certain of ECI's debt as a result of the ECI Acquisition, and an increase in interest expense reflecting the new debt entered into by the Company in connection with the ECI Acquisition. Pro forma adjustments also include the elimination of acquisition- and integration-related costs directly attributable to the acquisition from the year ended December 31, 2020 and inclusion of such costs in the year ended December 31, 2019.

The unaudited pro forma results do not reflect any operating efficiencies or potential cost savings that may result from the consolidation of the operations of Ribbon and ECI. Accordingly, these unaudited pro forma results are presented for illustrative purposes and are not intended to represent or be indicative of the actual results of operations of the combined

company that would have been achieved had the ECI Acquisition occurred at January 1, 2019, nor are they intended to represent or be indicative of future results of operations (in thousands, except per share amounts):


	Year ended December 31,
	2020		2019
	(unaudited)
Revenue	$	869,002	$	944,915
Net income (loss)	$	97,036	$	(250,337)
Diluted earnings (loss) per share	$	0.65	$	(1.76)

Anova Data, Inc.

On the Anova Acquisition Date, the Company acquired the business and technology assets of Anova, a private company headquartered in Westford, Massachusetts that provides advanced analytics solutions (the "Anova Acquisition"). The Anova Acquisition was completed in accordance with the terms and conditions of an asset purchase agreement, dated as of January 31, 2019 (the "Anova Asset Purchase Agreement"). The Company acquired Anova because it believed that the Anova Acquisition would reinforce and extend Ribbon's strategy to expand into network optimization, security and data monetization via big data analytics and machine learning.

As consideration for the Anova Acquisition, Ribbon issued 2.9 million shares of Ribbon common stock with a fair value of $15.2 million to Anova's sellers and equity holders on the Anova Acquisition Date and held back an additional 0.3 million shares with a fair value of $1.7 million, of which 316,551 shares were issued after post-closing adjustments on March 4, 2020. The Anova Deferred Consideration was included as a component of Accrued expenses and other current liabilities in the Company's consolidated balance sheet at December 31, 2019.

The Anova Acquisition has been accounted for as a business combination and the financial results of Anova have been included in the Company's consolidated financial statements for the period subsequent to the Anova Acquisition Date. The results for the year ended December 31, 2019 are not significant to the Company's consolidated financial statements. The Company has not provided pro forma financial information, as the historical amounts are not significant to the Company's consolidated financial statements.

As of December 31, 2019, the valuation of acquired assets, identifiable intangible assets and certain assumed liabilities was final. The finalization of this valuation resulted in a refinement of the allocation of purchase price between the identifiable intangible assets arising from the transaction, resulting in a $2.0 million reduction to the customer relationships intangible asset and an increase of $2.0 million to the developed technology intangible asset. The purchase consideration aggregating $16.9 million has been allocated to $11.2 million of identifiable intangible assets, comprised of $5.2 million of customer relationships and $6.0 million of developed technology, and working capital items aggregating $0.2 million of net assets acquired. The remaining unallocated amount of $5.5 million has been recorded as goodwill.

The valuation of the acquired intangible assets is inherently subjective and relies on significant unobservable inputs. The Company used an income approach to value the acquired intangible assets relating to developed technology and customer relationships. The valuation for each of these intangible assets was based on estimated projections of expected cash flows to be generated by the assets, discounted to the present value at discount rates commensurate with perceived risk. The valuation assumptions take into consideration the Company's estimates of customer attrition, technology obsolescence and revenue growth projections. The Company is amortizing the identifiable intangible assets in relation to the expected cash flows from the individual intangible assets over their respective useful lives, which have a weighted average life of 6.25 years (see Note 10).

The excess of purchase consideration over net tangible and identifiable intangible assets acquired was recorded as goodwill. The goodwill is deductible for tax purposes.

Edgewater Networks, Inc.

On the Edgewater Acquisition Date, the Company completed its acquisition of Edgewater, a private company headquartered in San Jose, California. The Edgewater Acquisition was completed in accordance with the terms and conditions

of the Agreement and Plan of Merger, dated as of June 24, 2018, by and among Ribbon, Merger Sub, Edgewater and Shareholder Representative Services LLC, a Colorado limited liability company, solely in its capacity as the initial holder representative (the "Edgewater Merger Agreement”). The Company acquired Edgewater because it believed that Edgewater would allow Ribbon to offer its global customer base a complete core-to-edge product portfolio, end-to-end service assurance and analytics solutions, and a fully integrated software-defined SD-WAN service.

As consideration for the Edgewater Acquisition, Ribbon paid, in the aggregate, $46.4 million of cash, net of cash acquired, and issued 4.2 million shares of Ribbon common stock to Edgewater's selling shareholders and holders of vested in-the-money options and warrants to acquire common stock of Edgewater (the "Edgewater Selling Stakeholders") on the Edgewater Acquisition Date, with additional cash payments of $30 million, of which $15 million was to be paid 6 months from the closing date and the other $15 million was to be paid as early as 9 months from the closing date and no later than 18 months from the closing date (the exact timing of which would depend on the amount of revenue generated from the sales of Edgewater products in 2018) ("Edgewater Deferred Consideration").

On February 15, 2019, the Company and the Edgewater Selling Stakeholders agreed to reduce the amount of Edgewater Deferred Consideration from $30 million to $21.9 million and agreed that all such deferred consideration would be payable on March 8, 2019. The Company paid the Edgewater Selling Stakeholders $21.9 million on March 8, 2019 and recorded the reduction to the Edgewater Deferred Consideration of $8.1 million in Other income (expense), net, in the Company's consolidated statement of operations and as a non-cash adjustment to reconcile net loss to cash flows provided by operating activities in the Company's consolidated statement of cash flows for the year ended December 31, 2019.

The Edgewater Acquisition has been accounted for as a business combination and the financial results of Edgewater have been included in the Company's consolidated financial statements for the period subsequent to its acquisition.

The Company finalized the valuation of acquired assets, identifiable intangible assets and certain assumed liabilities in the second quarter of 2019. A summary of the allocation of the purchase consideration for Edgewater is as follows (in thousands):


Fair value of consideration transferred:
Cash consideration:
Cash paid to Edgewater Selling Stakeholders	$	51,162
Less cash acquired	(4,773)
Net cash consideration	46,389
Unpaid cash consideration	30,000
Fair value of Ribbon stock issued	30,000
Fair value of equity awards assumed (see Note 21)	747
Fair value of total consideration	$	107,136

Fair value of assets acquired and liabilities assumed:
Current assets, net of cash acquired	$	16,098
Property and equipment	245
Intangible assets:

Developed technology	29,500
Customer relationships	26,100
Trade names	1,100
Goodwill	48,053
Other noncurrent assets	103
Deferred revenue	(2,749)
Other current liabilities	(9,926)
Deferred revenue, net of current	(669)
Other long-term liabilities	(719)
	$	107,136

intangible assets. The valuation for each of these intangible assets was based on estimated projections of expected cash flows to be generated by the assets, discounted to the present value at discount rates commensurate with perceived risk. The valuation assumptions take into consideration the Company's estimates of customer attrition, technology obsolescence and revenue growth projections. The Company is amortizing the identifiable intangible assets arising from the Edgewater Acquisition in relation to the expected cash flows from the individual intangible assets over their respective useful lives, which have a weighted average life of 8.38 years (see Note 10). Goodwill resulting from the transaction is primarily due to expected synergies between the combined companies and is not deductible for tax purposes.

The Company's revenue for the year ended December 31, 2018 included $21.5 million of revenue and $4.3 million of net loss attributable to Edgewater since the Edgewater Acquisition Date. The Company has not provided pro forma financial information, as the historical amounts are not significant to the Company's consolidated financial statements.

Acquisition-, Disposal- and Integration-Related Expenses

Acquisition-related expenses include those expenses related to acquisitions that would otherwise not have been incurred by the Company, including professional and services fees, such as legal, audit, consulting, paying agent and other fees, and expenses related to cash payments to certain former executives of the acquired businesses in connection with their employment agreements. Disposal-related expenses are professional and services fees related to disposals of subsidiaries or portions of the business. Integration-related expenses represent incremental costs related to combining the Company and its business acquisitions, such as third-party consulting and other third-party services related to merging the previously separate companies' systems and processes.

The acquisition-related professional and services fees recorded in the year ended December 31, 2020 primarily related to the ECI Acquisition and the disposal-related expenses related to the Company's sale of the Kandy Communications Business. The acquisition-related professional and services fees recorded in the year ended December 31, 2019 primarily related to the ECI Acquisition and, to a lesser extent, to the Anova Acquisition and other acquisition-related activities. The acquisition-related professional and services fees recorded in the year ended December 31, 2018 primarily related to the 2017 merger between Sonus Networks, Inc. and GENBAND (the "GENBAND Merger"), with nominal amounts related to the acquisition of Edgewater and other acquisition-related activities.

The components of Acquisition-, disposal- and integration-related expenses incurred in the years ended December 31, 2020, 2019 and 2018 were as follows (in thousands):


	Year ended December 31,
	2020		2019		2018
Professional and services fees (acquisition-related)	$	13,441	$	8,657	$	7,627
Management bonuses (acquisition-related)	—		—		1,972
Professional and services fees (disposal-related)	1,890		—		—
Integration-related expenses	1,833		4,296		7,352
	$	17,164	$	12,953	$	16,951

SALE OF KANDY COMMUNICATIONS BUSINESS	12 Months Ended
SALE OF KANDY COMMUNICATIONS BUSINESS	Dec. 31, 2020
Discontinued Operations and Disposal Groups [Abstract]
SALE OF KANDY COMMUNICATIONS BUSINESS	SALE OF KANDY COMMUNICATIONS BUSINESS On August 5, 2020, the Company announced that it had entered into a definitive agreement (the "Kandy Purchase Agreement") with American Virtual Cloud Technologies, Inc. ("AVCT") to sell the Kandy Communications Business. Under the Kandy Purchase Agreement, AVCT would purchase the assets and assume certain liabilities associated with the Kandy Communications Business, as well as all of the outstanding interests in Kandy Communications LLC, a subsidiary of the Company (the "Kandy Sale"). On December 1, 2020, the Company and AVCT entered into an amended and restated Purchase Agreement (the “Amended Kandy Agreement”). Under the terms of the Amended Kandy Agreement, AVCT agreed to pay to Ribbon $45.0 million, subject to certain adjustments, in the form of units of AVCT’s securities (the “AVCT Units”), with each AVCT Unit consisting of: (i) $1,000 in principal amount of AVCT’s Series A-1 convertible debentures (the “Debentures”); and (ii) one warrant to purchase 100 shares of AVCT common stock, $0.0001 par value (the “Warrants”), as consideration for the Kandy Sale (the "Kandy Consideration"). The Company received 43,778 AVCT Units as sale consideration on the Kandy Sale Date. The Debentures bear interest at a rate of 10% per annum, which will be added to the principal amount of the Debentures, except upon maturity, in which case accrued and unpaid interest is payable in cash. The entire principal of each Debenture, together with accrued and unpaid interest thereon, is due and payable on the earlier of the May 1, 2023 maturity date or the occurrence of a Change in Control as defined in the Amended Kandy Agreement. Each Debenture is convertible, in whole or in part, at any time at the Company's option into that number of shares of AVCT common stock, calculated by dividing the principal amount being converted, together with all accrued and unpaid interest thereon, by the applicable conversion price, initially $3.45. The Debentures are subject to mandatory redemption if the AVCT stock price is at or above $6.00 per share for 40 trading days in any 60 consecutive trading day period, subject to the satisfaction of certain other conditions. The conversion price is subject to customary adjustments including, but not limited to, stock dividends, stock splits and reclassifications. At the Company's option, up to $5.0 million of the Debentures may be redeemed by AVCT at par in the event AVCT raises at least $50.0 million in its offering of AVCT Units. As of February 19, 2021, the stock price had traded above $6.00 for 40 days within a 60 consecutive trading day period, and accordingly, the Debentures will be converted to shares of AVCT common stock upon the completion of customary regulatory filings by AVCT. The Warrants are independent of the Debentures and entitle the Company to purchase 4,377,800 shares of AVCT common stock at an exercise price of $0.01 per share. The Warrants expire on December 1, 2025, and were immediately exercisable on the Kandy Sale Date. The Company had not redeemed any of the Debentures or exercised any of the Warrants as of December 31, 2020. The Company is also subject to a lock-up provision which limits the Company's ability to sell any shares of AVCT common stock underlying the Debentures and the Warrants prior to June 1, 2021, except in certain transactions. The Company determined that the AVCT Units had a fair value of $84.9 million at the Kandy Sale Date, comprised of the Debentures with a fair value of $66.3 million and the Warrants with a fair value of $18.6 million. The value of the net assets sold to AVCT totaled $1.3 million, resulting in a gain on the sale of $83.6 million. The gain on the Kandy Sale is included as a component of Other income (expense), net, in the consolidated statement of operations for the year ended December 31, 2020. The Company calculates the fair value of the Debentures using a Lattice-based valuation approach, which utilizes a binomial tree to model the different paths the price of AVCT's common stock might take over the Debentures' life by using assumptions regarding the stock price volatility and risk-free interest rate. These results are then used to calculate the fair value of the Debentures at each measurement date. The Company uses the Black-Scholes valuation model for estimating the fair value of the Warrants at each measurement date. The fair value of the Warrants is affected by AVCT's stock price as well as valuation assumptions, including the volatility of AVCT's stock price, expected term of the option, risk-free interest rate and expected dividends. Both the Lattice and Black-Scholes valuation models are based on available market data, giving consideration to all of the rights and obligations of each instrument and precluding the use of "blockage" discounts or premiums in determining the fair value of a large block of financial instruments. The Company will calculate the fair value of the Debentures and Warrants at each quarter-end and record any adjustments to the fair values in Other income (expense), net. At December 31, 2020, the aggregate fair value of the Debentures and Warrants was $115.2 million, resulting in a gain of $30.3 million arising from the increase in fair values of the Debentures and Warrants for the period from the Kandy Sale Date to December 31, 2020. This gain is included as a component of Other income (expense), net, in the Company's consolidated statement of operations. The fair values of the Debentures and Warrants are reported as Investments in the Company's consolidated balance sheet at December 31, 2020 and are classified as Level 2 fair value measurements within the fair value hierarchy (see Note 6). The assets acquired and liabilities assumed by AVCT in connection with the Kandy Sale were primarily comprised of accounts receivable, property and equipment, trade accounts payable and employee-related accruals. The Company incurred $1.9 million of transaction costs, which are included as a component of Acquisition-, disposal- and integration-related expense in the consolidated statement of operations for the year ended December 31, 2020. The results of the Kandy Communications Business are excluded from the Company's consolidated results for the period subsequent to the Kandy Sale Date.

EARNINGS (LOSS) PER SHARE

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

EARNINGS (LOSS) PER SHARE

Basic earnings (loss) per share is computed by dividing net income (loss) by the weighted average number of shares outstanding during the period. For periods in which the Company reports net income, diluted net income per share is determined by using the weighted average number of common and dilutive common equivalent shares outstanding during the period unless the effect is antidilutive.

The calculations of shares used to compute basic and diluted earnings (loss) per share are as follows (in thousands):


	Year ended December 31,
	2020	2019	2018
Weighted average shares outstanding—basic	138,967	109,734	103,916
Potential dilutive common shares	5,683	—	—
Weighted average shares outstanding—diluted	144,650	109,734	103,916

Options to purchase the Company's common stock aggregating 0.2 million shares have not been included in the computation of diluted earnings per share for the year ended December 31, 2020 because their effect would have been antidilutive. Options to purchase the Company's common stock and unvested shares of restricted and performance-based stock and stock units aggregating 4.6 million shares have not been included in the computation of diluted loss per share for the year ended December 31, 2019 because their effect would have been antidilutive. Options to purchase the Company's common stock, unvested shares of restricted and performance-based stock and stock units, and shares in connection with future purchases under the Company's Amended and Restated 2000 Employee Stock Purchase Plan, as amended (the "ESPP"), aggregating 3.1 million shares have not been included in the computation of diluted loss per share for the year ended December 31, 2019 because their effect would have been antidilutive.

INVESTMENTS AND FAIR VALUE HIERARCHY

12 Months Ended

Dec. 31, 2020

Investments, All Other Investments [Abstract]

INVESTMENTS AND FAIR VALUE HIERARCHY

The Company's policy and historical practice has been to invest in debt instruments, primarily U.S. government-backed, municipal and corporate obligations, which management believes to be high quality (investment grade) credit instruments.

At December 31, 2020, the Company's investments were comprised of the Debentures and Warrants received as sale consideration for the Kandy Sale (see Note 4).

The Company did not hold any marketable securities at December 31, 2019, as its remaining available-for-sale marketable securities matured during the second quarter of 2019. As a result of the Company no longer holding any marketable securities or investments at December 31, 2019, the remaining tax effect on the unrealized gain on available-for-sale marketable securities was realized in the second quarter of 2019 and is included in the income tax provision in the Company's consolidated statement of operations for the year ended December 31, 2019 as a reclassification from Unrealized gain on available-for-sale marketable securities in the Company's consolidated statement of comprehensive loss. The Company had not sold any of its marketable securities in 2019 prior to their full maturity. During the year ended December 31, 2019, the Company recognized nominal gross gains and losses on the maturities of its marketable securities.

On a quarterly basis, the Company reviews its investments, if any, to determine if there have been any events that could create a credit impairment.

Fair Value Hierarchy

Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or a liability. The three-tier fair value hierarchy is based on the level of independent, objective evidence surrounding the inputs used to measure fair value. A financial instrument's categorization within the fair value hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The fair value hierarchy is as follows:

Level 1. Level 1 applies to assets or liabilities for which there are quoted prices in active markets for identical assets or liabilities.

Level 2. Level 2 applies to assets or liabilities for which there are inputs that are directly or indirectly observable in the marketplace, such as quoted prices for similar assets or liabilities in active markets or quoted prices for identical assets or liabilities in markets with insufficient volume or infrequent transactions (less active markets).

Level 3. Level 3 applies to assets or liabilities for which there are unobservable inputs to the valuation methodology that are significant to the measurement of the fair value of the assets or liabilities.

The classification of each asset or liability fair value measurement within the fair value hierarchy is determined based on the lowest level input that is significant to the fair value measurement in its entirety. Market activity is presumed to be orderly in the absence of evidence of forced or disorderly sales, although such sales may still be indicative of fair value. Applicable accounting guidance precludes the use of blockage factors or liquidity adjustments due to the quantity of securities held by an entity.

The Company's marketable securities, when applicable, are valued with the assistance of valuations provided by third-party pricing services, as derived from such services' pricing models. Inputs to the models may include, but are not limited to, reported trades, executable bid and asked prices, broker/dealer quotations, prices or yields of securities with similar characteristics, benchmark curves or information pertaining to the issuer, as well as industry and economic events. The pricing services may use a matrix approach, which considers information regarding securities with similar characteristics to determine the valuation for a security. The Company is ultimately responsible for the consolidated financial statements and underlying estimates. Accordingly, the Company assesses the reasonableness of the valuations provided by the third-party pricing services by reviewing actual trade data, broker/dealer quotes and other similar data, which are obtained from quoted market prices or other sources.

ACCOUNTS RECEIVABLE, NET

12 Months Ended

Dec. 31, 2020

Receivables [Abstract]

ACCOUNTS RECEIVABLE, NET

Accounts receivable, net, consisted of the following (in thousands):


	December 31,
	2020		2019
Accounts receivable	$	238,514	$	193,619
Allowance for doubtful accounts	(776)		(913)
Accounts receivable, net	$	237,738	$	192,706

The Company's allowance for doubtful accounts activity was as follows (in thousands):


Year ended December 31,	Balance at beginning of year		Charges to expense		Charges (credits) to other accounts		Write-offs		Balance at end of year
2020	$	913	$	686	$	94	$	(917)	$	776
2019	$	669	$	738	$	68	$	(562)	$	913
2018	$	73	$	351	$	620	$	(375)	$	669

INVENTORY

12 Months Ended

Dec. 31, 2020

Inventory Disclosure [Abstract]

INVENTORY

Inventory consisted of the following (in thousands):


	December 31,
	2020		2019

On-hand final assemblies and finished goods inventories	$	46,921	$	13,283
Deferred cost of goods sold	1,165		2,441
	48,086		15,724
Less noncurrent portion (included in Other assets)	(2,336)		(924)
Current portion	$	45,750	$	14,800

PROPERTY AND EQUIPMENT

12 Months Ended

Dec. 31, 2020

Property, Plant and Equipment [Abstract]

PROPERTY AND EQUIPMENT

Property and equipment consisted of the following (in thousands):


		December 31,
	Useful Life	2020		2019
Equipment	2-5 years	$	90,885	$	82,737
Software	2-5 years	32,244		27,939
Furniture and fixtures	3-5 years	3,092		1,283
Leasehold improvements	Shorter of the estimated lease term or useful life	37,263		23,975
		163,484		135,934
Less accumulated depreciation and amortization		(114,596)		(106,958)
Property and equipment, net		$	48,888	$	28,976

The Company recorded depreciation and amortization expense related to property and equipment of $17.2 million for the year ended December 31, 2020, $11.9 million for the year ended December 31, 2019 and $11.2 million for the year ended December 31, 2018. During each of the years ended December 31, 2020, 2019 and 2018, the Company disposed of certain property and equipment that was fully depreciated at the time of disposal, which resulted in reductions in both Cost and Accumulated depreciation.

Property and equipment under finance leases included in the amounts above were as follows (in thousands):


	December 31,
	2020		2019
Cost	$	2,908	$	4,401
Less accumulated depreciation	(1,925)		(1,981)
Property and equipment under finance leases, net	$	983	$	2,420

The net book values of the Company's property and equipment by geographic area were as follows (in thousands):


	December 31,
	2020		2019
United States	$	27,211	$	17,584
Canada	4,584		4,768
Asia/Pacific	6,078		5,146
Europe	1,171		1,204
Israel	9,613		20
Other	231		254
	$	48,888	$	28,976

INTANGIBLE ASSETS AND GOODWILL

12 Months Ended

Dec. 31, 2020

Goodwill and Intangible Assets Disclosure [Abstract]

INTANGIBLE ASSETS AND GOODWILL

The Company's intangible assets at December 31, 2020 and 2019 consisted of the following (in thousands):


December 31, 2020	Weighted average amortization period (years)	Cost		Accumulated amortization		Net carrying value
In-process research and development	*	$	34,000	$	—	$	34,000

Developed technology	7.93	306,380		143,050		163,330
Customer relationships	11.86	268,140		50,627		217,513
Trade names	3.88	5,000		2,487		2,513

Internal use software	3.00	730		730		—
	9.17	$	614,250	$	196,894	$	417,356


December 31, 2019	Weighted average amortization period (years)	Cost		Accumulated amortization		Net carrying value
In-process research and development	*	$	5,600	$	—	$	5,600

Developed technology	6.79	188,880		100,760		88,120
Customer relationships	9.46	152,140		33,350		118,790
Trade names	5.20	2,000		1,144		856

Internal use software	3.00	730		730		—
	7.82	$	349,350	$	135,984	$	213,366

* An in-process research and development intangible asset has an indefinite life until the product is generally available, at which time such asset is typically reclassified to developed technology, at which time the Company begins to amortize the asset. In the fourth quarter of 2020, the Company reclassified an in-process research and development intangible asset related to developed technology, as the associated product became generally available.

As previously discussed (see Note 2), for the year ended December 31, 2020, the Company reclassified amounts recorded for amortization of acquired intangible assets in prior period presentations from Cost of revenue - product and Sales and marketing expense to a separate line included in operating expenses in the consolidated statements of operations. Amounts reported as Amortization of acquired intangible assets for the years ended December 31, 2020, 2019 and 2018 were $60.9 million, $49.2 million and $49.7 million, respectively.

Estimated future amortization expense for the Company's intangible assets at December 31, 2020 was as follows (in thousands):


Years ending December 31,
2021	$	66,626
2022	60,104
2023	52,256
2024	44,048
2025	37,027
Thereafter	157,295
	$	417,356

Goodwill is recorded when the consideration for an acquisition exceeds the fair value of net tangible and identifiable intangible assets acquired. Effective in 2020, the Company's annual test for impairment of goodwill is completed as of October 1. Previously, the Company's annual test for impairment of goodwill was completed as of November 30.

As previously discussed, effective in the fourth quarter of 2020, the Company determined that it has two operating segments: Cloud and Edge, and IP Optical Networks. For the purpose of testing goodwill for impairment, all goodwill is

assigned to a reporting unit, which may be either an operating segment or a portion of an operating segment. The Company's reporting units are its operating segments. The Company determined that the goodwill assigned to the Cloud and Edge reporting unit was $224.9 million and the goodwill assigned to the IP Optical Networks reporting unit was $192.0 million. Upon completion of the Company's 2020 annual test for goodwill impairment, the Company determined that there was no impairment of goodwill in either of its reporting units.

Prior to the fourth quarter of 2020, the Company operated as a single operating segment with one reporting unit and consequently evaluated goodwill for impairment based on an evaluation of the fair value of the Company as a whole. Based on the results of the Company's 2019 annual impairment test, the Company determined that its carrying value exceeded its fair value and accordingly, the Company recorded an impairment charge of $164.3 million.

The Company performed its assessment for the year ended December 31, 2018 and determined that its fair value was in excess of its carrying value and accordingly, there was no impairment of goodwill.

At certain times during the years ended December 31, 2020, 2019 and 2018, including at the Company's annual test date in 2018, the Company's market capitalization was below its book value. While the Company had concluded that its fair value exceeded its carrying value at that date, the Company regularly monitored for changes in circumstances, including changes to the Company's performance, that could result in impairment of goodwill.

The changes in the carrying value of the Company's goodwill in the years ended December 31, 2020 and 2019 were as follows (in thousands):


	Cloud and Edge		IP Optical Networks		Total
Balance at December 31, 2018 (1)	$	383,655	$	—	$	383,655
Acquisition of Anova	5,541		—		5,541
Impairment of goodwill	(164,300)		—		(164,300)
Balance at December 31, 2019 (2)	224,896		—		224,896
Acquisition of ECI	—		191,996		191,996
Balance at December 31, 2020 (2)	$	224,896	$	191,996	$	416,892

(1) Balance is presented net of accumulated impairment losses of $3.1 million for the Cloud and Edge segment.

(2) Balance is presented net of accumulated impairment losses of $167.4 million for the Cloud and Edge segment.

The components of goodwill at December 31, 2020 and 2019 were as follows (in thousands):


	Cloud and Edge		IP Optical Networks		Total
Balance at December 31, 2019
Goodwill	$	392,302	$	—	$	392,302
Accumulated impairment losses	(167,406)		—		(167,406)
	224,896		—		224,896
Balance at December 31, 2020
Goodwill	$	392,302	$	191,996	$	584,298
Accumulated impairment losses	(167,406)		—		(167,406)
	$	224,896	$	191,996	$	416,892

ACCRUED EXPENSES AND OTHER

12 Months Ended

Dec. 31, 2020

Payables and Accruals [Abstract]

ACCRUED EXPENSES AND OTHER

Accrued expenses and other consisted of the following (in thousands):


	December 31,
	2020		2019
Employee compensation and related costs	$	66,039	$	27,166
Professional fees	11,451		13,331

Other	57,375		16,203
	$	134,865	$	56,700

WARRANTY

12 Months Ended

Dec. 31, 2020

Guarantees and Product Warranties [Abstract]

WARRANTY

The changes in the Company's warranty accrual balance in the year ended December 31, 2020 were as follows (in thousands):


Year ended December 31,	Balance at beginning of year		Assumed liability in connection with ECI Acquisition		Provision		Settlements		Balance at end of year
2020	$	—	$	16,251	$	4,687	$	(6,083)	$	14,855

RESTRUCTURING AND FACILITIES CONSOLIDATION INITIATIVES

12 Months Ended

Dec. 31, 2020

Restructuring and Related Activities [Abstract]

RESTRUCTURING AND FACILITIES CONSOLIDATION INITIATIVES

The Company recorded restructuring and related expense aggregating $16.2 million in the year ended December 31, 2020, $16.4 million in the year ended December 31, 2019 and $17.0 million in the year ended December 31, 2018. Restructuring and related expense includes restructuring expense (primarily severance and related costs), estimated future variable lease costs for vacated properties with no intent or ability of sublease, and accelerated rent amortization expense.

For restructuring events that involve lease assets and liabilities, the Company applies lease reassessment and modification guidance and evaluates the right-of-use assets for potential impairment. If the Company plans to exit all or distinct portions of a facility and does not have the ability or intent to sublease, the Company will accelerate the amortization of each of those lease components through the vacate date. The accelerated amortization is recorded as a component of Restructuring and related expense in the Company's consolidated statements of operations. Related variable lease expenses will continue to be expensed as incurred through the vacate date, at which time the Company will reassess the liability balance to ensure it appropriately reflects the remaining liability associated with the premises and record a liability for the estimated future variable lease costs.

Accelerated amortization of lease assets is recognized from the date that the Company commences the plan to fully or partially vacate a facility, for which there is no intent or ability to enter into a sublease, through the final vacate date. Amounts of accelerated rent amortization that are included as a component of restructuring and related expense are not included in the tables below, as the liability for the total lease payments for each respective facility is included as a component of Operating lease liabilities in the Company's consolidated balance sheets at December 31, 2020 and 2019, both current and noncurrent (see Note 22). The Company may incur additional future expense if it is unable to sublease other locations included in the Facilities Initiative.

The components of restructuring and related expense for the year ended December 31, 2020 and 2019 were as follows (in thousands):


	Year ended December 31,
	2020		2019
Severance and related costs	$	12,025	$	11,179
Variable and other facilities-related costs	3,605		1,528
Accelerated amortization of lease assets due to cease-use	605		3,692
	$	16,235	$	16,399

Prior to the adoption of ASC 842, the Company recorded restructuring accruals for future lease obligations related to vacated facilities at the time that it ceased usage of the respective facility. The components of Restructuring and related expense recorded in the year ended December 31, 2018 were as follows (in thousands):




Severance and related costs	15,217
Facilities	1,798
	$	17,015

2020 Restructuring Initiative

In 2020, the Company implemented a restructuring plan to eliminate certain positions and redundant facilities, primarily in connection with the ECI Acquisition, to further streamline the Company's global footprint and improve its operations (the "2020 Restructuring Initiative"). The 2020 Restructuring Initiative includes facility consolidations and a reduction in workforce, including three former executives of ECI for whom severance aggregating $1.1 million was recorded in the first quarter of 2020. In connection with this initiative, the Company expects to eliminate duplicate functions arising from the ECI Acquisition and support its efforts to integrate the two companies.

The Company recorded restructuring expense of $14.0 million in connection with the 2020 Restructuring Initiative in the year ended December 31, 2020, comprised of $11.5 million for severance and related costs for approximately 190 employees, including the aforementioned former executives of ECI, $2.0 million for variable and other facilities-related costs, and $0.5 million for accelerated amortization of lease assets. The Company expects these amounts will be fully paid in 2021. The Company expects that it will record additional restructuring and related expense approximating $8 million under the 2020 Restructuring Initiative in the aggregate for severance and planned facility consolidations. A summary of the 2020 Restructuring Initiative accrual activity for the year ended December 31, 2020 is as follows (in thousands):


	Balance at January 1, 2020		Initiatives charged to expense		Transfer to operating lease liability accounts		Cash payments		Balance at December 31, 2020
Severance	$	—	$	11,547	$	—	$	(6,310)	5,237
Facilities	—		2,478		(535)		(687)		1,256
	$	—	$	14,025	$	(535)	$	(6,997)	$	6,493

2019 Restructuring and Facilities Consolidation Initiative

In June 2019, the Company implemented a restructuring plan to further streamline the Company's global footprint, improve its operations and enhance its customer delivery (the "2019 Restructuring Initiative"). The 2019 Restructuring Initiative includes facility consolidations, refinement of the Company's research and development activities, and a reduction in workforce. The facility consolidations under the 2019 Restructuring Initiative (the "Facilities Initiative") include a consolidation of the Company's North Texas sites into a single campus, housing engineering, customer training and support, and administrative functions, as well as a reduction or elimination of certain excess and duplicative facilities worldwide. In addition, the Company is substantially consolidating its global software laboratories and server farms into two lower cost North American sites. The Company continues to evaluate its properties included in the Facilities Initiative for accelerated amortization and/or right-of-use asset impairment. The Company expects that the actions under the Facilities Initiative will be completed in 2021.

In connection with the 2019 Restructuring Initiative, the Company recorded restructuring and related expense of $2.3 million and $11.2 million in the years ended December 31, 2020 and 2019, respectively. The amount recorded in the

current year was comprised of $0.5 million for severance and related costs for approximately 5 employees, $1.7 million for variable and other facilities-related costs and $0.1 million for accelerated amortization of lease assets. The amount recorded in the year ended December 31, 2019 was comprised of $6.1 million for severance and related costs for approximately 120 employees, $1.4 million for variable and other facilities-related costs and $3.7 million for accelerated amortization of lease assets. The Company expects that all of the amount accrued for severance and related costs will be paid in 2021. The Company estimates that it will record nominal, if any, additional restructuring and related expense related to severance and related costs under the 2019 Restructuring Initiative.

Summaries of the 2019 Restructuring Initiative accrual activity for the years ended December 31, 2020 and 2019 are as follows (in thousands):


Year ended December 31, 2020	Balance at January 1, 2020		Initiatives charged to expense		Transfer to operating lease liability accounts		Cash payments		Balance at December 31, 2020
Severance	$	2,110	$	536	$	—	$	(2,473)	173
Facilities	991		1,732		(70)		(1,887)		766
	$	3,101	$	2,268	$	(70)	$	(4,360)	$	939


Year ended December 31, 2019	Balance at January 1, 2019		Initiatives charged to expense		Transfer to operating lease liability accounts	Cash payments		Balance at December 31, 2019
Severance	$	—	$	6,103	—	$	(3,993)	2,110
Facilities	—		5,064		(3,692)	(381)		991
	$	—	$	11,167	(3,692)	$	(4,374)	$	3,101

Merger Restructuring Initiative

In connection with the GENBAND Merger, the Company implemented a restructuring plan in the fourth quarter of 2017 to eliminate certain redundant positions and facilities within the combined companies (the "Merger Restructuring Initiative"). In connection with this initiative, the Company recorded $5.2 million of restructuring and related expense in 2019, virtually all of which was for severance and related costs for approximately 40 employees. The Company recorded $16.1 million of restructuring and related expense in 2018 in connection with this initiative, comprised of $14.7 million for severance for approximately 275 employees and $1.4 million for redundant facilities in the Czech Republic, Canada and the U.S. The Merger Restructuring Initiative was completed in 2020.

Summaries of the Merger Restructuring Initiative accrual activity for the years ended December 31, 2020 and 2019 are as follows (in thousands):


Year ended December 31, 2020	Balance at January 1, 2020		Adjustments for changes in estimate		Cash payments		Balance at December 31, 2020
Severance	$	409	$	(58)	$	(351)	$	—


Year ended December 31, 2019	Balance at January 1, 2019		Initiatives charged to expense		Adjustment for the impact of ASC 842 adoption		Cash payments		Balance at December 31, 2019
Severance	$	1,910	$	5,076	$	—	$	(6,577)	$	409
Facilities	771		156		(771)		(156)		—
	$	2,681	$	5,232	$	(771)	$	(6,733)	$	409

Assumed Restructuring Initiative

The Company assumed GENBAND's previously recorded restructuring liability, totaling $4.1 million, on the GENBAND Merger Date (the "GENBAND Restructuring Initiative"). Of this amount, $3.7 million related to severance and related costs

and $0.4 million related to facilities. Subsequent to the GENBAND Merger, the Company recorded $0.6 million in the aggregate in connection with the GENBAND Restructuring Initiative, comprised of $0.9 million of restructuring and related expense in 2018 and a credit of $0.3 million to restructuring and related expense in 2017 for changes in estimated costs for this previously recorded and assumed restructuring initiative. The GENBAND Restructuring Initiative was completed in 2019. In connection with the adoption of ASC 842, which was effective on January 1, 2019, the Company wrote off the remaining restructuring accrual related to facilities, as indicated in the table below (in thousands):


Year ended December 31, 2019	Balance at January 1, 2019		Adjustment for the impact of ASC 842 adoption		Balance at December 31, 2019

Facilities	$	117	$	(117)	$	—

2016 Restructuring Initiative

In July 2016, the Company announced a program (the "2016 Restructuring Initiative") to further accelerate its investment in new technologies to address the communications industry's migration to a cloud-based architecture and to support the Company's strategic initiatives, such as new products and an expanded go-to-market footprint in selected geographies and discrete vertical markets. The Company recorded $2.0 million of restructuring and related expense in the aggregate in connection with this initiative, comprised of $1.9 million for severance and related costs and $0.1 million to abandon its facility in Rochester, New York (the "Rochester Facility"). The actions under the 2016 Restructuring Initiative were completed in 2019.

A summary of the 2016 Restructuring Initiative accrual activity for the year ended December 31, 2019 is as follows (in thousands):


Year ended December 31, 2019	Balance at January 1, 2019		Cash payments		Balance at December 31, 2019

Facilities	$	58	$	(58)	$	—

Balance Sheet Classification

The current portions of accrued restructuring were $6.6 million and $2.6 million at December 31, 2020 and 2019, respectively, and are included as components of Accrued expenses in the consolidated balance sheets. The long-term portions of accrued restructuring are included as components of Other long-term liabilities in the consolidated balance sheets. The long-term portions of accrued restructuring were $0.8 million at December 31, 2020 and $0.9 million at December 31, 2019. The amount recorded as long-term at December 31, 2018 represented future lease payments on restructured facilities.

DEBT	12 Months Ended
DEBT	Dec. 31, 2020
Debt Disclosure [Abstract]
DEBT	DEBT 2018 Credit Facility On June 24, 2018, the Company amended its previous outstanding credit facility to, among other things, permit the Edgewater Acquisition and related transactions (the "2018 Credit Facility"). The indebtedness and other obligations under the 2018 Credit Facility were unconditionally guaranteed on a senior secured basis by the Company and each other material U.S. domestic subsidiary of the Company (collectively, the "Guarantors"). The 2018 Credit Facility was secured by first-priority liens on substantially all of the assets of the Borrower and the Guarantors, including the Company. The 2018 Credit Facility required periodic interest payments on outstanding borrowings until maturity. The Borrower could prepay all revolving loans under the 2018 Credit Facility at any time without premium or penalty (other than customary LIBOR breakage costs), subject to certain notice requirements. Revolving loans under the 2018 Credit Facility bore interest at the Borrower’s option at either the Eurodollar (LIBOR) rate plus a margin ranging from 2.50% to 3.00% per year or the base rate (the highest of the Federal Funds rate plus 0.50%, or the prime rate announced from time to time in The Wall Street Journal) plus a margin ranging from 1.50% to 2.00% per year (such margins being referred to as the “Applicable Margin”). The Applicable Margin varied depending on the Company’s consolidated leverage ratio (as defined in the 2018 Credit Facility). The base rate and the LIBOR rate were each subject to a zero percent floor. The Borrower was charged a commitment fee ranging from 0.25% to 0.40% per year on the daily amount of the unused portions of the commitments under the 2018 Credit Facility. Additionally, with respect to all letters of credit outstanding under the 2018 Credit Facility, the Borrower was charged a fronting fee of 0.125% per year and an outstanding letter of credit fee equal to the Applicable Margin for base rate loans ranging from 1.50% to 2.00% times the amount of the outstanding letters of credit. The 2018 Credit Facility required compliance with certain financial covenants, including a minimum consolidated quick ratio, minimum consolidated interest coverage ratio and maximum consolidated leverage ratio, all of which were defined in the 2018 Credit Facility and tested on a quarterly basis. In addition, the 2018 Credit Facility contained various covenants that, among other restrictions, limited the Company’s and its subsidiaries’ ability to enter into certain types of transactions, including, but not limited to: incurring or assuming indebtedness, making acquisitions or engaging in mergers, making investments, repurchasing equity and paying dividends, selling or otherwise transferring assets, changing the nature of its business and amending or making prepayments on certain junior debt. The 2018 Credit Facility contained events of default that are customary for a secured credit facility. If an event of default relating to bankruptcy or other insolvency events with respect to a borrower occurred, all obligations under the 2018 Credit Facility would immediately become due and payable. If any other event of default existed under the 2018 Credit Facility, the lenders could accelerate the maturity of the obligations outstanding under the 2018 Credit Facility and exercise other rights and remedies, including charging a default rate of interest equal to 2.00% per year above the rate that would otherwise be applicable. In addition, if any event of default existed under the 2018 Credit Facility, the lenders could commence foreclosure or other actions against the collateral. If any default existed under the 2018 Credit Facility, or if the Borrower was unable to make any of the representations and warranties as stated in the 2018 Credit Facility at the applicable time, the Borrower would be unable to borrow funds or have letters of credit issued under the 2018 Credit Facility, which, depending on the circumstances prevailing at that time, could have a material adverse effect on the Borrower’s liquidity and working capital. The 2018 Credit Facility was superseded by the 2019 Credit Facility, which was entered into on April 29, 2019 and which is discussed below. 2019 Credit Facility On April 29, 2019, the Company, as guarantor, and Ribbon Communications Operating Company, Inc., as borrower, entered into a syndicated, amended and restated credit facility (the "2019 Credit Facility"), which provided for a $50 million term loan facility that was advanced in full on April 29, 2019, and a $100 million revolving line of credit. The 2019 Credit Facility also included procedures for additional financial institutions to become syndicate lenders, or for any existing lender to increase its commitment under either the term loan facility or the revolving loan facility, subject to an aggregate increase of $75 million for incremental commitments under the 2019 Credit Facility. The 2019 Credit Facility was scheduled to mature in April 2024. At December 31, 2019, the Company had an outstanding term loan debt balance of $48.8 million and an outstanding revolving line of credit balance of $8.0 million with a combined average interest rate of 3.30%, and $5.4 million of outstanding letters of credit at an interest rate of 1.50%. The indebtedness and other obligations under the 2019 Credit Facility were unconditionally guaranteed on a senior secured basis by the Company and each other material U.S. domestic subsidiary of the Company (collectively, the “Guarantors”). The 2019 Credit Facility was secured by first-priority liens on substantially all of the assets of the Borrower and the Guarantors, including the Company. The 2019 Credit Facility required periodic interest payments on any outstanding borrowings under the facility. The Borrower could prepay all revolving loans under the 2019 Credit Facility at any time without premium or penalty (other than customary LIBOR breakage costs), subject to certain notice requirements. Revolving loans under the 2019 Credit Facility bore interest at the Borrower’s option at either the Eurodollar (LIBOR) rate plus a margin ranging from 1.50% to 3.00% per year or the base rate (the highest of the Federal Funds rate plus 0.50%, or the prime rate announced from time to time in The Wall Street Journal) plus a margin ranging from 0.50% to 2.00% per year (such margins being referred to as the “Applicable Margin”). The Applicable Margin varied depending on the Company’s consolidated leverage ratio (as defined in the 2019 Credit Facility). The base rate and the LIBOR rate were each subject to a zero percent floor. The 2019 Credit Facility required compliance with certain financial covenants, including a minimum consolidated quick ratio, minimum consolidated fixed charge coverage ratio and maximum consolidated leverage ratio, all of which were defined in the 2019 Credit Facility and tested on a quarterly basis. The Company was in compliance with all covenants of the 2019 Credit Facility at December 31, 2019. In addition, the 2019 Credit Facility contained various covenants that, among other restrictions, limited the Company’s and its subsidiaries’ ability to enter into certain types of transactions, including, but not limited to: incurring or assuming indebtedness; granting or assuming liens; making acquisitions or engaging in mergers; making dividend and certain other restricted payments; making investments; selling or otherwise transferring assets; engaging in transactions with affiliates; entering into sale and leaseback transactions; entering into burdensome agreements; changing the nature of its business; modifying its organizational documents; and amending or making prepayments on certain junior debt. The 2019 Credit Facility contained events of default that are customary for a secured credit facility. If an event of default relating to bankruptcy or other insolvency events with respect to a borrower occurred, all obligations under the 2019 Credit Facility would immediately become due and payable. If any other event of default existed under the 2019 Credit Facility, the lenders could accelerate the maturity of the obligations outstanding under the 2019 Credit Facility and exercise other rights and remedies, including charging a default rate of interest equal to 2.00% per year above the rate that would otherwise be applicable. In addition, if any event of default existed under the 2019 Credit Facility, the lenders could commence foreclosure or other actions against the collateral. If any default existed under the 2019 Credit Facility, or if the Borrower was unable to make any of the representations and warranties as stated in the 2019 Credit Facility at the applicable time, the Borrower would be unable to borrow funds or have letters of credit issued under the 2019 Credit Facility, which, depending on the circumstances prevailing at that time, could have had a material adverse effect on the Borrower’s liquidity and working capital. The 2019 Credit Facility was superseded by the 2020 Credit Facility, which was entered into on March 3, 2020, and which is discussed below. 2020 Credit Facility On March 3, 2020, the Company entered into a Senior Secured Credit Facilities Credit Agreement (as amended, the "2020 Credit Facility"), by and among the Company, as a guarantor, Ribbon Communications Operating Company, Inc., as the borrower ("Borrower"), Citizens Bank, N.A. ("Citizens"), as administrative agent, a lender, issuing lender, swingline lender, joint lead arranger and bookrunner, Santander Bank, N.A., as a lender, joint lead arranger and bookrunner, and the other lenders party thereto (each, together with Citizens Bank, N.A. and Santander Bank, N.A., referred to individually as a "Lender", and collectively, the "Lenders"). The proceeds of the Credit Agreement were used, in part, to pay off in full all obligations of the Company under the 2019 Credit Facility. The 2020 Credit Facility provides for $500 million of commitments from the Lenders to the Borrower, comprised of $400 million in term loans (the "2020 Term Loan Facility") and a $100 million facility available for revolving loans (the "2020 Revolving Credit Facility"). Under the 2020 Revolving Credit Facility, a $30 million sublimit is available for letters of credit and a $20 million submit is available for swingline loans. Under the 2020 Credit Facility, the Company was originally required to make quarterly principal payments aggregating approximately $10 million in the first year, $20 million per year for the following three years, and $30 million in the last year, with the remaining balance due on the maturity date. The 2020 Credit Facility also requires periodic interest payments until maturity. The indebtedness and other obligations under the 2020 Credit Facility are unconditionally guaranteed on a senior secured basis by the Company, Edgewater Networks, Inc., a wholly-owned subsidiary of the Company, and GENBAND Inc., wholly-owned subsidiary of the Company (together, the "Guarantors"). The facilities under the 2020 Credit Facility are secured by first-priority liens on substantially all of the assets of the Borrower and the Guarantors, including substantially all of the assets of the Company. The 2020 Credit Facility requires compliance with certain financial covenants, including a minimum Consolidated Fixed Charge Coverage Ratio and a maximum Consolidated Net Leverage Ratio (each as defined in the 2020 Credit Facility, and each tested on a quarterly basis). In addition, the 2020 Credit Facility contains various covenants that, among other restrictions, limit the Company's and its subsidiaries' ability to incur or assume indebtedness; grant or assume liens; make acquisitions or engage in mergers; sell, transfer, assign or convey assets; repurchase equity and make dividend and certain other restricted payments; make investments; engage in transactions with affiliates; enter into sale and leaseback transactions; enter into burdensome agreements; change the nature of its business; modify their organizational documents; and amend or make prepayments on certain junior debt. The 2020 Credit Facility contains events of default that are customary for a secured credit facility. If an event of default relating to bankruptcy or other insolvency events with respect to the Company or any of its subsidiaries occurs, all obligations under the 2020 Credit Facility will immediately become due and payable. If any other event of default occurs under the 2020 Credit Facility, the lenders may accelerate the maturity of the obligations outstanding under the 2020 Credit Facility and exercise other rights and remedies, including charging a default rate of interest equal to 2.00% per year above the rate that would otherwise be applicable. In addition, if any event of default exists under the 2020 Credit Facility, the lenders can commence foreclosure or other actions against the collateral. On August 18, 2020 (the "First Amendment Effective Date"), the Borrowers entered into a First Amendment to the 2020 Credit Facility (the "First Amendment"). Pursuant to an assignment and assumption agreement entered into by Citizens and certain affiliates of Whitehorse Capital on the First Amendment Date (collectively, "HIG Whitehorse"), and consented to by Citizens and the Borrower, $75 million of the 2020 Term Loan Facility, designated as the Term B Loan (the "Term B Loan"), was assigned from Citizens to HIG Whitehorse as of August 18, 2020. The remaining $325 million of the 2020 Term Loan Facility that was not assigned to HIG Whitehorse was deemed the Term A Loan (the "Term A Loan" and, together with the Term B Loan, the "Amended 2020 Term Loan Facility"). The Term A Loan and the 2020 Revolving Credit Facility mature in March 2025. The Term A Loan and 2020 Revolving Credit Facility bear interest at the Borrower's option at either the LIBOR rate plus a margin ranging from 1.50% to 3.50% per year, or the base rate (the highest of the Federal Funds Effective Rate (as defined in the 2020 Credit Facility) plus 0.50%, or the prime rate announced from time to time in The Wall Street Journal) plus a margin ranging from 0.50% to 2.50% per year (the "Applicable Margin"). The Applicable Margin varies depending on the Company's Consolidated Net Leverage Ratio (as defined in the 2020 Credit Facility). The base rate and the LIBOR rate are each subject to a zero percent floor. The Company is required to make quarterly principal payments on the Term A Loan aggregating approximately $10 million in the first year, $16 million per year in each of the next two years, $20 million in the fourth year and $16 million in the last year, with the final payment approximating $244 million due on the maturity date. The Borrower can prepay all amounts under the Term A Loan and the 2020 Revolving Credit Facility at any time without premium or penalty (other than customary LIBOR breakage costs), subject to certain notice requirements. The Term B Loan is scheduled to mature in March 2026 and bears interest, at the Borrower's option, at either the LIBOR rate plus a margin of 7.50% per year, or the base rate (the highest of the Federal Funds Effective Rate (as defined in the First Amendment) plus 0.50%, or the prime rate announced from time to time in The Wall Street Journal, plus a margin of 6.50% per year. The Term B Loan has a lower rate of amortization than the Term A Loan and is subject to a 1.0% premium if voluntarily repaid in connection with a repricing transaction (as defined in the 2020 Credit Facility) occurring prior to the six month anniversary of the First Amendment Effective Date. The Company is required to make quarterly principal payments totaling approximately $1 million in the first year and $8 million in the aggregate over the next four and a half years, with the final payment approximating $66 million. The First Amendment reduced the Borrower's ability to incur new tranches of term loans, or increases in commitments under the Amended 2020 Term Loan Facility or the 2020 Revolving Credit Facility. Specifically, such indebtedness can be incurred up to an aggregate dollar amount equal to 75% of the Company's Consolidated Adjusted EBITDA (as defined in the 2020 Credit Facility), reduced from 100% prior to the First Amendment, as of the most recently ended fiscal quarter for which financial statements have been delivered to the lenders, plus additional amounts, so long as the Borrower's Consolidated Net Leverage Ratio (as defined in the 2020 Credit Facility) does not exceed 2.25:1.00, reduced from 2.75:1.00 under the 2020 Credit Facility. The First Amendment also reduced the amount of Unrestricted Cash (as defined in the 2020 Credit Facility) used in calculating the Borrower's Consolidated Net Leverage Ratio from $25 million to $10 million. On December 1, 2020, the Borrowers entered into a Second Amendment to the 2020 Credit Facility to obtain consent for an equity exchange with AVCT in connection with the Kandy Sale, as well as to amend certain other provisions of the 2020 Credit Facility. At December 31, 2020, the Company had an outstanding Term A Loan balance of $318.5 million at an average interest rate of 3.4%, and an outstanding Term B Loan balance of $74.6 million at an average interest rate of 8.4%. The 2020 Revolving Credit Facility did not have an outstanding balance but had $5.6 million of letters of credit outstanding with an interest rate of 2.5%. The Company was in compliance with all covenants of the 2020 Credit Facility at December 31, 2020. Short-Term Loan From time to time, the Company may enter into uncommitted and unsecured short-term loans which it uses for financing exports in China. Three of these loans, aggregating $3.5 million at a weighted average interest rate of 3.97%, were entered into in March 2020, two of which were with China Zheshang Bank and one of which was with Bank of Communications Hangzhou Branch. These loans expired and were paid in full at various dates in June and July 2020. In July 2020, the Company entered into an uncommitted and unsecured short-term loan in the amount of $0.7 million at an interest rate of 4.0% with Bank of Communications Hangzhou Branch. This loan expired and was paid in full in November 2020. Letters of Credit and Performance and Bid Bonds The Company uses letters of credit and performance and bid bonds in the course of its business. At December 31, 2020, the Company had $32.6 million of letters of credit, bank guarantees, and performance and bid bonds outstanding (collectively, "Guarantees"), comprised of the $5.6 million of letters of credit under the 2020 Credit Agreement described above and $27.0 million of Guarantees under various uncommitted facilities. At December 31, 2020, the Company had cash collateral of $2.7 million supporting the Guarantees under its uncommitted facilities, which is included in Restricted cash in the consolidated balance sheet at December 31, 2020. Promissory Note In connection with the GENBAND Merger, on October 27, 2017, the Company issued a promissory note for $22.5 million to certain of GENBAND's equityholders (the "Promissory Note"). The Promissory Note did not amortize and the principal thereon was payable in full on the third anniversary of its execution. Interest on the Promissory Note was payable quarterly in arrears and accrued at a rate of 7.5% per year for the first six months after issuance, and thereafter at a rate of 10% per year. Interest that was not paid on the interest payment date would increase the principal amount of the Promissory Note. On April 29, 2019, concurrently with the closing of the 2019 Credit Facility as discussed above, the Company repaid in full all outstanding amounts under the Promissory Note, aggregating $24.7 million. The Company did not incur any early termination penalties in connection with this repayment.

OTHER LONG-TERM LIABILITIES

12 Months Ended

Dec. 31, 2020

Other Liabilities [Abstract]

OTHER LONG-TERM LIABILITIES

Other long-term liabilities consisted of the following (in thousands):


	December 31,
	2020		2019
Finance lease obligations	$	1,469	$	3,149

Restructuring	7,432		3,510
Pension obligations	11,132		9,954
Taxes payable	13,835		1,991
Interest rate swap	10,948		—
Warranty	14,855		—

Other	6,082		1,683
	65,753		20,287
Current portion	(17,472)		(3,698)
Long-term liabilities, net of current portion	$	48,281	$	16,589

The current portions of long-term liabilities are included as components of Accrued expenses and other in the Company's consolidated balance sheets.

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES

12 Months Ended

Dec. 31, 2020

Derivative Instruments and Hedging Activities Disclosure [Abstract]

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES

The Company is exposed to financial market risk related to foreign currency fluctuations and changes in interest rates. These exposures are actively monitored by management. To manage the volatility related to the exposure to changes in interest rates, the Company has entered into a derivative financial instrument. Management's objective is to reduce, where it is deemed appropriate to do so, fluctuations in earnings and cash flows associated with changes in interest rates. Ribbon's policies and practices are to use derivative financial instruments only to the extent necessary to manage exposures. Ribbon does not hold or issue derivative financial instruments for trading or speculative purposes.

The Company records derivatives on the balance sheet at fair value. The accounting for changes in the fair value of derivatives depends on the intended use of the derivative, whether the Company has elected to designate a derivative in a hedging relationship and apply hedge accounting and whether the hedging relationship has satisfied the criteria necessary to apply hedge accounting. Derivatives designated and qualifying as a hedge of the exposure to changes in the fair value of an asset, liability, or firm commitment attributable to a specific risk, such as interest rate risk, are considered fair value hedges. Derivatives designated and qualifying as a hedge of the exposure to variability in expected future cash flows, or other types of forecasted transactions, are considered cash flow hedges. Derivatives may also be designated as hedges of the foreign currency exposure of a net investment in a foreign operation. Hedge accounting generally provides for the matching of the timing of gain or loss recognition on the hedging instrument with the recognition of the changes in the fair value of the hedged asset or liability that are attributable to the hedged risk in a fair value hedge, or the earnings effect of the hedged forecasted transactions in a cash flow hedge. The Company may enter into derivative contracts that are intended to economically hedge certain of its risk even though hedge accounting does not apply or the Company elects not to apply hedge accounting.

Cash Flow Hedge of Interest Rate Risk

The Amended 2020 Term Loan Facility had an outstanding balance of $393.1 million at December 31, 2020. The 2020 Revolving Credit Facility was undrawn at December 31, 2020. The credit facilities under the 2020 Credit Agreement have variable interest rates based on LIBOR (see Note 14). As a result of exposure to interest rate movements, during March 2020, the Company entered into an interest rate swap arrangement, which effectively converted its $400 million term loan with its variable interest rate based upon one-month LIBOR to an aggregate fixed rate of 0.904%, plus a leverage-based margin as defined in the 2020 Credit Agreement. The Term A Loan continues to have a leverage-based margin and the Term B Loan has a fixed margin as defined in the 2020 Credit Agreement. The notional amount of this swap at December 31, 2020 was $400 million, and the swap matures on March 3, 2025, the same date the Term A Loan matures.

The Company’s objectives in using interest rate derivatives are to add stability to interest expense and to manage its exposure to interest rate movements. To accomplish this objective, the Company is using an interest rate swap as part of its interest rate risk management strategy. Interest rate swaps designated as cash flow hedges involve the receipt of variable amounts from a counterparty in exchange for the Company making fixed-rate payments over the life of the agreements without exchange of the underlying notional amount.

The effective portion of changes in the fair value of designated derivatives that qualify as cash flow hedges is recorded in accumulated other comprehensive (loss) income in the consolidated balance sheet and is subsequently reclassified into earnings in the period that the hedged forecasted transactions affect earnings. During the year ended December 31, 2020, such a derivative was used to hedge the variable cash flows associated with the credit facilities under the 2020 Credit Agreement, and the Company has accounted for this derivative as an effective hedge. Any ineffective portion of the change in the fair value of the derivative would be recognized directly in earnings.

Amounts reported in accumulated other comprehensive (loss) income related to the Company's derivative will be reclassified to interest expense as interest is accrued on the Company’s variable-rate debt. Based upon projected forward rates, the Company estimates as of December 31, 2020 that $3.2 million may be reclassified as an increase to interest expense over the next twelve months.

The impact of the Company’s derivative financial instrument on its consolidated statement of comprehensive income (loss) for the year ended December 31, 2020 was as follows (in thousands):





Loss recognized in other comprehensive loss on derivative (effective portion)	$	(12,671)
Amount reclassified from accumulated other comprehensive loss to interest expense (effective portion)	1,723
	$	(10,948)

The fair values and locations in the consolidated balance sheet at December 31, 2020 of the Company's derivative liability designated as a hedging instrument were as follows (in thousands):


	Balance sheet location
Interest rate derivative - liability derivative	Accrued expenses and other	$	3,157
Interest rate derivative - liability derivative	Other long-term liabilities	$	7,791

The Company has classified the interest rate derivative aggregating $10.9 million at December 31, 2020 as a Level 2 fair value measurement within the fair value hierarchy (see Note 6).

REVENUE RECOGNITION

12 Months Ended

Dec. 31, 2020

Revenue from Contract with Customer [Abstract]

REVENUE RECOGNITION

The Company's typical performance obligations include the following:

Performance Obligation

When Performance Obligation is Typically Satisfied

When Payment is Typically Due

Software and Product Revenue

Software licenses (perpetual or term)

Upon transfer of control; typically, when made available for download (point in time)

Generally, within 30 days of invoicing except for term licenses, which may be paid for over time

Software licenses (subscription)

Upon activation of hosted site (over time)

Generally, within 30 days of invoicing

Hardware

When control of the hardware passes to the customer; typically, upon delivery (point in time)

Generally, within 30 days of invoicing

Software upgrades

Upon transfer of control; typically, when made available for download (point in time)

Generally, within 30 days of invoicing

Customer Support Revenue

Customer support

Ratably over the course of the support contract (over time)

Generally, within 30 days of invoicing

Professional Services

Other professional services (excluding training services)

As work is performed (over time)

Generally, within 30 days of invoicing (upon completion of services)

Training

When the class is taught (point in time)

Generally, within 30 days of services being performed

Significant Judgments

The Company's contracts with customers often include promises to transfer multiple products and services to the customer. Determining whether products and services are considered distinct performance obligations that should be accounted for separately versus together may require significant judgment.

Judgment is required to determine the standalone selling price for each distinct performance obligation. The Company typically has more than one standalone selling price ("SSP") for individual products and services due to the stratification of those products and services by customers and circumstances. In these instances, the Company may use information such as the size of the customer and geographic region in determining the SSP.

Deferred Revenue

Deferred revenue is a contract liability representing amounts collected from or invoiced to customers in excess of revenue recognized. This results primarily from the billing of annual customer support agreements where the revenue is recognized over the term of the agreement. The value of deferred revenue will increase or decrease based on the timing of invoices and recognition of revenue.

Disaggregation of Revenue

The Company disaggregates its revenue from contracts with customers based on the nature of the products and services and the geographic regions in which each customer is domiciled. The Company's total revenue for the years ended December 31, 2020, 2019 and 2018 was disaggregated geographically as follows:


Year ended December 31, 2020	Product revenue		Service revenue (maintenance)		Service revenue (professional services)		Total revenue
United States	$	201,347	$	132,661	$	48,611	$	382,619
Europe, Middle East and Africa	149,567		73,475		25,226		248,268

Asia Pacific	90,201		36,628		19,627		146,456
Other	26,797		32,052		7,603		66,452
	$	467,912	$	274,816	$	101,067	$	843,795


Year ended December 31, 2019	Product revenue		Service revenue (maintenance)		Service revenue (professional services)		Total revenue
United States	$	170,937	$	133,271	$	37,085	$	341,293
Europe, Middle East and Africa	42,262		43,186		12,279		97,727

Asia Pacific	30,617		27,798		10,721		69,136
Other	18,214		29,973		6,768		54,955
	$	262,030	$	234,228	$	66,853	$	563,111


Year ended December 31, 2018	Product revenue		Service revenue (maintenance)		Service revenue (professional services)		Total revenue
United States	$	169,510	$	132,282	$	35,832	$	337,624
Europe, Middle East and Africa	37,833		46,856		11,794		96,483

Asia Pacific	53,683		23,555		9,427		86,665
Other	17,988		31,273		7,872		57,133
	$	279,014	$	233,966	$	64,925	$	577,905

The Company's product revenue from its direct sales program and from indirect sales through its channel partner program for the years ended December 31, 2020, 2019 and 2018 was as follows (in thousands):


	Year ended December 31,
	2020		2019		2018
Indirect sales through channel program	$	134,876	$	94,639	$	69,232
Direct sales	333,036		167,391		209,782
	$	467,912	$	262,030	$	279,014

The Company's product revenue from sales to enterprise customers and from sales to service provider customers for the years ended December 31, 2020, 2019 and 2018 was as follows (in thousands):


	Year ended December 31,
	2020		2019		2018
Sales to enterprise customers	$	138,469	$	70,548	$	57,534
Sales to service provider customers	329,443		191,482		221,480
	$	467,912	$	262,030	$	279,014

The Company's product revenue and service revenue components by segment for the years ended December 31, 2020, 2019 and 2018 was as follows (in thousands):


	Year ended December 31,
	2020	2019	2018
Product revenue
Cloud and Edge	275,445	262,030	279,014
IP Optical Networks	192,467	—	—
Total product revenue	467,912	262,030	279,014

Service revenue
Maintenance
Cloud and Edge	229,035	234,228	233,966
IP Optical Networks	45,781	—	—
Total maintenance revenue	274,816	234,228	233,966
Professional services
Cloud and Edge	78,790	66,853	64,925
IP Optical Networks	22,277	—	—
Total professional services revenue	101,067	66,853	64,925
Total service revenue	375,883	301,081	298,891

Revenue Contract Balances

The timing of revenue recognition, billings and cash collections results in billed accounts receivable, unbilled receivables, which are contract assets, and customer advances and deposits, which are contract liabilities, in the Company's consolidated balance sheets. Amounts are billed as work progresses in accordance with agreed-upon contractual terms, either at periodic intervals or upon achievement of contractual milestones. Completion of services and billing may occur subsequent to revenue recognition, resulting in contract assets. The Company may receive advances or deposits from its customers before revenue is recognized, resulting in contract liabilities which are classified as deferred revenue. These assets and liabilities are reported in the Company's consolidated balance sheets on a contract-by-contract basis as of the end of each reporting period. Changes in the contract asset and liability balances during the years ended December 31, 2020 and 2019 were not materially impacted by any factors other than billing and revenue recognition. Nearly all of the Company's deferred revenue balance is related to services revenue, primarily customer support contracts. Unbilled receivables stem primarily from engagements where services have been performed; however, billing cannot occur until services are completed.

In some arrangements, the Company allows customers to pay for term-based software licenses and products over the term of the software license. The Company also sells SaaS-based software under subscription arrangements, with payment terms over the term of the SaaS agreement. Amounts recognized as revenue in excess of amounts billed are recorded as unbilled receivables. Unbilled receivables that are anticipated to be invoiced in the next twelve months are included in Accounts receivable on the Company's consolidated balance sheets. The changes in the Company's accounts receivable, unbilled receivables and deferred revenue balances for the years ended December 31, 2020 and 2019 were as follows (in thousands):


	Accounts receivable		Unbilled accounts receivable		Deferred revenue (current)		Deferred revenue (long-term)
Balance at January 1, 2020	$	168,502	$	24,204	$	100,406	$	20,482
Increase (decrease), net	10,829		34,203		(3,582)		5,528
Balance at December 31, 2020	$	179,331	$	58,407	$	96,824	$	26,010


	Accounts receivable		Unbilled accounts receivable		Deferred revenue (current)		Deferred revenue (long-term)
Balance at January 1, 2019	$	174,310	$	13,543	$	105,087	$	17,572
Increase (decrease), net	(5,808)		10,661		(4,681)		2,910
Balance at December 31, 2019	$	168,502	$	24,204	$	100,406	$	20,482

The Company recognized approximately $99 million of revenue in the year ended December 31, 2020 that was recorded as deferred revenue at December 31, 2019 and approximately $94 million of revenue in the year ended December 31, 2019 that

was recorded as deferred revenue at December 31, 2018. Of the Company's deferred revenue reported as long-term in its consolidated balance sheet at December 31, 2020, the Company expects that approximately $15 million will be recognized as revenue in 2022, approximately $6 million will be recognized as revenue in 2023 and approximately $5 million will be recognized as revenue in 2024 and beyond.

All freight-related customer invoicing is recorded as revenue, while the shipping and handling costs that occur after control of the promised goods or services transfer to the customer are reported as fulfillment costs, a component of Cost of revenue - product in the Company's consolidated statements of operations.

Deferred Commissions Cost

Sales commissions earned by the Company's employees are considered incremental and recoverable costs of obtaining a contract with a customer. Under ASC 605, the costs associated with obtaining a customer contract were expensed in the period the revenue was earned. Under ASC 606, these payments have been deferred on our consolidated balance sheet and are being amortized over the expected life of the customer contract, which is five years. At December 31, 2020 and 2019, the Company had $4.1 million and $3.6 million, respectively, of deferred sales commissions capitalized.

- Definition

The entire disclosure of revenue from contract with customer to transfer good or service and to transfer nonfinancial asset. Includes, but is not limited to, disaggregation of revenue, credit loss recognized from contract with customer, judgment and change in judgment related to contract with customer, and asset recognized from cost incurred to obtain or fulfill contract with customer. Excludes insurance and lease contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-URI http://asc.fasb.org/topic&trid=49130388

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

OPERATING SEGMENT INFORMATION

12 Months Ended

Dec. 31, 2020

Segment Reporting [Abstract]

OPERATING SEGMENT INFORMATION

The Company has two reportable segments, which are intended to align with the manner in which the business is managed: Cloud and Edge, and IP Optical Networks.

The Cloud and Edge segment provides secure and reliable software and hardware products, solutions and services for enabling Voice over Internet Protocol ("VoIP") communications, Voice over Long-Term Evolution ("VoLTE") and Voice Over 5G ("VoNR") communications and Unified Communications and Collaboration ("UC&C") within service provider and enterprise networks and from the cloud. The Cloud and Edge products are increasingly software-centric and cloud-native for deployment on private, public or hybrid cloud infrastructures, in data centers, on enterprise premises and within service provider networks. Ribbon's Cloud and Edge product portfolio consists of our Session Border Controller ("SBC") products and our Network Transformation ("NTR") products.

The IP Optical Networks segment provides high-performance, secure and reliable hardware and software products solutions for IP networking, switching, routing and optical transport designed to support and enable technologies like 5G, distributed cloud computing and corresponding applications by delivering ultra-low cost-per-bit transport and multi-service flexibility. The IP Optical Networks portfolio offers multiple solutions, including 5G-native solutions for mobile backhaul, metro and edge aggregation, core networking, data center interconnect, legacy NTR and transport solutions for wholesale carriers. This portfolio is offered to service provider, enterprise and industry verticals with critical transport network infrastructures including utilities, government, defense, transportation, and education and research.

The Company has not provided segment asset information as such information is not provided to the CODM and accordingly, asset information is not used in assessing segment performance. Segment revenue and expense included in the tables below represent direct revenue and expense attributable to each segment. Please see Note 10 for information regarding the allocation of goodwill between segments.

The CODM utilizes revenue, adjusted gross margin (revenue divided by gross profit) and adjusted EBITDA (earnings before interest, taxes, depreciation and amortization) to measure and assess each segment's performance. The Company calculates adjusted gross margin by excluding from cost of revenue: stock-based compensation, acquisition-related inventory adjustments and acquisition-related facilities adjustments. The Company calculates adjusted EBITDA by excluding from income (loss) from operations: depreciation; amortization of acquired intangible assets; stock-based compensation; acquisition-related inventory adjustments; acquisition-related facilities adjustments; certain litigation costs; impairment of goodwill; settlement expense;, cancelled debt offering costs; acquisition-, disposal- and integration-related expense; and restructuring and related expense. These adjusted measures may also exclude other items in future periods that the Company believes are not part of the Company's core business. Adjusted gross profit and adjusted EBITDA are not financial measures determined in accordance with U.S. GAAP and may not be comparable to similarly titled measures used by other companies and should not be considered a substitute for income (loss) from operations or gross profit or other results reported in accordance with U.S.

GAAP. See below for a reconciliation of adjusted gross profit to gross profit and adjusted EBITDA to income (loss) from operations, as those are the most directly comparable U.S. GAAP measures.

Financial information for the IP Optical Networks segment is not presented for any years prior to 2020, as this segment arose from the ECI Acquisition, and accordingly is not included in the Company's consolidated financial statements for the years December 31, 2019 and 2018. The tables below provide net sales, adjusted gross profit, adjusted EBITDA and depreciation expense by reportable segment for the years ended December 31, 2020, 2019 and 2018 (in thousands):


	Year ended December 31,
	2020		2019		2018
Segment revenue:
Cloud and Edge	$	583,270	$	563,111	$	577,905
IP Optical Networks	260,525		—		—
Revenue	$	843,795	$	563,111	$	577,905



	Year ended December 31,
	2020		2019		2018
Segment adjusted gross profit:
Cloud and Edge	$	385,137	$	355,211	$	348,076
IP Optical Networks	110,845		—		—
Total segment adjusted gross profit	495,982		355,211		348,076


Stock-based compensation expense	(875)		(554)		(459)
Acquisition-related inventory and facilities adjustments	(2,000)		—		(309)


Gross profit	$	493,107	$	354,657	$	347,308


Segment adjusted EBITDA:
Cloud and Edge	$	135,678	$	85,701	$	51,934
IP Optical Networks	(4,512)		—		—
Total segment adjusted EBITDA	131,166		85,701		51,934


Depreciation	(17,188)		(11,949)		(11,200)
Amortization of intangible assets	(60,910)		(49,225)		(49,723)


Stock-based compensation	(13,899)		(12,601)		(11,072)
Acquisition-related inventory and facilities adjustments	(2,000)		—		(966)


Litigation costs	(2,101)		(7,734)		(7,682)
Impairment of goodwill	—		(164,300)		—
Settlement expense	—		—		(1,730)
Cancelled debt offering costs	—		—		(1,003)
Acquisition-, disposal- and integration-related expense	(17,164)		(12,953)		(16,951)
Restructuring and related expense	(16,235)		(16,399)		(17,015)

Income (loss) from operations	$	1,669	$	(189,460)	$	(65,408)

Depreciation expense:
Cloud and Edge	$	12,111	$	11,949	$	11,200
IP Optical Networks	5,077		—		—
Depreciation expense	$	17,188	$	11,949	$	11,200

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

MAJOR CUSTOMERS

12 Months Ended

Dec. 31, 2020

Risks and Uncertainties [Abstract]

MAJOR CUSTOMERS

MAJOR CUSTOMERSThe following customers contributed 10% or more of the Company's revenue in at least one of the years ended December

31, 2020, 2019 and 2018:


	Year ended December 31,
	2020	2019	2018
Verizon Communications Inc.	15%	17%	17%
AT&T Inc.	*	12%	*

* Less than 10% of total revenue.

At December 31, 2020, one customer accounted for 10% or more of the Company's accounts receivable balance, representing approximately 12% in the aggregate of total accounts receivable. At December 31, 2019, one customer accounted for 10% or more of the Company's accounts receivable balance, representing approximately 32% of total accounts receivable. The Company performs ongoing credit evaluations of its customers and generally does not require collateral on accounts receivable. The Company maintains an allowance for doubtful accounts and such losses have been within management's expectations.

COMMON STOCK REPURCHASES	12 Months Ended
COMMON STOCK REPURCHASES	Dec. 31, 2020
Equity [Abstract]
COMMON STOCK REPURCHASES	COMMON STOCK REPURCHASESIn the second quarter of 2019, the Company's Board of Directors (the "Board") approved a stock repurchase program (the "Repurchase Program") pursuant to which the Company may repurchase up to $75 million of its common stock prior to April 18, 2021. Repurchases under the Repurchase Program may be made in the open market, in privately negotiated transactions or otherwise, with the amount and timing of repurchases depending on market conditions and corporate discretion. The Repurchase Program does not obligate the Company to acquire any particular amount of common stock and may be extended, modified, suspended or discontinued at any time at the Board's discretion. The stock repurchases are being funded using the Company's working capital. During the year ended December 31, 2019, the Company spent $4.5 million, including transaction fees, to repurchase and retire 1.0 million shares of its common stock under the Repurchase Program. The Company did not repurchase any common stock during the year ended December 31, 2020. At December 31, 2020, the Company had $70.5 million remaining under the Repurchase Program for future repurchases.

STOCK-BASED COMPENSATION PLANS

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

STOCK-BASED COMPENSATION PLANS

2019 Stock Incentive Plan

At the Company's annual meeting of stockholders held on June 5, 2019, the Company's stockholders approved the Ribbon Communications Inc. Incentive Award Plan (the "2019 Plan"). The 2019 Plan had previously been approved by the Board, subject to stockholder approval. At the Company's annual meeting of stockholders held on June 2, 2020, the Company's stockholders approved an amendment to the 2019 Plan to increase the number of shares of the Company's common stock authorized for issuance under the 2019 Plan by 7.5 million shares.

Under the 2019 Plan, the Company may grant awards aggregating up to 14.5 million shares of common stock (subject to adjustment in the event of stock splits and other similar events), plus 5.1 million shares of common stock that remained available for issuance under the Company's Amended and Restated Stock Incentive Plan (the "2007 Plan") on June 5, 2019, plus any shares covered by awards under the 2007 Plan (or the Company's other prior equity compensation plans) that again become available for grant pursuant to the provisions of the 2007 Plan. The 2019 Plan provides for the grant of options to purchase the Company's common stock ("stock options"), stock appreciation rights ("SARs"), restricted stock awards ("RSAs"), performance-based stock awards ("PSAs"), restricted stock units ("RSUs"), performance-based stock units ("PSUs") and other stock- or cash-based awards. Awards can be granted under the 2019 Plan to the Company's employees, officers and non-employee directors, as well as consultants and advisors of the Company and its subsidiaries. At December 31, 2020, there were 8.9 million shares available for future issuance under the 2019 Plan.

2007 Plan

The Company's 2007 Plan provided for the award of stock options, SARs, RSAs, RSUs, PSAs, PSUs and other stock-based awards to employees, officers, non-employee directors, consultants and advisors of the Company and its subsidiaries. On and

following June 5, 2019, with the exception of shares underlying awards outstanding as of that date, no additional shares may be granted under the 2007 Plan.

2002 Stock Option Plan

In connection with the Edgewater Acquisition, the Company assumed Edgewater's Amended and Restated 2002 Stock Option Plan, converted all then-outstanding options to purchase Edgewater common stock (the "Assumed Options") to Ribbon stock options (the "Ribbon Replacement Options"), and subsequently renamed it the 2002 Stock Option Plan (the "2002 Plan"). The Ribbon Replacement Options are vesting under the same schedules as the respective Edgewater Options. The fair values of the Assumed Options were estimated using a Black-Scholes option pricing model. The Company recorded $0.7 million as additional purchase consideration for the fair value of the Assumed Options. The fair value of the Ribbon Replacement Options attributable to future service totaled $1.0 million, which will be fully expensed by the end of 2021.

2012 Stock Incentive Plan

In connection with the acquisition of Performance Technologies, Inc. ("PT"), the Company assumed PT's 2012 Amended Performance Technologies, Incorporated Omnibus Incentive Plan, and subsequently renamed it the 2012 Stock Incentive Plan (the "2012 Plan"). In December 2014, all of the unissued shares under the 2012 Plan were transferred to the 2007 Plan. Any outstanding awards under the 2012 Plan that in the future expire, terminate, are canceled, surrendered or forfeited, or are repurchased by the Company will be returned to the 2019 Plan. Accordingly, at December 31, 2020 there were no shares available for future issuance under the 2012 Plan.

2008 Stock Incentive Plan

In connection with the acquisition of Network Equipment Technologies, Inc. ("NET"), the Company assumed NET's 2008 Equity Incentive Plan and subsequently renamed it the 2008 Stock Incentive Plan (the "2008 Plan"). In December 2014, all of the unissued shares under the 2008 Plan were transferred to the 2007 Plan. Any outstanding awards under the 2008 Plan that in the future expire, terminate, are canceled, surrendered or forfeited, or are repurchased by the Company will be returned to the 2019 Plan. Accordingly, at December 31, 2020 there were no shares available for future issuance under the 2008 Plan.

Executive Equity Arrangements

Inducement Awards

In connection with his appointment as President and Chief Executive Officer of Ribbon, and as an inducement for Bruce McClelland's ("Mr. McClelland") commencement of employment, the Company awarded Mr. McClelland sign-on equity grants, comprised of an RSU grant and a PSU grant with both market service conditions (the "Inducement PSUs") on March 16, 2020. Subject to Mr. McClelland's continued employment, 462,963 RSUs are eligible to vest on the earlier of March 16, 2021 or the date of the consummation of a change in control of the Company and, upon vesting, will be settled in shares of Ribbon's common stock. The RSUs had a grant date fair value of $1.0 million on the date of grant. Subject to Mr. McClelland's continued employment, the PSUs are eligible to vest and be settled in up to 4,750,000 shares of Ribbon common stock upon the achievement of specified share price thresholds on or prior to September 1, 2024. These grants are reported in the applicable tables below.

Performance-Based Stock Grants

In addition to granting RSAs and RSUs and the aforementioned Inducement PSUs, to its executives and certain of its employees, the Company also grants PSUs to certain of its executives.

PSU Grants - 2020 and 2019. In both 2020 and 2019, the Company granted certain of its executives (the "2020 PSUs" and "2019 PSUs", respectively), of which 60% of each executive's PSU grant had both performance service conditions (the "Performance PSUs") and 40% had both market and service conditions (the "Market PSUs").

Each executive's Performance PSU grant is comprised of three consecutive fiscal year performance periods beginning in the year of grant (each, a "Fiscal Year Performance Period"), with one-third of the Performance PSUs attributable to each Fiscal

Year Performance Period. The number of shares that will be vest for each Fiscal Year Performance Period, if any, will be based on the achievement of certain metrics related to the Company's financial performance for the applicable year on a standalone basis (each, a "Fiscal Year Performance Condition"). The Company's achievement of the goals for each Fiscal Year Performance Condition (and the number of shares of Company common stock to vest as a result thereof) are being measured on a linear sliding scale in relation to specific threshold, target and stretch performance conditions, with any shares earned vesting in the first quarter of the fiscal year following the third Performance Period of the grant, pending each executive's continued employment with the Company through that date. The number of shares of common stock underlying the Performance PSUs that can be earned will in no event exceed 200% of the Performance PSUs. Shares subject to the Performance PSUs that fail to be earned will be forfeited.

The Market PSUs have one three-year performance period, beginning January 1 in the year of grant and ending on December 31, three years thereafter (the "Market Performance Period"). The number of shares subject to the Market PSUs that will vest, if any, will be dependent upon the Company's total shareholder return ("TSR") compared with the TSR of the companies included in the Nasdaq Telecommunications Index for the applicable Market Performance Period, measured by the Compensation Committee after the Market Performance Period ends, with any shares earned vesting in the first quarter of the fiscal year following the respective Market Performance Period, pending each executive's continued employment with the Company through that date. The number of shares of common stock underlying the Market PSUs that can be earned will in no event exceed 200% of the Market PSUs. Shares subject to the Market PSUs that fail to be earned will be forfeited.

In addition, in connection with his appointment as Executive Vice President and General Manager, Packet Optical Networking, the Company granted Sam Bucci 133,333 PSUs (the "Bucci Stock Price PSUs") with both market and service conditions. Subject to Mr. Bucci's continued employment, the Bucci Stock Price PSUs were eligible to vest and be settled in shares of Ribbon common stock upon the achievement of a specific share price threshold on or prior to January 31, 2022. The price share threshold was met on February 12, 2021 and the shares vested and were released on February 15, 2021.

2020 PSUs. From June through September 2020, the Company granted certain of its executives an aggregate of 823,369 PSUs, of which 494,020 PSUs had both performance and service conditions (the “2020 Performance PSUs”) and 329,349 had both market and service conditions (the “2020 Market PSUs”). The three Fiscal Year Performance Periods for the 2020 Performance PSUs are the years ended December 31, 2020, 2021 and 2022 (respectively, the “2020 Performance Period”, “2021 Performance Period” and “2022 Performance Period”). As of December 31, 2020, the Company determined that the grant date criteria for the 2021 Performance Period and the 2022 Performance Period had not been met, as the goals for these performance periods had not been established by the Company, and accordingly, no expense has been recorded related to these performance periods.

2019 PSUs. In March and April 2019, the Company granted certain of its executives an aggregate of 872,073 PSUs, of which 523,244 PSUs had both performance and service conditions (the "Performance PSUs") and 348,829 PSUs had both market and service conditions (the "Market PSUs"). The three Fiscal Year Performance Periods for the 2019 Performance PSUs are the years ended December 31, 2019, 2020 and 2021 (respectively, the “2019 Performance Period”, “2020 Performance Period” and “2021 Performance Period”). In the third quarter of 2019, the Company adjusted the goals for the 2019 Performance Period to reflect the changes to the Company's calculation of certain metrics. There was no incremental expense in connection with this modification. In March 2020, the Compensation Committee determined that the performance conditions for the 2019 Performance Period had been satisfied at the 30.493% level. As of December 31, 2020, the Company determined that the grant date criteria for the 2021 Fiscal Year Performance Period had not been met, as the goals for the 2021 Performance Period had not been established by the Company, and accordingly, no expense has been recorded related to this performance period.

PSU Grants - 2018. In May 2018, the Company granted its then-current President and Chief Executive Officer ("Mr. Hobbs") 195,000 PSUs with both performance and service conditions (the “2018 PSUs”). Of the 195,000 2018 PSUs, one-half each would vest based on the achievement of two separate metrics related to the Company’s 2018 financial performance (the “2018 Performance Conditions”). The Company’s achievement of the 2018 Performance Conditions (and the shares of Company common stock to vest as a result thereof) were measured on a linear sliding scale in relation to specific threshold, target and stretch performance conditions. The number of shares of common stock to be received upon vesting of the 2018 PSUs would in no event exceed 150% of the 2018 PSUs. The Compensation Committee ultimately determined that the performance conditions for the 2018 PSUs had been achieved at the 150% level, for a total of 292,500 shares eligible to be issued (the "2018 Shares Earned"), pending Mr. Hobbs' continued employment with the Company through December 31, 2020.

In connection with his separation from the Company effective December 31, 2019, the vesting schedule for the 2018 Shares Earned was accelerated and the shares were released on January 30, 2020. The release of these shares is included in the PSU table below.

Accounting for Performance PSUs. Once the grant date criteria have been met for a Fiscal Year Performance Period, the Company records stock-based compensation expense for the respective shares underlying the PSUs based on its assessment of the probability that the respective performance condition will be achieved and the level, if any, of such achievement. The Compensation Committee determines the number of shares earned, if any, after the Company's financial results for each Fiscal Year Performance Period are finalized. Upon the determination by the Compensation Committee of the number of shares that will be received upon vesting of the related Performance PSUs, such number of shares becomes fixed and the unamortized expense is recorded through the remainder of the service period, at which time such Performance PSUs earned, if any, will vest, pending each executive's continued employment with the Company through that date.

Accounting for Market PSUs. PSUs that include a market condition require the use of a Monte Carlo simulation approach to model future stock price movements based upon the risk-free rate of return, the volatility of each entity and the pair-wise covariance between each entity. These results are then used to calculate the grant date fair values of the respective PSUs. The Company is required to record expense for the PSUs with market conditions through their respective final vesting dates regardless of the number of shares that are ultimately earned.

Stock-for-Cash Bonus Election

In connection with the Company’s annual incentive program, certain executives of the Company were given the choice to receive a portion of their fiscal year 2018 bonuses (the “2018 Bonus”), if any were earned, in the form of shares of the Company’s common stock (the “2018 Bonus Shares”). Each executive could also elect not to participate in this program and to earn his or her 2018 Bonus, if any, in the form of cash. The Company determined that the grant date criteria for the 2018 Bonus Shares had not been met as of December 31, 2018, as the number of shares to be granted to each executive had not been determined. The Company recorded stock-based compensation expense totaling $1.1 million in connection with the Stock Bonus Program in 2018 and recorded a liability in connection with the future issuance of the 2018 Bonus Shares. This liability was reclassified to equity at the time the shares were granted on March 15, 2019.

Accelerated Vesting of Stock Units

In connection with the separation of several executives from the Company in the years ended December 31, 2020 and 2019, the Company accelerated the vesting of certain of their outstanding RSUs and PSUs in accordance with their respective terms of employment with the Company, with the potential for a portion of certain other PSUs aggregating approximately 43,000 shares to be released to two of these former executives on a pro rata basis subject to achievement of the related performance or market conditions for the performance periods through their respective 2020 separation dates.

Stock Options

The Company has not granted stock options since 2017. Outstanding stock options granted under the Company's plans expire either seven or ten years from the date of grant. The grant date fair value of stock options, adjusted for estimated forfeitures, is recognized as expense on a straight-line basis over the requisite service period, which is generally the vesting period. Forfeitures are estimated based on historical experience.

The activity related to the Company's outstanding stock options during the year ended December 31, 2020 was as follows:


	Number of Shares	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (in thousands)
Outstanding at January 1, 2020	297,124	$	11.55
Granted	—	$	—

Exercised	(38,288)	$	1.81
Forfeited	(6,055)	$	2.78
Expired	(45,071)	$	15.72
Outstanding at December 31, 2020	207,710	$	12.69	3.73	$	262
Vested or expected to vest at December 31, 2020	207,518	$	12.70	3.73	$	261
Exercisable at December 31, 2020	201,138	$	12.93	3.67	$	241

The total intrinsic values of options exercised were $0.1 million for the year ended December 31, 2020, $0.5 million for the year ended December 31, 2019 and approximately $39,000 for the year ended December 31, 2018.

The Company received cash from option exercises of $0.1 million in the year ended December 31, 2020, $0.2 million in the year ended December 31, 2019 and $0.1 million in the year ended December 31, 2018.

Restricted Stock Grants - Restricted Stock Awards and Restricted Stock Units

The Company's outstanding restricted stock grants consist of both RSAs and RSUs. Holders of unvested RSAs have voting rights and rights to receive dividends, if declared; however, these rights are forfeited if the underlying unvested RSA shares are forfeited. Holders of unvested RSUs do not have such voting and dividend rights. The grant date fair value of restricted stock grants, adjusted for estimated forfeitures, is recognized as expense on a straight-line basis over the requisite service period. The fair value of restricted stock grants is determined based on the market value of the Company's shares on the date of grant.

The activity related to the Company's RSAs for the year ended December 31, 2020 was as follows:


	Shares	Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2020	487,976	$	6.87
Granted	—	$	—


Vested	(360,204)	$	6.82
Forfeited	(40,789)	$	6.96
Unvested balance at December 31, 2020	86,983	$	7.04

The activity related to the Company's RSUs for the year ended December 31, 2020 was as follows:


	Shares	Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2020	2,790,060	$	5.11
Granted	6,550,106	$	2.96

Vested	(1,886,486)	$	4.65
Forfeited	(922,570)	$	3.50
Unvested balance at December 31, 2020	6,531,110	$	3.32

The total grant date fair value of vested restricted stock grant shares was $11.2 million in the year ended December 31, 2020, $9.9 million in the year ended December 31, 2019 and $9.7 million in the year ended December 31, 2018.

Performance-Based Stock Units

Holders of unvested PSUs do not have voting and dividend rights. The Company recognizes stock-based compensation expense for PSUs without market conditions on a straight-line basis, with the amount recorded based upon the expected level of achievement as of each period-end, recording cumulative adjustments in the period when the expected level of achievement changes. The Company recognizes the grant date fair value of PSUs on a graded attribution basis through the vest date of the respective awards so long as it remains probable that the related service conditions will be satisfied.

The activity related to the Company's PSUs for the year ended December 31, 2020 was as follows:


	Shares	Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2020	1,067,073	$	5.94
Granted	5,804,202	$	1.41

Vested	(323,752)	$	5.52
Forfeited	(511,592)	$	5.37
Unvested balance at December 31, 2020	6,035,931	$	1.56

The total grant date fair value of vested performance-based stock grant shares was $1.8 million in the year ended December 31, 2020, $0.1 million in the year ended December 31, 2019 and $0.6 million in the year ended December 31, 2018.

ESPP

The ESPP was designed to provide eligible employees of the Company and its participating subsidiaries an opportunity to purchase common stock of the Company through accumulated payroll deductions. The last purchase under the ESPP was on November 29, 2019, and the ESPP expired on May 20, 2020.

Stock-Based Compensation

The consolidated statements of operations included stock-based compensation for the years ended December 31, 2020, 2019 and 2018 as follows (in thousands):


	Year ended December 31,
	2020		2019		2018
Product cost of revenue	$	174	$	76	$	114
Service cost of revenue	701		478		345
Research and development	2,968		1,898		1,797
Sales and marketing	4,129		3,028		2,935
General and administrative	5,927		7,121		5,881
	$	13,899	$	12,601	$	11,072

There was an income tax benefit for employee stock-based compensation expense for the year ended December 31, 2020, but no income tax benefit for the years ended December 31, 2019 and 2018 due to the valuation allowance recorded.

In the year ended December 31, 2019, the Company recorded nominal incremental expense related to the accelerated vesting of RSUs and PSUs held by certain former executives of the Company in connection with their separations from the Company. Stock-based compensation expense recorded for the year ended December 31, 2019 included $1.6 million of incremental expense related to the accelerated vesting of RSUs and PSUs held by the former President and Chief Executive Officer in connection with his separation from the Company.

At December 31, 2020, there was $19.3 million, net of expected forfeitures, of unrecognized stock-based compensation expense related to unvested stock options, RSAs, RSUs and PSUs. This expense is expected to be recognized over a weighted average period of approximately two years.

Common Stock Reserved

At December 31, 2020, there were 8,888,677 shares of common stock reserved for future issuance under the 2019 Plan. The Company's policy is to issue authorized but unissued shares upon the exercise of stock options, to grant restricted common stock, to settle restricted stock units and performance-based stock units, and to authorize the purchase of shares of the Company's common stock under the ESPP.

LEASES

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

LEASES

The Company has operating and finance leases for corporate offices, research and development facilities, and certain equipment. Operating leases are reported separately in the Company's consolidated balance sheet at December 31, 2020 and 2019. Assets acquired under finance leases are included in Property and equipment, net, in the consolidated balance sheets at December 31, 2020 and 2019.

The Company determines if an arrangement is a lease at inception. A contract is determined to contain a lease component if the arrangement provides the Company with a right to control the use of an identified asset. Lease agreements may include lease and non-lease components. In such instances for all classes of underlying assets, the Company does not separate lease and non-lease components but rather, accounts for the entire arrangement under leasing guidance. Leases with an initial term of 12 months or less are not recorded on the balance sheet and lease expense for these leases is recognized on a straight-line basis over the lease term.

Right-of-use assets and lease liabilities are initially measured based on the present value of the future minimum fixed lease payments (i.e., fixed payments in the lease contract) over the lease term at the commencement date. As the Company's existing leases do not have a readily determinable implicit rate, the Company uses its incremental borrowing rate based on the information available at the commencement date in determining the present value of future minimum fixed lease payments. The Company calculates its incremental borrowing rate to reflect the interest rate that it would have to pay to borrow on a collateralized basis an amount equal to the lease payments in a similar economic environment over a similar term and considers its historical borrowing activities and market data from entities with comparable credit ratings in this determination. The measurement of the right-of-use asset also includes any lease payments made prior to the commencement date (excluding any lease incentives) and initial direct costs incurred. The Company assessed its right-of-use assets for impairment as of December 31, 2020 and 2019 and determined no impairment had occurred.

Lease terms may include options to extend or terminate the lease and the Company incorporates such options in the lease term when it has the unilateral right to make such an election and it is reasonably certain that the Company will exercise that option. In making this determination, the Company considers its prior renewal and termination history and planned usage of the assets under lease, incorporating expected market conditions.

In connection with the 2019 Restructuring Initiative, certain lease assets related to facilities are being partially or fully vacated as the Company consolidates its facilities. The Company has no plans to enter into sublease agreements for certain facilities. The Company ceased use of these facilities in the first and fourth quarters of 2020 and in the third quarter of 2019. Accordingly, the Company accelerated the amortization of the associated lease assets through the planned cease-use date of each facility, resulting in additional amortization expense of $0.6 million and $3.7 million in the years ended December 31, 2020 and 2019, respectively. The Company also recorded a liability aggregating $0.9 million in 2019 for all future estimated variable lease costs related to these facilities. This incremental accelerated amortization and accrual for all estimated future variable lease costs are included in Restructuring and related expense in the Company's consolidated statements of operations for the years ended December 31, 2020 and 2019. The Company may incur additional future expense if it is unable to sublease

other locations included in the Facilities Initiative.

The Company leases its corporate offices and other facilities under operating leases, which expire at various times through 2032. The Company's corporate headquarters is located in a leased facility in Westford, Massachusetts under a lease that expires in August 2028. The Company's finance leases primarily consist of equipment.

In December 2020, the Company began relocating from its leased Plano, Texas facility to the recently constructed building space in North Dallas, Texas as part of its 2019 Restructuring and Facilities Consolidation Initiative. The Company's relocation from its leased Plano, Texas facility is expected to be completed in the first quarter of 2021.

The Company's right-of-use lease assets and lease liabilities at December 31, 2020 and December 31, 2019 were as follows (in thousands):


		December 31,
	Classification	2020		2019
Assets
Operating lease assets	Operating lease right-of-use assets	$	69,757	$	36,654
Finance lease assets*	Property and equipment, net	983		2,420
Total leased assets		$	70,740	$	39,074

Liabilities
Current
Operating	Operating lease liabilities	$	17,023	$	7,719
Finance	Accrued expenses and other	902		1,005
Noncurrent
Operating	Operating lease liabilities, net of current	72,614		37,202
Finance	Other long-term liabilities	568		2,144
Total lease liabilities		$	91,107	$	48,070

* Finance lease assets were recorded net of accumulated depreciation of $1.9 million and $2.0 million at December 31, 2020 and December 31, 2019, respectively.

The components of lease expense for the year ended December 31, 2020 and 2019 were as follows (in thousands):


	Year ended December 31,
	2020		2019

Operating lease cost*	$	19,582	$	13,865
Finance lease cost
Amortization of leased assets	1,200		1,106
Interest on lease liabilities	173		265
Short-term lease cost	20,687		19,460
Variable lease costs (costs excluded from minimum fixed lease payments)**	2,713		3,264
Sublease income	(1,087)		(374)
Net lease cost	$	43,268	$	37,586

* Operating lease cost for the years ended December 31, 2020 and 2019 include $0.6 million and $3.7 million, respectively, of accelerated amortization for certain assets partially or fully vacated with no intent or ability to sublease.

** Variable lease costs for the year ended December 31, 2019 included an accrual of $0.9 million for all future estimated variable expenses related to certain assets partially or fully vacated with no intent or ability to sublease. No such variable costs were accrued in the year ended December 31, 2020.

The Company elected to use the alternative transition method upon adoption of ASC 842 on January 1, 2019. This method allowed entities to initially apply the standard at the adoption date with no subsequent adjustments to prior period lease costs for

comparability. As a result, operating leases in periods prior to the Company's adoption of ASC 842 were not recorded on the consolidated balance sheet. Prior to the adoption of ASC 842, rent expense (including any escalation clauses, free rent and other lease concessions) on operating leases was recognized on a straight-line basis over the minimum lease term, and this remains consistent with the Company's application of ASC 842. Rent expense was $11.9 million, interest expense for finance leases was approximately $52,000, and amortization expense for finance leases was $0.6 million for the year ended December 31, 2018.

Cash flow information related to the Company's leases for the years ended December 31, 2020 and 2019 was as follows (in thousands):


	Year ended December 31,
	2020		2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	19,161	$	10,559
Operating cash flows from finance leases	$	173	$	265
Financing cash flows from finance leases	$	1,279	$	913

Other information related to the Company's leases as of December 31, 2020 and 2019 was as follows (in thousands):


	December 31,
	2020		2019


Weighted average remaining lease term (years):
Operating leases	6.59		6.73
Finance leases	1.70		2.35
Weighted average discount rate:
Operating leases	5.67	%	6.50	%
Finance leases	6.15	%	7.54	%

Future minimum fixed lease payments under noncancelable leases at December 31, 2020 were as follows (in thousands):


	December 31, 2020
	Operating		Finance
	leases		leases
2021	$	21,366	$	981
2022	20,171		506
2023	17,312		62
2024	10,420		—
2025	8,544		—
2026 and beyond	32,516		—
Total lease payments	110,329		1,549
Less: interest	(20,692)		(80)
Present value of lease liabilities	$	89,637	$	1,469

LEASES

other locations included in the Facilities Initiative.

The Company's right-of-use lease assets and lease liabilities at December 31, 2020 and December 31, 2019 were as follows (in thousands):


		December 31,
	Classification	2020		2019
Assets
Operating lease assets	Operating lease right-of-use assets	$	69,757	$	36,654
Finance lease assets*	Property and equipment, net	983		2,420
Total leased assets		$	70,740	$	39,074

Liabilities
Current
Operating	Operating lease liabilities	$	17,023	$	7,719
Finance	Accrued expenses and other	902		1,005
Noncurrent
Operating	Operating lease liabilities, net of current	72,614		37,202
Finance	Other long-term liabilities	568		2,144
Total lease liabilities		$	91,107	$	48,070

* Finance lease assets were recorded net of accumulated depreciation of $1.9 million and $2.0 million at December 31, 2020 and December 31, 2019, respectively.

The components of lease expense for the year ended December 31, 2020 and 2019 were as follows (in thousands):


	Year ended December 31,
	2020		2019

Operating lease cost*	$	19,582	$	13,865
Finance lease cost
Amortization of leased assets	1,200		1,106
Interest on lease liabilities	173		265
Short-term lease cost	20,687		19,460
Variable lease costs (costs excluded from minimum fixed lease payments)**	2,713		3,264
Sublease income	(1,087)		(374)
Net lease cost	$	43,268	$	37,586

Cash flow information related to the Company's leases for the years ended December 31, 2020 and 2019 was as follows (in thousands):


	Year ended December 31,
	2020		2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	19,161	$	10,559
Operating cash flows from finance leases	$	173	$	265
Financing cash flows from finance leases	$	1,279	$	913

Other information related to the Company's leases as of December 31, 2020 and 2019 was as follows (in thousands):


	December 31,
	2020		2019


Weighted average remaining lease term (years):
Operating leases	6.59		6.73
Finance leases	1.70		2.35
Weighted average discount rate:
Operating leases	5.67	%	6.50	%
Finance leases	6.15	%	7.54	%

Future minimum fixed lease payments under noncancelable leases at December 31, 2020 were as follows (in thousands):


	December 31, 2020
	Operating		Finance
	leases		leases
2021	$	21,366	$	981
2022	20,171		506
2023	17,312		62
2024	10,420		—
2025	8,544		—
2026 and beyond	32,516		—
Total lease payments	110,329		1,549
Less: interest	(20,692)		(80)
Present value of lease liabilities	$	89,637	$	1,469

EMPLOYEE DEFINED CONTRIBUTION PLANS

12 Months Ended

Dec. 31, 2020

Retirement Benefits [Abstract]

EMPLOYEE DEFINED CONTRIBUTION PLANS

The Company offers 401(k) savings plans to eligible employees. The Company matches 50% of each employee's contributions to the 401(k) program up to 4% of the employee's eligible earnings, for a maximum match of 2% of eligible earnings.

The Company recorded expense related to its employee defined contribution plans aggregating $3.4 million in the year ended December 31, 2020, $4.0 million in the year ended December 31, 2019 and $3.2 million in the year ended December 31, 2018.

NON-U.S. EMPLOYEE DEFINED BENEFIT PLANS

The Company has defined benefit retirement plans that cover certain employees at various international locations. The Company's policy is to contribute amounts at least sufficient to satisfy the minimum amount required by applicable law and regulations or to directly pay benefits where appropriate. Benefits under the defined benefit plans are typically based either on years of service and the employee's compensation (generally during a fixed number of years immediately before retirement) or on annual credits. The range of assumptions that are used for these non-U.S. defined benefit plans reflect the different economic environments within the various countries.

In the year ended December 31, 2020, the Company assumed ECI's defined benefit plans in connection with the ECI Acquisition. These plans exist in several international locations where severance pay is either required by law for voluntary terminations or upon reaching a statutory retirement age. The Company adopted ECI's policy to fund notional accounts each month in the name of each employee to satisfy not only the severance amounts required by the applicable laws and regulations in certain countries, but also to satisfy severance for other types of terminations not necessarily required by law, but paid in accordance with company policy. Benefits funded and paid under these plans are based upon years of service and the employees' current compensation. At the ECI Acquisition Date, ECI accounted for these plans under the shutdown approach allowed under ASC 715, Compensation - Retirement Benefits (Topic 715) ("ASC 715"). Beginning December 31, 2020, in order to be consistent with the accounting methodology utilized for Ribbon's other defined benefit plans, the Company began to account for the ECI assumed plans using the actuarial cost approach, which is also allowed under ASC 715 for these types of plans. The range of assumptions that are utilized for these plans reflects the different economic environments within each country where such severance indemnities are required.

In 2020, regulatory changes occurred in the Netherlands that changed the Company's defined benefit pension plan there from a participating plan to a non-participating plan. This plan amendment triggered settlement accounting, resulting in a gain of $1.6 million, which is included in Other income (expense), net, in the Company's consolidated statement of operations for the year ended December 31, 2020. Prior to the amendment, the Company's Netherlands pension plan provided defined benefit accruals which were financed by insurance contracts that had a profit sharing feature. The pension benefits accrued were subject to future increases based on final earnings at the end of employment (the final average earnings formula). With the amendment in 2020, the final average earnings formula was frozen and the insurance contracts were converted to fully paid contracts. Following the amendment, pension accruals are now based upon a new formula that only considers current earnings (the career earnings formula) with the benefits still financed through insurance contracts. Ribbon has no further liability for pension benefits earned prior to the amendment as they are fully paid contracts. In addition, the insurance contract for the new benefit accruals has no profit sharing feature. Therefore, Ribbon has no current or future obligation to pay pension benefits promised in the Netherlands beyond the payment of premiums to the insurance company.

During the year ended December 31, 2019, in conjunction with the 2019 Restructuring Initiative, there were reductions in force that significantly reduced benefits that can be earned under the plan in one of our international locations that resulted in an immaterial curtailment loss. Settlement accounting was triggered in the year ended December 31, 2019 related to a reduction in force in one of our locations in 2018, resulting in an immaterial settlement gain.

During the year ended December 31, 2018, in conjunction connection with the Merger Restructuring Initiative, there were reductions in force that significantly reduced benefits that can be earned under the defined benefit plans in several international locations that resulted in curtailment accounting. A curtailment gain of $0.5 million was recognized in 2018 and included as a component of Other income (expense), net, in the Company's consolidated statement of operations. In the year ended December 31, 2018, settlement accounting was triggered in only one of these locations, resulting in an immaterial settlement charge.

A reconciliation of the changes in the benefit obligations and fair value of the assets of the defined benefit plans for the years ended December 31, 2020 and 2019, the funded status of the plans, and the amounts recognized in the consolidated balance sheets as of December 31, 2020 and 2019 were as follows (in thousands):


	Year ended December 31,
	2020		2019
Changes in projected benefit obligations:
Projected benefit obligation, beginning of year	$	11,784	$	10,848
Business combination	17,963		—
Service cost	1,459		335
Interest cost	46		140
Participant contributions	—		24
Plan amendments	(4,440)		—
Benefits and expenses paid	(1,976)		(44)
Net actuarial loss on obligation	231		1,059
Curtailment	—		82
Settlement	—		(660)

Projected benefit obligation, end of year	$	25,067	$	11,784

Changes in plan assets:
Fair value of plan assets, beginning of year	$	1,830	$	3,842
Business combination	13,188		—
Actual return on plan assets	1,077		(1,471)
Plan amendments	(588)		—
Employer contributions	798		139
Participant contributions	21		24
Administrative expenses	—		(21)
Benefits paid	(1,976)		(683)

Fair value of plan assets, end of year	$	14,350	$	1,830

Funded status at end of year	$	(10,717)	$	(9,954)

Amounts recognized in accumulated other comprehensive loss consist of:

Net actuarial loss	$	(102)	$	2,743


Amounts recognized in the consolidated balance sheets consist of:
Accrued expenses and other (current pension liability)	$	(435)	$	(74)
Other long-term liabilities (non-current pension liability)	(10,282)		(9,880)
Net amount recognized	$	(10,717)	$	(9,954)

The increase in the underfunded status of the Company's defined benefit plans at December 31, 2020 compared to December 31, 2019 was the result of the assumption of the ECI plans in connection with the ECI Acquisition, and a general decrease in discount rates which resulted in increases in projected benefit obligations, partially offset by the effect of the change in the benefit structure of the Netherlands plan from the plan amendment that occurred in 2020 as a result of regulatory changes.

Plans with underfunded or non-funded accumulated benefit obligations at December 31, 2020 and 2019 were as follows (in thousands):


	December 31,
	2020		2019
Aggregate projected benefit obligation	$	25,067	$	11,784
Aggregate accumulated benefit obligation	$	20,746	$	7,759
Aggregate fair value of plan assets	$	14,350	$	1,830

Net periodic benefit costs for the years ended December 31, 2020, 2019 and 2018 were as follows (in thousands):


	Year ended December 31,
	2020		2019		2018
Service cost	$	1,459	$	335	$	449
Interest cost	46		140		150
Expected return on plan assets	(343)		(14)		(45)
Plan asset expenses	20		21		22

Curtailment charge (credit)	—		13		(510)
Settlement (credit) charge	(1,557)		115		3

Net periodic benefit costs	$	(375)	$	610	$	69

The Company made benefit payments of $2.0 million, $0.7 million and $0.3 million in the years ended December 31, 2020, 2019 and 2018, respectively. These benefit payments included $0.7 million and $0.3 million of one-time lump sum payments to participants in the years ended December 31, 2019 and 2018, respectively. No one-time lump sum payments were made to participants in the year ended December 31, 2020. Expected benefit payments for the next ten years are as follows (in thousands):


Years ending December 31,
2021	$	1,508
2022	1,759
2023	1,471
2024	1,298
2025	989
2026 to 2030	8,674
	$	15,699

The changes in plan assets and benefit obligations recognized in other comprehensive income (loss) before tax for the years ended December 31, 2020, 2019 and 2018 were as follows (in thousands):


	Year ended December 31,
	2020		2019		2018
Net (gain) loss	$	(558)	$	2,526	$	(356)


Settlement gain	(1,557)		—		—
Total recognized in comprehensive income (loss)	$	(2,115)	$	2,526	$	(356)

The Company defers all actuarial gains and losses resulting from variances between actual results and economic estimates or actuarial assumptions. The unrecognized actuarial gains and losses are recorded as unrealized pension actuarial gains (losses) in the Company's consolidated balance sheets as a component of Accumulated other comprehensive income. These unrecognized gains and losses are amortized as a component of net periodic benefit cost when the net gains and losses exceed 10% of the greater of the market value of plan assets or the projected benefit obligation at the beginning of the year. Amortization of the amount included in Accumulated other comprehensive income into net periodic benefit cost is expected to total $0.1 million for the year ended December 31, 2021.

The principal weighted average assumptions used to determine the benefit obligation at December 31, 2020 and 2019 were as follows:


	December 31,
	2020		2019
Discount rate	2.16	%	0.68	%
Rate of compensation increase	2.41	%	2.88	%

The principal weighted average assumptions used to determine net period benefit cost for the years ended December 31, 2020, 2019 and 2018 were as follows:


	Year ended December 31,
	2020		2019		2018
Discount rate	0.68	%	1.30	%	1.50	%
Expected long-term return on plan assets	0.21	%	1.12	%	1.34	%
Rate of compensation increase	2.88	%	2.83	%	3.38	%

Assumed discount rates are used in the measurement of the projected and accumulated benefit obligations, as well as the service and interest cost components of net periodic pension cost. Estimated discount rates reflect the rates at which the pension benefits could be effectively settled. For each defined benefit plan, the Company chooses an estimated discount rate from a readily available market index rate, based upon high-quality fixed income investments, specific to the country or economic zone in which the benefits are paid and taking into account the duration of the plan and the number of participants.

The Company's plans in both the Netherlands and Switzerland are funded through insurance contracts, which have historically provided guaranteed interest credit. The fair value of these contracts is derived from the insurance companies' assessment of the minimum value of the benefits provided by the insurance contracts. The methodology used to value these plan assets has always assumed that the value of the plan assets equals the guaranteed insured benefits. For consistency, the same discount rate used in the valuation of the benefit obligations is used to place a value on the plan assets. The assets are assumed to grow each year in line with the discount rate, and therefore, the expected return on the assets is set equal to the discount rate. The fair value of the plan assets in Switzerland was $1.6 million at December 31, 2020 and $1.2 million at December 31, 2019. Due to the plan amendment in 2020 that changed the benefit structure of the Netherlands plan, the Company no longer has any obligation related to this plan beyond the payment of insurance premiums. Therefore, there is no projected benefit obligation and no plan assets in the Netherlands as of December 31, 2020. Plan assets for the Netherlands plan totaled $0.6 million at December 31, 2019. The Company classifies the fair value of its plan assets as Level 2 in the fair value hierarchy as discussed in Note 6.

During the years ended December 31, 2020, 2019 and 2018, employees in the Netherlands and Switzerland made contributions to the respective pension plans aggregating $21,000, $24,000 and $5,000, respectively. Employee contributions to these plans are based on a fixed 5% of the relevant pensionable earnings. The Company funds these plans by contributing at least the minimum amount required by applicable regulations and as recommended by an independent actuary. During the years ended December 31, 2020, 2019 and 2018, the Company contributed $0.8 million, $0.1 million and $0.3 million, respectively, to its pension plans. The Company expects to contribute $1.2 million to its defined benefit plans in 2021.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Publisher FASB
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

NON-U.S. EMPLOYEE DEFINED BENEFIT PLANS

12 Months Ended

Dec. 31, 2020

Retirement Benefits [Abstract]

NON-U.S. EMPLOYEE DEFINED BENEFIT PLANS

EMPLOYEE DEFINED CONTRIBUTION PLANS

NON-U.S. EMPLOYEE DEFINED BENEFIT PLANS


	Year ended December 31,
	2020		2019
Changes in projected benefit obligations:
Projected benefit obligation, beginning of year	$	11,784	$	10,848
Business combination	17,963		—
Service cost	1,459		335
Interest cost	46		140
Participant contributions	—		24
Plan amendments	(4,440)		—
Benefits and expenses paid	(1,976)		(44)
Net actuarial loss on obligation	231		1,059
Curtailment	—		82
Settlement	—		(660)

Projected benefit obligation, end of year	$	25,067	$	11,784

Changes in plan assets:
Fair value of plan assets, beginning of year	$	1,830	$	3,842
Business combination	13,188		—
Actual return on plan assets	1,077		(1,471)
Plan amendments	(588)		—
Employer contributions	798		139
Participant contributions	21		24
Administrative expenses	—		(21)
Benefits paid	(1,976)		(683)

Fair value of plan assets, end of year	$	14,350	$	1,830

Funded status at end of year	$	(10,717)	$	(9,954)

Amounts recognized in accumulated other comprehensive loss consist of:

Net actuarial loss	$	(102)	$	2,743


Amounts recognized in the consolidated balance sheets consist of:
Accrued expenses and other (current pension liability)	$	(435)	$	(74)
Other long-term liabilities (non-current pension liability)	(10,282)		(9,880)
Net amount recognized	$	(10,717)	$	(9,954)

Plans with underfunded or non-funded accumulated benefit obligations at December 31, 2020 and 2019 were as follows (in thousands):


	December 31,
	2020		2019
Aggregate projected benefit obligation	$	25,067	$	11,784
Aggregate accumulated benefit obligation	$	20,746	$	7,759
Aggregate fair value of plan assets	$	14,350	$	1,830

Net periodic benefit costs for the years ended December 31, 2020, 2019 and 2018 were as follows (in thousands):


	Year ended December 31,
	2020		2019		2018
Service cost	$	1,459	$	335	$	449
Interest cost	46		140		150
Expected return on plan assets	(343)		(14)		(45)
Plan asset expenses	20		21		22

Curtailment charge (credit)	—		13		(510)
Settlement (credit) charge	(1,557)		115		3

Net periodic benefit costs	$	(375)	$	610	$	69


Years ending December 31,
2021	$	1,508
2022	1,759
2023	1,471
2024	1,298
2025	989
2026 to 2030	8,674
	$	15,699

The changes in plan assets and benefit obligations recognized in other comprehensive income (loss) before tax for the years ended December 31, 2020, 2019 and 2018 were as follows (in thousands):


	Year ended December 31,
	2020		2019		2018
Net (gain) loss	$	(558)	$	2,526	$	(356)


Settlement gain	(1,557)		—		—
Total recognized in comprehensive income (loss)	$	(2,115)	$	2,526	$	(356)

The principal weighted average assumptions used to determine the benefit obligation at December 31, 2020 and 2019 were as follows:


	December 31,
	2020		2019
Discount rate	2.16	%	0.68	%
Rate of compensation increase	2.41	%	2.88	%

The principal weighted average assumptions used to determine net period benefit cost for the years ended December 31, 2020, 2019 and 2018 were as follows:


	Year ended December 31,
	2020		2019		2018
Discount rate	0.68	%	1.30	%	1.50	%
Expected long-term return on plan assets	0.21	%	1.12	%	1.34	%
Rate of compensation increase	2.88	%	2.83	%	3.38	%

- Definition

The entire disclosure for retirement benefits.

+ References

+ Details

INCOME TAXES

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

INCOME TAXES

The components of income (loss) from continuing operations before income taxes consisted of the following (in thousands):


	Year ended December 31,
	2020		2019		2018
Income (loss) before income taxes:
United States	$	123,817	$	(132,887)	$	(52,569)
Foreign	(30,500)		9,994		(20,841)
	$	93,317	$	(122,893)	$	(73,410)

The provision for income taxes from continuing operations consisted of the following (in thousands):


	Year ended December 31,
	2020		2019		2018
Provision (benefit) for income taxes:
Current:
Federal	$	677	$	11	$	561
State	1,310		128		128
Foreign	7,355		1,744		2,198
Total current	9,342		1,883		2,887
Deferred:
Federal	30,278		9,790		(8,481)
State	195		1,630		(1,414)
Foreign	(16,117)		383		(1,477)
Change in valuation allowance	(18,972)		(6,504)		11,885
Total deferred	(4,616)		5,299		513
Total	$	4,726	$	7,182	$	3,400

A reconciliation of the Company's effective tax rate for continuing operations to the statutory federal rate is as follows:


	Year ended December 31,
	2020		2019		2018
U.S. statutory income tax rate	21.0	%	21.0	%	21.0	%
State income taxes, net of federal benefit	1.1		(0.2)		(0.1)
Foreign income taxes	2.9		(1.0)		(5.7)



Foreign deemed dividends	(2.7)		(0.4)		(3.4)
Stock-based compensation	1.0		(0.7)		(0.3)
Tax credits	(2.8)		2.8		0.6
Uncertain tax positions	0.5		(0.2)		1.3


Valuation allowance	(20.3)		(0.7)		(16.1)
Goodwill amortization	0.6		0.4		0.3

Tax reform	—		(0.1)		—
Goodwill impairment	—		(25.4)		—

Other permanent adjustments	1.8		(1.5)		(1.4)
Permanent adjustments - foreign exchange	1.8		—		(0.9)
Other, net	0.2		0.2		0.1
Effective income tax rate	5.1	%	(5.8)	%	(4.6)	%

The following is a summary of the significant components of deferred income tax assets and liabilities (in thousands):


	December 31,
	2020		2019
Assets:
Net operating loss carryforwards	$	447,101	$	61,057
Capital loss carryforward	71,182		—
Research and development tax credits	45,031		32,879
Other tax credits	6,400		—

Deferred revenue	3,184		7,868
Accrued expenses	13,557		5,687
Inventory	2,603		4,618
Stock-based compensation	1,668		2,880
Fixed assets	4,613		5,461
Other temporary differences	4,051		2,138
	599,390		122,588
Valuation allowance	(496,439)		(94,980)
Total deferred tax assets	102,951		27,608
Liabilities:
Intangible assets	(75,794)		(22,470)

Mark-to-market investments	(17,631)		—
Unremitted foreign income	(15,717)		(4,827)
Total deferred tax liabilities	(109,142)		(27,297)
Total net deferred tax assets	$	(6,191)	$	311

The deferred tax assets and liabilities based on tax jurisdictions are presented in the Company's consolidated balance sheets as follows:


	December 31,
	2020		2019
Deferred income taxes - noncurrent assets	$	10,651	$	4,959
Deferred income taxes - noncurrent liabilities	(16,842)		(4,648)
	$	(6,191)	$	311

The largest increases in the year ended December 31, 2020 compared to the year ended December 31, 2019, including net operating loss carryforwards, intangible assets and the valuation allowance were primarily the result of the ECI Acquisition. The change in mark-to-market securities in the year ended December 31, 2020 was related to the Debentures and Warrants received as sale consideration in connection with the Kandy Sale.

At December 31, 2020, the Company had cumulative net operating losses ("NOLs") in the U.S. of $302.1 million. The Company, through the ECI Acquisition, also has $1.6 billion of Israel NOLs. The U.S. NOL carryforwards expire at various dates from 2021 through 2038. The Israel NOLs do not expire.

The Company also has available federal, state and foreign income tax credit carryforwards of $51.4 million that expire at various dates from 2021 through 2039.

Under the provisions of the Internal Revenue Code, the net operating losses and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service. Net operating losses and tax credit carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership of significant shareholders over a three-year period in excess of 50%, as defined under Sections 382 and 383 of the Internal Revenue Code, as well as a similar state provision. As a result of the Edgewater Acquisition in 2018, the Company acquired approximately $34 million of net operating loss carryforwards and approximately $6 million of tax credit carryforwards. Edgewater incurred an ownership change as a result of its acquisition by the Company; however, the Company does not expect that any of the net operating losses or tax credits related to Edgewater will expire unused. As a result of the ECI Acquisition, an additional $129.6 million of NOL was acquired related to the ECI U.S. subsidiary. ECI U.S. incurred an ownership change as a result of its acquisition by the

Company and the Company expects that, due to the limitations under Sections 382 and 383, all but approximately $8 million of the NOLs related to ECI U.S. will expire unused.

During 2020 and 2019, the Company performed an analysis to determine if, based on all available evidence, it considered it more likely than not that some portion or all of the recorded deferred tax assets will not be realized in a future period. As a result of the Company's evaluation, the Company concluded that there was insufficient positive evidence to overcome the more objective negative evidence related to its cumulative losses and other factors. Accordingly, the Company has maintained a valuation allowance against its U.S. deferred tax asset amounting to $73.0 million at December 31, 2020 and $71.4 million at December 31, 2019. A similar analysis and conclusion were made with regard to the valuation allowance on the deferred tax assets of the Company's Ireland subsidiary. The Ireland subsidiary's business model changed in 2020 to a limited risk distributor. As a result, the decision was made to release a portion of the valuation allowance because of the future income resulting in a tax benefit of $4.1 million. The valuation allowance for the capital loss carryforward of $8.8 million will remain, since there are no current plans to generate capital gains. In analyzing the deferred tax assets related to the Company's Canada subsidiaries at such time, the Company concluded that it was more likely than not that the Canadian federal credits would not be realized in a future period. This resulted in the Company's maintaining a valuation allowance of $12.3 million. In addition, because of continued losses, a valuation allowance of $2.3 million was maintained for the Company's Brazil subsidiary. The ECI Acquisition resulted in valuation allowances of $429.0 million against some of the acquired subsidiaries, comprised of $380.0 million related to the ECI Israel subsidiaries, $29.8 million related to ECI in the U.S., $13.7 million related to ECI Netherlands and $5.5 million in the aggregate related to other ECI subsidiaries. The deferred tax assets recognized with no valuation allowance at December 31, 2020 and 2019 primarily relate to foreign subsidiaries where recoverability is concluded to be more likely than not based on the Company's cost-plus compensation policy, as well as a state credit in the U.S.

A reconciliation of the Company's unrecognized tax benefits is as follows (in thousands):


	Year ended December 31,
	2020		2019		2018
Unrecognized tax benefits at January 1	$	2,932	$	3,461	$	4,528
Increases related to current year tax positions	485		292		74
Increases related to prior period tax positions	11,209		—		122

Decreases related to prior period tax positions	(572)		(821)		(1,263)


Unrecognized tax benefits at December 31	$	14,054	$	2,932	$	3,461

The Company accounts for interest and penalties related to uncertain tax positions as part of its provision for income taxes. The Company had $15.3 million, $3.6 million and $4.1 million of unrecognized tax benefits including penalties and interest at December 31, 2020, 2019 and 2018, respectively. Of these amounts, $13.9 million, $2.0 million and $1.8 million represent the amount of unrecognized tax benefits that, if recognized, would impact the effective income tax rate for the years ended December 31, 2020, 2019 and 2018, respectively. The Company recorded liabilities for potential penalties and interest of $0.5 million, $0.1 million and $0.1 million for the years ended December 31, 2020, 2019 and 2018, respectively. The Company had $1.3 million and $0.7 million accrued in Other long-term liabilities for penalties and interest at December 31, 2020 and 2019, respectively. The Company believes that it is reasonably possible that certain tax positions related to its unrecognized tax benefits will be effectively settled within the next twelve months.

The Company and its subsidiaries file income tax returns in the U.S. federal jurisdiction as well as various state and foreign jurisdictions. Generally, the tax years 2017 through 2020 remain open to examination by the major taxing jurisdictions to which the Company is subject. The Company's federal NOLs generated prior to 2017 could be adjusted on examination even though the year in which the loss was generated is otherwise closed by the statute of limitations.

As of December 31, 2020, the Company had ongoing income tax audits in certain foreign countries. Management believes that an adequate provision has been recorded for any adjustments that may result from tax examinations.

The ECI Acquisition was accounted for as a non-taxable business combination. U.S. federal and state deferred taxes were recorded as part of the business combination based on the differences between the tax basis of the acquired assets and assumed liabilities and their reported amounts for financial reporting purposes. The Company concluded that there was insufficient positive evidence to overcome the more objective negative evidence related to cumulative losses and other factors. The Company recorded identifiable intangible assets in Israel as part of the purchase accounting for the acquisition. For tax

purposes, the future amortization of these identifiable intangible assets will be non-deductible, thereby creating income. ECI Israel has $1.6 billion of NOLs that will be utilizable against the future tax income from these identifiable intangible assets. The Company is required to determine its ability to use the assets and analyze the valuation allowance previously established. The Company has determined it is not more likely that some of these net tax assets, mainly in Israel, will be recognized. As a result, a valuation allowance of $429.0 million has been established against ECI's deferred taxes.

The Anova Acquisition was accounted for as a business combination and the financial results of Anova have been included in the Company's consolidated financial statements for the period subsequent to the Anova Acquisition Date. The transaction is considered an asset acquisition for tax purposes. Accordingly, Ribbon recorded a stepped up basis in the assets.

The Edgewater Acquisition was accounted for as a non-taxable business combination. As a result, the valuation allowance has been reduced for the assumed net deferred tax liabilities, resulting in an income tax benefit of $0.7 million. This benefit was included as a component of the Company's tax provision for the year ended December 31, 2018. In 2019, an adjustment of $0.2 million was recorded, reducing the income tax benefit from the Edgewater Acquisition to $0.5 million.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References + Details

RELATED PARTIES	12 Months Ended
RELATED PARTIES	Dec. 31, 2020
Related Party Transactions [Abstract]
RELATED PARTIES	RELATED PARTIES As a portion of the consideration for the GENBAND Merger, on October 27, 2017, the Company issued a promissory note for $22.5 million to certain of GENBAND's equity holders who, following the GENBAND Merger, owned greater than five percent of the Company's outstanding shares. As described in Note 14 above, the promissory note did not amortize and the principal thereon was payable in full on the third anniversary of its execution. Interest on the promissory note was payable quarterly in arrears and accrued at a rate of 7.5% per year for the first six months after issuance, and thereafter at a rate of 10% per year. The failure to make any payment under the promissory note when due and, with respect to payment of any interest, the continuation of such failure for a period of thirty days thereafter, constituted an event of default under the promissory note. If an event of default occurs under the promissory note, the payees could have declared the entire balance of the promissory note due and payable (including principal and accrued and unpaid interest) within five business days of the payees' notification to the Company of such acceleration. At December 31, 2018, the Promissory Note balance was $24.1 million, comprised of $22.5 million of principal, plus $1.6 million of interest converted to principal. On April 29, 2019, the Company repaid in full all outstanding amounts under the Promissory Note, aggregating $24.7 million. The Company did not incur any early termination penalties in connection with this repayment.

COMMITMENTS AND CONTINGENCIES	12 Months Ended
COMMITMENTS AND CONTINGENCIES	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Litigation Settlement As previously disclosed, the Company was involved in six lawsuits (together, the "Lawsuits") with Metaswitch Networks Ltd., Metaswitch Networks Corp. and Metaswitch Inc. (collectively, "Metaswitch"). In five of the Lawsuits, the Company was the plaintiff, and in three of those five lawsuits, the Company was also a counterclaim defendant. In the sixth case, the Company was the defendant. On April 22, 2019, the Company and Metaswitch agreed to a binding mediator's proposal that resolved the six Lawsuits between the Company and Metaswitch (the "Lawsuits"). The Company and Metaswitch signed a Settlement and Cross-License Agreement on May 29, 2019 (the "Royalty Agreement"). Pursuant to the terms of the Royalty Agreement, Metaswitch agreed to pay the Company an aggregate amount of $63.0 million, which included cash payments of $37.5 million during the second quarter of 2019 and $25.5 million payable in three installments annually, beginning June 26, 2020, with such installment payments accruing interest at a rate of 4% per year. As part of the Royalty Agreement, the Company and Metaswitch (i) have released the other from all claims and liabilities; (ii) have licensed each party's existing patent portfolio to the other party; and (iii) have requested the applicable courts to dismiss the Lawsuits. The $63.0 million gain from the settlement is included in Other income (expense), net, in the Company's consolidated statement of operations for the year ended December 31, 2019, and had notes receivable for future payments of $25.5 million, comprised of $8.5 million in Other current assets and $17.0 million in Other assets in the consolidated balance sheet. The Company received $37.5 million of aggregate payments from Metaswitch in the second quarter of 2019 and $9.5 million, including $1.0 million of interest, in the second quarter of 2020. On July 6, 2020, the Company and Metaswitch signed a First Supplemental Agreement to the Settlement and Cross-License Agreement (the "Supplemental Agreement") under which Metaswitch could elect to repay the outstanding amounts under the Royalty Agreement early in exchange for a reduction of $0.25 million to the outstanding principal, from $17.0 million to $16.75 million, and the payment of no further interest by Metaswitch effective June 26, 2020. The Company recorded the reduction to the outstanding principal as a reduction to interest income. On July 14, 2020, Metaswitch paid the Company the remaining outstanding balance of $16.75 million. Contingencies Liabilities for Royalty Payments to the IIA Prior to the ECI Acquisition, ECI had received research and development grants from the IIA. The Company assumed ECI's contract with the IIA, which requires the Company to pay royalties to the IIA on proceeds from the sale of products which the Israeli government has supported by way of research and development grants. The royalties for grants prior to 2017 were calculated at the rates of 1.3% to 5.0% of the aggregated proceeds from the sale of such products developed at certain of the Company's R&D centers, up to an amount not exceeding 100% of such grants plus interest at LIBOR. Effective for grants approved in 2017 and thereafter, interest was calculated at the higher of LIBOR plus 1.5% to 2.75%. At December 31, 2020, the Company's maximum possible future royalties commitment, including $6.1 million of unpaid royalties accrued at December 31, 2020, was $44.0 million, including interest of $2.0 million, based on estimates of future product sales, grants received from the IIA and not yet repaid, and management's estimation of products still to be sold. Litigation On November 8, 2018, Ron Miller, a purported stockholder of the Company, filed a Class Action Complaint (the "Miller Complaint") in the United States District Court for the District of Massachusetts (the "Massachusetts District Court") against the Company and three of its former officers (collectively, the "Defendants"), claiming to represent a class of purchasers of Sonus common stock during the period from January 8, 2015 through March 24, 2015 and alleging violations of the federal securities laws. Similar to a previous complaint entitled Sousa et al. vs. Sonus Networks, Inc. et al., which was dismissed with prejudice by an order dated June 6, 2017, the Miller Complaint claims that the Defendants made misleading forward-looking statements concerning Sonus' expected fiscal first quarter of 2015 financial performance, which statements were also the subject of an August 7, 2018 Securities and Exchange Commission Cease and Desist Order, whose findings the Company neither admitted nor denied. The Miller plaintiffs are seeking monetary damages. After the Miller Complaint was filed, several parties filed and briefed motions seeking to be selected by the Massachusetts District Court to serve as a Lead Plaintiff in the action. On June 21, 2019, the Massachusetts District Court appointed a group as Lead Plaintiffs and the Lead Plaintiffs filed an amended complaint on July 19, 2019. On August 30, 2019, the Defendants filed a motion to dismiss the Miller Complaint and, on October 4, 2019, the Lead Plaintiffs filed an opposition to the motion to dismiss. The Defendants filed a reply to such opposition on November 1, 2019. There was an oral argument on the motion to dismiss on February 12, 2020. In addition, the Company is often a party to disputes and legal proceedings that it considers routine and incidental to its business. Management does not expect the results of any of these actions to have a material effect on the Company's business or consolidated financial statements.

QUARTERLY RESULTS (UNAUDITED)

12 Months Ended

Dec. 31, 2020

Quarterly Financial Information Disclosure [Abstract]

QUARTERLY RESULTS (UNAUDITED)

QUARTERLY RESULTS (UNAUDITED)The following tables present the Company's quarterly operating results for the years ended December 31, 2020 and 2019. The information for each of these quarters is unaudited and has been prepared on the same basis as the audited consolidated financial statements. In the opinion of management, all necessary adjustments, consisting only of normal recurring adjustments, have been included to present fairly the unaudited consolidated quarterly results when read in conjunction with the Company's audited consolidated financial statements and related notes.


	First Quarter (1)		Second Quarter		Third Quarter		Fourth Quarter
	(In thousands, except per share data)
Year ended December 31, 2020
Revenue	$	157,982	$	210,493	$	231,118	$	244,202
Cost of revenue (3)	67,458		87,226		96,164		99,840
Gross profit (3)	$	90,524	$	123,267	$	134,954	$	144,362
(Loss) income from operations	$	(28,740)	$	1,592	$	11,917	$	16,900

Net (loss) income	$	(33,170)	$	(8,251)	$	6,252	$	123,760
(Loss) earnings per share (4):
Basic	$	(0.27)	$	(0.06)	$	0.04	$	0.85
Diluted	$	(0.27)	$	(0.06)	$	0.04	$	0.81
Shares used in computing (loss) earnings per share:
Basic	120,992		144,483		144,948		145,311
Diluted	120,992		144,483		151,680		153,441


	First Quarter (2)		Second Quarter		Third Quarter (2)		Fourth Quarter
	(In thousands, except per share data)
Year ended December 31, 2019
Revenue	$	118,928	$	145,421	$	137,653	$	161,109
Cost of revenue (3)	52,694		54,656		49,254		51,850
Gross profit (3)	$	66,234	$	90,765	$	88,399	$	109,259
Loss (income) from operations	$	(36,228)	$	(7,096)	$	2,686	$	(148,822)

Net (loss) income	$	(30,832)	$	49,470	$	1,650	$	(150,363)
Loss (earnings) per share (4):
Basic	$	(0.29)	$	0.45	$	0.01	$	(1.36)
Diluted	$	(0.29)	$	0.45	$	0.01	$	(1.36)
Shares used in computing loss (earnings) per share:
Basic	108,167		110,394		110,080		110,269
Diluted	108,167		110,698		110,756		110,269

__________________________________

(1)Includes the results of ECI for the period subsequent to March 3, 2020.

(2)Includes the results of Anova for the period subsequent to February 28.

(3)Reflects the reductions to Cost of revenue arising from the reclassification of amortization of acquired intangible assets to operating expenses in 2020 of $9.0 million in the first quarter, $11.0 million in the second quarter and $11.6 million in the third quarter; and in 2019 of $9.7 million in the first quarter, $10.1 million in the second quarter, $9.5 million in the third quarter and $8.3 million in the fourth quarter.

(4)(Loss) earnings per share is calculated independently for each of the quarters presented; accordingly, the sum of the quarterly (loss) earnings per share amounts may not equal the total calculated for the year.

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements have been prepared in United States dollars, in accordance with accounting principles generally accepted in the United States ("GAAP"). On December 1, 2020 (the "Kandy Sale Date"), American Virtual Cloud Technologies, Inc. ("AVCT") completed the purchase of the Company's cloud-based enterprise service business (the "Kandy Communications Business"). The revenue and expenses of the Kandy Communications Business are not included in the Company's consolidated financial statements for the period subsequent to the Kandy Sale Date. On March 3, 2020 (the "ECI Acquisition Date"), the Company merged with ECI Telecom Group Ltd ("ECI") (the "ECI Acquisition"). The financial results of ECI are included in the Company's consolidated financial statements for the period subsequent to the ECI Acquisition Date. On February 28, 2019 (the "Anova Acquisition Date"), the Company acquired the business and technology assets of Anova Data, Inc. ("Anova"). The financial results of Anova are included in the Company's consolidated financial statements for the period subsequent to the Anova Acquisition Date. On August 3, 2018 (the "Edgewater Acquisition Date"), the Company completed the acquisition of Edgewater Networks, Inc. ("Edgewater" and such acquisition, the "Edgewater Acquisition"). The financial results of Edgewater are included in the Company's consolidated financial statements for the period subsequent to the Edgewater Acquisition Date.
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of Ribbon and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation.
Use of Estimates and Judgments	Use of Estimates and Judgments The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and judgments relied upon in preparing these consolidated financial statements include accounting for business combinations, revenue recognition for multiple element arrangements, inventory valuations, assumptions used to determine the fair value of stock-based compensation, intangible assets, goodwill, debentures and warrants, legal contingencies and recoverability of Ribbon's net deferred tax assets and the related valuation allowances. Ribbon regularly assesses these estimates and records changes in estimates in the period in which they become known. Ribbon bases its estimates on historical experience and various other assumptions that it believes to be reasonable under the circumstances. Actual results could differ from those estimates.
Reclassifications	Reclassifications In the fourth quarter of 2020, the Company reclassified amounts recorded for amortization of acquired intangible assets in prior presentations from Cost of revenue - product and Sales and marketing to a separate line included in operating expenses in the consolidated statements of operations, as management believes this presentation enhances the comparability of the Company's financial statements with industry peers. These reclassifications did not impact operating loss, net loss or loss per share for any historical periods. These reclassifications also did not impact the consolidated balance sheets or statements of cash flows for any historical periods. The Company did not reclassify depreciation of property and equipment related to production activities from cost of revenue to other accounts. In addition, certain other reclassifications, not affecting previously reported net loss, have been made to the previously issued financial statements to conform to the current year presentation.
Business Combinations	Business Combinations The Company recognizes identifiable assets acquired and liabilities assumed at their acquisition date fair values. Goodwill as of the acquisition date is measured as the excess of consideration transferred over the net of the acquisition date fair values of the assets acquired and the liabilities assumed and represents the expected future economic benefits arising from other assets acquired in the business combination that are not individually identified and separately recognized. While the Company uses its best estimates and assumptions as part of the purchase price allocation process to accurately value assets acquired and liabilities assumed at the acquisition date, its estimates are inherently uncertain and subject to refinement. As a result, during the measurement period, which may be up to one year from the acquisition date, the Company records adjustments to the assets acquired and liabilities assumed with the corresponding offset to goodwill to the extent that it identifies adjustments to the preliminary purchase price allocation. Upon the conclusion of the measurement period or final determination of the values of assets acquired and liabilities assumed, whichever comes first, any subsequent adjustments are recorded to the consolidated statements of operations.
Revenue Recognition	Revenue Recognition The Company derives revenue from two primary sources: products and services. Product revenue includes the Company's hardware and software that function together to deliver the products' essential functionality. Software and hardware are also sold on a standalone basis. Services include customer support (software updates, upgrades and technical support), consulting, design services, installation services and training. Generally, contracts with customers contain multiple performance obligations, consisting of products and services. For these contracts, the Company accounts for individual performance obligations separately if they are considered distinct. When an arrangement contains more than one performance obligation, the Company will allocate the transaction price to each performance obligation on a relative standalone selling price basis. The Company utilizes the observable price of goods and services when they are sold separately to similar customers in order to estimate standalone selling price. The Company's software licenses typically provide a perpetual right to use the Company's software. The Company also sells term-based software licenses that expire and Software-as-a-Service ("SaaS")-based software which are referred to as subscription arrangements. The Company does not customize its software nor are installation services required, as the customer has a right to utilize internal resources or a third-party service company. The software and hardware are delivered before related services are provided and are functional without professional services or customer support. The Company has concluded that its software licenses are functional intellectual property that are distinct, as the user can benefit from the software on its own. Product revenue is typically recognized upon transfer of control or when the software is made available for download, as this is the point the user of the software can direct the use of, and obtain substantially all of the remaining benefits from, the functional intellectual property. The Company begins to recognize software revenue related to the renewal of subscription software licenses at the start of the subscription period. The Company offers warranties on its products. Certain of the Company's warranties are considered to be assurance-type in nature, ensuring the product is functioning as intended. Assurance-type warranties do not represent separate performance obligations. The Company also sells separately-priced maintenance service contracts which qualify as service-type warranties and represent separate performance obligations. The Company does not allow and has no history of accepting product returns. Services revenue includes revenue from customer support and other professional services. Customer support includes software updates on a when-and-if-available basis, telephone support, integrated web-based support and bug fixes or patches. The Company sells its customer support contracts at a percentage of list or net product price. Customer support revenue is recognized ratably over the term of the customer support agreement, which is typically one year. The Company's professional services include consulting, technical support, resident engineer services, design services and installation services. Because control transfers over time, revenue is recognized based on progress toward completion of the performance obligation. The method to measure progress toward completion requires judgment and is based on the nature of the products or services to be provided. The Company generally uses the input method to measure progress for its contracts because it believes such method best depicts the transfer of assets to the customer, which occurs as the Company incurs costs for the contracts. However, in some instances, the Company uses the output method because it best depicts the transfer of asset to the customer. Under the cost-to-cost measure of progress, the progress toward completion is measured based on the ratio of costs incurred to date to the total estimated costs at completion of the performance obligation. When the measure of progress is based upon expended labor, progress toward completion is measured as the ratio of labor time expended to date versus the total estimated labor time required to complete the performance obligation. Revenue is recorded proportionally as costs are incurred or as labor is expended. Costs to fulfill these obligations include internal labor as well as subcontractor costs. Customer training includes courses offered by the Company. The related revenue is typically recognized as the training services are performed.
Operating Segments	Operating Segments The Company's chief operating decision maker (the "CODM") is its president and chief executive officer. Effective in the fourth quarter of 2020 and in connection with the ECI Acquisition, the CODM began to assess the Company's performance based on the performance of two separate organizations within Ribbon: the Cloud and Edge segment ("Cloud and Edge") and the IP Optical Networks segment ("IP Optical Networks"). Financial information for the IP Optical Networks segment is not presented for any years prior to 2020, as this segment arose from the ECI Acquisition, and accordingly is not included in the Company's consolidated financial statements for the years ended December 31, 2019 and 2018.
Financial Instruments	Financial Instruments The carrying amounts of Ribbon's financial instruments approximate their fair values and include accounts receivable, convertible debentures and warrants received as sale consideration, borrowings under a revolving credit facility, accounts payable and term debt. Investments in marketable securities are reported at fair value, with unrealized gains and losses excluded from earnings and reported, net of tax, in Accumulated other comprehensive income (loss), which is a component of stockholders' equity. Unrealized losses that are determined to be other-than-temporary, based on current and expected market conditions, are recognized in earnings. Declines in fair value determined to be credit-related are charged to earnings. The cost of marketable securities sold is determined by the specific identification method. Changes in fair value of investments classified as trading securities, such as the convertible debentures and warrants received as sale consideration, are recognized in earnings as components of Other income (expense), net. Financial instruments with remaining maturities or that are due within one year from the balance sheet date are classified as current. Financial instruments with maturities or that are payable more than one year from the balance sheet date are classified as noncurrent.
Restricted Cash	Restricted Cash The Company classifies as restricted cash all cash pledged as collateral to secure long-term obligations and all cash whose use is otherwise limited by contractual provisions. At December 31, 2020, the Company had $7.3 million of restricted cash, comprised of $4.6 million restricted in connection with a tax payment on certain fixed assets formerly held by ECI that were sold in connection with the ECI Acquisition, and $2.7 million of restricted short-term bank deposits pledged to secure certain performance and financial bonds as security for the Company's obligations under tenders, contracts and to one of its main subcontractors.
Transfers of Financial Assets	Transfers of Financial AssetsThe Company's IP Optical Networks segment maintains customer receivables factoring agreements with a number of financial institutions. Under the terms of these agreements, the Company may transfer receivables to the financial institutions, on a non-recourse basis, provided that the financial institutions approve the receivables in advance. The Company maintains credit insurance policies from major insurance providers or obtains letters of credit from the customers for a majority of its factored trade receivables. The Company accounts for the factoring of its financial assets as a sale of the assets and records the factoring fees, when incurred, as a component of interest expense in the consolidated statements of operations, and the proceeds from the sales of receivables are included in cash from operating activities in the consolidated statements of cash flows.
Foreign Currency Translation	Foreign Currency Translation For foreign subsidiaries where the functional currency is the local currency, assets and liabilities are translated into U.S. dollars at the current exchange rate on the balance sheet date. Revenue and expenses are translated at average rates of exchange prevailing during each period. Translation adjustments for these subsidiaries are included in Accumulated other comprehensive income. For foreign subsidiaries where the functional currency is the U.S. dollar, monetary assets and liabilities are translated into U.S. dollars at the current exchange rate on the balance sheet date. Nonmonetary assets and liabilities are remeasured into U.S. dollars at historical exchange rates. Revenue and expense items are translated at average rates of exchange prevailing during each period. Translation adjustments for these subsidiaries are included in Other income (expense), net. Realized and unrealized foreign currency exchange gains and losses arising from transactions denominated in currencies other than the subsidiary's functional currency are reflected in earnings.The Company records its foreign currency gains (losses) as a component of Other income (expense), net.
Inventory	Inventory Inventory is recorded at the lower of cost or market value using the first-in, first-out convention. The Company reduces the carrying value of inventory for those items that are potentially excess, obsolete or slow-moving based on changes in customer demand, technology developments or other economic factors. Ribbon writes down evaluation equipment (equipment at customer sites for testing and evaluation) at the time of shipment to its customers, as it is probable that the inventory value will not be realized. Deferred product costs represent deferred cost of revenue for product shipments to customers prior to satisfaction of Ribbon's revenue recognition criteria. The Company classifies inventory that is not expected to be consumed within one year from the balance sheet date as noncurrent and includes such inventory as a component of Other assets.
Debentures and Warrants	Debentures and Warrants. The Company has Debentures and Warrants that it received as sale consideration in connection with the sale of the Kandy Communications Business (see Note 4), which Ribbon accounts for in accordance with Accounting Standards Codification ("ASC") 820, Fair Value Measurement ("ASC 820)". The Company calculates the fair value of the Debentures using a Lattice-based valuation approach, which utilizes a binomial tree to model the different paths the price of AVCT's common stock might take over the Debentures' life by using assumptions regarding the stock price volatility and risk-free interest rate. These results are then used to calculate the fair value of the Debentures at each measurement date. The Company uses the Black-Scholes valuation model for estimating the fair value of the Warrants at each measurement date. The fair value of the Warrants is affected by AVCT's stock price as well as valuation assumptions, including the volatility of AVCT's stock price, expected term of the option, risk-free interest rate and expected dividends. Both the Lattice and Black-Scholes valuation models are based on available market data, giving consideration to all of the rights and obligations of each instrument and precluding the use of "blockage" discounts or premiums in determining the fair value of a large lock of financial instruments. The Company is calculating the fair value of the Debentures and Warrants at each quarter-end and recording any adjustments to the fair values in Other income (expense), net. The fair values of the Debentures and Warrants are reported as Investments in the Company's consolidated balance sheet at December 31, 2020.
Property and Equipment	Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation. Expenditures for maintenance and repairs are charged to expense as incurred. Depreciation is computed using the straight-line method over the estimated useful lives of the related assets, which range from two to five years. Leasehold improvements are amortized over the lesser of the lease term or five years. When an asset is sold or retired, the cost and related accumulated depreciation or amortization are eliminated, and the resulting gain or loss, if any, is recognized in income (loss) from operations in the consolidated statement of operations. The Company reviews property and equipment for impairment in the same manner as intangible assets discussed below. Software development costs associated with internal use software are incurred in three stages of development: the preliminary project stage, the application development stage and the post-implementation stage. Costs incurred during the preliminary project and post-implementation stages are expensed as incurred. Certain qualifying costs incurred during the application development stage are capitalized as property and equipment. Internal use software is amortized on a straight-line basis over its estimated useful life of three years, beginning when the software is ready for its intended use.
Intangible Assets and Goodwill	Intangible Assets and Goodwill The Company's intangible assets are comprised of in-process research and development, developed technology, customer relationships, trade names, and internal use software. Intangible assets are reviewed for impairment when events or changes in circumstances indicate that their carrying amounts may not be recoverable based upon the estimated undiscounted cash flows. Recoverability of intangible assets with estimated lives and other long-lived assets is measured by a comparison of the carrying amount of an asset or asset group to future net undiscounted cash flows expected to be generated by the asset or asset group. If these comparisons indicate that an asset is not recoverable, the Company will recognize an impairment loss for the amount by which the carrying value of the asset or asset group exceeds the related estimated fair value. Estimated fair value is based on either discounted future operating cash flows or appraised values, depending on the nature of the asset. The Company amortizes its intangible assets over their respective useful lives, with the exception of in-process research and development, which has an indefinite life until the product is generally available, at which time such asset is typically reclassified to developed technology, and the Company begins to amortize this asset. See Note 10 for additional information regarding the Company's intangible assets. Goodwill is recorded when the consideration for an acquisition exceeds the fair value of net tangible and identifiable intangible assets acquired. Goodwill is not amortized, but instead is tested for impairment at least annually, or more frequently if indicators of potential impairment exist, by comparing the fair value of the Company's reporting unit to its carrying value. Prior to 2020, the Company's annual test for impairment of goodwill was completed as of November 30. Effective in 2020, the Company changed its annual goodwill impairment test date from November 30 to October 1. This change did not have a material impact on the Company's consolidated financial statements. As described above, effective in the fourth quarter of 2020, the Company determined that it has two operating segments: Cloud and Edge, and IP Optical Networks. For the purpose of testing goodwill for impairment, all goodwill is assigned to a reporting unit, which may be either an operating segment or a portion of an operating segment. The Company's reporting units are its operating segments. The Company performs a fair value analysis using both an income and market approach, which encompasses a discounted cash flow analysis and a guideline public company analysis using selected multiples. The Company assesses each valuation methodology based upon the relevance and availability of the data at the time the valuation is performed and the methodologies are weighted appropriately. Any impairment charges are reported separately in the Company's consolidated statements of operations.
Stock-Based Compensation	Stock-Based Compensation The Company's stock-based compensation cost is measured at the grant date based on the fair value of the award and is recognized as expense over the requisite service period, which generally represents the vesting period, and includes an estimate of the awards that will be forfeited. The Company uses the Black-Scholes valuation model for estimating the fair value on the date of grant of stock options. The fair value of stock option awards is affected by the Company's stock price as well as valuation assumptions, including the volatility of Ribbon's stock price, expected term of the option, risk-free interest rate and expected dividends. The Company may grant performance-based stock units ("PSUs") that include a market condition to certain of its executives. The Company uses a Monte Carlo simulation approach to model future stock price movements based upon the risk-free rate of return, the volatility of each entity and the pair-wise covariance between each entity. These results are then used to calculate the grant date fair values of the PSUs.
Concentration of Risk	Concentration of Risk The financial instruments that potentially subject Ribbon to concentrations of credit risk are cash, restricted cash and accounts receivable. The Company's cash equivalents and investments were managed by one financial institution at December 31, 2020. Historically, the Company has not experienced significant losses due to such bank depository concentration. The Company's investments at December 31, 2020 consisted of securities of AVCT (see Note 4). The Company did not hold any investments at December 31, 2019. Certain components and software licenses from third parties used in Ribbon's products are procured from single sources of supply. The failure of a supplier, including a subcontractor, to deliver on schedule could delay or interrupt Ribbon's delivery of products and thereby materially adversely affect Ribbon's revenue and operating results.
Advertising Costs	Advertising CostsAdvertising costs are expensed as incurred and included as a component of Sales and marketing expense in the Company's consolidated statements of operations.
Loss Contingencies and Reserves	Loss Contingencies and Reserves Ribbon is subject to ongoing business risks arising in the ordinary course of business, including legal claims, that affect the estimation process of the carrying value of assets, the recording of liabilities and the possibility of various loss contingencies. An estimated loss contingency is accrued when it is probable that a liability has been incurred or an asset has been impaired and the amount of loss can be reasonably estimated. Ribbon regularly evaluates current information available to determine whether such amounts should be adjusted and records changes in estimates in the period they become known. An allowance for doubtful accounts is estimated based on the Company's assessment of the collectability of specific customer accounts. Ribbon accrues for royalties for technology that it licenses from vendors based on established royalty rates and usage. Ribbon is periodically contacted by third parties who claim that Ribbon's products infringe on certain intellectual property of a third party. Ribbon evaluates these claims and accrues amounts when it is probable that the obligation has been incurred and the amounts are reasonably estimable.
Warranty	WarrantyThe Company records warranty liabilities for estimated costs of fulfilling its obligations under standard limited hardware and software warranties at the time of sale. The specific warranty terms and conditions vary depending upon the country in which the Company does business, but generally includes material costs, technical support, labor and associated overhead over a period ranging from one to three years. The Company assumed ECI's warranty liability in connection with the ECI Acquisition.
Research and Development Grants	Research and Development Grants The Company records grants received from the Office of the Innovation Authority of the Israeli Ministry of Economics (the "IIA") as a reduction to Research and development expense. Royalties payable to the IIA are recognized pursuant to sales of related products and are included in Cost of revenue - product.
Accounting for Leases	Accounting for Leases The Company accounts for its leases in accordance with Accounting Standards Codification ("ASC") 842, Leases ("ASC 842"), which was adopted effective January 1, 2019 using the alternative transition method, which allowed entities to initially apply ASC 842 at the adoption date with no adjustments to prior period lease costs for comparability (see Note 22). The Company has operating and finance leases for corporate offices, research and development facilities, and certain equipment. Operating leases are reported separately in the Company's consolidated balance sheets at December 31, 2020 and 2019. Assets acquired under finance leases are included in Property and equipment, net, in the consolidated balance sheets at December 31, 2020 and 2019. The Company determines if an arrangement is a lease at inception. A contract is determined to contain a lease component if the arrangement provides the Company with a right to control the use of an identified asset. Lease agreements may include lease and non-lease components. In such instances for all classes of underlying assets, the Company does not separate lease and non-lease components but rather, accounts for the entire arrangement under leasing guidance. Leases with an initial term of 12 months or less are not recorded on the balance sheet and lease expense for these leases is recognized on a straight-line basis over the lease term. For operating leases, lease expense for minimum fixed lease payments is recognized on a straight-line basis over the lease term. The expense for finance leases includes both interest and amortization expense components, with the interest component calculated based on the effective interest method and the amortization component calculated based on straight-line amortization of the right-of-use asset over the lease term. Lease contracts may contain variable lease costs, such as common area maintenance, utilities and tax reimbursements that vary over the term of the contract. Variable lease costs are not included in minimum fixed lease payments and as a result, are excluded from the measurement of the right-of-use assets and lease liabilities. The Company expenses all variable lease costs as incurred.
Accounting for Income Taxes	Accounting for Income Taxes Deferred tax assets and liabilities are recognized for the expected future consequences of events that have been reflected in the consolidated financial statements. Deferred tax assets and liabilities are determined based on the differences between the financial reporting and tax basis of assets and liabilities and operating loss carryforwards, using tax rates expected to be in effect for the years in which the differences are expected to reverse. The Company records valuation allowances to reduce deferred income tax assets to the amount that is more likely than not to be realized. The Company has provided for income taxes on the undistributed earnings of its non-U.S. subsidiaries as of December 31, 2020, excluding Ireland and Israel. These subsidiaries, excluding Ireland and Israel, are cost-plus or limited risk distributors that are not anticipated to need to use excess funds locally. Accordingly, the Company is required to recognize and record deferred taxes in 2020. The deferred taxes are recorded on the entire outside basis differences related to the foreign subsidiaries, the largest of these differences being undistributed earnings. At December 31, 2020, the Company had a deferred tax liability of $15.7 million related to withholding taxes in various countries. The Company determines whether it is more likely than not that a tax position will be sustained upon examination. If it is not more likely than not that a position will be sustained, no amount of the benefit attributable to the position is recognized. The tax benefit to be recognized of any tax position that meets the more likely than not recognition threshold is calculated as the largest amount that is more than 50% likely of being realized upon resolution of the contingency. The Company accounts for interest and penalties related to uncertain tax positions as part of its provision for income taxes.
Defined Benefit Plans	Defined Benefit Plans The Company has defined benefit plans for some of its employees at various international locations. The Company recognizes retirement benefit assets or liabilities in the consolidated balance sheets reflecting the funded status of pension and other retirement benefit plans. Retirement benefit assets and liabilities are adjusted for the difference between the benefit obligations and the plan assets at fair value (measured at year-end), with the offset recorded directly to stockholders' equity through accumulated other comprehensive income (loss), net of tax. The amount recorded in stockholders' equity represents the after-tax unamortized actuarial gains or losses, unamortized transition obligations and unamortized prior service costs.
Recent Accounting Pronouncements	Recent Accounting Pronouncements The Financial Accounting Standards Board ("FASB") has issued the following accounting pronouncements, all of which became effective for the Company in 2020 and none of which had a material impact on the Company's consolidated financial statements: In March 2020, the FASB issued Accounting Standards Update ("ASU") 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting ("ASU 2020-04"), which provides optional expedients and exceptions for applying generally accepted accounting principles to contract modifications and hedging relationships, subject to meeting certain criteria that reference LIBOR or another reference rate expected to be discontinued. In March 2020, the FASB issued ASU 2020-03, Codification Improvements to Financial Instruments ("ASU 2020-03"), which makes narrow-scope amendments related to topics regarding fair value option disclosures, applicability of the portfolio exception in Accounting Standards Codification ("ASC") 820 to nonfinancial items, disclosures for depository and lending institutions, cross reference to guidance in ASC 470-50 on line of credit or revolving debt arrangements, cross reference to net asset value practical expedient in ASC 820-10, interaction between ASC 842 and ASC 326 and between ASC 326 and ASC 860-20. In August 2018, the FASB issued ASU 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”), which provides guidance on implementation costs incurred in a cloud computing arrangement (“CCA”) that is a service contract. ASU 2018-15 amends ASC 350, Intangibles - Goodwill and Other (“ASC 350”) to include in its scope implementation costs of a CCA that is a service contract and clarifies that a customer should apply the guidance in ASC 350-40 to determine which implementation costs should be capitalized in such a CCA. In August 2018, the FASB issued ASU 2018-14, Compensation - Retirement Benefits - Defined Benefit Plans - General (Subtopic 715-20): Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans (“ASU 2018-14”), which amends ASC 715, Compensation - Retirement Benefits, to add, remove and clarify disclosure requirements related to defined benefit pension and other postretirement plans. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”), which changes the fair value measurement requirements of ASC 820, Fair Value Measurement. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ("ASU 2016-13"), which adds an impairment model that is based on expected losses rather than incurred losses. Under ASU 2016-13, an entity recognizes as an allowance its estimate of expected credit losses, which the FASB believes will result in more timely recognition of such losses. In April and May 2019, the FASB issued ASU 2019-04, Codification Improvements to Topic 326, Financial Instruments - Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments ("ASU 2019-04") and ASU 2019-05 Financial Instruments - Credit Losses (Topic 326): Targeted Transition Relief ("ASU 2019-05"), respectively. ASU 2019-04 provides transition relief for entities adopting ASU 2016-13 and ASU 2019-05 clarifies certain aspects of the accounting for credit losses, hedging activities and financial instruments in connection with the adoption of ASU 2016-13. The FASB has issued the following accounting pronouncement which became effective for the Company in 2021, which the Company does not believe will have a material impact on its consolidated financial statements upon adoption: In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes ("ASU 2019-12"), which modifies ASC 740 to simplify the accounting for income taxes. ASU 2019-12 addresses the accounting for hybrid tax regimes, tax basis step-up in goodwill obtained in a transaction that is not a business combination, separate financial statements of legal entities not subject to tax, intraperiod tax allocation exception to incremental approach, ownership changes in investments - changes from a subsidiary to an equity method investment, ownership changes in investments - changes from an equity method investment to a subsidiary, interim period accounting for enacted changes in tax law and year-to-date loss limitation in interim period tax accounting.

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Schedule of Error Corrections and Prior Period Adjustments

These reclassifications for the years ended December 31, 2019 and 2018 were as follows (in thousands):


	Year ended December 31, 2019						Year ended December 31, 2018
	Prior presentation		Amounts reclassified		Revised presentation		Prior presentation		Amounts reclassified		Revised presentation
Product revenue	$	262,030	$	—	$	262,030	$	279,014	$	—	$	279,014
Service revenue	301,081		—		301,081		298,891		—		298,891
Total revenue	563,111		—		563,111		577,905		—		577,905
Cost of revenue - product	133,347		(37,573)		95,774		142,185		(38,976)		103,209
Cost of revenue - service	112,680		—		112,680		127,388		—		127,388
Total cost of revenue	246,027		(37,573)		208,454		269,573		(38,976)		230,597
Total gross profit	317,084		37,573		354,657		308,332		38,976		347,308
Research and development	141,060		—		141,060		145,462		—		145,462
Sales and marketing	117,962		(11,652)		106,310		128,276		(10,747)		117,529
General and administrative	53,870		—		53,870		66,036		—		66,036
Amortization of acquired intangible assets	—		49,225		49,225		—		49,723		49,723
Impairment of goodwill	164,300		—		164,300		—		—		—
Acquisition-, disposal- and integration-related	12,953		—		12,953		16,951		—		16,951
Restructuring and related	16,399		—		16,399		17,015		—		17,015
Total operating expenses	506,544		37,573		544,117		373,740		38,976		412,716
Operating loss	$	(189,460)	$	—	$	(189,460)	$	(65,408)	$	—	$	(65,408)

BUSINESS ACQUISITONS (Tables)

12 Months Ended

Dec. 31, 2020

Business Combinations [Abstract]

Summary of preliminary allocation of purchase consideration

A summary of the allocation of the purchase consideration for ECI is as follows (in thousands):


Fair value of consideration transferred:
Cash consideration:
Repayment of ECI outstanding debt obligations	$	183,266


Cash paid to selling shareholders	139,244
Payment to selling shareholders from sale of ECI real estate assets	33,400
Less cash and restricted cash acquired	(9,058)
Net cash consideration	346,852

Fair value of Ribbon stock issued	108,550

Fair value of total consideration	$	455,402

Fair value of assets acquired and liabilities assumed:
Current assets, net of cash and restricted cash acquired	$	120,203
Property and equipment	54,913
Intangible assets:
In-process research and development	34,000
Developed technology	111,900
Customer relationships	116,000
Trade names	3,000
Goodwill	191,996


Other noncurrent assets	37,528

Deferred revenue	(4,369)
Other current liabilities	(146,618)

Deferred revenue, net of current	(3,726)
Deferred tax liability	(13,308)
Other long-term liabilities	(46,117)
	$	455,402

A summary of the allocation of the purchase consideration for Edgewater is as follows (in thousands):


Fair value of consideration transferred:
Cash consideration:
Cash paid to Edgewater Selling Stakeholders	$	51,162
Less cash acquired	(4,773)
Net cash consideration	46,389
Unpaid cash consideration	30,000
Fair value of Ribbon stock issued	30,000
Fair value of equity awards assumed (see Note 21)	747
Fair value of total consideration	$	107,136

Fair value of assets acquired and liabilities assumed:
Current assets, net of cash acquired	$	16,098
Property and equipment	245
Intangible assets:

Developed technology	29,500
Customer relationships	26,100
Trade names	1,100
Goodwill	48,053
Other noncurrent assets	103
Deferred revenue	(2,749)
Other current liabilities	(9,926)
Deferred revenue, net of current	(669)
Other long-term liabilities	(719)
	$	107,136

Unaudited pro forma results


	Year ended December 31,
	2020		2019
	(unaudited)
Revenue	$	869,002	$	944,915
Net income (loss)	$	97,036	$	(250,337)
Diluted earnings (loss) per share	$	0.65	$	(1.76)

Schedule of components of acquisition related costs

The components of Acquisition-, disposal- and integration-related expenses incurred in the years ended December 31, 2020, 2019 and 2018 were as follows (in thousands):


	Year ended December 31,
	2020		2019		2018
Professional and services fees (acquisition-related)	$	13,441	$	8,657	$	7,627
Management bonuses (acquisition-related)	—		—		1,972
Professional and services fees (disposal-related)	1,890		—		—
Integration-related expenses	1,833		4,296		7,352
	$	17,164	$	12,953	$	16,951

EARNINGS (LOSS) PER SHARE (Tables)

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Schedule of calculations of shares used to compute basic and diluted earnings (loss) per share

The calculations of shares used to compute basic and diluted earnings (loss) per share are as follows (in thousands):


	Year ended December 31,
	2020	2019	2018
Weighted average shares outstanding—basic	138,967	109,734	103,916
Potential dilutive common shares	5,683	—	—
Weighted average shares outstanding—diluted	144,650	109,734	103,916

ACCOUNTS RECEIVABLE, NET (Tables)

12 Months Ended

Dec. 31, 2020

Receivables [Abstract]

Schedule of accounts receivable, net

Accounts receivable, net, consisted of the following (in thousands):


	December 31,
	2020		2019
Accounts receivable	$	238,514	$	193,619
Allowance for doubtful accounts	(776)		(913)
Accounts receivable, net	$	237,738	$	192,706

Schedule of allowance for doubtful accounts

The Company's allowance for doubtful accounts activity was as follows (in thousands):


Year ended December 31,	Balance at beginning of year		Charges to expense		Charges (credits) to other accounts		Write-offs		Balance at end of year
2020	$	913	$	686	$	94	$	(917)	$	776
2019	$	669	$	738	$	68	$	(562)	$	913
2018	$	73	$	351	$	620	$	(375)	$	669

INVENTORY (Tables)

12 Months Ended

Dec. 31, 2020

Inventory Disclosure [Abstract]

Schedule of inventory

Inventory consisted of the following (in thousands):


	December 31,
	2020		2019

On-hand final assemblies and finished goods inventories	$	46,921	$	13,283
Deferred cost of goods sold	1,165		2,441
	48,086		15,724
Less noncurrent portion (included in Other assets)	(2,336)		(924)
Current portion	$	45,750	$	14,800

PROPERTY AND EQUIPMENT (Tables)

12 Months Ended

Dec. 31, 2020

Property, Plant and Equipment [Abstract]

Schedule of property and equipment

Property and equipment consisted of the following (in thousands):


		December 31,
	Useful Life	2020		2019
Equipment	2-5 years	$	90,885	$	82,737
Software	2-5 years	32,244		27,939
Furniture and fixtures	3-5 years	3,092		1,283
Leasehold improvements	Shorter of the estimated lease term or useful life	37,263		23,975
		163,484		135,934
Less accumulated depreciation and amortization		(114,596)		(106,958)
Property and equipment, net		$	48,888	$	28,976

Property and equipment under finance leases included in the amounts above were as follows (in thousands):


	December 31,
	2020		2019
Cost	$	2,908	$	4,401
Less accumulated depreciation	(1,925)		(1,981)
Property and equipment under finance leases, net	$	983	$	2,420

The net book values of the Company's property and equipment by geographic area were as follows (in thousands):


	December 31,
	2020		2019
United States	$	27,211	$	17,584
Canada	4,584		4,768
Asia/Pacific	6,078		5,146
Europe	1,171		1,204
Israel	9,613		20
Other	231		254
	$	48,888	$	28,976

INTANGIBLE ASSETS AND GOODWILL (Tables)

12 Months Ended

Dec. 31, 2020

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of intangible assets

The Company's intangible assets at December 31, 2020 and 2019 consisted of the following (in thousands):


December 31, 2020	Weighted average amortization period (years)	Cost		Accumulated amortization		Net carrying value
In-process research and development	*	$	34,000	$	—	$	34,000

Developed technology	7.93	306,380		143,050		163,330
Customer relationships	11.86	268,140		50,627		217,513
Trade names	3.88	5,000		2,487		2,513

Internal use software	3.00	730		730		—
	9.17	$	614,250	$	196,894	$	417,356


December 31, 2019	Weighted average amortization period (years)	Cost		Accumulated amortization		Net carrying value
In-process research and development	*	$	5,600	$	—	$	5,600

Developed technology	6.79	188,880		100,760		88,120
Customer relationships	9.46	152,140		33,350		118,790
Trade names	5.20	2,000		1,144		856

Internal use software	3.00	730		730		—
	7.82	$	349,350	$	135,984	$	213,366

Schedule of estimated future amortization expense for intangible assets

Estimated future amortization expense for the Company's intangible assets at December 31, 2020 was as follows (in thousands):


Years ending December 31,
2021	$	66,626
2022	60,104
2023	52,256
2024	44,048
2025	37,027
Thereafter	157,295
	$	417,356

Schedule of goodwill

The changes in the carrying value of the Company's goodwill in the years ended December 31, 2020 and 2019 were as follows (in thousands):


	Cloud and Edge		IP Optical Networks		Total
Balance at December 31, 2018 (1)	$	383,655	$	—	$	383,655
Acquisition of Anova	5,541		—		5,541
Impairment of goodwill	(164,300)		—		(164,300)
Balance at December 31, 2019 (2)	224,896		—		224,896
Acquisition of ECI	—		191,996		191,996
Balance at December 31, 2020 (2)	$	224,896	$	191,996	$	416,892

(1) Balance is presented net of accumulated impairment losses of $3.1 million for the Cloud and Edge segment.

(2) Balance is presented net of accumulated impairment losses of $167.4 million for the Cloud and Edge segment.

The components of goodwill at December 31, 2020 and 2019 were as follows (in thousands):


	Cloud and Edge		IP Optical Networks		Total
Balance at December 31, 2019
Goodwill	$	392,302	$	—	$	392,302
Accumulated impairment losses	(167,406)		—		(167,406)
	224,896		—		224,896
Balance at December 31, 2020
Goodwill	$	392,302	$	191,996	$	584,298
Accumulated impairment losses	(167,406)		—		(167,406)
	$	224,896	$	191,996	$	416,892

ACCRUED EXPENSES AND OTHER (Tables)

12 Months Ended

Dec. 31, 2020

Payables and Accruals [Abstract]

Schedule of accrued expenses

Accrued expenses and other consisted of the following (in thousands):


	December 31,
	2020		2019
Employee compensation and related costs	$	66,039	$	27,166
Professional fees	11,451		13,331

Other	57,375		16,203
	$	134,865	$	56,700

WARRANTY (Tables)

12 Months Ended

Dec. 31, 2020

Guarantees and Product Warranties [Abstract]

Schedule of changes in accrual balance

The changes in the Company's warranty accrual balance in the year ended December 31, 2020 were as follows (in thousands):


Year ended December 31,	Balance at beginning of year		Assumed liability in connection with ECI Acquisition		Provision		Settlements		Balance at end of year
2020	$	—	$	16,251	$	4,687	$	(6,083)	$	14,855

RESTRUCTURING AND FACILITIES CONSOLIDATION INITIATIVES (Tables)

12 Months Ended

Dec. 31, 2020

Restructuring and Related Activities [Abstract]

Summary of restructuring accrual activity

The components of restructuring and related expense for the year ended December 31, 2020 and 2019 were as follows (in thousands):


	Year ended December 31,
	2020		2019
Severance and related costs	$	12,025	$	11,179
Variable and other facilities-related costs	3,605		1,528
Accelerated amortization of lease assets due to cease-use	605		3,692
	$	16,235	$	16,399

The components of Restructuring and related expense recorded in the year ended December 31, 2018 were as follows (in thousands):




Severance and related costs	15,217
Facilities	1,798
	$	17,015


	Balance at January 1, 2020		Initiatives charged to expense		Transfer to operating lease liability accounts		Cash payments		Balance at December 31, 2020
Severance	$	—	$	11,547	$	—	$	(6,310)	5,237
Facilities	—		2,478		(535)		(687)		1,256
	$	—	$	14,025	$	(535)	$	(6,997)	$	6,493

Summaries of the 2019 Restructuring Initiative accrual activity for the years ended December 31, 2020 and 2019 are as follows (in thousands):


Year ended December 31, 2020	Balance at January 1, 2020		Initiatives charged to expense		Transfer to operating lease liability accounts		Cash payments		Balance at December 31, 2020
Severance	$	2,110	$	536	$	—	$	(2,473)	173
Facilities	991		1,732		(70)		(1,887)		766
	$	3,101	$	2,268	$	(70)	$	(4,360)	$	939


Year ended December 31, 2019	Balance at January 1, 2019		Initiatives charged to expense		Transfer to operating lease liability accounts	Cash payments		Balance at December 31, 2019
Severance	$	—	$	6,103	—	$	(3,993)	2,110
Facilities	—		5,064		(3,692)	(381)		991
	$	—	$	11,167	(3,692)	$	(4,374)	$	3,101

Summaries of the Merger Restructuring Initiative accrual activity for the years ended December 31, 2020 and 2019 are as follows (in thousands):


Year ended December 31, 2020	Balance at January 1, 2020		Adjustments for changes in estimate		Cash payments		Balance at December 31, 2020
Severance	$	409	$	(58)	$	(351)	$	—


Year ended December 31, 2019	Balance at January 1, 2019		Initiatives charged to expense		Adjustment for the impact of ASC 842 adoption		Cash payments		Balance at December 31, 2019
Severance	$	1,910	$	5,076	$	—	$	(6,577)	$	409
Facilities	771		156		(771)		(156)		—
	$	2,681	$	5,232	$	(771)	$	(6,733)	$	409


Year ended December 31, 2019	Balance at January 1, 2019		Adjustment for the impact of ASC 842 adoption		Balance at December 31, 2019

Facilities	$	117	$	(117)	$	—

A summary of the 2016 Restructuring Initiative accrual activity for the year ended December 31, 2019 is as follows (in thousands):


Year ended December 31, 2019	Balance at January 1, 2019		Cash payments		Balance at December 31, 2019

Facilities	$	58	$	(58)	$	—

OTHER LONG-TERM LIABILITIES (Tables)

12 Months Ended

Dec. 31, 2020

Other Liabilities [Abstract]

Schedule of other long-term liabilities

Other long-term liabilities consisted of the following (in thousands):


	December 31,
	2020		2019
Finance lease obligations	$	1,469	$	3,149

Restructuring	7,432		3,510
Pension obligations	11,132		9,954
Taxes payable	13,835		1,991
Interest rate swap	10,948		—
Warranty	14,855		—

Other	6,082		1,683
	65,753		20,287
Current portion	(17,472)		(3,698)
Long-term liabilities, net of current portion	$	48,281	$	16,589

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Tables)

12 Months Ended

Dec. 31, 2020

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Schedule of impact of derivative financial instrument on condensed consolidated statement of operations

The impact of the Company’s derivative financial instrument on its consolidated statement of comprehensive income (loss) for the year ended December 31, 2020 was as follows (in thousands):





Loss recognized in other comprehensive loss on derivative (effective portion)	$	(12,671)
Amount reclassified from accumulated other comprehensive loss to interest expense (effective portion)	1,723
	$	(10,948)

Schedule of derivative liability designed as a hedging instrument

The fair values and locations in the consolidated balance sheet at December 31, 2020 of the Company's derivative liability designated as a hedging instrument were as follows (in thousands):


	Balance sheet location
Interest rate derivative - liability derivative	Accrued expenses and other	$	3,157
Interest rate derivative - liability derivative	Other long-term liabilities	$	7,791

REVENUE RECOGNITION (Tables)

12 Months Ended

Dec. 31, 2020

Revenue from Contract with Customer [Abstract]

Schedule of timing of performance obligation

The Company's typical performance obligations include the following:

Performance Obligation

When Performance Obligation is Typically Satisfied

When Payment is Typically Due

Software and Product Revenue

Software licenses (perpetual or term)

Upon transfer of control; typically, when made available for download (point in time)

Generally, within 30 days of invoicing except for term licenses, which may be paid for over time

Software licenses (subscription)

Upon activation of hosted site (over time)

Generally, within 30 days of invoicing

Hardware

When control of the hardware passes to the customer; typically, upon delivery (point in time)

Generally, within 30 days of invoicing

Software upgrades

Upon transfer of control; typically, when made available for download (point in time)

Generally, within 30 days of invoicing

Customer Support Revenue

Customer support

Ratably over the course of the support contract (over time)

Generally, within 30 days of invoicing

Professional Services

Other professional services (excluding training services)

As work is performed (over time)

Generally, within 30 days of invoicing (upon completion of services)

Training

When the class is taught (point in time)

Generally, within 30 days of services being performed

Disaggregation of revenue

The Company's total revenue for the years ended December 31, 2020, 2019 and 2018 was disaggregated geographically as follows:


Year ended December 31, 2020	Product revenue		Service revenue (maintenance)		Service revenue (professional services)		Total revenue
United States	$	201,347	$	132,661	$	48,611	$	382,619
Europe, Middle East and Africa	149,567		73,475		25,226		248,268

Asia Pacific	90,201		36,628		19,627		146,456
Other	26,797		32,052		7,603		66,452
	$	467,912	$	274,816	$	101,067	$	843,795


Year ended December 31, 2019	Product revenue		Service revenue (maintenance)		Service revenue (professional services)		Total revenue
United States	$	170,937	$	133,271	$	37,085	$	341,293
Europe, Middle East and Africa	42,262		43,186		12,279		97,727

Asia Pacific	30,617		27,798		10,721		69,136
Other	18,214		29,973		6,768		54,955
	$	262,030	$	234,228	$	66,853	$	563,111


Year ended December 31, 2018	Product revenue		Service revenue (maintenance)		Service revenue (professional services)		Total revenue
United States	$	169,510	$	132,282	$	35,832	$	337,624
Europe, Middle East and Africa	37,833		46,856		11,794		96,483

Asia Pacific	53,683		23,555		9,427		86,665
Other	17,988		31,273		7,872		57,133
	$	279,014	$	233,966	$	64,925	$	577,905


	Year ended December 31,
	2020		2019		2018
Indirect sales through channel program	$	134,876	$	94,639	$	69,232
Direct sales	333,036		167,391		209,782
	$	467,912	$	262,030	$	279,014

The Company's product revenue from sales to enterprise customers and from sales to service provider customers for the years ended December 31, 2020, 2019 and 2018 was as follows (in thousands):


	Year ended December 31,
	2020		2019		2018
Sales to enterprise customers	$	138,469	$	70,548	$	57,534
Sales to service provider customers	329,443		191,482		221,480
	$	467,912	$	262,030	$	279,014

The Company's product revenue and service revenue components by segment for the years ended December 31, 2020, 2019 and 2018 was as follows (in thousands):


	Year ended December 31,
	2020	2019	2018
Product revenue
Cloud and Edge	275,445	262,030	279,014
IP Optical Networks	192,467	—	—
Total product revenue	467,912	262,030	279,014

Service revenue
Maintenance
Cloud and Edge	229,035	234,228	233,966
IP Optical Networks	45,781	—	—
Total maintenance revenue	274,816	234,228	233,966
Professional services
Cloud and Edge	78,790	66,853	64,925
IP Optical Networks	22,277	—	—
Total professional services revenue	101,067	66,853	64,925
Total service revenue	375,883	301,081	298,891

Schedule of customer assets and liabilities

The changes in the Company's accounts receivable, unbilled receivables and deferred revenue balances for the years ended December 31, 2020 and 2019 were as follows (in thousands):


	Accounts receivable		Unbilled accounts receivable		Deferred revenue (current)		Deferred revenue (long-term)
Balance at January 1, 2020	$	168,502	$	24,204	$	100,406	$	20,482
Increase (decrease), net	10,829		34,203		(3,582)		5,528
Balance at December 31, 2020	$	179,331	$	58,407	$	96,824	$	26,010


	Accounts receivable		Unbilled accounts receivable		Deferred revenue (current)		Deferred revenue (long-term)
Balance at January 1, 2019	$	174,310	$	13,543	$	105,087	$	17,572
Increase (decrease), net	(5,808)		10,661		(4,681)		2,910
Balance at December 31, 2019	$	168,502	$	24,204	$	100,406	$	20,482

OPERATING SEGMENT INFORMATION (Tables)

12 Months Ended

Dec. 31, 2020

Segment Reporting [Abstract]

Schedule of Segment Reporting Information

The tables below provide net sales, adjusted gross profit, adjusted EBITDA and depreciation expense by reportable segment for the years ended December 31, 2020, 2019 and 2018 (in thousands):


	Year ended December 31,
	2020		2019		2018
Segment revenue:
Cloud and Edge	$	583,270	$	563,111	$	577,905
IP Optical Networks	260,525		—		—
Revenue	$	843,795	$	563,111	$	577,905



	Year ended December 31,
	2020		2019		2018
Segment adjusted gross profit:
Cloud and Edge	$	385,137	$	355,211	$	348,076
IP Optical Networks	110,845		—		—
Total segment adjusted gross profit	495,982		355,211		348,076


Stock-based compensation expense	(875)		(554)		(459)
Acquisition-related inventory and facilities adjustments	(2,000)		—		(309)


Gross profit	$	493,107	$	354,657	$	347,308


Segment adjusted EBITDA:
Cloud and Edge	$	135,678	$	85,701	$	51,934
IP Optical Networks	(4,512)		—		—
Total segment adjusted EBITDA	131,166		85,701		51,934


Depreciation	(17,188)		(11,949)		(11,200)
Amortization of intangible assets	(60,910)		(49,225)		(49,723)


Stock-based compensation	(13,899)		(12,601)		(11,072)
Acquisition-related inventory and facilities adjustments	(2,000)		—		(966)


Litigation costs	(2,101)		(7,734)		(7,682)
Impairment of goodwill	—		(164,300)		—
Settlement expense	—		—		(1,730)
Cancelled debt offering costs	—		—		(1,003)
Acquisition-, disposal- and integration-related expense	(17,164)		(12,953)		(16,951)
Restructuring and related expense	(16,235)		(16,399)		(17,015)

Income (loss) from operations	$	1,669	$	(189,460)	$	(65,408)

Depreciation expense:
Cloud and Edge	$	12,111	$	11,949	$	11,200
IP Optical Networks	5,077		—		—
Depreciation expense	$	17,188	$	11,949	$	11,200

MAJOR CUSTOMERS (Tables)

12 Months Ended

Dec. 31, 2020

Risks and Uncertainties [Abstract]

Schedule of Customers Contributing 10% or More of the Revenue

The following customers contributed 10% or more of the Company's revenue in at least one of the years ended December

31, 2020, 2019 and 2018:


	Year ended December 31,
	2020	2019	2018
Verizon Communications Inc.	15%	17%	17%
AT&T Inc.	*	12%	*

* Less than 10% of total revenue.

STOCK-BASED COMPENSATION PLANS (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Schedule of activity related to outstanding stock options

The activity related to the Company's outstanding stock options during the year ended December 31, 2020 was as follows:


	Number of Shares	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (in thousands)
Outstanding at January 1, 2020	297,124	$	11.55
Granted	—	$	—

Exercised	(38,288)	$	1.81
Forfeited	(6,055)	$	2.78
Expired	(45,071)	$	15.72
Outstanding at December 31, 2020	207,710	$	12.69	3.73	$	262
Vested or expected to vest at December 31, 2020	207,518	$	12.70	3.73	$	261
Exercisable at December 31, 2020	201,138	$	12.93	3.67	$	241

Schedule of activity related to unvested restricted stock grants

The activity related to the Company's RSAs for the year ended December 31, 2020 was as follows:


	Shares	Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2020	487,976	$	6.87
Granted	—	$	—


Vested	(360,204)	$	6.82
Forfeited	(40,789)	$	6.96
Unvested balance at December 31, 2020	86,983	$	7.04

The activity related to the Company's RSUs for the year ended December 31, 2020 was as follows:


	Shares	Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2020	2,790,060	$	5.11
Granted	6,550,106	$	2.96

Vested	(1,886,486)	$	4.65
Forfeited	(922,570)	$	3.50
Unvested balance at December 31, 2020	6,531,110	$	3.32

Schedule of activity related to performance stock awards

The activity related to the Company's PSUs for the year ended December 31, 2020 was as follows:


	Shares	Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2020	1,067,073	$	5.94
Granted	5,804,202	$	1.41

Vested	(323,752)	$	5.52
Forfeited	(511,592)	$	5.37
Unvested balance at December 31, 2020	6,035,931	$	1.56

Schedule of stock-based compensation expenses which are included in condensed consolidated statement of operations

The consolidated statements of operations included stock-based compensation for the years ended December 31, 2020, 2019 and 2018 as follows (in thousands):


	Year ended December 31,
	2020		2019		2018
Product cost of revenue	$	174	$	76	$	114
Service cost of revenue	701		478		345
Research and development	2,968		1,898		1,797
Sales and marketing	4,129		3,028		2,935
General and administrative	5,927		7,121		5,881
	$	13,899	$	12,601	$	11,072

LEASES (Tables)

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

Schedule of right-of-use lease assets and lease liabilities

The Company's right-of-use lease assets and lease liabilities at December 31, 2020 and December 31, 2019 were as follows (in thousands):


		December 31,
	Classification	2020		2019
Assets
Operating lease assets	Operating lease right-of-use assets	$	69,757	$	36,654
Finance lease assets*	Property and equipment, net	983		2,420
Total leased assets		$	70,740	$	39,074

Liabilities
Current
Operating	Operating lease liabilities	$	17,023	$	7,719
Finance	Accrued expenses and other	902		1,005
Noncurrent
Operating	Operating lease liabilities, net of current	72,614		37,202
Finance	Other long-term liabilities	568		2,144
Total lease liabilities		$	91,107	$	48,070

* Finance lease assets were recorded net of accumulated depreciation of $1.9 million and $2.0 million at December 31, 2020 and December 31, 2019, respectively.

Schedule of components of lease expense

The components of lease expense for the year ended December 31, 2020 and 2019 were as follows (in thousands):


	Year ended December 31,
	2020		2019

Operating lease cost*	$	19,582	$	13,865
Finance lease cost
Amortization of leased assets	1,200		1,106
Interest on lease liabilities	173		265
Short-term lease cost	20,687		19,460
Variable lease costs (costs excluded from minimum fixed lease payments)**	2,713		3,264
Sublease income	(1,087)		(374)
Net lease cost	$	43,268	$	37,586

Cash flow information related to the Company's leases for the years ended December 31, 2020 and 2019 was as follows (in thousands):


	Year ended December 31,
	2020		2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	19,161	$	10,559
Operating cash flows from finance leases	$	173	$	265
Financing cash flows from finance leases	$	1,279	$	913

Other information related to the Company's leases as of December 31, 2020 and 2019 was as follows (in thousands):


	December 31,
	2020		2019


Weighted average remaining lease term (years):
Operating leases	6.59		6.73
Finance leases	1.70		2.35
Weighted average discount rate:
Operating leases	5.67	%	6.50	%
Finance leases	6.15	%	7.54	%

Schedule of future minimum fixed operating lease payments

Future minimum fixed lease payments under noncancelable leases at December 31, 2020 were as follows (in thousands):


	December 31, 2020
	Operating		Finance
	leases		leases
2021	$	21,366	$	981
2022	20,171		506
2023	17,312		62
2024	10,420		—
2025	8,544		—
2026 and beyond	32,516		—
Total lease payments	110,329		1,549
Less: interest	(20,692)		(80)
Present value of lease liabilities	$	89,637	$	1,469

Schedule of future minimum fixed finance lease payments

Future minimum fixed lease payments under noncancelable leases at December 31, 2020 were as follows (in thousands):


	December 31, 2020
	Operating		Finance
	leases		leases
2021	$	21,366	$	981
2022	20,171		506
2023	17,312		62
2024	10,420		—
2025	8,544		—
2026 and beyond	32,516		—
Total lease payments	110,329		1,549
Less: interest	(20,692)		(80)
Present value of lease liabilities	$	89,637	$	1,469

NON-U.S. EMPLOYEE DEFINED BENEFIT PLANS (Tables)

12 Months Ended

Dec. 31, 2020

Retirement Benefits [Abstract]

Schedule of changes in projected benefit obligations, fair value of plan assets, and funded status of plan


	Year ended December 31,
	2020		2019
Changes in projected benefit obligations:
Projected benefit obligation, beginning of year	$	11,784	$	10,848
Business combination	17,963		—
Service cost	1,459		335
Interest cost	46		140
Participant contributions	—		24
Plan amendments	(4,440)		—
Benefits and expenses paid	(1,976)		(44)
Net actuarial loss on obligation	231		1,059
Curtailment	—		82
Settlement	—		(660)

Projected benefit obligation, end of year	$	25,067	$	11,784

Changes in plan assets:
Fair value of plan assets, beginning of year	$	1,830	$	3,842
Business combination	13,188		—
Actual return on plan assets	1,077		(1,471)
Plan amendments	(588)		—
Employer contributions	798		139
Participant contributions	21		24
Administrative expenses	—		(21)
Benefits paid	(1,976)		(683)

Fair value of plan assets, end of year	$	14,350	$	1,830

Funded status at end of year	$	(10,717)	$	(9,954)

Amounts recognized in accumulated other comprehensive loss consist of:

Net actuarial loss	$	(102)	$	2,743


Amounts recognized in the consolidated balance sheets consist of:
Accrued expenses and other (current pension liability)	$	(435)	$	(74)
Other long-term liabilities (non-current pension liability)	(10,282)		(9,880)
Net amount recognized	$	(10,717)	$	(9,954)

Schedule of accumulated benefit obligations

Plans with underfunded or non-funded accumulated benefit obligations at December 31, 2020 and 2019 were as follows (in thousands):


	December 31,
	2020		2019
Aggregate projected benefit obligation	$	25,067	$	11,784
Aggregate accumulated benefit obligation	$	20,746	$	7,759
Aggregate fair value of plan assets	$	14,350	$	1,830

Schedule of net benefit costs

Net periodic benefit costs for the years ended December 31, 2020, 2019 and 2018 were as follows (in thousands):


	Year ended December 31,
	2020		2019		2018
Service cost	$	1,459	$	335	$	449
Interest cost	46		140		150
Expected return on plan assets	(343)		(14)		(45)
Plan asset expenses	20		21		22

Curtailment charge (credit)	—		13		(510)
Settlement (credit) charge	(1,557)		115		3

Net periodic benefit costs	$	(375)	$	610	$	69

Schedule of expected benefit payments

Expected benefit payments for the next ten years are as follows (in thousands):


Years ending December 31,
2021	$	1,508
2022	1,759
2023	1,471
2024	1,298
2025	989
2026 to 2030	8,674
	$	15,699

Schedule of defined benefit plan amounts recognized in other comprehensive income (loss)

The changes in plan assets and benefit obligations recognized in other comprehensive income (loss) before tax for the years ended December 31, 2020, 2019 and 2018 were as follows (in thousands):


	Year ended December 31,
	2020		2019		2018
Net (gain) loss	$	(558)	$	2,526	$	(356)


Settlement gain	(1,557)		—		—
Total recognized in comprehensive income (loss)	$	(2,115)	$	2,526	$	(356)

Schedule of assumptions used

The principal weighted average assumptions used to determine the benefit obligation at December 31, 2020 and 2019 were as follows:


	December 31,
	2020		2019
Discount rate	2.16	%	0.68	%
Rate of compensation increase	2.41	%	2.88	%

The principal weighted average assumptions used to determine net period benefit cost for the years ended December 31, 2020, 2019 and 2018 were as follows:


	Year ended December 31,
	2020		2019		2018
Discount rate	0.68	%	1.30	%	1.50	%
Expected long-term return on plan assets	0.21	%	1.12	%	1.34	%
Rate of compensation increase	2.88	%	2.83	%	3.38	%

INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Schedule of income (loss) before taxes

The components of income (loss) from continuing operations before income taxes consisted of the following (in thousands):


	Year ended December 31,
	2020		2019		2018
Income (loss) before income taxes:
United States	$	123,817	$	(132,887)	$	(52,569)
Foreign	(30,500)		9,994		(20,841)
	$	93,317	$	(122,893)	$	(73,410)

Schedule of income tax expense (benefit)

The provision for income taxes from continuing operations consisted of the following (in thousands):


	Year ended December 31,
	2020		2019		2018
Provision (benefit) for income taxes:
Current:
Federal	$	677	$	11	$	561
State	1,310		128		128
Foreign	7,355		1,744		2,198
Total current	9,342		1,883		2,887
Deferred:
Federal	30,278		9,790		(8,481)
State	195		1,630		(1,414)
Foreign	(16,117)		383		(1,477)
Change in valuation allowance	(18,972)		(6,504)		11,885
Total deferred	(4,616)		5,299		513
Total	$	4,726	$	7,182	$	3,400

Schedule of effective income tax rate reconciliation

A reconciliation of the Company's effective tax rate for continuing operations to the statutory federal rate is as follows:


	Year ended December 31,
	2020		2019		2018
U.S. statutory income tax rate	21.0	%	21.0	%	21.0	%
State income taxes, net of federal benefit	1.1		(0.2)		(0.1)
Foreign income taxes	2.9		(1.0)		(5.7)



Foreign deemed dividends	(2.7)		(0.4)		(3.4)
Stock-based compensation	1.0		(0.7)		(0.3)
Tax credits	(2.8)		2.8		0.6
Uncertain tax positions	0.5		(0.2)		1.3


Valuation allowance	(20.3)		(0.7)		(16.1)
Goodwill amortization	0.6		0.4		0.3

Tax reform	—		(0.1)		—
Goodwill impairment	—		(25.4)		—

Other permanent adjustments	1.8		(1.5)		(1.4)
Permanent adjustments - foreign exchange	1.8		—		(0.9)
Other, net	0.2		0.2		0.1
Effective income tax rate	5.1	%	(5.8)	%	(4.6)	%

Summary of deferred tax assets and liabilities

The following is a summary of the significant components of deferred income tax assets and liabilities (in thousands):


	December 31,
	2020		2019
Assets:
Net operating loss carryforwards	$	447,101	$	61,057
Capital loss carryforward	71,182		—
Research and development tax credits	45,031		32,879
Other tax credits	6,400		—

Deferred revenue	3,184		7,868
Accrued expenses	13,557		5,687
Inventory	2,603		4,618
Stock-based compensation	1,668		2,880
Fixed assets	4,613		5,461
Other temporary differences	4,051		2,138
	599,390		122,588
Valuation allowance	(496,439)		(94,980)
Total deferred tax assets	102,951		27,608
Liabilities:
Intangible assets	(75,794)		(22,470)

Mark-to-market investments	(17,631)		—
Unremitted foreign income	(15,717)		(4,827)
Total deferred tax liabilities	(109,142)		(27,297)
Total net deferred tax assets	$	(6,191)	$	311

The deferred tax assets and liabilities based on tax jurisdictions are presented in the Company's consolidated balance sheets as follows:


	December 31,
	2020		2019
Deferred income taxes - noncurrent assets	$	10,651	$	4,959
Deferred income taxes - noncurrent liabilities	(16,842)		(4,648)
	$	(6,191)	$	311

Schedule of unrecognized tax benefits

A reconciliation of the Company's unrecognized tax benefits is as follows (in thousands):


	Year ended December 31,
	2020		2019		2018
Unrecognized tax benefits at January 1	$	2,932	$	3,461	$	4,528
Increases related to current year tax positions	485		292		74
Increases related to prior period tax positions	11,209		—		122

Decreases related to prior period tax positions	(572)		(821)		(1,263)


Unrecognized tax benefits at December 31	$	14,054	$	2,932	$	3,461

QUARTERLY RESULTS (UNAUDITED) (Tables)

12 Months Ended

Dec. 31, 2020

Quarterly Financial Information Disclosure [Abstract]

Schedule of quarterly financial information

In the opinion of management, all necessary adjustments, consisting only of normal recurring adjustments, have been included to present fairly the unaudited consolidated quarterly results when read in conjunction with the Company's audited consolidated financial statements and related notes.


	First Quarter (1)		Second Quarter		Third Quarter		Fourth Quarter
	(In thousands, except per share data)
Year ended December 31, 2020
Revenue	$	157,982	$	210,493	$	231,118	$	244,202
Cost of revenue (3)	67,458		87,226		96,164		99,840
Gross profit (3)	$	90,524	$	123,267	$	134,954	$	144,362
(Loss) income from operations	$	(28,740)	$	1,592	$	11,917	$	16,900

Net (loss) income	$	(33,170)	$	(8,251)	$	6,252	$	123,760
(Loss) earnings per share (4):
Basic	$	(0.27)	$	(0.06)	$	0.04	$	0.85
Diluted	$	(0.27)	$	(0.06)	$	0.04	$	0.81
Shares used in computing (loss) earnings per share:
Basic	120,992		144,483		144,948		145,311
Diluted	120,992		144,483		151,680		153,441


	First Quarter (2)		Second Quarter		Third Quarter (2)		Fourth Quarter
	(In thousands, except per share data)
Year ended December 31, 2019
Revenue	$	118,928	$	145,421	$	137,653	$	161,109
Cost of revenue (3)	52,694		54,656		49,254		51,850
Gross profit (3)	$	66,234	$	90,765	$	88,399	$	109,259
Loss (income) from operations	$	(36,228)	$	(7,096)	$	2,686	$	(148,822)

Net (loss) income	$	(30,832)	$	49,470	$	1,650	$	(150,363)
Loss (earnings) per share (4):
Basic	$	(0.29)	$	0.45	$	0.01	$	(1.36)
Diluted	$	(0.29)	$	0.45	$	0.01	$	(1.36)
Shares used in computing loss (earnings) per share:
Basic	108,167		110,394		110,080		110,269
Diluted	108,167		110,698		110,756		110,269

__________________________________

(1)Includes the results of ECI for the period subsequent to March 3, 2020.

(2)Includes the results of Anova for the period subsequent to February 28.

NATURE OF THE BUSINESS (Details)	Dec. 31, 2020 country
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of countries	35

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2020 USD ($) segment	Sep. 30, 2020 segment	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Property, Plant and Equipment [Line Items]
Maximum measurement period from the acquisition date within which company records adjustments to the assets acquired and liabilities assumed			1 year
Revenue agreement term			1 year
Number of operating segments \| segment	2	1
Restricted cash current	$ 7,269		$ 7,269	$ 0
Cash received from the sale of certain accounts receivable			119,800
Interest expense			900
Transaction gains (losses)			(2,961)	(1,090)	$ (4,611)
Advertising expense			800	500	500
Warranty	14,855		14,855	0
Accrued expenses and other	6,500		6,500
Other long-term liabilities	8,400		8,400
Deferred income taxes	16,842		$ 16,842	4,648
Percent threshold			50.00%
Foreign Tax Authority
Property, Plant and Equipment [Line Items]
Deferred income taxes	15,700		$ 15,700
General and Administrative Expense
Property, Plant and Equipment [Line Items]
Transaction gains (losses)			(3,000)	$ (1,100)	$ 4,600
Tax Payment on Certain Fixed Assets
Property, Plant and Equipment [Line Items]
Restricted cash	4,600		4,600
Restricted Short-term Bank Deposits
Property, Plant and Equipment [Line Items]
Restricted cash	$ 2,700		$ 2,700
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			5 years
Software
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			3 years
Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			2 years
Standard Product Warranty Period			1 year
Minimum \| Software
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			2 years
Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			5 years
Standard Product Warranty Period			3 years
Maximum \| Software
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			5 years
Operating Segments
Property, Plant and Equipment [Line Items]
Number of operating segments \| segment	2

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Reclassifications (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue									$ 843,795,000	$ 563,111,000	$ 577,905,000
Total cost of revenue									350,688,000	208,454,000	230,597,000
Gross profit	$ 144,362,000	$ 134,954,000	$ 123,267,000	$ 90,524,000	$ 109,259,000	$ 88,399,000	$ 90,765,000	$ 66,234,000	493,107,000	354,657,000	347,308,000
Research and development									194,525,000	141,060,000	145,462,000
Sales and marketing									139,318,000	106,310,000	117,529,000
General and administrative									63,286,000	53,870,000	66,036,000
Amortization of acquired intangible assets										49,225,000	49,723,000
Impairment of goodwill									0	164,300,000	0
Acquisition-, disposal- and integration-related									17,164,000	12,953,000	16,951,000
Restructuring and related									16,235,000	16,399,000	17,015,000
Total operating expenses									491,438,000	544,117,000	412,716,000
(Loss) income from operations	$ 16,900,000	$ 11,917,000	$ 1,592,000	$ (28,740,000)	$ (148,822,000)	$ 2,686,000	$ (7,096,000)	$ (36,228,000)	1,669,000	(189,460,000)	(65,408,000)
Prior presentation
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue										563,111,000	577,905,000
Total cost of revenue										246,027,000	269,573,000
Gross profit										317,084,000	308,332,000
Research and development										141,060,000	145,462,000
Sales and marketing										117,962,000	128,276,000
General and administrative										53,870,000	66,036,000
Amortization of acquired intangible assets										0	0
Impairment of goodwill										164,300,000	0
Acquisition-, disposal- and integration-related										12,953,000	16,951,000
Restructuring and related										16,399,000	17,015,000
Total operating expenses										506,544,000	373,740,000
(Loss) income from operations										(189,460,000)	(65,408,000)
Amounts reclassified
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue										0	0
Total cost of revenue										(37,573,000)	(38,976,000)
Gross profit										37,573,000	38,976,000
Research and development										0	0
Sales and marketing										(11,652,000)	(10,747,000)
General and administrative										0	0
Amortization of acquired intangible assets										49,225,000	49,723,000
Impairment of goodwill										0	0
Acquisition-, disposal- and integration-related										0	0
Restructuring and related										0	0
Total operating expenses										37,573,000	38,976,000
(Loss) income from operations										0	0
Product revenue
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue									467,912,000	262,030,000	279,014,000
Total cost of revenue									204,772,000	95,774,000	103,209,000
Product revenue \| Prior presentation
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue										262,030,000	279,014,000
Total cost of revenue										133,347,000	142,185,000
Product revenue \| Amounts reclassified
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue										0	0
Total cost of revenue										(37,573,000)	(38,976,000)
Service
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue									375,883,000	301,081,000	298,891,000
Total cost of revenue									$ 145,916,000	112,680,000	127,388,000
Service \| Prior presentation
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue										301,081,000	298,891,000
Total cost of revenue										112,680,000	127,388,000
Service \| Amounts reclassified
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue										0	0
Total cost of revenue										$ 0	$ 0

BUSINESS ACQUISITIONS - ECI Narrative (Details) - USD ($) shares in Millions		3 Months Ended		12 Months Ended
	Nov. 14, 2019	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Net cash consideration				$ 346,852,000	$ 0	$ 46,389,000
Severance
Business Acquisition [Line Items]
Net long term liabilities		$ 4,700,000		4,700,000
Term Loan Facility
Business Acquisition [Line Items]
Commitments from lender	$ 400,000,000
Revolving Credit Facility
Business Acquisition [Line Items]
Commitments from lender	100,000,000
ECI
Business Acquisition [Line Items]
Proceeds from sale of real estate assets	$ 33,400,000
Revenue				260,500,000
Net loss				52,900,000
ECI
Business Acquisition [Line Items]
Common stock to be issued (in shares)	32.5
Fair value of Ribbon stock issued	$ 108,600,000			108,550,000
Net cash consideration	322,500,000			346,852,000
Repayment of ECI outstanding debt obligations	183,300,000
Payment to selling shareholders	$ 139,200,000			$ 139,244,000
Increase to other long-term liabilities		$ 13,200,000
Reduction to current inventory			$ 10,400,000
Reduction to noncurrent inventory			7,000,000.0
Increase (decrease) to identifiable intangible assets			11,000,000.0
Net increase to goodwill			2,500,000
Indemnification receivable			5,700,000
Weighted average useful life of intangible assets (in years)				12 years 4 months 17 days
ECI \| In-process research and development
Business Acquisition [Line Items]
Increase (decrease) to identifiable intangible assets			3,000,000.0
ECI \| Developed technology
Business Acquisition [Line Items]
Increase (decrease) to identifiable intangible assets			5,000,000.0
ECI \| Customer relationships
Business Acquisition [Line Items]
Increase (decrease) to identifiable intangible assets			2,000,000.0
ECI \| Trade names
Business Acquisition [Line Items]
Increase (decrease) to identifiable intangible assets			$ 1,000,000.0

BUSINESS ACQUISITONS - Summary of Preliminary Allocation of Purchase Consideration (Details) - USD ($) $ in Thousands		12 Months Ended
	Nov. 14, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash consideration:
Net cash consideration		$ 346,852	$ 0	$ 46,389
Fair value of assets acquired and liabilities assumed:
Goodwill		416,892	$ 224,896	$ 383,655
ECI
Cash consideration:
Repayment of ECI outstanding debt obligations		183,266
Cash paid to selling shareholders	$ 139,200	139,244
Payment to selling shareholders from sale of ECI real estate assets		33,400
Less cash and restricted cash acquired		(9,058)
Net cash consideration	322,500	346,852
Fair value of Ribbon stock issued	$ 108,600	108,550
Fair value of total consideration		455,402
Fair value of assets acquired and liabilities assumed:
Current assets, net of cash and restricted cash acquired		120,203
Property and equipment		54,913
Goodwill		191,996
Other noncurrent assets		37,528
Deferred revenue		(4,369)
Other current liabilities		(146,618)
Deferred revenue, net of current		(3,726)
Deferred tax liability		(13,308)
Other long-term liabilities		(46,117)
Assets acquired and liabilities assumed		455,402
ECI \| In-process research and development
Fair value of assets acquired and liabilities assumed:
Intangible assets		34,000
ECI \| Developed technology
Fair value of assets acquired and liabilities assumed:
Intangible assets		111,900
ECI \| Customer relationships
Fair value of assets acquired and liabilities assumed:
Intangible assets		116,000
ECI \| Trade names
Fair value of assets acquired and liabilities assumed:
Intangible assets		$ 3,000

BUSINESS ACQUISITONS - Unaudited Pro Forma Results (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Business Combinations [Abstract]
Revenue	$ 869,002	$ 944,915
Net income (loss)	$ 97,036	$ (250,337)
Diluted earnings (loss) per share (in dollars per share)	$ 0.65	$ (1.76)

BUSINESS ACQUISITONS - Anova Data Narrative (Details) - USD ($) $ in Thousands			12 Months Ended
	Mar. 04, 2020	Jan. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Goodwill			$ 416,892	$ 224,896	$ 383,655
Anova Data, Inc.
Business Acquisition [Line Items]
Common stock to be issued (in shares)		2,900,000
Shares of common stock issued as purchase		$ 15,200
Number of additional shares potentially issued (in number of shares)		300,000
Fair value of additional shares potentially issued		$ 1,700
Number of shares issued after post-closing adjustments (in shares)	316,551
Fair value of total consideration				16,900
Intangible assets				11,200
Net assets acquired				200
Goodwill				5,500
Weighted average useful life of intangible assets (in years)			6 years 3 months
Anova Data, Inc. \| Customer relationships
Business Acquisition [Line Items]
Increase (decrease) to identifiable intangible assets				(2,000)
Intangible assets				5,200
Anova Data, Inc. \| Developed technology
Business Acquisition [Line Items]
Increase (decrease) to identifiable intangible assets				2,000
Intangible assets				$ 6,000

BUSINESS ACQUISITONS - Edgewater Networks, Inc (Details) - USD ($) $ in Thousands, shares in Millions		12 Months Ended
	Jun. 24, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Mar. 08, 2019	Feb. 15, 2019
Business Acquisition [Line Items]
Cash, net of cash acquired		$ 346,852	$ 0	$ 46,389
Other income (expense), net		112,690	70,444	(3,772)
Edgewater
Business Acquisition [Line Items]
Cash, net of cash acquired	$ 46,400	$ 46,389
Common stock to be issued (in shares)	4.2
Deferred purchase consideration	$ 30,000				$ 21,900	$ 21,900
Deferred cash payments, within 6 months from closing date	15,000
Deferred cash payments, within 9 to 18 months from closing date	$ 15,000
Other income (expense), net			$ 8,100
Weighted average useful life of intangible assets (in years)			8 years 4 months 17 days
Revenue				21,500
Net loss attributable to acquisition				$ 4,300

BUSINESS ACQUISITONS - Schedule of Edgewater Purchase Price Allocation (Details) - USD ($) $ in Thousands		12 Months Ended
	Jun. 24, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash consideration:
Net cash consideration		$ 346,852	$ 0	$ 46,389
Intangible assets:
Goodwill		416,892	$ 224,896	$ 383,655
Edgewater
Cash consideration:
Cash paid to Edgewater Selling Stakeholders		51,162
Less cash and restricted cash acquired		(4,773)
Net cash consideration	$ 46,400	46,389
Unpaid cash consideration		30,000
Fair value of Ribbon stock issued		30,000
Fair value of equity awards assumed	$ 700	747
Fair value of total consideration		107,136
Fair value of assets acquired and liabilities assumed:
Current assets, net of cash and restricted cash acquired		16,098
Property and equipment		245
Intangible assets:
Goodwill		48,053
Other noncurrent assets		103
Deferred revenue		(2,749)
Other current liabilities		(9,926)
Deferred revenue, net of current		(669)
Other long-term liabilities		(719)
Assets acquired and liabilities assumed		107,136
Edgewater \| Developed technology
Intangible assets:
Intangible assets		29,500
Edgewater \| Customer relationships
Intangible assets:
Intangible assets		26,100
Edgewater \| Trade names
Intangible assets:
Intangible assets		$ 1,100

BUSINESS ACQUISITONS - Schedule of Acquisition- and Integration-related Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Combinations [Abstract]
Professional and services fees (acquisition-related)	$ 13,441	$ 8,657	$ 7,627
Management bonuses (acquisition-related)	0	0	1,972
Professional and services fees (disposal-related)	1,890	0	0
Integration-related expenses	1,833	4,296	7,352
Acquisition- and integration-related	$ 17,164	$ 12,953	$ 16,951

SALE OF KANDY COMMUNICATIONS BUSINESS (Details) $ / shares in Units, $ in Thousands			12 Months Ended
	Feb. 19, 2021 day $ / shares	Dec. 01, 2020 USD ($) day $ / shares shares	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Increase in fair value of investments			$ 30,296	$ 0	$ 0
Professional and services fees (disposal-related)			1,890	$ 0	$ 0
Kandy Communications Business \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration from sale		$ 45,000
Principal amount of debentures		$ 1
Number of warrants acquired (in shares) \| shares		1
Number of shares entitled from warrant (in shares) \| shares		100
Par value of common stock (in dollars per share) \| $ / shares		$ 0.0001
Number of AVCT Units acquired (in shares) \| shares		43,778
Interest rate		10.00%
Debenture, conversion price (in dollars per share) \| $ / shares		$ 3.45
Debenture, stock price trigger (in dollars per share) \| $ / shares		$ 6.00
Debenture, number of trading days \| day		40
Debenture, number of consecutive trading days \| day		60
Amount from option to redeem debentures		$ 5,000
Threshold amount raised in offering		$ 50,000
Number of shares of common stock entitled from warrants (in shares) \| shares		4,377,800
Exercise price of warrants (in dollars per share) \| $ / shares		$ 0.01
Fair value of AVCT units		$ 84,900	115,200
Fair value of debentures		66,300
Fair value of warrants		18,600
Net assets sold		$ 1,300
Gain on sale			83,600
Increase in fair value of investments			30,300
Professional and services fees (disposal-related)			$ 1,900
Kandy Communications Business \| Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debenture, stock price trigger (in dollars per share) \| $ / shares	$ 6.00
Debenture, number of trading days \| day	40
Debenture, number of consecutive trading days \| day	60

EARNINGS (LOSS) PER SHARE (Details) - shares shares in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of weighted average shares outstanding from basic to diluted
Weighted average shares outstanding - basic (in shares)	145,311	144,948	144,483	120,992	110,269	110,080	110,394	108,167	138,967	109,734	103,916
Potential dilutive common shares (in shares)									5,683	0	0
Weighted average shares outstanding - diluted (in shares)	153,441	151,680	144,483	120,992	110,269	110,756	110,698	108,167	144,650	109,734	103,916
Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities not included in computation of diluted loss per share (in shares)									200	3,100
Options, restricted and performance-based stock and stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities not included in computation of diluted loss per share (in shares)										4,600

ACCOUNTS RECEIVABLE, NET - Schedule of Accounts Receivable, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Receivables [Abstract]
Accounts receivable	$ 238,514	$ 193,619
Allowance for doubtful accounts	(776)	(913)	$ (669)	$ (73)
Accounts receivable, net	$ 237,738	$ 192,706

ACCOUNTS RECEIVABLE, NET - Schedule of Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year	$ 913	$ 669	$ 73
Charges to expense	686	738	351
Charges (credits) to other accounts	94	68	620
Write-offs	(917)	(562)	(375)
Balance at end of year	$ 776	$ 913	$ 669

INVENTORY (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
On-hand final assemblies and finished goods inventories	$ 46,921	$ 13,283
Deferred cost of goods sold	1,165	2,441
Gross inventory	48,086	15,724
Less noncurrent portion (included in Other assets)	(2,336)	(924)
Current portion	$ 45,750	$ 14,800

PROPERTY AND EQUIPMENT - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 163,484	$ 135,934
Less accumulated depreciation and amortization	(114,596)	(106,958)
Property and equipment, net	$ 48,888	28,976
Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 90,885	82,737
Equipment \| Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Equipment \| Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Software
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Property and equipment, gross	$ 32,244	27,939
Software \| Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Software \| Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 3,092	1,283
Furniture and fixtures \| Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Furniture and fixtures \| Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Property and equipment, gross	$ 37,263	$ 23,975

PROPERTY AND EQUIPMENT - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Depreciation and amortization of property and equipment	$ 17,188	$ 11,949	$ 11,200

PROPERTY AND EQUIPMENT - Property and Equipment Under Finance Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Cost	$ 2,908	$ 4,401
Less accumulated depreciation	(1,925)	(1,981)
Property and equipment under finance leases, net	$ 983	$ 2,420

PROPERTY AND EQUIPMENT - Property and Equipment by Geographic Area (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, net	$ 48,888	$ 28,976
Property and equipment, net		28,976
United States
Property, Plant and Equipment [Line Items]
Property and equipment, net	27,211
Property and equipment, net		17,584
Canada
Property, Plant and Equipment [Line Items]
Property and equipment, net	4,584
Property and equipment, net		4,768
Asia/Pacific
Property, Plant and Equipment [Line Items]
Property and equipment, net	6,078
Property and equipment, net		5,146
Europe
Property, Plant and Equipment [Line Items]
Property and equipment, net	1,171
Property and equipment, net		1,204
Israel
Property, Plant and Equipment [Line Items]
Property and equipment, net	9,613
Property and equipment, net		20
Other
Property, Plant and Equipment [Line Items]
Property and equipment, net	$ 231
Property and equipment, net		$ 254

INTANGIBLE ASSETS AND GOODWILL -Schedule of Intangible Assets and Amortization (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period (years)	9 years 2 months 1 day	7 years 9 months 25 days
Cost	$ 614,250	$ 349,350
Accumulated amortization	196,894	135,984
Net carrying value	417,356	213,366
Estimated future amortization expense for intangible assets
2021	66,626
2022	60,104
2023	52,256
2024	44,048
2025	37,027
Thereafter	157,295
Total	417,356
In-process research and development
Finite-Lived Intangible Assets [Line Items]
Cost	34,000	5,600
Accumulated amortization	0	0
Net carrying value	$ 34,000	$ 5,600
Developed technology
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period (years)	7 years 11 months 4 days	6 years 9 months 14 days
Cost	$ 306,380	$ 188,880
Accumulated amortization	143,050	100,760
Net carrying value	$ 163,330	$ 88,120
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period (years)	11 years 10 months 9 days	9 years 5 months 15 days
Cost	$ 268,140	$ 152,140
Accumulated amortization	50,627	33,350
Net carrying value	$ 217,513	$ 118,790
Trade names
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period (years)	3 years 10 months 17 days	5 years 2 months 12 days
Cost	$ 5,000	$ 2,000
Accumulated amortization	2,487	1,144
Net carrying value	$ 2,513	$ 856
Internal use software
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period (years)	3 years	3 years
Cost	$ 730	$ 730
Accumulated amortization	730	730
Net carrying value	$ 0	$ 0

INTANGIBLE ASSETS AND GOODWILL - Narrative (Details)	3 Months Ended	9 Months Ended	12 Months Ended
INTANGIBLE ASSETS AND GOODWILL - Narrative (Details)	Dec. 31, 2020 USD ($) segment	Sep. 30, 2020 segment	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Goodwill [Line Items]
Amortization and impairment			$ 60,900,000	$ 49,200,000	$ 49,700,000
Number of operating segments \| segment	2	1
Goodwill	$ 416,892,000		416,892,000	224,896,000	383,655,000
Impairment of goodwill			$ 0	164,300,000	0
Number of reportable operating segments \| segment		1	2
Cloud and Edge
Goodwill [Line Items]
Goodwill	224,896,000		$ 224,896,000	224,896,000	383,655,000
Impairment of goodwill			164,300,000
IP Optical Networks
Goodwill [Line Items]
Goodwill	$ 191,996,000		$ 191,996,000	0	$ 0
Impairment of goodwill				$ 0

INTANGIBLE ASSETS AND GOODWILL - Schedule of Changes in Carrying Value of Goodwill (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Roll Forward]
Goodwill at the beginning of the period	$ 224,896,000	$ 383,655,000
Impairment of goodwill	0	(164,300,000)	$ 0
Goodwill, Ending Balance	416,892,000	224,896,000	383,655,000
Accumulated impairment losses	(167,406,000)	(167,406,000)
Cloud and Edge
Goodwill [Roll Forward]
Goodwill at the beginning of the period	224,896,000	383,655,000
Impairment of goodwill	(164,300,000)
Goodwill, Ending Balance	224,896,000	224,896,000	383,655,000
Accumulated impairment losses	(167,406,000)	(167,406,000)	(3,100,000)
IP Optical Networks
Goodwill [Roll Forward]
Goodwill at the beginning of the period	0	0
Impairment of goodwill		0
Goodwill, Ending Balance	191,996,000	0	$ 0
Accumulated impairment losses	0	0
Anova Data, Inc.
Goodwill [Roll Forward]
Goodwill at the beginning of the period	5,500,000
Acquisition		5,541,000
Goodwill, Ending Balance		5,500,000
Anova Data, Inc. \| Cloud and Edge
Goodwill [Roll Forward]
Acquisition		5,541,000
Anova Data, Inc. \| IP Optical Networks
Goodwill [Roll Forward]
Acquisition		$ 0
ECI
Goodwill [Roll Forward]
Acquisition	191,996,000
Goodwill, Ending Balance	191,996,000
ECI \| Cloud and Edge
Goodwill [Roll Forward]
Acquisition	0
ECI \| IP Optical Networks
Goodwill [Roll Forward]
Acquisition	$ 191,996,000

INTANGIBLE ASSETS AND GOODWILL - Schedule of Components of Goodwill (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill, gross	$ 584,298	$ 392,302
Accumulated impairment losses	(167,406)	(167,406)
Goodwill	416,892	224,896	$ 383,655
Cloud and Edge
Goodwill [Line Items]
Goodwill, gross	392,302	392,302
Accumulated impairment losses	(167,406)	(167,406)	(3,100)
Goodwill	224,896	224,896	383,655
IP Optical Networks
Goodwill [Line Items]
Goodwill, gross	191,996	0
Accumulated impairment losses	0	0
Goodwill	$ 191,996	$ 0	$ 0

ACCRUED EXPENSES AND OTHER (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Employee compensation and related costs	$ 66,039	$ 27,166
Professional fees	11,451	13,331
Other	57,375	16,203
Total	$ 134,865	$ 56,700

WARRANTY (Details) $ in Thousands	12 Months Ended
WARRANTY (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Movement in Standard Product Warranty Accrual [Roll Forward]
Balance at beginning of year	$ 0
Assumed liability in connection with ECI Acquisition	16,251
Provision	4,687
Settlements	(6,083)
Balance at end of year	$ 14,855

RESTRUCTURING AND FACILITIES CONSOLIDATION INITIATIVES - Narrative (Details) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Jul. 31, 2016 USD ($)	Mar. 31, 2020 USD ($) executive	Dec. 31, 2020 USD ($) employee	Dec. 31, 2019 USD ($) employee	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Oct. 27, 2017 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring expense			$ 16,235	$ 16,399	$ 17,015
Severance and related costs			12,025	11,179	15,217
Accelerated amortization of lease assets due to cease-use			605	3,692
Restructuring reserve current			6,600	2,600
Long-term portions of accrued restructuring			800	900
2020 Restructuring Initiative
Restructuring Cost and Reserve [Line Items]
Restructuring expense			14,025
Severance and related costs		$ 1,100
Accelerated amortization of lease assets due to cease-use			500
Restructuring and related expense			8,000
2020 Restructuring Initiative \| Severance
Restructuring Cost and Reserve [Line Items]
Restructuring expense			$ 11,547
Number of positions eliminated \| employee			190
2020 Restructuring Initiative \| Variable and Other Facilities Costs
Restructuring Cost and Reserve [Line Items]
Restructuring expense			$ 2,000
2020 Restructuring Initiative \| Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring expense			2,478
2019 Restructuring Initiative
Restructuring Cost and Reserve [Line Items]
Restructuring expense			$ 2,268	11,167
Number of positions eliminated \| employee			5
Accelerated amortization of lease assets due to cease-use			$ 100
Restructuring charges, net of adjustments			2,300	11,200
2019 Restructuring Initiative \| Severance
Restructuring Cost and Reserve [Line Items]
Restructuring expense			536	$ 6,103
Number of positions eliminated \| employee				120
Restructuring charges, net of adjustments			500	$ 6,100
2019 Restructuring Initiative \| Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring expense			1,732	5,064
Accelerated amortization of lease assets due to cease-use				3,700
Restructuring charges, net of adjustments			1,700	1,400
Merger Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring expense			$ 1,400	$ 5,232	16,100
Number of positions eliminated \| employee			275	40
Severance and related costs			$ 14,700
Merger Restructuring \| Severance
Restructuring Cost and Reserve [Line Items]
Restructuring expense				$ 5,076
Merger Restructuring \| Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring expense				$ 156
GENBAND Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring expense					600
Restructuring liability assumed							$ 4,100
GENBAND Restructuring \| Severance
Restructuring Cost and Reserve [Line Items]
Restructuring liability assumed							3,700
GENBAND Restructuring \| Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring liability assumed							$ 400
2016 Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring expense	$ 2,000
2016 Restructuring \| Severance
Restructuring Cost and Reserve [Line Items]
Restructuring expense	1,900
2016 Restructuring \| Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring expense	$ 100
Executive Officer \| 2020 Restructuring Initiative \| Severance
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated \| executive		3
Restructuring Estimate \| GENBAND Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring expense					$ 900	$ 300

RESTRUCTURING AND FACILITIES CONSOLIDATION INITIATIVES - Components of Restructuring Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restructuring and Related Activities [Abstract]
Severance and related costs	$ 12,025	$ 11,179	$ 15,217
Variable and other facilities-related costs	3,605	1,528	1,798
Accelerated amortization of lease assets due to cease-use	605	3,692
Restructuring and related	$ 16,235	$ 16,399	$ 17,015

RESTRUCTURING AND FACILITIES CONSOLIDATION INITIATIVES - Restructuring Initiatives (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2016	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		$ 3,510
Initiatives charged to expense		16,235	$ 16,399	$ 17,015
Balance at the end of the period		7,432	3,510
Accounting Standards Update [Extensible List]					us-gaap:AccountingStandardsUpdate201409Member
2019 Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		3,101	0
Initiatives charged to expense		2,268	11,167
Transfer to operating lease liability accounts		(70)	(3,692)
Cash payments		(4,360)	(4,374)
Balance at the end of the period		939	3,101	0
Merger Restructuring
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		409	2,681
Initiatives charged to expense		1,400	5,232	16,100
Transfer to operating lease liability accounts			(771)
Cash payments			(6,733)
Balance at the end of the period			409	2,681
GENBAND Restructuring
Restructuring Reserve [Roll Forward]
Initiatives charged to expense				600
2016 Restructuring
Restructuring Reserve [Roll Forward]
Initiatives charged to expense	$ 2,000
2020 Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		0
Initiatives charged to expense		14,025
Transfer to operating lease liability accounts		(535)
Cash payments		(6,997)
Balance at the end of the period		6,493	0
Severance \| 2019 Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		2,110	0
Initiatives charged to expense		536	6,103
Transfer to operating lease liability accounts		0	0
Cash payments		(2,473)	(3,993)
Balance at the end of the period		173	2,110	0
Severance \| Merger Restructuring
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		409	1,910
Initiatives charged to expense			5,076
Transfer to operating lease liability accounts		(58)	0
Cash payments		(351)	(6,577)
Balance at the end of the period		0	409	1,910
Severance \| 2016 Restructuring
Restructuring Reserve [Roll Forward]
Initiatives charged to expense	1,900
Severance \| 2020 Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		0
Initiatives charged to expense		11,547
Transfer to operating lease liability accounts		0
Cash payments		(6,310)
Balance at the end of the period		5,237	0
Facilities
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		900
Balance at the end of the period			900
Facilities \| 2019 Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		991	0
Initiatives charged to expense		1,732	5,064
Transfer to operating lease liability accounts		(70)	(3,692)
Cash payments		(1,887)	(381)
Balance at the end of the period		766	991	0
Facilities \| Merger Restructuring
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		0	771
Initiatives charged to expense			156
Transfer to operating lease liability accounts			(771)
Cash payments			(156)
Balance at the end of the period			0	771
Facilities \| GENBAND Restructuring
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		0	117
Adjustment for the impact of ASC 842 adoption			(117)
Balance at the end of the period			0	117
Facilities \| 2016 Restructuring
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		0	58
Initiatives charged to expense	$ 100
Cash payments			(58)
Balance at the end of the period			0	$ 58
Facilities \| 2020 Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		0
Initiatives charged to expense		2,478
Transfer to operating lease liability accounts		(535)
Cash payments		(687)
Balance at the end of the period		$ 1,256	$ 0
Accounting Standards Update 2016-02
Restructuring Reserve [Roll Forward]
Accounting Standards Update [Extensible List]				us-gaap:AccountingStandardsUpdate201602Member

DEBT - 2018 Credit Facility (Details) - 2018 Credit Facility - Revolving Credit Facility - Line of Credit	12 Months Ended
	Dec. 31, 2020
Debt Instrument [Line Items]
Fronting fee percentage	0.125%
Default rate percentage	2.00%
Minimum
Debt Instrument [Line Items]
Commitment fee percentage	0.25%
Letter of credit, fee multiplier	1.50%
Maximum
Debt Instrument [Line Items]
Commitment fee percentage	0.40%
Letter of credit, fee multiplier	2.00%
LIBOR
Debt Instrument [Line Items]
Floor on variable rate	0.00%
LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	2.50%
LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	3.00%
Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate	0.50%
Floor on variable rate	0.00%
Additional Applicable Margin \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	1.50%
Additional Applicable Margin \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	2.00%

DEBT - 2019 and 2020 Credit Facilities (Details)				12 Months Ended
DEBT - 2019 and 2020 Credit Facilities (Details)	Aug. 18, 2020 USD ($)	Mar. 03, 2020 USD ($)	Apr. 29, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Nov. 14, 2019 USD ($)
Debt Instrument [Line Items]
Letters of credit outstanding				$ 32,600,000
Revolving Credit Facility
Debt Instrument [Line Items]
Commitments from lender						$ 100,000,000
Term Loan Facility
Debt Instrument [Line Items]
Commitments from lender						$ 400,000,000
2019 Credit Facility
Debt Instrument [Line Items]
Outstanding balance					$ 48,800,000
2019 Credit Facility \| Revolving Credit Facility
Debt Instrument [Line Items]
Principal amount			$ 50,000,000
Increase commitment under debt instrument			75,000,000
2019 Credit Facility \| Revolving Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Commitments from lender			$ 100,000,000
Outstanding balance					$ 8,000,000.0
Debt interest rate					3.30%
Default rate percentage				2.00%
2019 Credit Facility \| Revolving Credit Facility \| Line of Credit \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate				0.00%
2019 Credit Facility \| Revolving Credit Facility \| Line of Credit \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate				1.50%
2019 Credit Facility \| Revolving Credit Facility \| Line of Credit \| LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate				3.00%
2019 Credit Facility \| Revolving Credit Facility \| Line of Credit \| Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate				0.50%
2019 Credit Facility \| Revolving Credit Facility \| Line of Credit \| Additional Applicable Margin \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate				0.50%
2019 Credit Facility \| Revolving Credit Facility \| Line of Credit \| Additional Applicable Margin \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate				2.00%
2019 Credit Facility \| Letter of Credit \| Line of Credit
Debt Instrument [Line Items]
Outstanding balance					$ 5,400,000
Debt interest rate					1.50%
2020 Credit Facility
Debt Instrument [Line Items]
Commitments from lender		$ 500,000,000
Default rate percentage		2.00%
Repayments of principal in first year				$ 10,000,000
Repayments of principal in year two				20,000,000
Repayments of principal in year three				20,000,000
Repayments of principal in year four				20,000,000
Repayments of principal in last year				$ 30,000,000
Percentage of consolidated adjusted EBITDA	75.00%	100.00%
2020 Credit Facility \| Minimum
Debt Instrument [Line Items]
Consolidated net leverage ratio	2.25
Borrower's consolidated net leverage ratio	$ 25,000,000
2020 Credit Facility \| Maximum
Debt Instrument [Line Items]
Consolidated net leverage ratio	2.75
Borrower's consolidated net leverage ratio	$ 10,000,000
2020 Credit Facility \| Revolving Credit Facility
Debt Instrument [Line Items]
Commitments from lender		$ 100,000,000
2020 Credit Facility \| Revolving Credit Facility \| Line of Credit \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	0.00%
2020 Credit Facility \| Letter of Credit
Debt Instrument [Line Items]
Commitments from lender		30,000,000
Debt interest rate				2.50%
Letters of credit outstanding				$ 5,600,000
2020 Credit Facility \| Term Loan Facility
Debt Instrument [Line Items]
Principal amount				400,000,000
Commitments from lender		400,000,000
Outstanding balance				393,100,000
Repayments of principal in first year	$ 10,000,000
2020 Credit Facility \| Swingline Loan
Debt Instrument [Line Items]
Commitments from lender		$ 20,000,000
2020 Credit Facility \| Term Loan Facility, Term B Loan
Debt Instrument [Line Items]
Commitments from lender	75,000,000
Outstanding balance				$ 74,600,000
Debt interest rate				8.40%
Repayments of principal in first year	1,000,000
Repayments of principal in year two	8,000,000
Repayments of principal in year three	8,000,000
Repayments of principal in year four	8,000,000
Repayments of principal in last year	8,000,000
Repayments of principal on the maturity date	$ 66,000,000
Premium percentage from voluntary repayment	1.00%
2020 Credit Facility \| Term Loan Facility, Term B Loan \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	7.50%
2020 Credit Facility \| Term Loan Facility, Term B Loan \| Additional Applicable Margin
Debt Instrument [Line Items]
Basis spread on variable rate	6.50%
2020 Credit Facility \| Term Loan Facility, Term B Loan \| Prime Rate \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	0.50%
2020 Credit Facility \| Term Loan Facility, Term A Loan
Debt Instrument [Line Items]
Commitments from lender	$ 325,000,000
Outstanding balance				$ 318,500,000
Debt interest rate				3.40%
Repayments of principal in year two	16,000,000
Repayments of principal in year three	16,000,000
Repayments of principal in year four	20,000,000
Repayments of principal in last year	16,000,000
Repayments of principal on the maturity date	$ 244,000,000
2020 Credit Facility \| Term Loan Facility, Term A Loan \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	1.50%
2020 Credit Facility \| Term Loan Facility, Term A Loan \| LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	3.50%
2020 Credit Facility \| Term Loan Facility, Term A Loan \| Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate	0.50%
2020 Credit Facility \| Term Loan Facility, Term A Loan \| Additional Applicable Margin \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	0.50%
2020 Credit Facility \| Term Loan Facility, Term A Loan \| Additional Applicable Margin \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	2.50%

DEBT - Short-Term Loan (Details) $ in Millions	Dec. 31, 2020 USD ($) loan	Jul. 31, 2020 USD ($)	Mar. 31, 2020 country loan
Short-term Debt [Line Items]
Number of uncommitted and unsecured short-term loans outstanding \| loan	3
Short-term loans \| $	$ 3.5
Interest rate	3.97%
China Zheshang Bank
Short-term Debt [Line Items]
Number of uncommitted and unsecured short-term loans outstanding \| loan			2
Bank Of Communications Hangzhou Branch
Short-term Debt [Line Items]
Number of uncommitted and unsecured short-term loans outstanding \| country			1
Short-term loans \| $		$ 0.7
Interest rate		4.00%

DEBT - Letters of Credit and Performance and Bid Bonds (Details) $ in Millions	Dec. 31, 2020 USD ($)
Line of Credit Facility [Line Items]
Letters of credit outstanding	$ 32.6
Cash collateral	2.7
Various Uncommitted Facilities
Line of Credit Facility [Line Items]
Letters of credit outstanding	27.0
2020 Credit Facility \| Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding	$ 5.6

DEBT - Promissory Note (Details) - USD ($) $ in Millions	Apr. 29, 2019	Dec. 31, 2020	Oct. 27, 2017
GENBAND
Debt Instrument [Line Items]
Notes payable			$ 22.5
Promissory note interest rate		10.00%	7.50%
GENBAND \| Minimum
Debt Instrument [Line Items]
Promissory note interest rate		7.50%
GENBAND \| Maximum
Debt Instrument [Line Items]
Promissory note interest rate		10.00%
Notes Payable, Other Payables \| Promissory Note
Debt Instrument [Line Items]
Repayments of outstanding amounts	$ 24.7

OTHER LONG-TERM LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Other Liabilities [Abstract]
Finance lease obligations	$ 1,469	$ 3,149
Restructuring	7,432	3,510
Pension obligations	11,132	9,954
Taxes payable	13,835	1,991
Interest rate derivative - liability derivative	10,948	0
Warranty	14,855	0
Other	6,082	1,683
Long-term liabilities	65,753	20,287
Current portion	(17,472)	(3,698)
Long-term liabilities, net of current portion	$ 48,281	$ 16,589

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Narrative (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Reclassified as an increase to interest expense over the next twelve months	$ 3,200,000
Interest rate derivative - liability derivative	10,948,000	$ 0
Interest Rate Swap
Derivative [Line Items]
Notional amount	400,000,000
Interest Rate Swap \| Significant other observable inputs (Level 2)
Derivative [Line Items]
Interest rate derivative - liability derivative	10,900,000
2020 Credit Facility \| Term Loan Facility
Derivative [Line Items]
Outstanding balance	393,100,000
Principal amount	$ 400,000,000
Fixed rate	0.904%

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Impact of Derivative Financial Instrument on Condensed Consolidated Statement of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Loss recognized in other comprehensive loss on derivative (effective portion)	$ (12,671)
Amount reclassified from accumulated other comprehensive loss to interest expense (effective portion)	1,723
Other comprehensive income (loss), cash flow hedge, gain (loss), after reclassification, before tax, parent	$ (10,948)	$ 0	$ 0

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Fair Values and Locations in the Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Interest rate derivative - liability derivative	$ (10,948)	$ 0
Interest Rate Swap \| Accrued expenses and other
Derivative [Line Items]
Interest rate derivative - liability derivative	3,157
Interest Rate Swap \| Other long-term liabilities
Derivative [Line Items]
Interest rate derivative - liability derivative	$ 7,791

REVENUE RECOGNITION - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Total revenue	$ 843,795	$ 563,111	$ 577,905
Cloud and Edge
Disaggregation of Revenue [Line Items]
Total revenue	583,270	563,111	577,905
IP Optical Networks
Disaggregation of Revenue [Line Items]
Total revenue	260,525	0	0
Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	467,912	262,030	279,014
Product revenue \| Cloud and Edge
Disaggregation of Revenue [Line Items]
Total revenue	275,445	262,030	279,014
Product revenue \| IP Optical Networks
Disaggregation of Revenue [Line Items]
Total revenue	192,467	0	0
Product revenue \| Sales to enterprise customers
Disaggregation of Revenue [Line Items]
Total revenue	138,469	70,548	57,534
Product revenue \| Sales to service provider customers
Disaggregation of Revenue [Line Items]
Total revenue	329,443	191,482	221,480
Product revenue \| Indirect sales through channel program
Disaggregation of Revenue [Line Items]
Total revenue	134,876	94,639	69,232
Product revenue \| Direct sales
Disaggregation of Revenue [Line Items]
Total revenue	333,036	167,391	209,782
Service
Disaggregation of Revenue [Line Items]
Total revenue	375,883	301,081	298,891
Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	274,816	234,228	233,966
Service revenue (maintenance) \| Cloud and Edge
Disaggregation of Revenue [Line Items]
Total revenue	229,035	234,228	233,966
Service revenue (maintenance) \| IP Optical Networks
Disaggregation of Revenue [Line Items]
Total revenue	45,781	0	0
Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	101,067	66,853	64,925
Service revenue (professional services) \| Cloud and Edge
Disaggregation of Revenue [Line Items]
Total revenue	78,790	66,853	64,925
Service revenue (professional services) \| IP Optical Networks
Disaggregation of Revenue [Line Items]
Total revenue	22,277	0	0
United States
Disaggregation of Revenue [Line Items]
Total revenue	382,619	341,293	337,624
United States \| Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	201,347	170,937	169,510
United States \| Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	132,661	133,271	132,282
United States \| Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	48,611	37,085	35,832
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenue	248,268	97,727	96,483
Europe, Middle East and Africa \| Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	149,567	42,262	37,833
Europe, Middle East and Africa \| Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	73,475	43,186	46,856
Europe, Middle East and Africa \| Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	25,226	12,279	11,794
Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	146,456	69,136	86,665
Asia Pacific \| Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	90,201	30,617	53,683
Asia Pacific \| Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	36,628	27,798	23,555
Asia Pacific \| Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	19,627	10,721	9,427
Other
Disaggregation of Revenue [Line Items]
Total revenue	66,452	54,955	57,133
Other \| Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	26,797	18,214	17,988
Other \| Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	32,052	29,973	31,273
Other \| Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	$ 7,603	$ 6,768	$ 7,872

REVENUE RECOGNITION - Schedule of Customer Assets & Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Accounts receivable
Beginning balance	$ 168,502	$ 174,310
Increase (decrease), net	10,829	(5,808)
Ending balance	179,331	168,502
Unbilled accounts receivable
Beginning balance	24,204	13,543
Increase (decrease), net	34,203	10,661
Ending balance	58,407	24,204
Deferred revenue (current)
Beginning balance	100,406	105,087
Increase (decrease), net	(3,582)	(4,681)
Ending balance	96,824	100,406
Deferred revenue (long-term)
Beginning balance	20,482	17,572
Increase (decrease), net	5,528	2,910
Ending balance	$ 26,010	$ 20,482

REVENUE RECOGNITION - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue recognized	$ 99.0	$ 94.0
Customer contract expected life (in years)	5 years
Deferred sales commissions capitalized	$ 4.1	$ 3.6
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue to be recognized	$ 15.0
Revenue, remaining performance obligation, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue to be recognized	$ 6.0
Revenue, remaining performance obligation, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue to be recognized	$ 5.0
Revenue, remaining performance obligation, period

OPERATING SEGMENT INFORMATION (Details)	3 Months Ended								9 Months Ended	12 Months Ended
OPERATING SEGMENT INFORMATION (Details)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2020 segment	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting [Abstract]
Number of reportable operating segments \| segment									1	2
Segment Reporting Information [Line Items]
Total revenue										$ 843,795,000	$ 563,111,000	$ 577,905,000
Total segment adjusted gross profit										495,982,000	355,211,000	348,076,000
Stock-based compensation expense										(875,000)	(554,000)	(459,000)
Acquisition-related inventory and facilities adjustments										(2,000,000)	0	(309,000)
Gross profit	$ 144,362,000	$ 134,954,000	$ 123,267,000	$ 90,524,000	$ 109,259,000	$ 88,399,000	$ 90,765,000	$ 66,234,000		493,107,000	354,657,000	347,308,000
Adjusted EBITDA										131,166,000	85,701,000	51,934,000
Depreciation										(17,188,000)	(11,949,000)	(11,200,000)
Amortization of intangible assets										(60,910,000)	(49,225,000)	(49,723,000)
Stock-based compensation										(13,899,000)	(12,601,000)	(11,072,000)
Acquisition-related inventory and facilities adjustments										(2,000,000)	0	(966,000)
Litigation costs										(2,101,000)	(7,734,000)	(7,682,000)
Impairment of goodwill										0	(164,300,000)	0
Settlement expense										0	0	(1,730,000)
Cancelled debt offering costs										0	0	(1,003,000)
Acquisition-, disposal- and integration-related expense										(17,164,000)	(12,953,000)	(16,951,000)
Restructuring and related expense										(16,235,000)	(16,399,000)	(17,015,000)
Income (loss) from operations										1,669,000	(189,460,000)	(65,408,000)
Depreciation expense:
Depreciation expense										17,188,000	11,949,000	11,200,000
Cloud and Edge
Segment Reporting Information [Line Items]
Total revenue										583,270,000	563,111,000	577,905,000
Total segment adjusted gross profit										385,137,000	355,211,000	348,076,000
Adjusted EBITDA										135,678,000	85,701,000	51,934,000
Depreciation										(12,111,000)	(11,949,000)	(11,200,000)
Impairment of goodwill										(164,300,000)
Depreciation expense:
Depreciation expense										12,111,000	11,949,000	11,200,000
IP Optical Networks
Segment Reporting Information [Line Items]
Total revenue										260,525,000	0	0
Total segment adjusted gross profit										110,845,000	0	0
Adjusted EBITDA										(4,512,000)	0	0
Depreciation										(5,077,000)	0	0
Impairment of goodwill											0
Depreciation expense:
Depreciation expense										$ 5,077,000	$ 0	$ 0

MAJOR CUSTOMERS (Details) - Customer	12 Months Ended
MAJOR CUSTOMERS (Details) - Customer	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue \| Verizon Communications Inc.
Concentration Risk [Line Items]
Concentration risk, percentage	15.00%	17.00%	17.00%
Revenue \| AT&T Inc.
Concentration Risk [Line Items]
Concentration risk, percentage		12.00%
Accounts Receivable
Concentration Risk [Line Items]
Concentration risk, percentage	12.00%	32.00%

COMMON STOCK REPURCHASES (Details) - USD ($) shares in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2019
Class of Stock [Line Items]
Payments for repurchase of common stock	$ 0	$ 4,536,000	$ 0
Repurchase Program
Class of Stock [Line Items]
Authorized amount				$ 75,000,000
Payments for repurchase of common stock		$ 4,500,000
Shares repurchased and retired (in shares)		1.0
Remaining authorized repurchase amount	$ 70,500,000

STOCK-BASED COMPENSATION PLANS - Amended and Restate Stock Incentive Plan (Details) - shares	Dec. 31, 2020	Jun. 02, 2020	Jun. 05, 2019
2019 Plan
Stock-based compensation
Number of shares authorized (in shares)		7,500,000	14,500,000
Shares available for future issuance (in shares)	8,888,677
Amended and Restated Stock Incentive Plan
Stock-based compensation
Number of shares authorized (in shares)			5,100,000

STOCK-BASED COMPENSATION PLANS - Stock Options Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
	Jun. 24, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock-based compensation
Proceeds from the exercise of stock options		$ 70	$ 235	$ 73
2012 plan
Stock-based compensation
Shares available for future issuance under plan		0
2008 plan
Stock-based compensation
Shares available for future issuance under plan		0
Stock Options
Stock-based compensation
Intrinsic value of options exercised		$ 100	500	39
Proceeds from the exercise of stock options		100	$ 200	$ 100
Edgewater
Stock-based compensation
Additional purchase consideration	$ 700	$ 747
Fair value of ribbon replacement options	$ 1,000
Minimum \| 2008 plan
Stock-based compensation
Award expiration period (in years)		7 years
Maximum \| 2008 plan
Stock-based compensation
Award expiration period (in years)		10 years

STOCK-BASED COMPENSATION PLANS - Executive Equity Arrangements (Details) $ in Thousands		1 Months Ended		2 Months Ended	4 Months Ended	12 Months Ended
	Mar. 16, 2020 USD ($) shares	Mar. 31, 2020	May 31, 2018 metric shares	Apr. 30, 2019 shares	Sep. 30, 2020 shares	Dec. 31, 2020 USD ($) executive performance_period shares	Dec. 31, 2019 USD ($) performance_period shares	Dec. 31, 2018 USD ($)
Stock-based compensation
Stock-based compensation expense \| $						$ 13,899	$ 12,601	$ 11,072
RSUs
Stock-based compensation
Eligible to vest (in shares)	462,963					6,531,110	2,790,060
Fair market value on date of grant \| $	$ 1,000
Maximum number of shares to be settled (in shares)	4,750,000
Granted (in shares)						6,550,106
Vested (in shares)						1,886,486
PSUs
Stock-based compensation
Eligible to vest (in shares)						6,035,931	1,067,073
Granted (in shares)				872,073	823,369	5,804,202
Vested (in shares)						323,752
PSUs, Performance Based
Stock-based compensation
Granted percentage						60.00%
Percent of performance metrics achieved						200.00%
Number of performance periods \| performance_period						3
Vesting rights percentage						33.33%
PSUs, Market Based
Stock-based compensation
Granted percentage							40.00%
Percent of performance metrics achieved						200.00%
Performance period (in years)						3 years
Number of performance periods \| performance_period						1
Bucci Stock Price PSUs \| PSUs
Stock-based compensation
Granted (in shares)						133,333
2020 Performance Share Units \| PSUs
Stock-based compensation
Number of performance periods \| performance_period						3
2020 Performance Share Units \| PSUs, Performance Based
Stock-based compensation
Granted (in shares)					494,020
2020 Performance Share Units \| PSUs, Market Based
Stock-based compensation
Granted (in shares)					329,349
2019 Performance Share Units \| PSUs
Stock-based compensation
Number of performance periods \| performance_period							3
Achievement level (as a percentage)		30.493%
2019 Performance Share Units \| PSUs, Performance Based
Stock-based compensation
Granted (in shares)				523,244
2019 Performance Share Units \| PSUs, Market Based
Stock-based compensation
Granted (in shares)				348,829
2018 Bonus Shares
Stock-based compensation
Stock-based compensation expense \| $								$ 1,100
Accelerated Vesting Of Stock Units
Stock-based compensation
Maximum number of shares to be settled (in shares)						43,000
Number of executives \| executive						2
Executive Officer \| 2018 Performance Share Units \| PSUs
Stock-based compensation
Percent of performance metrics achieved			150.00%
Granted (in shares)			195,000
Vesting rights percentage			50.00%
Number of separate metrics \| metric			2
Vested (in shares)			292,500

STOCK-BASED COMPENSATION PLANS - Stock Option (Details) - Stock Options $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares
Number of Shares
Outstanding at the beginning of the period (in shares) \| shares	297,124
Granted (in shares) \| shares	0
Exercised (in shares) \| shares	(38,288)
Forfeited (in shares) \| shares	(6,055)
Expired (in shares) \| shares	(45,071)
Outstanding at the end of the period (in shares) \| shares	207,710
Vested or expected to vest at the end of the period (in shares) \| shares	207,518
Exercisable at the end of the period (in shares) \| shares	201,138
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share) \| $ / shares	$ 11.55
Granted (in dollars per share) \| $ / shares	0
Exercised (in dollars per share) \| $ / shares	1.81
Forfeited (in dollars per share) \| $ / shares	2.78
Expired (in dollars per share) \| $ / shares	15.72
Outstanding at the end of the period (in dollars per share) \| $ / shares	12.69
Vested or expected to vest at the end of the period (in dollars per share) \| $ / shares	12.70
Exercisable at the end of the period (in dollars per share) \| $ / shares	$ 12.93
Weighted Average Remaining Contractual Term (years)
Outstanding at the end of the period	3 years 8 months 23 days
Vested or expected to vest at the end of the period	3 years 8 months 23 days
Exercisable at the end of the period	3 years 8 months 1 day
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars) \| $	$ 262
Vested or expected to vest at the end of the period (in dollars) \| $	261
Exercisable at the end of the period (in dollars) \| $	$ 241

STOCK-BASED COMPENSATION PLANS - Restricted Stock Awards and Units and Performance-Based Stock Units (Details) - USD ($) $ / shares in Units, $ in Thousands	2 Months Ended	4 Months Ended	12 Months Ended
	Apr. 30, 2019	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Weighted Average Grant Date Fair Value
Total grant date fair value of shares that vested during the period			$ 7,927	$ 7,422	$ 8,312
RSAs
Shares
Unvested balance at the beginning of the period (in shares)			487,976
Granted (in shares)			0
Vested (in shares)			(360,204)
Forfeited (in shares)			(40,789)
Unvested balance at the end of the period (in shares)			86,983	487,976
Weighted Average Grant Date Fair Value
Unvested balance at the beginning of the period (in dollars per share)			$ 6.87
Granted (in dollars per share)			0
Vested (in dollars per share)			6.82
Forfeited (in dollars per share)			6.96
Unvested balance at end of the period (in dollars per share)			$ 7.04	$ 6.87
Total grant date fair value of shares that vested during the period			$ 11,200	$ 9,900	9,700
RSUs
Shares
Unvested balance at the beginning of the period (in shares)			2,790,060
Granted (in shares)			6,550,106
Vested (in shares)			(1,886,486)
Forfeited (in shares)			(922,570)
Unvested balance at the end of the period (in shares)			6,531,110	2,790,060
Weighted Average Grant Date Fair Value
Unvested balance at the beginning of the period (in dollars per share)			$ 5.11
Granted (in dollars per share)			2.96
Vested (in dollars per share)			4.65
Forfeited (in dollars per share)			3.50
Unvested balance at end of the period (in dollars per share)			$ 3.32	$ 5.11
PSUs
Shares
Unvested balance at the beginning of the period (in shares)			1,067,073
Granted (in shares)	872,073	823,369	5,804,202
Vested (in shares)			(323,752)
Forfeited (in shares)			(511,592)
Unvested balance at the end of the period (in shares)			6,035,931	1,067,073
Weighted Average Grant Date Fair Value
Unvested balance at the beginning of the period (in dollars per share)			$ 5.94
Granted (in dollars per share)			1.41
Vested (in dollars per share)			5.52
Forfeited (in dollars per share)			5.37
Unvested balance at end of the period (in dollars per share)			$ 1.56	$ 5.94
Total grant date fair value of shares that vested during the period			$ 1,800	$ 100	$ 600

STOCK-BASED COMPENSATION PLANS - Schedule of Stock-Based Compensation (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock-based compensation
Stock-based compensation expense	$ 13,899,000	$ 12,601,000	$ 11,072,000
Tax benefit from stock based compensation expense		0	0
Fair value of the assumed awards attributable to future stock-based compensation expense	$ 19,300,000
Expected period for unrecognized expense	2 years
Stock Options \| GENBAND
Stock-based compensation
Stock-based compensation expense		1,600,000
Product cost of revenue
Stock-based compensation
Stock-based compensation expense	$ 174,000	76,000	114,000
Service cost of revenue
Stock-based compensation
Stock-based compensation expense	701,000	478,000	345,000
Research and development
Stock-based compensation
Stock-based compensation expense	2,968,000	1,898,000	1,797,000
Sales and marketing
Stock-based compensation
Stock-based compensation expense	4,129,000	3,028,000	2,935,000
General and administrative
Stock-based compensation
Stock-based compensation expense	$ 5,927,000	$ 7,121,000	$ 5,881,000

STOCK-BASED COMPENSATION PLANS - Common Stock Reserved (Details)	Dec. 31, 2020 shares
2019 Plan
Stock-based compensation
Shares available for future issuance (in shares)	8,888,677

LEASES - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
LEASES - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Additional amortization expense	$ 605	$ 3,692
Restructuring	7,432	3,510
Rent expense			$ 11,900
Interest expense for finance leases			52
Amortization expense for finance leases			600
Facilities
Lessee, Lease, Description [Line Items]
Restructuring		900
2019 Restructuring Initiative
Lessee, Lease, Description [Line Items]
Additional amortization expense	100
Restructuring	939	3,101	0
2019 Restructuring Initiative \| Facilities
Lessee, Lease, Description [Line Items]
Additional amortization expense		3,700
Restructuring	$ 766	$ 991	$ 0

LEASES - Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets
Operating lease assets	$ 69,757	$ 36,654
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization	us-gaap:PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization
Finance lease assets	$ 983	$ 2,420
Total leased assets	70,740	39,074
Current
Operating	$ 17,023	$ 7,719
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccountsPayableAndOtherAccruedLiabilitiesCurrent	us-gaap:AccountsPayableAndOtherAccruedLiabilitiesCurrent
Finance	$ 902	$ 1,005
Noncurrent
Operating	$ 72,614	$ 37,202
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent
Finance	$ 568	$ 2,144
Total lease liabilities	91,107	48,070
Finance lease, accumulated deprecation	$ 1,925	$ 1,981

LEASES - Components of Lease Expense (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease cost	$ 19,582,000	$ 13,865,000
Finance lease cost
Amortization of leased assets	1,200,000	1,106,000
Interest on lease liabilities	173,000	265,000
Short-term lease cost	20,687,000	19,460,000
Variable lease costs (costs excluded from minimum fixed lease payments)	2,713,000	3,264,000
Sublease income	(1,087,000)	(374,000)
Net lease cost	43,268,000	37,586,000
Accelerated rent amortization	605,000	3,692,000
Variable lease, payment	$ 0	$ 900,000

LEASES - Other Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 19,161	$ 10,559
Operating cash flows from finance leases	173	265
Financing cash flows from finance leases	$ 1,279	$ 913
Weighted average remaining lease term (years):
Operating leases	6 years 7 months 2 days	6 years 8 months 23 days
Finance leases	1 year 8 months 12 days	2 years 4 months 6 days
Weighted average discount rate:
Operating leases	5.67%	6.50%
Finance leases	6.15%	7.54%

LEASES - Future Minimum Lease Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Operating leases
2021	$ 21,366
2022	20,171
2023	17,312
2024	10,420
2025	8,544
2026 and beyond	32,516
Total lease payments	110,329
Less: interest	(20,692)
Present value of lease liabilities	89,637
Finance leases
2021	981
2022	506
2023	62
2024	0
2025	0
2026 and beyond	0
Total lease payments	1,549
Less: interest	(80)
Present value of lease liabilities	$ 1,469	$ 3,149

EMPLOYEE DEFINED CONTRIBUTION PLANS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Employer matching percent of employees' contribution	50.00%
Employer matching contribution percentage of employees' gross pay	4.00%
Maximum employer match percentage per employee	2.00%
Defined contribution expense	$ 3.4	$ 4.0	$ 3.2

NON-U.S. EMPLOYEE DEFINED BENEFIT PLANS - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Settlement gain	$ 1,557	$ (115)	$ (3)
Curtailment gain	0	(13)	510
Benefits paid	$ 1,976	683	300
One-time lump sum payments to participants		700	300
Net gains and losses amortization threshold	10.00%
Expected amortization of gain (loss) in the next fiscal year	$ 100
Fair value of combined plan assets	14,350	1,830	3,842
Participant contributions	$ 21	24	5
Fixed contributions per employee, percent	5.00%
Employer pension plan contributions	$ 798	139	$ 300
Expected future employer contributions to pension plans in 2020	1,200
Switzerland
Defined Benefit Plan Disclosure [Line Items]
Fair value of combined plan assets	1,600	1,200
Netherlands
Defined Benefit Plan Disclosure [Line Items]
Fair value of combined plan assets	$ 0	$ 600

NON-U.S. EMPLOYEE DEFINED BENEFIT PLANS - Changes in Benefit Obligations and Fair Value of Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Changes in projected benefit obligations:
Projected benefit obligation, beginning of year	$ 11,784	$ 10,848
Business combination	17,963	0
Service cost	1,459	335	$ 449
Interest cost	46	140	150
Participant contributions	0	24
Plan amendments	(4,440)	0
Benefits and expenses paid	(1,976)	(44)
Net actuarial loss on obligation	231	1,059
Curtailment	0	82
Settlement	0	(660)
Projected benefit obligation, end of year	25,067	11,784	10,848
Changes in plan assets:
Fair value of plan assets, beginning of year	1,830	3,842
Business combination	13,188	0
Actual return on plan assets	1,077	(1,471)
Plan amendments	(588)	0
Employer contributions	798	139	300
Participant contributions	21	24	5
Administrative expenses	0	(21)
Benefits paid	(1,976)	(683)	(300)
Fair value of plan assets, end of year	14,350	1,830	$ 3,842
Funded status at end of year	(10,717)	(9,954)
Net actuarial loss	(102)	2,743
Amounts recognized in the consolidated balance sheets consist of:
Accrued expenses and other (current pension liability)	(435)	(74)
Other long-term liabilities (non-current pension liability)	(10,282)	(9,880)
Net amount recognized	$ (10,717)	$ (9,954)

NON-U.S. EMPLOYEE DEFINED BENEFIT PLANS - Accumulated Benefit Obligation (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Aggregate projected benefit obligation	$ 25,067	$ 11,784
Aggregate accumulated benefit obligation	20,746	7,759
Aggregate fair value of plan assets	$ 14,350	$ 1,830	$ 3,842

- Definition

Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

+ References + Details

NON-U.S. EMPLOYEE DEFINED BENEFIT PLANS - Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Service cost	$ 1,459	$ 335	$ 449
Interest cost	46	140	150
Expected return on plan assets	(343)	(14)	(45)
Plan asset expenses	20	21	22
Curtailment charge (credit)	0	13	(510)
Settlement (credit) charge	(1,557)	115	3
Net periodic benefit costs	$ (375)	$ 610	$ 69

NON-U.S. EMPLOYEE DEFINED BENEFIT PLANS - Expected Future Benefit Payments (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Retirement Benefits [Abstract]
2021	$ 1,508
2022	1,759
2023	1,471
2024	1,298
2025	989
2026 to 2030	8,674
Expected future benefit payments	$ 15,699

NON-U.S. EMPLOYEE DEFINED BENEFIT PLANS - Change Recognized in Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Net (gain) loss	$ (558)	$ 2,526	$ (356)
Settlement gain	(1,557)	0	0
Total recognized in comprehensive income (loss)	$ (2,115)	$ 2,526	$ (356)

NON-U.S. EMPLOYEE DEFINED BENEFIT PLANS - Assumptions for Benefit Obligation (Details)	Dec. 31, 2020	Dec. 31, 2019
Retirement Benefits [Abstract]
Discount rate	2.16%	0.68%
Rate of compensation increase	2.41%	2.88%

NON-U.S. EMPLOYEE DEFINED BENEFIT PLANS - Assumption for Net Periodic Benefit Cost (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Discount rate	0.68%	1.30%	1.50%
Expected long-term return on plan assets	0.21%	1.12%	1.34%
Rate of compensation increase	2.88%	2.83%	3.38%

INCOME TAXES - Schedule of Income (Loss) Before Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income (loss) before income taxes:
United States	$ 123,817	$ (132,887)	$ (52,569)
Foreign	(30,500)	9,994	(20,841)
Income (loss) before income taxes	$ 93,317	$ (122,893)	$ (73,410)

INCOME TAXES - Schedule of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current:
Federal	$ 677	$ 11	$ 561
State	1,310	128	128
Foreign	7,355	1,744	2,198
Total current	9,342	1,883	2,887
Deferred:
Federal	30,278	9,790	(8,481)
State	195	1,630	(1,414)
Foreign	(16,117)	383	(1,477)
Change in valuation allowance	(18,972)	(6,504)	11,885
Total deferred	(4,616)	5,299	513
Total	$ 4,726	$ 7,182	$ 3,400

INCOME TAXES - Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
U.S. statutory income tax rate	21.00%	21.00%	21.00%
State income taxes, net of federal benefit	1.10%	(0.20%)	(0.10%)
Foreign income taxes	2.90%	(1.00%)	(5.70%)
Foreign deemed dividends	(2.70%)	(0.40%)	(3.40%)
Stock-based compensation	1.00%	(0.70%)	(0.30%)
Tax credits	(2.80%)	2.80%	0.60%
Uncertain tax positions	0.50%	(0.20%)	1.30%
Valuation allowance	(20.30%)	(0.70%)	(16.10%)
Goodwill amortization	0.60%	0.40%	0.30%
Tax reform	0	(0.001)	0
Goodwill impairment	0.00%	(25.40%)	0.00%
Other permanent adjustments	1.80%	(1.50%)	(1.40%)
Permanent adjustments - foreign exchange	1.80%	0.00%	(0.90%)
Other, net	0.20%	0.20%	0.10%
Effective income tax rate	5.10%	(5.80%)	(4.60%)

INCOME TAXES - Summary of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets:
Net operating loss carryforwards	$ 447,101	$ 61,057
Capital loss carryforward	71,182	0
Research and development tax credits	45,031	32,879
Other tax credits	6,400	0
Deferred revenue	3,184	7,868
Accrued expenses	13,557	5,687
Inventory	2,603	4,618
Stock-based compensation	1,668	2,880
Fixed assets	4,613	5,461
Other temporary differences	4,051	2,138
Deferred tax assets, gross	599,390	122,588
Valuation allowance	(496,439)	(94,980)
Total deferred tax assets	102,951	27,608
Liabilities:
Intangible assets	(75,794)	(22,470)
Mark-to-market investments	(17,631)	0
Unremitted foreign income	(15,717)	(4,827)
Total deferred tax liabilities	(109,142)	(27,297)
Total net deferred tax assets	(6,191)
Total net deferred tax assets		311
Deferred income taxes - noncurrent assets	10,651	4,959
Deferred income taxes - noncurrent liabilities	$ (16,842)	$ (4,648)

INCOME TAXES - Narrative (Details) - USD ($)	12 Months Ended
INCOME TAXES - Narrative (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 24, 2018
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	$ 51,400,000
Significant change in shareholder ownership, period of change	3 years
Significant change in shareholder ownership, benchmark percentage	50.00%
Deferred tax assets, valuation allowance	$ 496,439,000	$ 94,980,000
increase (decrease) in valuation allowance	18,972,000	6,504,000	$ (11,885,000)
Unrecognized tax benefits, income tax penalties and interest accrued	15,300,000	3,600,000	4,100,000
Unrecognized tax benefits that would impact effective tax rate	13,900,000	2,000,000.0	1,800,000
Unrecognized tax benefits, income tax penalties and interest expense	500,000	100,000	100,000
Income tax expense (benefit)	4,726,000	7,182,000	3,400,000
Other long-term liabilities
Operating Loss Carryforwards [Line Items]
Unrecognized tax benefits, income tax penalties and interest accrued	1,300,000	700,000
Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	302,100,000
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Deferred tax assets, valuation allowance	73,000,000.0	71,400,000
increase (decrease) in valuation allowance	(4,100,000)
Israel
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	1,600,000,000
Capital Loss Carryforward
Operating Loss Carryforwards [Line Items]
Tax credit carryforward, valuation allowance	8,800,000
Edgewater
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards acquired				$ 34,000,000
Tax credit carryforwards acquired				6,000,000
Deferred tax assets, valuation allowance		200,000
Income tax expense (benefit)		$ (500,000)	$ (700,000)
GENBAND
Operating Loss Carryforwards [Line Items]
Deferred tax assets, valuation allowance	12,300,000
ECI
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards acquired				$ 129,600,000
Tax credit carryforwards acquired	8,000,000
Deferred tax assets, valuation allowance	429,000,000.0
ECI \| Israel
Operating Loss Carryforwards [Line Items]
Deferred tax assets, valuation allowance	380,000,000.0
Other ECI
Operating Loss Carryforwards [Line Items]
Deferred tax assets, valuation allowance	5,500,000
BRAZIL \| GENBAND
Operating Loss Carryforwards [Line Items]
Deferred tax assets, valuation allowance	2,300,000
U.S \| ECI
Operating Loss Carryforwards [Line Items]
Deferred tax assets, valuation allowance	29,800,000
Netherlands \| ECI
Operating Loss Carryforwards [Line Items]
Deferred tax assets, valuation allowance	13,700,000
Israel \| ECI
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 1,600,000,000

INCOME TAXES - Schedule of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at January 1	$ 2,932	$ 3,461	$ 4,528
Increases related to current year tax positions	485	292	74
Increases related to prior period tax positions	11,209	0	122
Decreases related to prior period tax positions	(572)	(821)	(1,263)
Unrecognized tax benefits at December 31	$ 14,054	$ 2,932	$ 3,461

RELATED PARTIES (Details) $ in Millions		12 Months Ended
RELATED PARTIES (Details) $ in Millions	Apr. 29, 2019 USD ($)	Dec. 31, 2020 day	Dec. 31, 2018 USD ($)	Oct. 27, 2017 USD ($)
Related Party Transaction [Line Items]
Ownership percent threshold for promissory note issuance to equity holders				5.00%
Promissory note continuation of failure period		30 days
Number of business days \| day		5
Interest converted to principal			$ 1.6
Promissory Note
Related Party Transaction [Line Items]
Promissory note balance			24.1
Interest converted to principal			$ 22.5
Promissory Note \| Notes Payable, Other Payables
Related Party Transaction [Line Items]
Repayments of outstanding amounts	$ 24.7
GENBAND
Related Party Transaction [Line Items]
Notes payable				$ 22.5
Promissory note interest rate		10.00%		7.50%

COMMITMENTS AND CONTINGENCIES (Details) $ in Thousands				3 Months Ended		12 Months Ended
COMMITMENTS AND CONTINGENCIES (Details) $ in Thousands	Jul. 14, 2020 USD ($)	Jun. 26, 2020 USD ($)	Apr. 22, 2019 USD ($) country	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2020 USD ($) segment case	Dec. 31, 2019 USD ($)	Jun. 25, 2020 USD ($)	May 29, 2019 USD ($) installment	Nov. 08, 2018 executive	Dec. 31, 2017
Loss Contingencies [Line Items]
Ongoing lawsuits			6			6
Damages awarded from other party			$ 63,000
Cash payments from settlement	$ 16,750			$ 9,500	$ 37,500
Annual installment receivable							$ 25,500		$ 25,500
Number of installments \| installment									3
Installment payments interest rate (as a percentage)									4.00%
Gain from settlement							63,000
Cash payments from settlement, interest				$ 1,000
Reduction to annual installment receivable		$ 250
Sale of stock grant interest (as a percentage)											100.00%
Maximum future unpaid royalty commitment						$ 6,100
Maximum future royalty commitment						44,000
Maximum future royalty commitment, interest						$ 2,000
Number of former officers \| executive										3
Litigation Case, Plaintiff
Loss Contingencies [Line Items]
Ongoing lawsuits \| segment						5
Litigation Case, Counterclaim Defendant
Loss Contingencies [Line Items]
Ongoing lawsuits \| segment						3
Minimum
Loss Contingencies [Line Items]
Annual installment receivable								$ 16,750
Royalties rates (as a percentage)											1.30%
Maximum
Loss Contingencies [Line Items]
Annual installment receivable								$ 17,000
Royalties rates (as a percentage)											5.00%
LIBOR \| Minimum
Loss Contingencies [Line Items]
Basis spread on variable rate						1.50%
LIBOR \| Maximum
Loss Contingencies [Line Items]
Basis spread on variable rate						2.75%
Other Current Assets
Loss Contingencies [Line Items]
Annual installment receivable							8,500
Other Noncurrent Assets
Loss Contingencies [Line Items]
Annual installment receivable							$ 17,000

QUARTERLY RESULTS (UNAUDITED) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 244,202	$ 231,118	$ 210,493	$ 157,982	$ 161,109	$ 137,653	$ 145,421	$ 118,928
Cost of revenue	99,840	96,164	87,226	67,458	51,850	49,254	54,656	52,694
Gross profit	144,362	134,954	123,267	90,524	109,259	88,399	90,765	66,234	$ 493,107	$ 354,657	$ 347,308
(Loss) income from operations	16,900	11,917	1,592	(28,740)	(148,822)	2,686	(7,096)	(36,228)	1,669	(189,460)	(65,408)
Net income (loss)	$ 123,760	$ 6,252	$ (8,251)	$ (33,170)	$ (150,363)	$ 1,650	$ 49,470	$ (30,832)	$ 88,591	$ (130,075)	$ (76,810)
Loss (earnings) per share:
Basic (in dollars per share)	$ 0.85	$ 0.04	$ (0.06)	$ (0.27)	$ (1.36)	$ 0.01	$ 0.45	$ (0.29)	$ 0.64	$ (1.19)	$ (0.74)
Diluted (in dollars per share)	$ 0.81	$ 0.04	$ (0.06)	$ (0.27)	$ (1.36)	$ 0.01	$ 0.45	$ (0.29)	$ 0.61	$ (1.19)	$ (0.74)
Shares used in computing (loss) earnings per share:
Basic (in shares)	145,311	144,948	144,483	120,992	110,269	110,080	110,394	108,167	138,967	109,734	103,916
Diluted (in shares)	153,441	151,680	144,483	120,992	110,269	110,756	110,698	108,167	144,650	109,734	103,916
Amortization of acquired intangible assets to operating expenses		$ 11,600	$ 11,000	$ 9,000	$ 8,300	$ 9,500	$ 10,100	$ 9,700