Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2018	Apr. 17, 2018
Document And Entity Information
Entity Registrant Name	RIBBON COMMUNICATIONS INC.
Entity Central Index Key	0001708055
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		104,087,213

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 58,589	$ 57,073
Marketable securities	23,724	17,224
Accounts receivable, net	125,504	165,156
Inventory	21,422	21,303
Other current assets	22,192	21,463
Total current assets	251,431	282,219
Property and equipment, net	24,002	24,780
Intangible assets, net	232,105	244,414
Goodwill	335,716	335,716
Investments	2,225	9,031
Deferred income taxes	8,154	8,434
Other assets	7,445	6,289
Total assets	861,078	910,883
Current liabilities:
Revolving credit facility	20,000	20,000
Accounts payable	37,119	45,851
Accrued expenses and other	62,749	76,380
Deferred revenue	103,162	100,571
Total current liabilities	223,030	242,802
Long-term debt, related party	22,500	22,500
Deferred revenue, net of current	14,218	14,184
Deferred income taxes	3,092	2,787
Other long-term liabilities	13,203	13,189
Total liabilities	276,043	295,462
Commitments and contingencies (Note 15)
Stockholders' equity:
Preferred stock, $0.01 par value per share; 10,000,000 shares authorized, none issued and outstanding	0	0
Common stock, $0.0001 par value per share; 240,000,000 shares authorized; 102,054,720 shares issued and outstanding at March 31, 2018; 101,752,856 shares issued and outstanding at December 31, 2017	10	10
Additional paid-in capital	1,687,231	1,684,768
Accumulated deficit	(1,105,366)	(1,072,426)
Accumulated other comprehensive income	3,160	3,069
Total stockholders' equity	585,035	615,421
Total liabilities and stockholders' equity	$ 861,078	$ 910,883

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	240,000,000	240,000,000
Common stock, shares issued	102,054,720	101,752,856
Common stock, shares outstanding	102,054,720	101,752,856

Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue:
Product	$ 51,531	$ 25,395
Service	69,649	27,973
Total revenue	121,180	53,368
Cost of revenue:
Product	33,014	9,753
Service	32,893	9,867
Total cost of revenue	65,907	19,620
Gross profit	55,273	33,748
Operating expenses:
Research and development	39,049	20,209
Sales and marketing	31,926	14,676
General and administrative	15,601	9,019
Acquisition- and integration-related	4,412	56
Restructuring	6,668	570
Total operating expenses	97,656	44,530
Loss from operations	(42,383)	(10,782)
Interest income (expense), net	(599)	258
Other income, net	248	1
Loss before income taxes	(42,734)	(10,523)
Income tax provision	(2,170)	(123)
Net loss	$ (44,904)	$ (10,646)
Loss per share:
Basic (in dollars per share)	$ (0.44)	$ (0.22)
Diluted (in dollars per share)	$ (0.44)	$ (0.22)
Shares used to compute loss per share:
Basic (in shares)	101,917	49,114
Diluted (in shares)	101,917	49,114

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (44,904)	$ (10,646)
Other comprehensive income, net of tax:
Foreign currency translation adjustments	163	125
Unrealized (loss) gain on available-for sale marketable securities, net of reclassification adjustments for realized amounts	(72)	3
Other comprehensive income, net of tax	91	128
Comprehensive loss, net of tax	$ (44,813)	$ (10,518)

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net loss	$ (44,904)	$ (10,646)
Adjustments to reconcile net loss to cash flows provided by operating activities:
Depreciation and amortization of property and equipment	2,507	1,823
Amortization of intangible assets	12,309	2,259
Stock-based compensation	2,824	3,263
Deferred income taxes	528	238
Changes in operating assets and liabilities:
Accounts receivable	39,763	14,324
Inventory	(412)	315
Other operating assets	(2,182)	(405)
Accounts payable	(8,976)	(651)
Accrued expenses and other long-term liabilities	(12,820)	(10,530)
Deferred revenue	14,755	3,614
Net cash provided by operating activities	3,392	3,604
Cash flows from investing activities:
Purchases of property and equipment	(1,827)	(998)
Purchases of marketable securities	0	(18,632)
Sale/maturities of marketable securities	245	15,693
Net cash used in investing activities	(1,582)	(3,937)
Cash flows from financing activities:
Borrowings under revolving line of credit	10,000	0
Principal payments on revolving line of credit	(10,000)	0
Principal payments of capital lease obligations	(118)	(10)
Payment of debt issuance costs	(22)	0
Proceeds from the sale of common stock in connection with employee stock purchase plan and exercise of stock options	10	644
Payment of tax withholding obligations related to net share settlements of restricted stock awards	(370)	(496)
Net cash (used in) provided by financing activities	(500)	138
Effect of exchange rate changes on cash and cash equivalents	206	203
Net increase in cash and cash equivalents	1,516	8
Cash and cash equivalents, beginning of year	57,073	31,923
Cash and cash equivalents, end of period	58,589	31,931
Supplemental disclosure of cash flow information:
Interest paid	667	66
Income taxes paid	1,003	490
Income tax refunds received	196	80
Supplemental disclosure of non-cash investing activities:
Capital expenditures incurred, but not yet paid	368	318
Supplemental disclosure of non-cash financing activities:
Total fair value of restricted stock awards, restricted stock units and performance-based stock units on date vested	$ 5,253	$ 2,852

BASIS OF PRESENTATION	3 Months Ended
BASIS OF PRESENTATION	Mar. 31, 2018
Accounting Policies [Abstract]
BASIS OF PRESENTATION	BASIS OF PRESENTATION Business Ribbon is a leading provider of network communications solutions to telecommunications, wireless and cable service providers and enterprises of all sizes across industry verticals. With over 1,000 customers around the globe, including some of the largest telecommunications service providers and enterprises in the world, Ribbon enables service providers and enterprises to modernize their communications networks and provide secure RTC solutions to their customers and employees. By securing and enabling reliable and scalable IP networks, Ribbon helps service providers and enterprises adopt the next generation of software-based virtualized and cloud communications technologies to drive new, incremental revenue while protecting their existing revenue streams. Ribbon's solutions provide a secure way for its customers to connect and leverage multivendor, multiprotocol communications systems and applications across their networks and the cloud, around the world and in a rapidly changing ecosystem of IP-enabled devices such as smartphones and tablets. In addition, Ribbon's solutions secure the evolution to cloud-based delivery of UC solutions - both for service providers transforming to a cloud-based network and for enterprises using cloud-based UC. Ribbon goes to market through both direct sales and indirect channels globally, leveraging the assistance of resellers, and provides ongoing support to its customers through a global services team with experience in design, deployment and maintenance of some of the world's largest IP networks. The Merger with GENBAND (see Note 2) was completed in October 2017. As a result of the Merger, Ribbon believes it is better positioned to enable network transformations to IP and to cloud-based networks for service providers and enterprise customers worldwide, with a broader and deeper sales footprint, increased ability to invest in growth, more efficient and effective research and development, and a comprehensive RTC product offering. Basis of Presentation In the opinion of management, the accompanying unaudited condensed consolidated financial statements include all adjustments, consisting only of normal recurring items, necessary for their fair presentation with accounting principles generally accepted in the United States of America ("GAAP") and with the rules and regulations of the U.S. Securities and Exchange Commission ("SEC"). On October 27, 2017 (the "Merger Date"), Sonus Networks, Inc. ("Sonus") consummated an acquisition as specified in an Agreement and Plan of Merger (the "Merger Agreement") with Solstice Sapphire Investments, Inc. ("NewCo") and certain of its wholly-owned subsidiaries, GENBAND Holdings Company, GENBAND Inc. and GENBAND II, Inc. (collectively, "GENBAND") pursuant to which, following a series of merger transactions (collectively, the "Merger"), Sonus and GENBAND each became a wholly-owned subsidiary of NewCo, with Sonus deemed the acquirer in the transaction for accounting purposes. Subsequently, on November 28, 2017, the Company changed its name to "Ribbon Communications Inc." The condensed consolidated financial statements of the Company represent the consolidated financial statements of Sonus, prior to the Merger Date, and the condensed consolidated financial statements of Ribbon, on and after the Merger Date. The financial results of GENBAND are included in Ribbon's condensed consolidated financial statements beginning on the Merger Date. Interim results are not necessarily indicative of results for a full year or any future interim period. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the Company's Annual Report on Form 10-K for the year ended December 31, 2017 (the "Annual Report"), which was filed with the SEC on March 8, 2018. Significant Accounting Policies The Company's significant accounting policies are disclosed in Note 2 to the Consolidated Financial Statements included in the Annual Report. There were no material changes to the significant accounting policies during the three months ended March 31, 2018, apart from the Company's accounting policy related to revenue recognition, as discussed below. Effective January 1, 2018, the Company adopted Accounting Standards Codification ("ASC") 606, Revenue from Contracts with Customers ("ASC 606" or the "New Revenue Standard"), the new standard on revenue from contracts with customers, which codified Accounting Standards Update ("ASU") 2014-09, Revenue from Contracts with Customers ("ASU 2014-09"). As a result, the Company changed its accounting policy for revenue recognition to ensure compliance with ASC 606 and is described below. Revenue Recognition Policy The Company derives revenues 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 and technical support), consulting, design services, installation services and training. A typical contract includes both product and services. Generally, contracts with customers contain multiple performance obligations. For these contracts, the Company accounts for individual performance obligations separately if they are distinct. The transaction price is allocated to the separate performance obligations on a relative standalone selling price basis. Standalone selling prices are typically estimated based on observable transactions when these services are sold on a standalone basis. The 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. The product revenue is typically recognized upon transfer of control or when the software is made available for download, as this is the point that 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 does not recognize software revenue related to the renewal of subscription software licenses earlier than the beginning of the subscription period. Hardware product is generally sold with software to provide the customer solution. Services revenue includes revenue from customer support and other professional services. The Company offers warranties on its products. Certain of the Company's warranties are considered to be assurance-type in nature and do not cover anything beyond ensuring that the product is functioning as intended. Based on the guidance in ASC 606, 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. 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 related to the support. 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 best depicts the transfer of assets to the customer, which occurs as the Company incurs costs for the contracts. 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. Revenue is recorded proportionally as costs are incurred. Costs to fulfill these obligations include labor and subcontractor costs. Customer training includes courses offered by the Company. The related revenue is typically recognized as the training services are performed. Principles of Consolidation The condensed consolidated financial statements include the accounts of Ribbon and its wholly-owned subsidiaries. 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 revenues 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, including determining the standalone selling prices of performance obligations; inventory valuations; assumptions used to determine the fair value of stock-based compensation; intangible assets and goodwill valuations, including impairments; 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 Certain reclassifications have been made to the previously issued financial statements to conform to the current period presentation, none of which affected net loss as previously reported. Fair Value of Financial Instruments The carrying amounts of the Company's financial instruments, which include cash equivalents; marketable securities; investments; accounts receivable; revolving credit facility; accounts payable; long-term debt, related party; and other long-term liabilities; approximate their fair values. Operating Segments The Company operates in a single segment, as the chief operating decision maker makes decisions and assesses performance at the company level. Operating segments are identified as components of an enterprise about which separate discrete financial information is utilized for evaluation by the chief operating decision maker in making decisions regarding resource allocation and assessing performance. To date, the chief operating decision maker has made such decisions and assessed performance at the company level, as one segment. The Company's chief operating decision maker is its President and Chief Executive Officer. Foreign Currency Translation As part of ongoing merger integration activities, the Company conducted an assessment of the functional currencies of its foreign subsidiaries. The Company concluded that the U.S. dollar is the appropriate functional currency for the majority of the former GENBAND foreign subsidiaries, based on its assessment of underlying factors. As such, the functional currency was changed to the U.S. dollar effective January 1, 2018. Recent Accounting Pronouncements In February 2018, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income ("ASU 2018-02"), which amends ASC 220 to allow a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act and requires entities to provide certain disclosures regarding stranded tax effects. ASU 2018-02 is effective for the Company beginning January 1, 2019, with early adoption permitted. The Company is currently assessing the potential impact of the adoption of ASU 2018-02 on its consolidated financial statements. In May 2014, the FASB issued ASU 2014-09, which, among other things, clarified the implementation of the new revenue guidance and delayed the adoption by one year, to January 1, 2018.The New Revenue Standard outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. The core principle of the revenue model is that an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In applying the revenue model to contracts within its scope, an entity identifies the contract(s) with a customer, identifies the performance obligations in the contract, determines the transaction price, allocates the transaction price to the performance obligations in the contract and recognizes revenue when (or as) the entity satisfies a performance obligation. Effective January 1, 2018, the Company adopted the New Revenue Standard using the modified retrospective option and has identified the necessary changes to its policies, processes, systems and controls. Under the modified retrospective method, the Company is applying the New Revenue Standard to all contracts not yet completed as of January 1, 2018, recognizing in beginning Accumulated deficit an adjustment for the cumulative effect of the change and providing additional disclosures comparing results to those as if the Company was still following the previous accounting standards. Under ASC 605, the Company concluded it did not have VSOE for certain elements in software bundled arrangements, which resulted in revenue being recognized ratably over the longest performance period. The majority of the transition adjustment related to these arrangements. In connection with the adoption of ASC 606, as of January 1, 2018, the Company recorded an adjustment to decrease Accumulated deficit by approximately $12 million and capitalized certain commission costs resulting directly from securing contracts which were previously expensed. In May 2017, the FASB issued ASU 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting ("ASU 2017-09"), which amends the scope of modification accounting for share-based payment arrangements such that an entity would not apply modification accounting if the fair value, vesting conditions and classification of the awards are the same immediately before and after the modification. ASU 2017-09 became effective for the Company beginning January 1, 2018 for both interim and annual reporting periods. The adoption of ASU 2017-09 did not have a material impact on the Company's condensed consolidated financial statements. In March 2017, the FASB issued ASU 2017-07, Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Post Retirement Benefit Cost ("ASU 2017-07"). ASU 2017-07 amends the requirements in ASC 715 to require entities to disaggregate the current-service-cost component from the other components of net benefit cost (the "other components") and include it with other current compensation costs for related employees, present the other components elsewhere in the income statement and outside of income from operations if such a subtotal is presented and disclose the income statement lines that contain the other components if they are not presented on appropriately described separate lines. ASU 2017-07 became effective for the Company beginning January 1, 2018 for both interim and annual reporting periods. The adoption of ASU 2017-07 did not have a material impact on the Company's condensed consolidated financial statements. In October 2016, the FASB issued ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory ("ASU 2016-16"), which removes the prohibition in ASC 740, Income Taxes, against the immediate recognition of the current and deferred income tax effects of intra-entity transfers of assets other than inventory. ASU 2016-16 is effective for the Company beginning January 1, 2019 for both interim and annual reporting periods. The Company does not believe that the adoption of this standard will have a material impact on its consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments ("ASU 2016-15"), which adds or clarifies guidance on eight cash flow issues, including debt prepayment or debt extinguishment costs, settlement of zero-coupon debt instruments or certain other debt instruments, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies, distributions received from equity method investees, beneficial interests in securitization transactions and separately identifiable cash flows and application of the predominance principle. ASU 2016-15 became effective for the Company beginning January 1, 2018 for both interim and annual reporting periods. Entities must apply the guidance retrospectively to all periods presented but may apply it prospectively from the earliest date practicable if retrospective application would be impracticable. The adoption of ASU 2016-15 did not have a material impact on the Company's condensed consolidated financial statements. 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. ASU 2016-13 is effective for the Company beginning January 1, 2020 for both interim and annual reporting periods, with early adoption permitted. The Company does not expect the adoption of ASU 2016-13 will have a material impact on its consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) Section A - Leases: Amendments to the FASB Accounting Standards Codification ("ASU 2016-02"), its new standard on accounting for leases. ASU 2016-02 introduces a lessee model that brings most leases onto the balance sheet. ASU 2016-02 eliminates the current GAAP requirement for an entity to use bright-line tests in determining lease classification. ASU 2016-02 is effective for the Company for both interim and annual periods beginning January 1, 2019. Upon adoption of ASU 2016-02, the Company will recognize lease obligations for the right to use these assets in connection with its existing lease agreements. In January 2018, the FASB issued ASU 2018-01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842, which provided additional clarification and implementation guidance. The Company is currently assessing the potential impact of the adoption of ASU 2016-02 and related clarification guidance on its consolidated financial statements and accordingly, such amounts to be recognized on the balance sheet have yet to be determined.

BUSINESS ACQUISITION

3 Months Ended

Mar. 31, 2018

Business Combinations [Abstract]

BUSINESS ACQUISITIONS

BUSINESS ACQUISITION

GENBAND Merger

On October 27, 2017, Sonus consummated an acquisition as specified in the Merger Agreement with NewCo and GENBAND such that, following the Merger, Sonus and GENBAND each became a wholly-owned subsidiary of NewCo, with Sonus deemed the acquirer in the transaction for accounting purposes. On November 28, 2017, the Company changed its name to "Ribbon Communications Inc."

Prior to the Merger, GENBAND was a Cayman Islands exempted company limited by shares that was formed on April 7, 2010. Through its wholly owned operating subsidiaries, GENBAND created rapid communications and applications for service providers, enterprises, independent software vendors, system integrators and developers globally. A majority of GENBAND's shares were held by JPMorgan Chase & Co. and managed by One Equity Partners ("OEP"). GENBAND shares were not listed on an exchange or quoted on any automated services, and there was no established trading market for GENBAND shares.

The Company believes that Sonus' and GENBAND's complementary products, solutions and strategies position the combined company to deliver comprehensive solutions to service providers and enterprises migrating to a virtualized all-IP environment in an expanded customer and global footprint.

Pursuant to the Merger Agreement, NewCo issued 50.9 million shares of Sonus common stock to the GENBAND equity holders, with the number of shares issued in the aggregate to the GENBAND equity holders equal to the number of shares of Sonus common stock outstanding immediately prior to the closing date of the Merger, such that former stockholders of Sonus would own approximately 50%, and former shareholders of GENBAND would own approximately 50%, of the shares of NewCo common stock issued and outstanding immediately following the consummation of the Merger.

In addition, NewCo repaid GENBAND’s long-term debt, including both principal and unpaid interest, to a related party of GENBAND totaling $48 million and repaid GENBAND’s management fees due to an affiliate of OEP totaling $10.3 million. NewCo also issued a promissory note for $22.5 million to certain GENBAND equity holders.

NewCo assumed the liability under GENBAND's revolving credit facility with Silicon Valley Bank, which had outstanding borrowings and letters of credit totaling $17.9 million and $2.9 million, respectively, at October 27, 2017. At October 27, 2017, the outstanding borrowings had an average interest rate of 4.67%.

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

As of March 31, 2018, the valuation of acquired assets, identifiable intangible assets and certain assumed liabilities is preliminary. The Company is still in the process of investigating the facts and circumstances existing as of the Merger Date in order to finalize its valuation. The Company expects to finalize the valuation of the assets acquired and liabilities assumed in the third quarter of 2018.

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



Fair value of consideration transferred:
Cash consideration:
Repayment of GENBAND long-term debt and accrued interest, related party	$	47,973
Payment of GENBAND management fees due to majority shareholder	10,302
Less cash acquired	(15,324		)
Net cash consideration	42,951
Fair value of Sonus stock issued	413,982
Promissory note issued to GENBAND equity holders	22,500
Fair value of total consideration	$	479,433

Fair value of assets acquired and liabilities assumed:
Current assets, net of cash acquired	$	99,126
Property and equipment	16,770
Intangible assets:
In-process research and development	5,600
Developed technology	129,000
Customer relationships	101,300
Trade names	900
Goodwill	285,825
Other noncurrent assets	6,732
Revolving credit facility	(17,930		)
Deferred revenue	(32,390		)
Other current liabilities	(80,023		)
Deferred revenue, net of current	(6,804		)
Other long-term liabilities	(28,673		)
	$	479,433

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 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 will reclassify its in-process research and development intangible asset to developed technology intangible asset in the period that the related product becomes generally available and begin to record amortization expense for the developed technology intangible asset at that time. 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 8.3 years (see Note 6). Goodwill resulting from the transaction is primarily due to expected synergies between the combined companies and is not deductible for tax purposes.

Pro Forma Results

The following unaudited pro forma information presents the condensed combined results of operations of Sonus and GENBAND for the three months ended March 31, 2017 as if the Merger had been completed on January 1, 2017, with adjustments to give effect to pro forma events that are directly attributable to the Merger. These pro forma adjustments include a reduction of historical GENBAND revenue for the fair value adjustment related to acquired deferred revenue, an increase in amortization expense for the acquired identifiable intangible assets, a decrease in historical GENBAND interest expense reflecting the extinguishment of certain of GENBAND's debt as a result of the Merger, net of the interest expense recorded in connection with the promissory note issued to certain GENBAND equity holders as part of the purchase consideration and the elimination of revenue and costs related to sales transactions between Sonus and GENBAND.

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 Sonus and GENBAND. 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 Merger occurred at the beginning of the period presented, nor are they intended to represent or be indicative of future results of operations (in thousands, except per share amounts):



	Three months ended March 31, 2017

Revenue	$	128,705
Net loss	$	(42,750	)
Loss per share	$	(0.42	)

Acquisition- and Integration-Related Expenses

Acquisition- and integration-related expenses include those expenses related to acquisitions that would otherwise not have been incurred by the Company. The acquisition-related expenses include 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. The integration-related expenses represent incremental costs related to combining the two companies, such as third-party consulting and other third-party services related to merging the two separate companies' systems and processes. The amount recorded in the three months ended March 31, 2018 relates to the Merger. The amount recorded in the three months ended March 31, 2017 relates to professional fees incurred in connection with the Company's September 2016 acquisition of Taqua, LLC. The Company's acquisition- and integration-related expense for the three months ended March 31, 2018 and 2017 were as follows (in thousands):




	Three months ended
	March 31, 2018		March 31, 2017
Professional and services fees (acquisition-related)	$	210	$	56
Management bonuses (acquisition-related)	1,674		—
Integration-related expenses	2,528		—
	$	4,412	$	56

EARNINGS (LOSS) PER SHARE

3 Months Ended

Mar. 31, 2018

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 earnings 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 loss per share were as follows (in thousands):



	Three months ended
	March 31, 2018	March 31, 2017
Weighted average shares outstanding—basic	101,917	49,114
Potential dilutive common shares	—	—
Weighted average shares outstanding—diluted	101,917	49,114

Options to purchase the Company's common stock and unvested shares of restricted and performance-based stock aggregating 2.7 million have not been included in the computation of diluted loss per share for the three months ended March 31, 2018 because their effect would have been antidilutive. Options to purchase the Company's common stock, unvested shares of restricted and performance-based stock and shares in connection with future purchases under the Company's Amended and Restated 2000 Employee Stock Purchase Plan, as amended (the "ESPP"), totaling 8.4 million shares for the three months ended March 31, 2017 have not been included in the computation of diluted loss per share because their effect would have been antidilutive.

CASH EQUIVALENTS, MARKETABLE SECURITIES AND INVESTMENTS

3 Months Ended

Mar. 31, 2018

Investments, All Other Investments [Abstract]

CASH EQUIVALENTS AND INVESTMENTS

CASH EQUIVALENTS, MARKETABLE SECURITIES AND INVESTMENTS

The Company invests in debt instruments, primarily U.S. government-backed, municipal and corporate obligations, which management believes to be high quality (investment grade) credit instruments.

The Company did not sell any of its available-for-sale securities in either the three months ended March 31, 2018 or 2017. Investments with continuous unrealized losses for one year or greater at March 31, 2018 were nominal.

On a quarterly basis, the Company reviews its marketable securities and investments to determine if there have been any events that could create a credit impairment. Based on its reviews, the Company does not believe that any impairment existed with its current holdings at March 31, 2018.

The amortized cost, gross unrealized gains and losses and fair value of the Company's marketable debt securities and investments at March 31, 2018 and December 31, 2017 were comprised of the following (in thousands):



	March 31, 2018
	Amortized cost		Unrealized gains		Unrealized losses			Fair value
Cash equivalents	$	1,929	$	—	$	—		$	1,929

Marketable securities
U.S. government agency notes	$	6,090	$	—	$	(30	)	$	6,060
Corporate debt securities	11,905		—		(67		)	11,838
Certificates of deposit	5,826		—		—			5,826
	$	23,821	$	—	$	(97	)	$	23,724
Investments
U.S. government agency notes	$	1,995	$	—	$	(15	)	$	1,980
Certificates of deposit	245		—		—			245
	$	2,240	$	—	$	(15	)	$	2,225



	December 31, 2017
	Amortized cost		Unrealized gains		Unrealized losses			Fair value
Cash equivalents	$	1,254	$	—	$	—		$	1,254

Marketable securities
U.S. government agency notes	$	4,091	$	—	$	(19	)	$	4,072
Corporate debt securities	8,048		—		(31		)	8,017
Certificates of deposit	5,135		—		—			5,135
	$	17,274	$	—	$	(50	)	$	17,224
Investments
U.S. government agency notes	$	3,992	$	—	$	(28	)	$	3,964
Corporate debt securities	3,908		—		(24		)	3,884
Certificates of deposit	1,183		—		—			1,183
	$	9,083	$	—	$	(52	)	$	9,031

The Company's available-for-sale debt securities classified as Investments in the condensed consolidated balance sheets at March 31, 2018 and December 31, 2017 mature after one year but within two years or less from the balance sheet date.

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 following table shows the fair value of the Company's financial assets at March 31, 2018 and December 31, 2017. These financial assets are comprised of the Company's available-for-sale debt securities and reported under the captions Cash and cash equivalents, Marketable securities and Investments in the condensed consolidated balance sheets (in thousands):



			Fair value measurements at March 31, 2018 using:
	Total carrying value at March 31, 2018		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
Cash equivalents	$	1,929	$	1,929	$	—	$	—

Marketable securities
U.S. government agency notes	$	6,060	$	—	$	6,060	$	—
Corporate debt securities	11,838		—		11,838		—
Certificates of deposit	5,826		—		5,826		—
	$	23,724	$	—	$	23,724	$	—
Investments
U.S. government agency notes	$	1,980	$	—	$	1,980	$	—
Certificates of deposit	245		—		245		—
	$	2,225	$	—	$	2,225	$	—



			Fair value measurements at December 31, 2017 using:
	Total carrying value at December 31, 2017		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
Cash equivalents	$	1,254	$	1,254	$	—	$	—

Marketable securities
U.S. government agency notes	$	4,072	$	—	$	4,072	$	—
Corporate debt securities	8,017		—		8,017		—
Certificates of deposit	5,135		—		5,135		—
	$	17,224	$	—	$	17,224	$	—
Investments
U.S. government agency notes	$	3,964	$	—	$	3,964	$	—
Corporate debt securities	3,884		—		3,884		—
Certificates of deposit	1,183		—		1,183		—
	$	9,031	$	—	$	9,031	$	—

The Company's marketable securities and investments have been 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 condensed 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.

INVENTORY

3 Months Ended

Mar. 31, 2018

Inventory Disclosure [Abstract]

INVENTORY

Inventory at March 31, 2018 and December 31, 2017 consisted of the following (in thousands):



	March 31, 2018			December 31, 2017
On-hand final assemblies and finished goods inventories	$	18,288		$	18,374
Deferred cost of goods sold	4,471			4,569
	22,759			22,943
Less current portion	(21,422		)	(21,303		)
Noncurrent portion (included in Other assets)	$	1,337		$	1,640

INTANGIBLE ASSETS AND GOODWILL

3 Months Ended

Mar. 31, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

INTANGIBLE ASSETS AND GOODWILL

The Company's intangible assets at March 31, 2018 and December 31, 2017 consisted of the following (in thousands):



March 31, 2018	Weighted average amortization period (years)	Cost		Accumulated amortization		Net carrying value
In-process research and development	*	$	5,600	$	—	$	5,600
Developed technology	6.90	153,380		33,803		119,577
Customer relationships	9.32	120,840		14,620		106,220
Trade names	3.00	900		192		708
Internal use software	3.00	730		730		—
	7.77	$	281,450	$	49,345	$	232,105



December 31, 2017	Weighted average amortization period (years)	Cost		Accumulated amortization		Net carrying value
In-process research and development	*	$	5,600	$	—	$	5,600
Developed technology	6.90	153,380		24,211		129,169
Customer relationships	9.32	120,840		12,015		108,825
Trade names	3.00	900		80		820
Internal use software	3.00	730		730		—
	7.77	$	281,450	$	37,036	$	244,414

* 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.

Amortization expense for intangible assets for the three months ended March 31, 2018 and 2017 was as follows (in thousands):



	Three months ended				Statement of operations classification
	March 31, 2018		March 31, 2017		Statement of operations classification
Developed technology	$	9,592	$	1,566	Cost of revenue - product
Customer relationships	2,605		693		Sales and marketing
Trade names	112		—		Sales and marketing
	$	12,309	$	2,259

Estimated future amortization expense for the Company's intangible assets at March 31, 2018 was as follows (in thousands):



Years ending December 31,
Remainder of 2018	$	33,704
2019	38,940
2020	38,421
2021	31,970
2022	26,032
Thereafter	63,038
	$	232,105

The changes in the carrying value of the Company's goodwill in the three months ended March 31, 2018 and 2017 were as follows (in thousands):




Balance at January 1	2018			2017
Goodwill	$	338,822		$	52,499
Accumulated impairment losses	(3,106		)	(3,106		)
	335,716			49,393
Purchase accounting adjustments - acquisition of Taqua, LLC	—			498
Balance at March 31	$	335,716		$	49,891

Balance at March 31
Goodwill	$	338,822		$	52,997
Accumulated impairment losses	(3,106		)	(3,106		)
	$	335,716		$	49,891

- Definition

The entire disclosure for the aggregate amount of goodwill and a description of intangible assets, which may include (a) for amortizable intangible assets (also referred to as finite-lived intangible assets), the carrying amount, the amount of any significant residual value, and the weighted-average amortization period, (b) for intangible assets not subject to amortization (also referred to as indefinite-lived intangible assets), the carrying amount, and (c) the amount of research and development assets acquired and written off in the period, including the line item in the income statement in which the amounts written off are aggregated, if not readily apparent from the income statement. Also discloses (a) for amortizable intangibles assets in total and by major class, the gross carrying amount and accumulated amortization, the total amortization expense for the period, and the estimated aggregate amortization expense for each of the five succeeding fiscal years, (b) for intangible assets not subject to amortization the carrying amount in total and by major class, and (c) for goodwill, in total and for each reportable segment, the changes in the carrying amount of goodwill during the period (including the aggregate amount of goodwill acquired, the aggregate amount of impairment losses recognized, and the amount of goodwill included in the gain (loss) on disposal of a reporting unit). If any part of goodwill has not been allocated to a reportable segment, discloses the unallocated amount and the reasons for not allocating. For each impairment loss recognized related to an intangible asset (excluding goodwill), discloses: (a) a description of the impaired intangible asset and the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method for determining fair value, (c) the caption in the income statement or the statement of activities in which the impairment loss is aggregated, and (d) the segment in which the impaired intangible asset is reported. For each goodwill impairment loss recognized, discloses: (a) a description of the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method of determining the fair value of the associated reporting unit, and (c) if a recognized impairment loss is an estimate not finalized and the reasons why the estimate is not final. May also disclose the nature and amount of any significant adjustments made to a previous estimate of an impairment loss.

+ References + Details

ACCRUED EXPENSES

3 Months Ended

Mar. 31, 2018

Payables and Accruals [Abstract]

ACCRUED EXPENSES

Accrued expenses at March 31, 2018 and December 31, 2017 consisted of the following (in thousands):



	March 31, 2018		December 31, 2017
Employee compensation and related costs	$	31,365	$	37,782
Professional fees	12,155		13,743
Other	19,229		24,855
	$	62,749	$	76,380

RESTRUCTURING ACCRUALS

3 Months Ended

Mar. 31, 2018

Restructuring and Related Activities [Abstract]

RESTRUCTURING ACCRUALS

The Company recorded restructuring expense aggregating $6.7 million in the three months ended March 31, 2018 and $0.6 million in the three months ended March 31, 2017.

Merger Restructuring Initiative

In connection with the Merger, the Company's management approved 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 $8.5 million of restructuring expense in the fourth quarter of 2017 for severance and related costs for approximately 120 employees. The Company recorded $6.5 million in the three months ended March 31, 2018 in connection with this initiative for severance and related costs for approximately 115 employees. The Company anticipates it will record additional future expense in connection with this initiative for headcount and redundant facilities aggregating approximately $15 million as it continues to combine the two businesses and benefit from operational synergies. The Company expects that the amounts accrued at March 31, 2018 will be paid in 2018 and that the payments related to the expected additional future expense will be completed by early 2019.

A summary of the Merger Restructuring Initiative accrual activity for the three months ended March 31, 2018 is as follows (in thousands):



	Balance at January 1, 2018		Initiatives charged to expense		Adjustments for changes in estimate			Cash payments			Balance at March 31, 2018
Severance	$	7,595	$	6,528	$	(40	)	$	(6,663	)	$	7,420

Assumed Restructuring Initiative

The Company assumed GENBAND's previously recorded restructuring liability, totaling $4.1 million, on the 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. The Company recorded adjustments aggregating $0.2 million in the three months ended March 31, 2018 for changes in estimated costs previously accrued. These adjustments were primarily related to additional facilities costs in connection with this assumed restructuring initiative. The Company does not expect to record additional expense in connection with this initiative with the exception of any additional adjustments for changes in estimated costs. The Company expects that the payments related to this assumed liability will be completed in 2018. A summary of the GENBAND Restructuring Initiative accrual activity for the three months ended March 31, 2018 is as follows (in thousands):



	Balance at January 1, 2018		Initiatives charged to expense		Adjustments for changes in estimate		Cash payments			Balance at March 31, 2018
Severance	$	1,916	$	—	$	22	$	(1,460	)	$	478
Facilities	205		—		158		(124		)	239
	$	2,121	$	—	$	180	$	(1,584	)	$	717

2016 Restructuring Initiative

In July 2016, the Company announced a program (the "2016 Restructuring Initiative") to further accelerate its investment in new technologies, as the communications industry migrates to a cloud-based architecture and as the Company pursues new 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 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 Company recorded $0.2 million in the three months ended March 31, 2017 in connection with the 2016 Restructuring Initiative. The Company did not record expense in connection with this initiative in the three months ended March 31, 2018. The actions under the 2016 Restructuring Initiative have been implemented and accordingly, the Company does not expect to record additional expense in connection with this initiative. The amounts accrued for severance and related costs had been fully paid by the end of the third quarter of 2017. The Company expects that the amounts accrued for facilities will be paid by the end of October 2019, when the lease on the Rochester Facility expires.

A summary of the 2016 Restructuring Initiative accrual activity for the three months ended March 31, 2018 is as follows (in thousands):



	Balance at January 1, 2018		Initiatives charged to expense		Adjustments for changes in estimate		Cash payments			Balance at March 31, 2018
Facilities	$	95	$	—	$	—	$	(9	)	$	86

Taqua Restructuring Initiative

In connection with the acquisition of Taqua, the Company's management approved a restructuring plan in the third quarter of 2016 to eliminate certain redundant positions within the combined companies. On October 24, 2016, the Audit Committee of the Company's Board of Directors approved a broader Taqua restructuring plan related to headcount and redundant facilities (both restructuring plans, the "Taqua Restructuring Initiative"). The Company recorded $1.8 million of restructuring expense in the aggregate in connection with this initiative, comprised of $1.2 million for severance and related costs and $0.6 million related to the elimination of redundant facilities. The actions under the Taqua Restructuring Initiative have been implemented and accordingly, the Company does not expect to record additional expense in connection with this initiative. The amounts accrued for severance and related costs had been fully paid by the end of the third quarter of 2017. The Company expects that the amounts accrued for facilities will be paid by the end of 2018.

In connection with the Taqua Restructuring Initiative, the Company recorded $0.4 million of restructuring expense in the three months ended March 31, 2017, primarily related to redundant facilities. A summary of the Taqua Restructuring Initiative accrual activity for the three months ended March 31, 2018 is as follows (in thousands):



	Balance at January 1, 2018		Initiatives charged to expense		Adjustments for changes in estimate		Cash payments			Balance at March 31, 2018
Facilities	$	365	$	—	$	—	$	(76	)	$	289

Balance Sheet Classification

The current portions of accrued restructuring are included as a component of Accrued expenses and the long-term portions of accrued restructuring are included as a component of Other long-term liabilities in the condensed consolidated balance sheets. The current portions of accrued restructuring totaled $8.4 million at March 31, 2018 and $10.0 million at December 31, 2017. The long-term portions of accrued restructuring totaled $0.1 million at March 31, 2018 and $0.2 million at December 31, 2017. The long-term amounts represent future lease payments on restructured facilities.

DEBT	3 Months Ended
DEBT	Mar. 31, 2018
Debt Disclosure [Abstract]
DEBT	DEBT Assumed Senior Secured Credit Agreement On the Merger Date and in connection with the Merger, the Company assumed GENBAND's Senior Secured Credit Agreement with Silicon Valley Bank (the "Prior Credit Agreement"), which had outstanding borrowings and letters of credit totaling $17.9 million and $2.9 million, respectively, and an average interest rate of 4.67%. GENBAND had entered into the Prior Credit Agreement with Silicon Valley Bank ("SVB") effective July 1, 2016, with two of its operating subsidiaries as borrowers and GENBAND as the guarantor. The Prior Credit Agreement had a maturity date of July 1, 2019 and provided for revolving loans, including letters of credit and swingline loans, not to exceed $50 million in total, with potential further increases of $75 million available for a total revolving line of credit of up to $125 million. Senior Secured Credit Facility On December 21, 2017, the Company entered into a Senior Secured Credit Facilities Credit Agreement (the “Credit Facility”), by and among the Company, as a guarantor, Sonus Networks, Inc., as the borrower (“Borrower”), Silicon Valley Bank, as administrative agent (in such capacity, the “Administrative Agent”), issuing lender, swingline lender and lead arranger and the lenders party thereto (each referred to individually as a “Lender”, and collectively, the “Lenders”), which refinanced the Prior Credit Agreement. The Credit Facility includes $100 million of commitments, the full amount of which is available for revolving loans, a $15 million sublimit that is available for letters of credit and a $15 million sublimit that is available for swingline loans. The Credit Facility is scheduled to mature in December 2021, subject to a springing maturity if, on or before July 14, 2020, the existing promissory note issued to certain shareholders is not converted or extended to March 2022 or later. The Credit Facility includes procedures for additional financial institutions to become lenders, or for any existing lender to increase its commitment under the facility, subject to an available increase of $50 million for all incremental commitments under the Credit Facility. The indebtedness and other obligations under the Credit Facility are unconditionally guaranteed on a senior secured basis by the Company and GENBAND US LLC, a wholly-owned domestic subsidiary of the Company (collectively, the “Guarantors”) and each other material US domestic subsidiary of the Company. The Credit Facility is secured by first-priority liens on substantially all of the assets of the Borrower and the Guarantors, including the Company. The Credit Facility requires periodic interest payments until maturity. The Borrower may prepay all revolving loans under the Credit Facility at any time without premium or penalty (other than customary LIBOR breakage costs), subject to certain notice requirements. Revolving loans under the Credit Facility bear 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 varies depending on the Company’s consolidated leverage ratio (as defined in the Credit Facility). The base rate and the LIBOR rate are each subject to a zero percent floor. The Borrower is 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 Credit Facility. Additionally, with respect to all letters of credit outstanding under the Credit Facility, the Borrower is 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 Credit Facility requires compliance with financial covenants of a minimum consolidated quick ratio, minimum consolidated interest coverage ratio and maximum consolidated leverage ratio, all of which are defined in the Credit Facility and tested on a quarterly basis. In addition, the Credit Facility contains various covenants that, among other restrictions, limit 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 Company was in compliance with all covenants of the Credit Facility as of March 31, 2018 and December 31, 2017. The 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 a borrower occurs, all obligations under the Credit Facility will immediately become due and payable. If any other event of default exists under the Credit Facility, the lenders may accelerate the maturity of the obligations outstanding under the 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 Credit Facility, the lenders may commence foreclosure or other actions against the collateral. If any default exists under the Credit Facility, or if the Borrower is unable to make any of the representations and warranties as stated in the Credit Facility at the applicable time, the Borrower will be unable to borrow funds or have letters of credit issued under the 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. At March 31, 2018, the Company had an outstanding debt balance of $20.0 million at an average interest rate of 5.55% and $3.3 million of outstanding letters of credit at an average interest rate of 1.75% under the Credit Facility. At December 31, 2017, the Company had an outstanding debt balance of $20.0 million at an interest rate of 4.51% and $2.9 million of outstanding letters of credit at an average interest rate of 2.00% under the Credit Facility. Promissory Note In connection with the Merger, on October 27, 2017, the Company issued a promissory note for $22.5 million to certain of GENBAND's equity holders (the "Promissory Note"). The Promissory Note does not amortize and the principal thereon is payable in full on the third anniversary of its execution. Interest on the Promissory Note is payable quarterly in arrears and accrues 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, constitutes an event of default under the Promissory Note. If an event of default occurs under the Promissory Note, the payees may declare 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. Sonus Credit Agreement Sonus maintained a credit agreement by and among Sonus, as Borrower, Bank of America, N.A. ("Bank of America"), as Administrative Agent, Swing Line Lender and L/C Issuer, and the other lenders from time to time party thereto, entered into on June 27, 2014 (as amended, the "Sonus Credit Agreement"). The Sonus Credit Agreement expired by its terms on June 30, 2017 and was not renewed.

REVENUE RECOGNITION

3 Months Ended

Mar. 31, 2018

Revenue from Contract with Customer [Abstract]

REVENUE RECOGNITION

The Company accounts for revenue in accordance with ASC 606, which the Company adopted on January 1, 2018 using the modified retrospective method.

The Company derives revenues 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 and technical support), consulting, design services, installation services and training. A typical contract includes both product and services. Generally, contracts with customers contain multiple performance obligations. For these contracts, the Company accounts for individual performance obligations separately if they are distinct. The transaction price is allocated to the separate performance obligations on a relative standalone selling price basis. Standalone selling prices ("SSP") are typically estimated based on observable transactions when these services are sold on a standalone basis.

The software licenses typically provide a perpetual right to use the Company's software. The Company also sells term-based software licenses that expire and 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. The product revenue is typically recognized upon transfer of control or when the software is made available for download. The Company does not recognize software revenue related to the renewal of subscription software licenses earlier than the beginning of the subscription period. Hardware product is generally sold with software to provide the customer solution.

Services revenue includes revenue from customer support and other professional services. The Company offers warranties on its products. Certain of the Company's warranties are considered to be assurance-type in nature and do not cover anything beyond ensuring that the product is functioning as intended. Based on the guidance in ASC 606, 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.

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 related to the support. 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 best depicts the transfer of assets to the customer which occurs as the Company incurs costs for the contracts. 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. Revenue is recorded proportionally as costs are incurred. Costs to fulfill these obligations include labor and subcontractor costs.

Customer training includes courses offered by the Company. The related revenue is typically recognized as the training services are 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. In instances where SSP is not directly observable, such as when the Company does not sell the product or service separately, the Company determines the SSP using information that may include market conditions and other observable inputs. The Company typically has more than one 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 represents 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 revenue for the three months ended March 31, 2018 was disaggregated as follows:



Three months ended March 31, 2018	Product revenue		Service revenue (maintenance)		Service revenue (professional services)		Total revenue
United States	$	17,801	$	31,649	$	7,434	$	56,884
Europe, Middle East and Africa	11,420		11,148		2,833		25,401
Japan	5,670		2,853		955		9,478
Other Asia Pacific	12,887		3,097		1,069		17,053
Other	3,753		7,315		1,296		12,364
	$	51,531	$	56,062	$	13,587	$	121,180



Three months ended March 31, 2017	Product revenue		Service revenue (maintenance)		Service revenue (professional services)		Total revenue
United States	$	17,407	$	15,401	$	3,208	$	36,016
Europe, Middle East and Africa	3,136		2,401		835		6,372
Japan	2,992		2,556		1,984		7,532
Other Asia Pacific	934		976		94		2,004
Other	926		422		96		1,444
	$	25,395	$	21,756	$	6,217	$	53,368

International revenue, both as a percentage of total revenue and absolute dollars, may vary from one period to the next, and accordingly, historical data may not be indicative of future periods.

Approximately 16% of the Company's product revenue in the three months ended March 31, 2018 was from indirect sales through its channel partner program, compared to approximately 34% in the three months ended March 31, 2017.

The Company's product revenue from sales to enterprise customers was approximately 14% of product revenue in the three months ended March 31, 2018, compared to approximately 28% in the three months ended March 31, 2017. These sales were made both through the Company's direct sales team and indirect sales channel partners.

Revenue Contract Balances

The timing of revenue recognition, billings and cash collections results in billed accounts receivable, unbilled receivables (contract assets) and customer advances and deposits (contract liabilities) in the Company's condensed 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. 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. These assets and liabilities are reported in the Company's condensed consolidated balance sheets on a contract-by-contract basis as of the end of each reporting period. Deposits are liquidated when revenue is recognized. Changes in the contract asset and liability balances during the three-month period ended March 31, 2018 were not materially impacted by any other factors. Amounts collected in advance of services being provided are accounted for as deferred revenue. 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 condensed consolidated balance sheets. The changes in the Company's accounts receivable, unbilled receivables and deferred revenue balances for the three months ended March 31, 2018 were as follows (in thousands):



	Accounts receivable			Unbilled accounts receivable			Deferred revenue (current)		Deferred revenue (long-term)
Balance at January 1, 2018	$	149,122		$	16,034		$	100,571	$	14,184
Increase (decrease), net	(39,485		)	(167		)	2,591		34
Balance at March 31, 2018	$	109,637		$	15,867		$	103,162	$	14,218

The decrease in accounts receivable is primarily the result of lower software, hardware and customer support billings. The increase in deferred revenue is primarily the result of an increase in deferred customer support revenue related to software and hardware product transactions and customer support renewals, most of which will be recognized over the next twelve months. The Company recognized $32.6 million of revenue in the three months ended March 31, 2018 that was recorded as deferred revenue at December 31, 2017.

The Company expects to recognize the majority of the deferred revenue amount reported as long-term in its condensed consolidated balance sheet at March 31, 2018 by the end of fiscal 2020.

Deferred Commissions Cost

Sales commissions earned by the Company's employees are considered incremental and recoverable costs of obtaining a contract with a customer. The costs associated with obtaining a customer contract were previously expensed in the period the revenue was earned. Under ASC 606, these payments have been deferred on our condensed consolidated balance sheet and amortized over the expected life of the customer contract.

Adoption of ASC 606

Under the modified retrospective method, the Company applied ASC 606 to those contracts which were not completed as of January 1, 2018. Results for reporting periods beginning January 1, 2018 are presented under ASC 606, which prior period amounts have not been adjusted and will continue to be reported in accordance with the Company's historical accounting treatment under ASC 605, Revenue Recognition ("ASC 605").

The Company recorded a net reduction to Accumulated deficit of $12.0 million at January 1, 2018 due to the cumulative impact of adopting ASC 606, primarily related to software orders with non-VSOE services revenue. Had the Company continued to recognize revenue under ASC 605, the Company would have recognized approximately $0.8 million more revenue in the three months ended March 31, 2018.

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)	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)	Within 30 days of invoicing

Hardware	When control of the appliances 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)	At the beginning of the contract period

Professional Services
Other professional services (excluding education services)	As work is performed (over time)	Within 30 days of invoicing (upon completion of services)

Training	When the class is taught (point in time)	Within 30 days of services being performed

STOCK-BASED COMPENSATION PLANS

3 Months Ended

Mar. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

STOCK-BASED COMPENSATION PLANS

Amended and Restated Stock Incentive Plan

The Company's Amended and Restated Stock Incentive Plan, as amended (the "Plan"), provides for the award of options to purchase the Company's common stock ("stock options"), stock appreciation rights ("SARs"), restricted common stock awards ("RSAs"), restricted common stock units ("RSUs"), performance-based stock awards ("PSAs"), performance-based stock units ("PSUs") and other stock-based awards to employees, officers, directors (including those directors who are not employees or officers of the Company), consultants and advisors of the Company and its subsidiaries.

Executive Equity Arrangements

In 2015, the Company began to grant PSUs to certain of its executives. The terms of each PSU grant are such that up to one-third of the shares subject to the respective PSU grant will vest, if at all, on each of the respective first, second and third anniversaries of the date of grant, depending on the Company's total shareholder return ("TSR") compared to the TSR of the companies included in the Nasdaq Telecommunications Index for the same fiscal year, measured by the Compensation Committee of the Board of Directors (the "Compensation Committee") after each of the fiscal years as defined by each grant (each, a "Performance Period"). The shares determined to be earned will vest on the anniversary of the grant date following each Performance Period. Shares subject to the PSUs that fail to be earned will be forfeited.

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

On March 31, 2017, the Company granted an aggregate of 165,000 PSUs with both market and service conditions to five of its executives (the "2017 PSUs"). In March 2018, the Compensation Committee determined that the performance metrics for the 2017 PSUs for the 2017 Performance Period had been achieved at the 130% level, and accordingly, 33,584 shares in the aggregate were released to the three executives holding such outstanding grants, comprised of 25,834 shares, representing the 100% achievement target, granted on March 31, 2017 and 7,750 shares, representing the 30% achievement over target, granted on March 31, 2018. The grant of the additional shares and the release of the earned shares, both of which occurred on March 31, 2018, are included in the PSU table below.

On April 1, 2016, the Company granted an aggregate of 131,250 PSUs with both market and service conditions to six of its executives (the "2016 PSUs"). In March 2018, the Compensation Committee determined that the performance metrics for the 2016 PSUs for the 2017 Performance Period had been achieved at the 130% level, and accordingly, 16,250 shares in the aggregate were released to the two executives holding such outstanding grants, comprised of 12,500 shares, representing the 100% achievement target, granted on April 1, 2016 and 3,750 shares, representing the 30% achievement over target, granted on April 1, 2018. The grant of the additional shares and the release of the earned shares, both of which occurred on April 1, 2018, will be included in the Company's PSU table in its Quarterly Report on Form 10-Q for the quarterly period ending June 30, 2018.

On March 16, 2015, the Company granted an aggregate of 131,250 PSUs with both market and service conditions to eight of its executives (the "2015 PSUs"). In March 2018, the Compensation Committee determined that the performance metrics for the 2015 PSUs for the 2017 Performance Period had been achieved at the 112% level, and accordingly, 7,934 shares in the aggregate were released to the two executives holding such outstanding grants, comprised of 7,084 shares, representing the 100% achievement target, granted on March 16, 2015 and 850 shares, representing the 12% achievement over target, granted on March 16, 2018. The grant of the additional shares and the release of the earned shares, both of which occurred on March 16, 2018, are included in the PSU table below.

Stock Options

The activity related to the Company's outstanding stock options for the three months ended March 31, 2018 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, 2018	435,187		$	14.71
Granted	—		$	—
Exercised	(2,583	)	$	3.70
Forfeited	—		$	—
Expired	(45,738	)	$	15.46
Outstanding at March 31, 2018	386,866		$	14.69	3.99	$	—
Vested or expected to vest at March 31, 2018	386,866		$	14.69	3.99	$	—
Exercisable at March 31, 2018	386,866		$	14.69	3.99	$	—

The Company did not grant any stock options in the three months ended March 31, 2018. Additional information regarding the Company's stock options for the three months ended March 31, 2018 was as follows:



	Three months ended
	March 31, 2018
Weighted average grant date fair value of stock options granted	$	—
Total intrinsic value of stock options exercised (in thousands)	$	8
Cash received from the exercise of stock options (in thousands)	$	10

Restricted Stock Awards and Units

The activity related to the Company's RSAs for the three months ended March 31, 2018 was as follows:



	Shares		Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2018	1,696,582		$	7.68
Granted	939,864		$	7.06
Vested	(480,168	)	$	9.95
Forfeited	(116,522	)	$	7.46
Unvested balance at March 31, 2018	2,039,756		$	7.05

The activity related to the Company's RSUs for the three months ended March 31, 2018 was as follows:



	Shares		Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2018	17,932		$	6.99
Granted	219,000		$	7.04
Vested	(10,114	)	$	6.58
Forfeited	(822	)	$	6.85
Unvested balance at March 31, 2018	225,996		$	7.06

The total fair value of shares of restricted stock granted under RSAs and RSUs that vested during the three months ended March 31, 2018 was $4.8 million.

Performance-Based Stock Units

The activity related to the Company's PSUs for the three months ended March 31, 2018 was as follows:



	Shares		Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2018	60,834		$	9.65
Granted	8,600		$	9.22
Vested	(41,518	)	$	9.85
Forfeited	—		$	—
Unvested balance at March 31, 2018	27,916		$	9.22

The total fair value of shares of restricted stock granted under PSUs that vested during the three months ended March 31, 2018 was $0.4 million.

Employee Stock Purchase Plan

The Company's ESPP is 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 ESPP provides for six-month offering periods with the purchase price of the stock equal to 85% of the lesser of the market price on the first or last day of the offering period. The maximum number of shares of common stock an employee may purchase during each offering period is 500, subject to certain adjustments pursuant to the ESPP.

In May 2017, the Compensation Committee determined to suspend all offering periods under the ESPP effective September 1, 2017 and until such time after the closing of the then-pending merger with GENBAND as the Compensation Committee determines is best in its sole discretion.

Stock-Based Compensation

The condensed consolidated statements of operations include stock-based compensation for the three months ended March 31, 2018 and 2017 as follows (in thousands):



	Three months ended
	March 31, 2018		March 31, 2017
Product cost of revenue	$	51	$	99
Service cost of revenue	132		317
Research and development	900		1,317
Sales and marketing	874		(88		)
General and administrative	867		1,618
	$	2,824	$	3,263

There is no income tax benefit for employee stock-based compensation expense for the three months ended March 31, 2018 or March 31, 2017 due to the valuation allowance recorded.

At March 31, 2018, there was $10.9 million, net of expected forfeitures, of unrecognized stock-based compensation expense related to unvested stock options, awards, units and ESPP shares. This expense is expected to be recognized over a weighted average period of approximately two years.

MAJOR CUSTOMERS

3 Months Ended

Mar. 31, 2018

Risks and Uncertainties [Abstract]

MAJOR CUSTOMERS

The following customer contributed 10% or more of the Company's revenue in the three months ended March 31, 2018 and 2017:



	Three months ended
	March 31, 2018	March 31, 2017
Verizon Communications Inc.	12%	17%

There were no other customers that contributed 10% or more of the Company's revenue in the three months ended March 31, 2018 or 2017.

At March 31, 2018, one customer accounted for 10% or more of the Company's accounts receivable balance, representing approximately 21% of the Company's total accounts receivable. At December 31, 2017, two customers accounted for 10% or more of the Company's accounts receivable balance, representing approximately 31% in the aggregate 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.

RELATED PARTY TRANSACTIONS	3 Months Ended
RELATED PARTY TRANSACTIONS	Mar. 31, 2018
Related Party Transactions [Abstract]
RELATED PARTY TRANSACTIONS	RELATED PARTY TRANSACTIONS As a portion of the consideration for the 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 Merger, owned greater than five percent of the Company's outstanding shares. As described in Note 9 above, the promissory note does not amortize and the principal thereon is payable in full on the third anniversary of its execution. Interest on the promissory note is payable quarterly in arrears and accrues 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, constitutes an event of default under the promissory note. If an event of default occurs under the promissory note, the payees may declare 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.

INCOME TAXES	3 Months Ended
INCOME TAXES	Mar. 31, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The Company's income tax provisions for the three months ended March 31, 2018 and 2017 reflect the Company's estimates of the effective rates expected to be applicable for the respective full years, adjusted for any discrete events, which are recorded in the period that they occur. These estimates are reevaluated each quarter based on the Company's estimated tax expense for the full year. The estimated effective rates for the three months ended March 31, 2018 and 2017 do not include any benefit for the Company's domestic or Ireland losses, as the Company has concluded that a valuation allowance on any domestic or Ireland benefit is required. On December 22, 2017, the U.S. government enacted comprehensive tax legislation commonly referred to as the Tax Cuts and Jobs Act (the "Tax Act"). The Tax Act makes broad and complex changes to the U.S. tax code, including, but not limited to: reducing the U.S. federal corporate tax rate from 35% to 21%; requiring companies to pay a one-time transition tax on certain unrepatriated earnings of foreign subsidiaries; generally eliminating U.S. federal income taxes on dividends from foreign subsidiaries; requiring a current inclusion in U.S. federal taxable income of certain earnings (the Global Intangible Low-taxed Income ("GILTI")) of controlled foreign corporations; eliminating the corporate alternative minimum tax ("AMT") and changing how existing AMT credits can be realized; creating the base erosion anti-abuse tax ("BEAT"); creating a new limitation on deductible interest expense; changing rules related to uses and limitations of net operating loss carryforwards created in tax years beginning after December 31, 2017; providing a tax deduction for foreign derived intangible income ("FDII"); and changing rules related to deductibility of compensation for certain officers. The impact of certain effects of the Tax Act was provisionally recognized in the period in which the new legislation was enacted per guidance in Staff Accounting Bulletin 118, which allows for a measurement period to complete the accounting for certain elements of the tax reform. The Company has previously provided for a provisional impact related to remeasured deferred tax assets based on the new federal income tax rate of 21%. The Company has also previously provided for the provisional impact related to the Tax Act's change to the federal NOL and AMT carryovers. The total estimated impact of $4.8 million was reflected in net income, and increased the tax benefit for the year ended December 31, 2017. During the three months ended March 31, 2018, the Company recorded an adjustment that reduced the benefit of the provisional impact relating to the change in its deferred tax assets by $0.2 million as a result of the new federal tax rate of 21%. The Company will continue to refine its calculations as additional analysis is completed and expects to complete the accounting for the impact of the Tax Act within the measurement period. The Company cannot currently predict with certainty how the Tax Act will affect its financial position or results of operations.

COMMITMENTS AND CONTINGENCIES	3 Months Ended
COMMITMENTS AND CONTINGENCIES	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES The Company is fully cooperating with an SEC inquiry regarding the development and issuance of Sonus’ first quarter 2015 revenue and earnings guidance. Following recent communications with the SEC's Division of Enforcement (the "Staff"), the Company has reached an agreement in principle to resolve this matter. The Company is negotiating the terms of an order with the Staff in which it will neither admit nor deny, and that as part of the settlement the Company will agree to pay a $1.9 million civil penalty and agree not to violate the securities laws in the future. The Company recorded $1.9 million in the year ended December 31, 2017, including $0.3 million in the three months ended December 31, 2017, for potential fines in connection with this investigation. The Company is involved in five lawsuits with Metaswitch Networks Ltd., Metaswitch Networks Corp. and Metaswitch Inc. (collectively, “Metaswitch”). First, on January 21, 2014, GENBAND and the Company’s indirectly-owned subsidiary, GENBAND US LLC, filed a complaint alleging that Metaswitch infringed certain patents owned by GENBAND. Following unsuccessful mediation, a trial took place and on January 15, 2016 the jury awarded approximately $8.2 million in past royalty damages to GENBAND, which neither GENBAND nor the Company has recorded. On September 29, 2016, the court confirmed the jury verdict following motions from both parties. On March 22, 2018, the district court entered final judgment awarding GENBAND $8.9 million in royalties for damages through January 15, 2016 at rates set by the court; pre and post-judgment interest and costs. On April 10, 2018, the clerk of the court set the awarded costs at $0.4 million. On April 19, 2018, Metaswitch filed a notice of appeal on the judgment. On April 18, 2018, Sonus filed a complaint alleging that Metaswitch is continuing to infringe the patents from the first lawsuit above through sales of Metaswitch's allegedly "redesigned" products. This suit seeks a finding that Metaswitch's infringement is willful. This suit also alleges false advertising and seeks damages resulting from allegedly false and misleading statements Metaswitch made regarding the first lawsuit. Through Sonus and the Company's indirectly-owned subsidiary, GENBAND US LLC, the Company is involved in a lawsuit with Metaswitch regarding claims that Metaswitch misappropriated trade secrets of GENBAND. This case is pending in state court in Dallas County, Texas, and stems from claims originally brought in a patent lawsuit between GENBAND and Metaswitch. The state court action was filed on March 28, 2017. Metaswitch filed its answer on April 21, 2017, in which it asserted counterclaims against GENBAND. On August 16, 2017, Metaswitch amended its counterclaims against GENBAND. The Texas state court has set a trial for this case in November 2018. Through Sonus, the Company is involved in two patent infringement lawsuits with Metaswitch asserting the infringement of a total of ten patents that came into the Company from Sonus. Sonus filed these two lawsuits on March 8, 2018. At this time, it is not possible to predict the outcome of the litigation matters with Metaswitch, but the Company does not expect the results of any of these actions to have a material adverse effect on its business or consolidated financial statements. 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.

BASIS OF PRESENTATION (Policies)	3 Months Ended
BASIS OF PRESENTATION (Policies)	Mar. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation In the opinion of management, the accompanying unaudited condensed consolidated financial statements include all adjustments, consisting only of normal recurring items, necessary for their fair presentation with accounting principles generally accepted in the United States of America ("GAAP") and with the rules and regulations of the U.S. Securities and Exchange Commission ("SEC"). On October 27, 2017 (the "Merger Date"), Sonus Networks, Inc. ("Sonus") consummated an acquisition as specified in an Agreement and Plan of Merger (the "Merger Agreement") with Solstice Sapphire Investments, Inc. ("NewCo") and certain of its wholly-owned subsidiaries, GENBAND Holdings Company, GENBAND Inc. and GENBAND II, Inc. (collectively, "GENBAND") pursuant to which, following a series of merger transactions (collectively, the "Merger"), Sonus and GENBAND each became a wholly-owned subsidiary of NewCo, with Sonus deemed the acquirer in the transaction for accounting purposes. Subsequently, on November 28, 2017, the Company changed its name to "Ribbon Communications Inc." The condensed consolidated financial statements of the Company represent the consolidated financial statements of Sonus, prior to the Merger Date, and the condensed consolidated financial statements of Ribbon, on and after the Merger Date. The financial results of GENBAND are included in Ribbon's condensed consolidated financial statements beginning on the Merger Date. Interim results are not necessarily indicative of results for a full year or any future interim period. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the Company's Annual Report on Form 10-K for the year ended December 31, 2017 (the "Annual Report"), which was filed with the SEC on March 8, 2018.
Revenue Recognition Policy	Revenue Recognition Policy The Company derives revenues 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 and technical support), consulting, design services, installation services and training. A typical contract includes both product and services. Generally, contracts with customers contain multiple performance obligations. For these contracts, the Company accounts for individual performance obligations separately if they are distinct. The transaction price is allocated to the separate performance obligations on a relative standalone selling price basis. Standalone selling prices are typically estimated based on observable transactions when these services are sold on a standalone basis. The 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. The product revenue is typically recognized upon transfer of control or when the software is made available for download, as this is the point that 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 does not recognize software revenue related to the renewal of subscription software licenses earlier than the beginning of the subscription period. Hardware product is generally sold with software to provide the customer solution. Services revenue includes revenue from customer support and other professional services. The Company offers warranties on its products. Certain of the Company's warranties are considered to be assurance-type in nature and do not cover anything beyond ensuring that the product is functioning as intended. Based on the guidance in ASC 606, 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. 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 related to the support. 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 best depicts the transfer of assets to the customer, which occurs as the Company incurs costs for the contracts. 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. Revenue is recorded proportionally as costs are incurred. Costs to fulfill these obligations include labor and subcontractor costs. Customer training includes courses offered by the Company. The related revenue is typically recognized as the training services are performed.
Principles of Consolidation	Principles of Consolidation The condensed consolidated financial statements include the accounts of Ribbon and its wholly-owned subsidiaries. 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 revenues 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, including determining the standalone selling prices of performance obligations; inventory valuations; assumptions used to determine the fair value of stock-based compensation; intangible assets and goodwill valuations, including impairments; 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 Certain reclassifications have been made to the previously issued financial statements to conform to the current period presentation, none of which affected net loss as previously reported.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of the Company's financial instruments, which include cash equivalents; marketable securities; investments; accounts receivable; revolving credit facility; accounts payable; long-term debt, related party; and other long-term liabilities; approximate their fair values.
Operating Segments	Operating Segments The Company operates in a single segment, as the chief operating decision maker makes decisions and assesses performance at the company level. Operating segments are identified as components of an enterprise about which separate discrete financial information is utilized for evaluation by the chief operating decision maker in making decisions regarding resource allocation and assessing performance. To date, the chief operating decision maker has made such decisions and assessed performance at the company level, as one segment. The Company's chief operating decision maker is its President and Chief Executive Officer.
Foreign Currency Translations	Foreign Currency Translation As part of ongoing merger integration activities, the Company conducted an assessment of the functional currencies of its foreign subsidiaries. The Company concluded that the U.S. dollar is the appropriate functional currency for the majority of the former GENBAND foreign subsidiaries, based on its assessment of underlying factors. As such, the functional currency was changed to the U.S. dollar effective January 1, 2018.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2018, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income ("ASU 2018-02"), which amends ASC 220 to allow a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act and requires entities to provide certain disclosures regarding stranded tax effects. ASU 2018-02 is effective for the Company beginning January 1, 2019, with early adoption permitted. The Company is currently assessing the potential impact of the adoption of ASU 2018-02 on its consolidated financial statements. In May 2014, the FASB issued ASU 2014-09, which, among other things, clarified the implementation of the new revenue guidance and delayed the adoption by one year, to January 1, 2018.The New Revenue Standard outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. The core principle of the revenue model is that an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In applying the revenue model to contracts within its scope, an entity identifies the contract(s) with a customer, identifies the performance obligations in the contract, determines the transaction price, allocates the transaction price to the performance obligations in the contract and recognizes revenue when (or as) the entity satisfies a performance obligation. Effective January 1, 2018, the Company adopted the New Revenue Standard using the modified retrospective option and has identified the necessary changes to its policies, processes, systems and controls. Under the modified retrospective method, the Company is applying the New Revenue Standard to all contracts not yet completed as of January 1, 2018, recognizing in beginning Accumulated deficit an adjustment for the cumulative effect of the change and providing additional disclosures comparing results to those as if the Company was still following the previous accounting standards. Under ASC 605, the Company concluded it did not have VSOE for certain elements in software bundled arrangements, which resulted in revenue being recognized ratably over the longest performance period. The majority of the transition adjustment related to these arrangements. In connection with the adoption of ASC 606, as of January 1, 2018, the Company recorded an adjustment to decrease Accumulated deficit by approximately $12 million and capitalized certain commission costs resulting directly from securing contracts which were previously expensed. In May 2017, the FASB issued ASU 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting ("ASU 2017-09"), which amends the scope of modification accounting for share-based payment arrangements such that an entity would not apply modification accounting if the fair value, vesting conditions and classification of the awards are the same immediately before and after the modification. ASU 2017-09 became effective for the Company beginning January 1, 2018 for both interim and annual reporting periods. The adoption of ASU 2017-09 did not have a material impact on the Company's condensed consolidated financial statements. In March 2017, the FASB issued ASU 2017-07, Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Post Retirement Benefit Cost ("ASU 2017-07"). ASU 2017-07 amends the requirements in ASC 715 to require entities to disaggregate the current-service-cost component from the other components of net benefit cost (the "other components") and include it with other current compensation costs for related employees, present the other components elsewhere in the income statement and outside of income from operations if such a subtotal is presented and disclose the income statement lines that contain the other components if they are not presented on appropriately described separate lines. ASU 2017-07 became effective for the Company beginning January 1, 2018 for both interim and annual reporting periods. The adoption of ASU 2017-07 did not have a material impact on the Company's condensed consolidated financial statements. In October 2016, the FASB issued ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory ("ASU 2016-16"), which removes the prohibition in ASC 740, Income Taxes, against the immediate recognition of the current and deferred income tax effects of intra-entity transfers of assets other than inventory. ASU 2016-16 is effective for the Company beginning January 1, 2019 for both interim and annual reporting periods. The Company does not believe that the adoption of this standard will have a material impact on its consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments ("ASU 2016-15"), which adds or clarifies guidance on eight cash flow issues, including debt prepayment or debt extinguishment costs, settlement of zero-coupon debt instruments or certain other debt instruments, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies, distributions received from equity method investees, beneficial interests in securitization transactions and separately identifiable cash flows and application of the predominance principle. ASU 2016-15 became effective for the Company beginning January 1, 2018 for both interim and annual reporting periods. Entities must apply the guidance retrospectively to all periods presented but may apply it prospectively from the earliest date practicable if retrospective application would be impracticable. The adoption of ASU 2016-15 did not have a material impact on the Company's condensed consolidated financial statements. 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. ASU 2016-13 is effective for the Company beginning January 1, 2020 for both interim and annual reporting periods, with early adoption permitted. The Company does not expect the adoption of ASU 2016-13 will have a material impact on its consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) Section A - Leases: Amendments to the FASB Accounting Standards Codification ("ASU 2016-02"), its new standard on accounting for leases. ASU 2016-02 introduces a lessee model that brings most leases onto the balance sheet. ASU 2016-02 eliminates the current GAAP requirement for an entity to use bright-line tests in determining lease classification. ASU 2016-02 is effective for the Company for both interim and annual periods beginning January 1, 2019. Upon adoption of ASU 2016-02, the Company will recognize lease obligations for the right to use these assets in connection with its existing lease agreements. In January 2018, the FASB issued ASU 2018-01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842, which provided additional clarification and implementation guidance. The Company is currently assessing the potential impact of the adoption of ASU 2016-02 and related clarification guidance on its consolidated financial statements and accordingly, such amounts to be recognized on the balance sheet have yet to be determined.

BUSINESS ACQUISITION (Tables)

3 Months Ended

Mar. 31, 2018

Business Combinations [Abstract]

Schedule of Recognized Identified Assets Acquired and Liabilities Assumed

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



Fair value of consideration transferred:
Cash consideration:
Repayment of GENBAND long-term debt and accrued interest, related party	$	47,973
Payment of GENBAND management fees due to majority shareholder	10,302
Less cash acquired	(15,324		)
Net cash consideration	42,951
Fair value of Sonus stock issued	413,982
Promissory note issued to GENBAND equity holders	22,500
Fair value of total consideration	$	479,433

Fair value of assets acquired and liabilities assumed:
Current assets, net of cash acquired	$	99,126
Property and equipment	16,770
Intangible assets:
In-process research and development	5,600
Developed technology	129,000
Customer relationships	101,300
Trade names	900
Goodwill	285,825
Other noncurrent assets	6,732
Revolving credit facility	(17,930		)
Deferred revenue	(32,390		)
Other current liabilities	(80,023		)
Deferred revenue, net of current	(6,804		)
Other long-term liabilities	(28,673		)
	$	479,433

Pro Forma Information

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 Merger occurred at the beginning of the period presented, nor are they intended to represent or be indicative of future results of operations (in thousands, except per share amounts):



	Three months ended March 31, 2017

Revenue	$	128,705
Net loss	$	(42,750	)
Loss per share	$	(0.42	)

Schedule of Components of Acquisition Related Costs

The Company's acquisition- and integration-related expense for the three months ended March 31, 2018 and 2017 were as follows (in thousands):




	Three months ended
	March 31, 2018		March 31, 2017
Professional and services fees (acquisition-related)	$	210	$	56
Management bonuses (acquisition-related)	1,674		—
Integration-related expenses	2,528		—
	$	4,412	$	56

EARNINGS (LOSS) PER SHARE (Tables)

3 Months Ended

Mar. 31, 2018

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 loss per share were as follows (in thousands):



	Three months ended
	March 31, 2018	March 31, 2017
Weighted average shares outstanding—basic	101,917	49,114
Potential dilutive common shares	—	—
Weighted average shares outstanding—diluted	101,917	49,114

CASH EQUIVALENTS, MARKETABLE SECURITIES AND INVESTMENTS (Tables)

3 Months Ended

Mar. 31, 2018

Investments, All Other Investments [Abstract]

Schedule of amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments



	March 31, 2018
	Amortized cost		Unrealized gains		Unrealized losses			Fair value
Cash equivalents	$	1,929	$	—	$	—		$	1,929

Marketable securities
U.S. government agency notes	$	6,090	$	—	$	(30	)	$	6,060
Corporate debt securities	11,905		—		(67		)	11,838
Certificates of deposit	5,826		—		—			5,826
	$	23,821	$	—	$	(97	)	$	23,724
Investments
U.S. government agency notes	$	1,995	$	—	$	(15	)	$	1,980
Certificates of deposit	245		—		—			245
	$	2,240	$	—	$	(15	)	$	2,225



	December 31, 2017
	Amortized cost		Unrealized gains		Unrealized losses			Fair value
Cash equivalents	$	1,254	$	—	$	—		$	1,254

Marketable securities
U.S. government agency notes	$	4,091	$	—	$	(19	)	$	4,072
Corporate debt securities	8,048		—		(31		)	8,017
Certificates of deposit	5,135		—		—			5,135
	$	17,274	$	—	$	(50	)	$	17,224
Investments
U.S. government agency notes	$	3,992	$	—	$	(28	)	$	3,964
Corporate debt securities	3,908		—		(24		)	3,884
Certificates of deposit	1,183		—		—			1,183
	$	9,083	$	—	$	(52	)	$	9,031

Schedule of fair value of financial assets



			Fair value measurements at March 31, 2018 using:
	Total carrying value at March 31, 2018		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
Cash equivalents	$	1,929	$	1,929	$	—	$	—

Marketable securities
U.S. government agency notes	$	6,060	$	—	$	6,060	$	—
Corporate debt securities	11,838		—		11,838		—
Certificates of deposit	5,826		—		5,826		—
	$	23,724	$	—	$	23,724	$	—
Investments
U.S. government agency notes	$	1,980	$	—	$	1,980	$	—
Certificates of deposit	245		—		245		—
	$	2,225	$	—	$	2,225	$	—



			Fair value measurements at December 31, 2017 using:
	Total carrying value at December 31, 2017		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
Cash equivalents	$	1,254	$	1,254	$	—	$	—

Marketable securities
U.S. government agency notes	$	4,072	$	—	$	4,072	$	—
Corporate debt securities	8,017		—		8,017		—
Certificates of deposit	5,135		—		5,135		—
	$	17,224	$	—	$	17,224	$	—
Investments
U.S. government agency notes	$	3,964	$	—	$	3,964	$	—
Corporate debt securities	3,884		—		3,884		—
Certificates of deposit	1,183		—		1,183		—
	$	9,031	$	—	$	9,031	$	—

INVENTORY (Tables)

3 Months Ended

Mar. 31, 2018

Inventory Disclosure [Abstract]

Schedule of inventory

Inventory at March 31, 2018 and December 31, 2017 consisted of the following (in thousands):



	March 31, 2018			December 31, 2017
On-hand final assemblies and finished goods inventories	$	18,288		$	18,374
Deferred cost of goods sold	4,471			4,569
	22,759			22,943
Less current portion	(21,422		)	(21,303		)
Noncurrent portion (included in Other assets)	$	1,337		$	1,640

INTANGIBLE ASSETS AND GOODWILL (Tables)

3 Months Ended

Mar. 31, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of intangible assets

The Company's intangible assets at March 31, 2018 and December 31, 2017 consisted of the following (in thousands):



March 31, 2018	Weighted average amortization period (years)	Cost		Accumulated amortization		Net carrying value
In-process research and development	*	$	5,600	$	—	$	5,600
Developed technology	6.90	153,380		33,803		119,577
Customer relationships	9.32	120,840		14,620		106,220
Trade names	3.00	900		192		708
Internal use software	3.00	730		730		—
	7.77	$	281,450	$	49,345	$	232,105



December 31, 2017	Weighted average amortization period (years)	Cost		Accumulated amortization		Net carrying value
In-process research and development	*	$	5,600	$	—	$	5,600
Developed technology	6.90	153,380		24,211		129,169
Customer relationships	9.32	120,840		12,015		108,825
Trade names	3.00	900		80		820
Internal use software	3.00	730		730		—
	7.77	$	281,450	$	37,036	$	244,414

Schedule of amortization expense related to intangible assets

Amortization expense for intangible assets for the three months ended March 31, 2018 and 2017 was as follows (in thousands):



	Three months ended				Statement of operations classification
	March 31, 2018		March 31, 2017		Statement of operations classification
Developed technology	$	9,592	$	1,566	Cost of revenue - product
Customer relationships	2,605		693		Sales and marketing
Trade names	112		—		Sales and marketing
	$	12,309	$	2,259

Schedule of estimated future amortization expense for intangible assets

Estimated future amortization expense for the Company's intangible assets at March 31, 2018 was as follows (in thousands):



Years ending December 31,
Remainder of 2018	$	33,704
2019	38,940
2020	38,421
2021	31,970
2022	26,032
Thereafter	63,038
	$	232,105

Schedule of goodwill

The changes in the carrying value of the Company's goodwill in the three months ended March 31, 2018 and 2017 were as follows (in thousands):




Balance at January 1	2018			2017
Goodwill	$	338,822		$	52,499
Accumulated impairment losses	(3,106		)	(3,106		)
	335,716			49,393
Purchase accounting adjustments - acquisition of Taqua, LLC	—			498
Balance at March 31	$	335,716		$	49,891

Balance at March 31
Goodwill	$	338,822		$	52,997
Accumulated impairment losses	(3,106		)	(3,106		)
	$	335,716		$	49,891

RESTRUCTURING ACCRUALS (Tables)

3 Months Ended

Mar. 31, 2018

Restructuring and Related Activities [Abstract]

Summary of restructuring accrual activity

A summary of the Taqua Restructuring Initiative accrual activity for the three months ended March 31, 2018 is as follows (in thousands):



	Balance at January 1, 2018		Initiatives charged to expense		Adjustments for changes in estimate		Cash payments			Balance at March 31, 2018
Facilities	$	365	$	—	$	—	$	(76	)	$	289

A summary of the Merger Restructuring Initiative accrual activity for the three months ended March 31, 2018 is as follows (in thousands):



	Balance at January 1, 2018		Initiatives charged to expense		Adjustments for changes in estimate			Cash payments			Balance at March 31, 2018
Severance	$	7,595	$	6,528	$	(40	)	$	(6,663	)	$	7,420

A summary of the GENBAND Restructuring Initiative accrual activity for the three months ended March 31, 2018 is as follows (in thousands):



	Balance at January 1, 2018		Initiatives charged to expense		Adjustments for changes in estimate		Cash payments			Balance at March 31, 2018
Severance	$	1,916	$	—	$	22	$	(1,460	)	$	478
Facilities	205		—		158		(124		)	239
	$	2,121	$	—	$	180	$	(1,584	)	$	717

A summary of the 2016 Restructuring Initiative accrual activity for the three months ended March 31, 2018 is as follows (in thousands):



	Balance at January 1, 2018		Initiatives charged to expense		Adjustments for changes in estimate		Cash payments			Balance at March 31, 2018
Facilities	$	95	$	—	$	—	$	(9	)	$	86

REVENUE RECOGNITION (Tables)

3 Months Ended

Mar. 31, 2018

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue

The Company's revenue for the three months ended March 31, 2018 was disaggregated as follows:



Three months ended March 31, 2018	Product revenue		Service revenue (maintenance)		Service revenue (professional services)		Total revenue
United States	$	17,801	$	31,649	$	7,434	$	56,884
Europe, Middle East and Africa	11,420		11,148		2,833		25,401
Japan	5,670		2,853		955		9,478
Other Asia Pacific	12,887		3,097		1,069		17,053
Other	3,753		7,315		1,296		12,364
	$	51,531	$	56,062	$	13,587	$	121,180



Three months ended March 31, 2017	Product revenue		Service revenue (maintenance)		Service revenue (professional services)		Total revenue
United States	$	17,407	$	15,401	$	3,208	$	36,016
Europe, Middle East and Africa	3,136		2,401		835		6,372
Japan	2,992		2,556		1,984		7,532
Other Asia Pacific	934		976		94		2,004
Other	926		422		96		1,444
	$	25,395	$	21,756	$	6,217	$	53,368

Schedule of Customer Assets and Liabilities

The changes in the Company's accounts receivable, unbilled receivables and deferred revenue balances for the three months ended March 31, 2018 were as follows (in thousands):



	Accounts receivable			Unbilled accounts receivable			Deferred revenue (current)		Deferred revenue (long-term)
Balance at January 1, 2018	$	149,122		$	16,034		$	100,571	$	14,184
Increase (decrease), net	(39,485		)	(167		)	2,591		34
Balance at March 31, 2018	$	109,637		$	15,867		$	103,162	$	14,218

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)	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)	Within 30 days of invoicing

Hardware	When control of the appliances 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)	At the beginning of the contract period

Professional Services
Other professional services (excluding education services)	As work is performed (over time)	Within 30 days of invoicing (upon completion of services)

Training	When the class is taught (point in time)	Within 30 days of services being performed

STOCK-BASED COMPENSATION PLANS (Tables)

3 Months Ended

Mar. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of activity related to outstanding stock options

The activity related to the Company's outstanding stock options for the three months ended March 31, 2018 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, 2018	435,187		$	14.71
Granted	—		$	—
Exercised	(2,583	)	$	3.70
Forfeited	—		$	—
Expired	(45,738	)	$	15.46
Outstanding at March 31, 2018	386,866		$	14.69	3.99	$	—
Vested or expected to vest at March 31, 2018	386,866		$	14.69	3.99	$	—
Exercisable at March 31, 2018	386,866		$	14.69	3.99	$	—

Schedule of stock options, additional information

Additional information regarding the Company's stock options for the three months ended March 31, 2018 was as follows:



	Three months ended
	March 31, 2018
Weighted average grant date fair value of stock options granted	$	—
Total intrinsic value of stock options exercised (in thousands)	$	8
Cash received from the exercise of stock options (in thousands)	$	10

Schedule of activity related to unvested restricted stock grants

The activity related to the Company's RSAs for the three months ended March 31, 2018 was as follows:



	Shares		Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2018	1,696,582		$	7.68
Granted	939,864		$	7.06
Vested	(480,168	)	$	9.95
Forfeited	(116,522	)	$	7.46
Unvested balance at March 31, 2018	2,039,756		$	7.05

The activity related to the Company's RSUs for the three months ended March 31, 2018 was as follows:



	Shares		Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2018	17,932		$	6.99
Granted	219,000		$	7.04
Vested	(10,114	)	$	6.58
Forfeited	(822	)	$	6.85
Unvested balance at March 31, 2018	225,996		$	7.06

Schedule of activity related to performance stock awards

The activity related to the Company's PSUs for the three months ended March 31, 2018 was as follows:



	Shares		Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2018	60,834		$	9.65
Granted	8,600		$	9.22
Vested	(41,518	)	$	9.85
Forfeited	—		$	—
Unvested balance at March 31, 2018	27,916		$	9.22

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

The condensed consolidated statements of operations include stock-based compensation for the three months ended March 31, 2018 and 2017 as follows (in thousands):



	Three months ended
	March 31, 2018		March 31, 2017
Product cost of revenue	$	51	$	99
Service cost of revenue	132		317
Research and development	900		1,317
Sales and marketing	874		(88		)
General and administrative	867		1,618
	$	2,824	$	3,263

MAJOR CUSTOMERS (Tables)

3 Months Ended

Mar. 31, 2018

Risks and Uncertainties [Abstract]

Schedule of customers contributing 10% or more of the revenue

The following customer contributed 10% or more of the Company's revenue in the three months ended March 31, 2018 and 2017:



	Three months ended
	March 31, 2018	March 31, 2017
Verizon Communications Inc.	12%	17%

BASIS OF PRESENTATION - Narrative (Details) $ in Millions	3 Months Ended
BASIS OF PRESENTATION - Narrative (Details) $ in Millions	Mar. 31, 2018 segment	Dec. 31, 2017 USD ($) customer
Number of customers \| customer		1,000
Number of reportable operating segments \| segment	1
Accounting Standards Update 2014-09 \| Retained earnings
Adjustment to accumulated deficit in connection with adoption of ASC 606 \| $		$ 12.0

BUSINESS ACQUISITION - GENBAND Merger (Narrative) (Details) - USD ($)		3 Months Ended	12 Months Ended
	Oct. 27, 2017	Mar. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Average interest rate		5.55%	4.51%
Weighted average useful life of intangible assets		8 years 3 months 18 days
Former Sonus Networks Inc. Shareholders
Business Acquisition [Line Items]
Percentage of ownership after transaction			50.00%
Former GENBAND Holdings Company Shareholders
Business Acquisition [Line Items]
Sale of stock, percentage of ownership after transaction	50.00%
GENBAND
Business Acquisition [Line Items]
Shares issued as consideration in connection with acquisition of GENBAND (in shares)	50,900,000.0
Repayment of GENBAND long-term debt and accrued interest, related party	$ 47,973,000
Payment of GENBAND management fees due to majority shareholder	10,302,000
Promissory note issued to GENBAND equity holders	$ 22,500,000.0
Average interest rate	4.67%
GENBAND \| Outstanding Borrowings
Business Acquisition [Line Items]
Debt assumed as part of GENBAND merger	$ 17,900,000
GENBAND \| Letters of Credit
Business Acquisition [Line Items]
Debt assumed as part of GENBAND merger	$ 2,900,000

BUSINESS ACQUISITION - Schedule of GENBAND Business Acquisition (Details) - USD ($)	Oct. 27, 2017	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash consideration:
Fair value of Sonus stock issued	$ 413,982,000
Intangible assets:
Goodwill		$ 335,716,000	$ 335,716,000	$ 49,891,000	$ 49,393,000
GENBAND
Cash consideration:
Repayment of GENBAND long-term debt and accrued interest, related party	47,973,000
Payment of GENBAND management fees due to majority shareholder	10,302,000
Less cash acquired	(15,324,000)
Net cash consideration	42,951,000
Promissory note issued to GENBAND equity holders	22,500,000.0
Fair value of total consideration	479,433,000
Fair value of assets acquired and liabilities assumed:
Current assets, net of cash acquired	99,126,000
Property and equipment	16,770,000
Intangible assets:
Goodwill	285,825,000
Other noncurrent assets	6,732,000
Revolving credit facility	(17,930,000)
Deferred revenue	(32,390,000)
Other current liabilities	(80,023,000)
Deferred revenue, net of current	(6,804,000)
Other long-term liabilities	(28,673,000)
Total	479,433,000
In-process research and development \| GENBAND
Intangible assets:
Finite-lived intangibles	5,600,000
Developed technology \| GENBAND
Intangible assets:
Finite-lived intangibles	129,000,000
Customer relationships \| GENBAND
Intangible assets:
Finite-lived intangibles	101,300,000
Trade names \| GENBAND
Intangible assets:
Finite-lived intangibles	$ 900,000

BUSINESS ACQUISITION - Schedule of GENBAND Pro Forma Results (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares
Business Combinations [Abstract]
Revenue	$ 128,705
Net loss	$ (42,750)
Loss (in dollars per share) \| $ / shares	$ (0.42)

BUSINESS ACQUISITION - Summary of Acquisition Related Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Business Acquisition [Line Items]
Total	$ 4,412	$ 56
GENBAND
Business Acquisition [Line Items]
Professional and services fees (acquisition-related)	210
Management bonuses (acquisition-related)	1,674
Integration-related expenses	2,528
Total	$ 4,412
Taqua, LLC
Business Acquisition [Line Items]
Professional and services fees (acquisition-related)		56
Management bonuses (acquisition-related)		0
Integration-related expenses		0
Total		$ 56

EARNINGS (LOSS) PER SHARE - (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reconciliation of weighted average shares outstanding from basic to diluted
Weighted average shares outstanding—basic	101,917	49,114
Potential dilutive common shares	0	0
Weighted average shares outstanding—diluted	101,917	49,114
Common stock and unvested shares of restricted stock not included because their effect would have been antidilutive (in shares)	2,700	8,400

CASH EQUIVALENTS, MARKETABLE SECURITIES AND INVESTMENTS - Narrative (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Period considered to classify available-for-sale securities as investments	1 year
Minimum
Schedule of Available-for-sale Securities [Line Items]
Period considered to classify available-for-sale securities as investments	1 year	1 year
Maximum
Schedule of Available-for-sale Securities [Line Items]
Period considered to classify available-for-sale securities as investments	2 years	2 years

CASH EQUIVALENTS, MARKETABLE SECURITIES AND INVESTMENTS - Schedule of Activity for Short-Term Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Cash equivalents, amortized cost	$ 1,929	$ 1,254
Cash equivalents, fair value	1,929	1,254
Marketable securities, amortized cost	23,821	17,274
Marketable securities, unrealized gains	0	0
Marketable securities, unrealized losses	(97)	(50)
Marketable securities, fair value	23,724	17,224
Investments, amortized cost	2,240	9,083
Investments, unrealized gains	0	0
Investments, unrealized losses	(15)	(52)
Investments, fair value	2,225	9,031
U.S. government agency notes
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Marketable securities, amortized cost	6,090	4,091
Marketable securities, unrealized gains	0	0
Marketable securities, unrealized losses	(30)	(19)
Marketable securities, fair value	6,060	4,072
Investments, amortized cost	1,995	3,992
Investments, unrealized gains	0	0
Investments, unrealized losses	(15)	(28)
Investments, fair value	1,980	3,964
Corporate debt securities
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Marketable securities, amortized cost	11,905	8,048
Marketable securities, unrealized gains	0	0
Marketable securities, unrealized losses	(67)	(31)
Marketable securities, fair value	11,838	8,017
Investments, amortized cost		3,908
Investments, unrealized gains		0
Investments, unrealized losses		(24)
Investments, fair value		3,884
Certificates of deposit
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Marketable securities, amortized cost	5,826	5,135
Marketable securities, unrealized gains	0	0
Marketable securities, unrealized losses	0	0
Marketable securities, fair value	5,826	5,135
Investments, amortized cost	245	1,183
Investments, unrealized gains	0	0
Investments, unrealized losses	0	0
Investments, fair value	$ 245	$ 1,183

CASH EQUIVALENTS, MARKETABLE SECURITIES AND INVESTMENTS - Schedule of Short-Term Investments by Measurement (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	$ 1,929	$ 1,254
Marketable securities, fair value	23,724	17,224
Investments, fair value	2,225	9,031
Total carrying value
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value		1,254
Marketable securities, fair value		17,224
Investments, fair value		9,031
Quoted prices in active markets (Level 1)
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	1,929	1,254
Marketable securities, fair value	0	0
Investments, fair value	0	0
Significant other observable inputs (Level 2)
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	0	0
Marketable securities, fair value	23,724	17,224
Investments, fair value	2,225	9,031
Significant unobservable inputs (Level 3)
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	0	0
Marketable securities, fair value	0	0
Investments, fair value	0	0
U.S. government agency notes
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	6,060
Investments, fair value	1,980
U.S. government agency notes \| Total carrying value
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value		4,072
Investments, fair value		3,964
U.S. government agency notes \| Quoted prices in active markets (Level 1)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value	0	0
U.S. government agency notes \| Significant other observable inputs (Level 2)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	6,060	4,072
Investments, fair value	1,980	3,964
U.S. government agency notes \| Significant unobservable inputs (Level 3)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value	0	0
Corporate debt securities
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	11,838
Corporate debt securities \| Total carrying value
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value		8,017
Investments, fair value		3,884
Corporate debt securities \| Quoted prices in active markets (Level 1)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value		0
Corporate debt securities \| Significant other observable inputs (Level 2)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	11,838	8,017
Investments, fair value		3,884
Corporate debt securities \| Significant unobservable inputs (Level 3)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value		0
Certificates of deposit
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	5,826
Investments, fair value	245
Certificates of deposit \| Total carrying value
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value		5,135
Investments, fair value		1,183
Certificates of deposit \| Quoted prices in active markets (Level 1)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value	0	0
Certificates of deposit \| Significant other observable inputs (Level 2)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	5,826	5,135
Investments, fair value	245	1,183
Certificates of deposit \| Significant unobservable inputs (Level 3)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value	$ 0	$ 0

INVENTORY - (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
On-hand final assemblies and finished goods inventories	$ 18,288	$ 18,374
Deferred cost of goods sold	4,471	4,569
Gross inventory	22,759	22,943
Less current portion	(21,422)	(21,303)
Inventory, Noncurrent	$ 1,337	$ 1,640

INTANGIBLE ASSETS AND GOODWILL - (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Intangible Assets And Goodwill
Weighted average amortization period (years)	7 years 9 months 8 days		7 years 9 months 8 days
Cost	$ 281,450		$ 281,450
Accumulated amortization	49,345		37,036
Net carrying value	232,105		244,414
Amortization expense	12,309	$ 2,259
Estimated future amortization expense for intangible assets
Remainder of 2018	33,704
2019	38,940
2020	38,421
2021	31,970
2022	26,032
Thereafter	63,038
Total	232,105
In-process research and development
Intangible Assets And Goodwill
Cost	5,600		5,600
Accumulated amortization	0		0
Net carrying value	$ 5,600		$ 5,600
Developed technology
Intangible Assets And Goodwill
Weighted average amortization period (years)	6 years 10 months 25 days		6 years 10 months 25 days
Cost	$ 153,380		$ 153,380
Accumulated amortization	33,803		24,211
Net carrying value	119,577		$ 129,169
Amortization expense	$ 9,592	1,566
Customer relationships
Intangible Assets And Goodwill
Weighted average amortization period (years)	9 years 3 months 27 days		9 years 3 months 25 days
Cost	$ 120,840		$ 120,840
Accumulated amortization	14,620		12,015
Net carrying value	106,220		$ 108,825
Amortization expense	$ 2,605	693
Trade names
Intangible Assets And Goodwill
Weighted average amortization period (years)	3 years		3 years
Cost	$ 900		$ 900
Accumulated amortization	192		80
Net carrying value	708		$ 820
Amortization expense	$ 112	$ 0
Internal use software
Intangible Assets And Goodwill
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 - Schedule of Changes in Carrying Value of Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill			$ 338,822	$ 338,822	$ 52,997	$ 52,499
Accumulated impairment losses			(3,106)	(3,106)	(3,106)	(3,106)
Goodwill	$ 335,716	$ 49,891	$ 335,716	$ 335,716	$ 49,891	$ 49,393
Goodwill, end of period	335,716	49,891
Taqua, LLC
Goodwill [Roll Forward]
Purchase accounting adjustments - acquisition of Taqua, LLC	$ 0	$ 498

ACCRUED EXPENSES - Schedule of Acrrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Employee compensation and related costs	$ 31,365	$ 37,782
Professional fees	12,155	13,743
Other	19,229	24,855
Total	$ 62,749	$ 76,380

RESTRUCTURING ACCRUALS - Narrative (Details) $ in Thousands	3 Months Ended
RESTRUCTURING ACCRUALS - Narrative (Details) $ in Thousands	Mar. 31, 2018 USD ($) employee	Dec. 31, 2017 USD ($) employee	Mar. 31, 2017 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring	$ 6,668		$ 570
Merger Restructuring Initiative
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated \| employee	115	120
Merger Restructuring Initiative \| Severance
Restructuring Cost and Reserve [Line Items]
Restructuring	$ 6,528	$ 8,500
Restructuring reserve	$ 7,420	$ 7,595

RESTRUCTURING ACCRUALS - Merger Restructuring Activities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) employee	Dec. 31, 2017 USD ($) employee	Mar. 31, 2017 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	$ 6,668		$ 570
Merger Restructuring Initiative
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated \| employee	115	120
Expected restructuring and related costs	$ 15,000
Severance \| Merger Restructuring Initiative
Restructuring and Related Activities [Abstract]
Restructuring reserve	7,420	$ 7,595
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	$ 6,528	$ 8,500

RESTRUCTURING ACCRUALS - Rollforward (Details) - USD ($)	3 Months Ended			8 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Jun. 30, 2017	Jun. 30, 2017
Restructuring Reserve [Roll Forward]
Initiatives charged to expense	$ 6,668,000		$ 570,000
GENBAND Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	2,121,000
Initiatives charged to expense	0
Adjustments for changes in estimate	180,000
Cash payments	(1,584,000)
Balance at the end of the period	717,000	$ 2,121,000
2016 Restructuring Initiative
Restructuring Reserve [Roll Forward]
Initiatives charged to expense	0		200,000		$ 2,000,000
Taqua Restructuring Incentive
Restructuring Reserve [Roll Forward]
Initiatives charged to expense			$ 400,000	$ 1,800,000
Severance \| Merger Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	7,595,000
Initiatives charged to expense	6,528,000	8,500,000
Adjustments for changes in estimate	(40,000)
Cash payments	(6,663,000)
Balance at the end of the period	7,420,000	7,595,000
Severance \| GENBAND Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	1,916,000
Initiatives charged to expense	0
Adjustments for changes in estimate	22,000
Cash payments	(1,460,000)
Balance at the end of the period	478,000	1,916,000
Severance \| 2016 Restructuring Initiative
Restructuring Reserve [Roll Forward]
Initiatives charged to expense					1,900,000
Severance \| Taqua Restructuring Incentive
Restructuring Reserve [Roll Forward]
Initiatives charged to expense				1,200,000
Facilities \| GENBAND Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	205,000
Initiatives charged to expense	0
Adjustments for changes in estimate	158,000
Cash payments	(124,000)
Balance at the end of the period	239,000	205,000
Facilities \| 2016 Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	95,000
Initiatives charged to expense	0				$ 100,000
Adjustments for changes in estimate	0
Cash payments	(9,000)
Balance at the end of the period	86,000	95,000
Facilities \| Taqua Restructuring Incentive
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	365,000
Initiatives charged to expense	0			$ 600,000
Adjustments for changes in estimate	0
Cash payments	(76,000)
Balance at the end of the period	$ 289,000	$ 365,000

RESTRUCTURING ACCRUALS - Assumed Restructuring Initiative (Details) - GENBAND - USD ($) $ in Millions	Mar. 31, 2018	Oct. 27, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring liabilities		$ 4.1
Expected restructuring and related costs	$ 0.2
Severance
Restructuring Cost and Reserve [Line Items]
Restructuring liabilities		3.7
Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring liabilities		$ 0.4

RESTRUCTURING ACCRUALS - Balance Sheet Classification (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Restructuring and Related Activities [Abstract]
Current portion of accrued restructuring reserve		$ 10.0	$ 8.4
Long-term portion of accrued restructuring	$ 0.1	$ 0.2

DEBT - Assumed Senior Secured Credit Agreement (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017	Dec. 21, 2017	Oct. 27, 2017
Debt Instrument [Line Items]
Average interest rate	5.55%	4.51%
Revolving Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Line of credit potential increases			$ 100,000,000
Silicon Valley Bank \| Revolving Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Current borrowing capacity for line of credit	$ 50,000,000
Potential further increases	75,000,000
Line of credit potential increases	$ 125,000,000
GENBAND
Debt Instrument [Line Items]
Average interest rate				4.67%
Line of Credit \| GENBAND
Debt Instrument [Line Items]
Debt assumed as part of GENBAND merger				$ 17,900,000
Letter of Credit \| GENBAND
Debt Instrument [Line Items]
Debt assumed as part of GENBAND merger				$ 2,900,000

DEBT - Senior Secured Credit Facility (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 21, 2017
Debt Instrument [Line Items]
Outstanding debt	$ 20,000,000	$ 20,000,000
Debt interest rate	5.55%	4.51%
Line of Credit
Debt Instrument [Line Items]
Commitment potential aggregate increase amount			$ 50,000,000
Revolving Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Commitments from lender			100,000,000
Fronting fee percentage	0.125%
Default rate percentage	2.00%
Revolving Credit Facility \| Line of Credit \| Minimum
Debt Instrument [Line Items]
Commitment fee percentage	0.25%
Letter of credit, fee multiplier	1.50%
Revolving Credit Facility \| Line of Credit \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	2.00%
Commitment fee percentage	0.40%
Letter of credit, fee multiplier	2.00%
Revolving Credit Facility \| Line of Credit \| London Interbank Offered Rate (LIBOR) \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	2.50%
Revolving Credit Facility \| Line of Credit \| London Interbank Offered Rate (LIBOR) \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	3.00%
Revolving Credit Facility \| Line of Credit \| Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate	0.50%
Revolving Credit Facility \| Line of Credit \| Additional Applicable Margin \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	1.50%
Letter of Credit \| Line of Credit
Debt Instrument [Line Items]
Commitments from lender			15,000,000
Outstanding debt	$ 3,300,000	$ 2,900,000
Debt interest rate	1.75%	2.00%
Swingline loan \| Line of Credit
Debt Instrument [Line Items]
Commitments from lender			$ 15,000,000

DEBT - Promissory Note (Details) - GENBAND - USD ($)	Mar. 31, 2018	Oct. 27, 2017
Debt Instrument [Line Items]
Promissory note issued to GENBAND equity holders		$ 22,500,000.0
Minimum
Debt Instrument [Line Items]
Promissory note interest rate	7.50%
Maximum
Debt Instrument [Line Items]
Promissory note interest rate	10.00%

REVENUE RECOGNITION (Details) - USD ($) $ in Thousands	3 Months Ended
REVENUE RECOGNITION (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Revenue recognized that was previously recorded as deferred revenue	$ 32,600
Revenues	121,180	$ 53,368
Retained earnings \| Accounting Standards Update 2014-09
Adjustment to accumulated deficit in connection with adoption of ASC 606			$ 12,000
Difference between Revenue Guidance in Effect before and after Topic 606 \| Accounting Standards Update 2014-09
Revenues	$ 800
Product \| Sales Revenue, Net
Concentration risk, percentage	14.00%	28.00%
Channel partner program \| Product \| Sales Revenue, Net
Concentration risk, percentage	16.00%	34.00%

REVENUE RECOGNITION - Schedule of Customer Assets & Liabilities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Accounts receivable
Beginning balance	$ 149,122
Increase (decrease), net	(39,485)
Ending balance	109,637
Unbilled accounts receivable
Beginning balance	16,034
Increase (decrease), net	(167)
Ending balance	15,867
Deferred revenue (current)
Beginning balance	100,571
Increase (decrease), net	2,591
Ending balance	103,162
Deferred revenue (long-term)
Beginning balance	14,184
Increase (decrease), net	34
Ending balance	$ 14,218

REVENUE RECOGNITION - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 121,180	$ 53,368
United States
Disaggregation of Revenue [Line Items]
Revenues	56,884	36,016
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenues	25,401	6,372
Japan
Disaggregation of Revenue [Line Items]
Revenues	9,478	7,532
Other Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	17,053	2,004
Other
Disaggregation of Revenue [Line Items]
Revenues	12,364	1,444
Product revenue
Disaggregation of Revenue [Line Items]
Revenues	51,531	25,395
Product revenue \| United States
Disaggregation of Revenue [Line Items]
Revenues	17,801	17,407
Product revenue \| Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenues	11,420	3,136
Product revenue \| Japan
Disaggregation of Revenue [Line Items]
Revenues	5,670	2,992
Product revenue \| Other Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	12,887	934
Product revenue \| Other
Disaggregation of Revenue [Line Items]
Revenues	3,753	926
Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Revenues	56,062	21,756
Service revenue (maintenance) \| United States
Disaggregation of Revenue [Line Items]
Revenues	31,649	15,401
Service revenue (maintenance) \| Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenues	11,148	2,401
Service revenue (maintenance) \| Japan
Disaggregation of Revenue [Line Items]
Revenues	2,853	2,556
Service revenue (maintenance) \| Other Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	3,097	976
Service revenue (maintenance) \| Other
Disaggregation of Revenue [Line Items]
Revenues	7,315	422
Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Revenues	13,587	6,217
Service revenue (professional services) \| United States
Disaggregation of Revenue [Line Items]
Revenues	7,434	3,208
Service revenue (professional services) \| Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenues	2,833	835
Service revenue (professional services) \| Japan
Disaggregation of Revenue [Line Items]
Revenues	955	1,984
Service revenue (professional services) \| Other Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	1,069	94
Service revenue (professional services) \| Other
Disaggregation of Revenue [Line Items]
Revenues	$ 1,296	$ 96

STOCK-BASED COMPENSATION PLANS - Executive Equity Arrangements (Details) - PSUs					1 Months Ended	3 Months Ended
	Apr. 01, 2018 shares	Mar. 31, 2017 executive shares	Apr. 01, 2016 executive shares	Mar. 16, 2015 executive shares	Mar. 31, 2018 executive shares	Mar. 31, 2018 shares
Stock-based compensation
Granted (in shares)						8,600
Vested (in shares)						41,518
2017 Performance Share Units
Stock-based compensation
Granted (in shares)		165,000
Number of executives granted shares \| executive		5
Percent of performance metrics achieved					130.00%
Vested (in shares)					33,584
Number of executives shares were released to \| executive					3
2016 Performance Share Units
Stock-based compensation
Granted (in shares)			131,250
Number of executives granted shares \| executive			6
Percent of performance metrics achieved					130.00%
Vested (in shares)					16,250
Number of executives shares were released to \| executive					2
2015 Performance Share Units
Stock-based compensation
Granted (in shares)				131,250
Number of executives granted shares \| executive				8
Percent of performance metrics achieved					112.00%
Vested (in shares)					7,934
Number of executives shares were released to \| executive					2
March 31, 2017 \| 2017 Performance Share Units
Stock-based compensation
Percent of performance metrics achieved					100.00%
Vested (in shares)					25,834
March 31, 2018 \| 2017 Performance Share Units
Stock-based compensation
Vested (in shares)					7,750
Percent of achievement over target					30.00%
April 1, 2016 \| 2016 Performance Share Units
Stock-based compensation
Percent of performance metrics achieved					100.00%
Vested (in shares)					12,500
April 1, 2018 \| Subsequent Event \| 2016 Performance Share Units
Stock-based compensation
Vested (in shares)	3,750
Percent of achievement over target	30.00%
March 16, 2015 \| 2015 Performance Share Units
Stock-based compensation
Percent of performance metrics achieved					100.00%
Vested (in shares)					7,084
March 16, 2018 \| 2015 Performance Share Units
Stock-based compensation
Vested (in shares)					850
Percent of achievement over target					12.00%

STOCK-BASED COMPENSATION PLANS - Schedules (Details) - USD ($)				1 Months Ended	3 Months Ended
	Mar. 31, 2017	Apr. 01, 2016	Mar. 16, 2015	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017
Weighted average grant-date fair value
Total fair value of restricted stock awards, restricted stock units and performance-based stock units on date vested					$ 5,253,000	$ 2,852,000
Stock-based compensation expense (reversal)					2,824,000	3,263,000
Tax benefit from stock based compensation expense					0
Fair value of the assumed awards attributable to future stock-based compensation expense				$ 10,900,000	$ 10,900,000
Expected period for unrecognized expense					2 years
Product cost of revenue
Weighted average grant-date fair value
Stock-based compensation expense (reversal)					$ 51,000	99,000
Service cost of revenue
Weighted average grant-date fair value
Stock-based compensation expense (reversal)					132,000	317,000
Research and development
Weighted average grant-date fair value
Stock-based compensation expense (reversal)					900,000	1,317,000
Sales and marketing
Weighted average grant-date fair value
Stock-based compensation expense (reversal)					874,000	(88,000)
General and administrative
Weighted average grant-date fair value
Stock-based compensation expense (reversal)					$ 867,000	$ 1,618,000
PSUs
Change in unvested restricted stock awards
Unvested balance at the beginning of the period (in shares)					60,834
Granted (in shares)					8,600
Vested (in shares)					(41,518)
Forfeited (in shares)					0
Unvested balance at the end of the period (in shares)				27,916	27,916
Weighted average grant-date fair value
Unvested balance at the end of the period (in dollars per share)					$ 9.65
Granted (in dollars per share)					9.22
Vested (in dollars per share)					9.85
Forfeited (in dollars per share)					0.00
Unvested balance at end of the period (in dollars per share)				$ 9.22	$ 9.22
Total fair value of restricted stock awards, restricted stock units and performance-based stock units on date vested					$ 400,000
Stock Options
Number of shares
Outstanding at the beginning of the period (in shares)					435,187
Granted (in shares)					0
Exercised (in shares)					(2,583)
Forfeited (in shares)					0
Expired (in shares)					(45,738)
Outstanding at the end of the period (in shares)				386,866	386,866
Vested or expected to vest at the end of the period (in shares)				386,866	386,866
Exercisable at the end of the period (in shares)				386,866	386,866
Weighted average exercise price
Outstanding at the beginning of the period (in dollars per share)					$ 14.71
Granted (in dollars per share)					0.00
Exercised (in dollars per share)					3.70
Forfeited (in dollars per share)					0.00
Expired (in dollars per share)					15.46
Outstanding at the end of the period (in dollars per share)				$ 14.69	14.69
Vested or expected to vest at the end of the period (in dollars per share)				14.69	14.69
Exercisable at the end of the period (in dollars per share)				$ 14.69	$ 14.69
Weighted average remaining contractual life (in years)
Outstanding at the end of the period					3 years 11 months 28 days
Vested or expected to vest at the end of the period					3 years 11 months 28 days
Exercisable at the end of the period					3 years 11 months 28 days
Aggregate intrinsic value (in dollars)
Outstanding at the end of the period (in dollars)				$ 0	$ 0
Vested or expected to vest at the end of the period (in dollars)				0	0
Exercisable at the end of the period (in dollars)				$ 0	$ 0
Weighted average grant date fair value of stock options granted (in dollars per share)					$ 0.00
Total intrinsic values of stock options exercised (in dollars)					$ 8,000
Cash received from the exercise of stock options (in dollars)					$ 10,000
RSAs
Change in unvested restricted stock awards
Unvested balance at the beginning of the period (in shares)					1,696,582
Granted (in shares)					939,864
Vested (in shares)					(480,168)
Forfeited (in shares)					(116,522)
Unvested balance at the end of the period (in shares)				2,039,756	2,039,756
Weighted average grant-date fair value
Unvested balance at the end of the period (in dollars per share)					$ 7.68
Granted (in dollars per share)					7.06
Vested (in dollars per share)					9.95
Forfeited (in dollars per share)					7.46
Unvested balance at end of the period (in dollars per share)				$ 7.05	$ 7.05
Total fair value of restricted stock awards, restricted stock units and performance-based stock units on date vested					$ 4,800,000
RSUs
Change in unvested restricted stock awards
Unvested balance at the beginning of the period (in shares)					17,932
Granted (in shares)					219,000
Vested (in shares)					(10,114)
Forfeited (in shares)					(822)
Unvested balance at the end of the period (in shares)				225,996	225,996
Weighted average grant-date fair value
Unvested balance at the end of the period (in dollars per share)					$ 6.99
Granted (in dollars per share)					7.04
Vested (in dollars per share)					6.58
Forfeited (in dollars per share)					6.85
Unvested balance at end of the period (in dollars per share)				$ 7.06	$ 7.06
Employee Stock
Weighted average grant-date fair value
Offering period					6 months
Purchase price of common stock (percentage)					85.00%
Maximum number of shares purchasable per employee					500
2017 Performance Share Units \| PSUs
Change in unvested restricted stock awards
Granted (in shares)	165,000
Vested (in shares)				(33,584)
2016 Performance Share Units \| PSUs
Change in unvested restricted stock awards
Granted (in shares)		131,250
Vested (in shares)				(16,250)
2015 Performance Share Units \| PSUs
Change in unvested restricted stock awards
Granted (in shares)			131,250
Vested (in shares)				(7,934)

MAJOR CUSTOMERS - (Details) - Customer	3 Months Ended		12 Months Ended
MAJOR CUSTOMERS - (Details) - Customer	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Revenue \| Verizon Communications Inc.
MAJOR CUSTOMERS
Concentration risk, percentage	12.00%	17.00%
Accounts receivable balance
MAJOR CUSTOMERS
Concentration risk, percentage	21.00%		31.00%

RELATED PARTIES (Details) - GENBAND - USD ($)	Mar. 31, 2018	Oct. 27, 2017
Related Party Transaction [Line Items]
Promissory note issued to GENBAND equity holders		$ 22,500,000.0
Minimum
Related Party Transaction [Line Items]
Promissory note interest rate	7.50%
Maximum
Related Party Transaction [Line Items]
Promissory note interest rate	10.00%

INCOME TAXES - (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
INCOME TAXES - (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Tax Act impact on tax benefit		$ 4.8
Decrease in net deferred tax asset as a result of Tax Act	$ 0.2

COMMITMENTS AND CONTINGENCIES (Details) $ in Millions					3 Months Ended	12 Months Ended
COMMITMENTS AND CONTINGENCIES (Details) $ in Millions	Apr. 10, 2018 USD ($)	Mar. 22, 2018 USD ($)	Mar. 08, 2018 cases	Jan. 15, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2018 cases
Loss Contingencies [Line Items]
Ongoing lawsuits \| cases							5
Royalty damages awarded				$ 8.2
Damages awarded from other party		$ 8.9
Number of lawsuits \| cases			2
Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Civil penalty					$ 0.3	$ 1.9
Subsequent Event
Loss Contingencies [Line Items]
Awarded judgment interests and costs	$ 0.4