Document and Entity Information	3 Months Ended
Document and Entity Information	Mar. 27, 2015	Apr. 21, 2015
Document And Entity Information
Entity Registrant Name	SONUS NETWORKS INC
Entity Central Index Key	0001105472
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 27, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		49,444,160
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes

Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 27, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 18,092	$ 41,157
Marketable securities	65,708	64,443
Accounts receivable, net of allowance for doubtful accounts of $46 at March 27, 2015 and $58 at December 31, 2014	55,612	62,943
Inventory	25,147	22,114
Deferred income taxes	1,037	991
Other current assets	15,085	15,239
Total current assets	180,681	206,887
Property and equipment, net	18,329	17,845
Intangible assets, net	31,547	22,594
Goodwill	40,310	39,263
Investments	29,045	42,407
Deferred income taxes	1,001	1,043
Other assets	3,081	2,596
Total assets	303,994	332,635
Current liabilities:
Accounts payable	5,322	7,497
Accrued expenses	22,254	32,149
Current portion of deferred revenue	40,386	36,967
Current portion of long-term liabilities	750	794
Total current liabilities	68,712	77,407
Deferred revenue	8,207	8,009
Deferred income taxes	1,802	1,623
Other long-term liabilities	4,042	5,246
Total liabilities	82,763	92,285
Commitments and contingencies (Note 15)
Stockholders' equity:
Preferred stock, $0.01 par value per share; 5,000,000 shares authorized, none issued and outstanding	0	0
Common stock, $0.001 par value per share; 120,000,000 shares authorized; 49,443,729 shares issued and outstanding at March 27, 2015; 49,357,033 shares issued and outstanding at December 31, 2014	49	49
Additional paid-in capital	1,226,319	1,226,226
Accumulated deficit	(1,010,706)	(991,347)
Accumulated other comprehensive income	5,569	5,422
Total stockholders' equity	221,231	240,350
Total liabilities and stockholders' equity	$ 303,994	$ 332,635

Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 27, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 46	$ 58
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	49,443,729	49,357,033
Common stock, shares outstanding	49,443,729	49,357,033

Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 27, 2015	Mar. 28, 2014
Revenue:
Product	$ 24,865	$ 45,140
Service	25,280	25,602
Total revenue	50,145	70,742
Cost of revenue:
Product	11,648	13,663
Service	9,267	10,656
Total cost of revenue	20,915	24,319
Gross profit	29,230	46,423
Operating expenses:
Research and development	19,339	18,972
Sales and marketing	19,765	19,581
General and administrative	9,224	11,186
Acquisition-related	107	1,306
Restructuring	(339)	1,169
Total operating expenses	48,096	52,214
Loss from operations	(18,866)	(5,791)
Interest income, net	28	35
Other income, net	45	2,335
Loss before income taxes	(18,793)	(3,421)
Income tax provision	(566)	(532)
Net loss	$ (19,359)	$ (3,953)
Loss per share
Basic (in dollars per share)	$ (0.39)	$ (0.07)
Diluted (in dollars per share)	$ (0.39)	$ (0.07)
Shares used to compute loss per share:
Basic (in shares)	49,423	53,080
Diluted (in shares)	49,423	53,080

Consolidated Statements of Comprehensive Loss (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 27, 2015	Mar. 28, 2014
Statement of Comprehensive Income [Abstract]
Net loss	$ (19,359)	$ (3,953)
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	42	94
Unrealized gain (loss) on available-for sale marketable securities, net of tax	105	(10)
Other comprehensive income, net of tax	147	84
Comprehensive loss, net of tax	$ (19,212)	$ (3,869)

Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 27, 2015	Mar. 28, 2014
Cash flows from operating activities:
Net loss	$ (19,359)	$ (3,953)
Adjustments to reconcile net loss to cash flows provided by operating activities:
Depreciation and amortization of property and equipment	2,575	2,917
Amortization of intangible assets	1,647	1,029
Stock-based compensation	4,820	5,774
Loss on disposal of property and equipment	12	55
Deferred income taxes	155	176
Changes in operating assets and liabilities:
Accounts receivable	7,302	22,973
Inventory	(3,034)	2,337
Other operating assets	(75)	(259)
Accounts payable	(2,115)	(1,551)
Accrued expenses and other long-term liabilities	(13,014)	(7,754)
Deferred revenue	3,610	(538)
Net cash (used in) provided by operating activities	(17,476)	21,206
Cash flows from investing activities:
Purchases of property and equipment	(2,512)	(3,287)
Business acquisition, net of cash acquired	(10,147)	(34,010)
Purchases of marketable securities	(1,649)	0
Maturities/sales of marketable securities	13,518	87,646
Net cash (used in) provided by investing activities	(790)	50,349
Cash flows from financing activities:
Proceeds from sale of common stock in connection with employee stock purchase plan	1,668	1,197
Proceeds from exercise of stock options	1,687	3,444
Payment of tax withholding obligations related to net share settlements of restricted stock awards	(1,995)	(1,530)
Repurchase of common stock	(6,084)	(75,385)
Principal payments of capital lease obligations	(20)	(24)
Net cash used in financing activities	(4,744)	(72,298)
Effect of exchange rate changes on cash and cash equivalents	(55)	91
Net decrease in cash and cash equivalents	(23,065)	(652)
Cash and cash equivalents, beginning of year	41,157	72,423
Cash and cash equivalents, end of period	18,092	71,771
Supplemental disclosure of cash flow information:
Interest paid	8	2
Income taxes paid	151	751
Income tax refunds received	20	0
Supplemental disclosure of non-cash investing activities:
Capital expenditures incurred, but not yet paid	881	384
Business acquisition purchase consideration - assumed equity awards	$ 0	$ 1,671

BASIS OF PRESENTATION	3 Months Ended
BASIS OF PRESENTATION	Mar. 27, 2015
Accounting Policies [Abstract]
BASIS OF PRESENTATION	BASIS OF PRESENTATION Business Sonus Networks, Inc. (“Sonus” or the “Company”) is a leading provider of networked solutions for communications service providers (e.g., telecommunications, wireless and cable service providers) and enterprises to help them advance, protect and unify their communications and improve collaboration. Sonus helps many of the world's leading communications service providers and enterprises embrace the next generation of Session Initiation Protocol ("SIP") and 4G/LTE (Long Term Evolution)-based solutions, including Voice over IP ("VoIP") video and Unified Communications ("UC") through secure, reliable and scalable Internet Protocol ("IP") networks. Sonus' products include session border controllers ("SBCs"), diameter signaling controllers ("DSCs"), policy/routing servers, media and signaling gateways and network analytics tools. The Company utilizes both direct and indirect sales channels to reach its target customers. Customers and prospective customers in the service provider space are traditional and emerging communications service providers, including long distance carriers, local exchange carriers, Internet service providers, wireless operators, cable operators, international telephone companies and carriers that provide services to other carriers. Enterprise customers and target enterprise customers include financial institutions, retailers, state and local governments, and other multinational corporations. 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"). 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, 2014 (the "Annual Report") filed with the SEC on February 25, 2015. We effected a one-for-five reverse stock split of our issued, outstanding and authorized common stock, which became effective as of the commencement of trading on the NASDAQ Global Select Market on January 30, 2015. Unless otherwise indicated, all references herein to shares outstanding and share issuances have been adjusted to give effect to our January 2015 reverse stock split. On January 2, 2015 (the "Treq Asset Acquisition Date"), the Company acquired from Treq Labs, Inc. ("Treq") certain assets related to Treq's business of designing, developing, marketing, selling, servicing and maintaining software defined networking ("SDN") technology, SDN controller software and SDN management software (the "SDN Business"). The financial results of the SDN Business are included in the Company's condensed consolidated financial statements starting on the Treq Asset Acquisition Date. On February 19, 2014 (the "PT Acquisition Date"), the Company completed the acquisition of Performance Technologies, Incorporated ("PT"). The financial results of PT are included in the Company's condensed consolidated financial statements starting on the PT Acquisition Date. 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 27, 2015. Principles of Consolidation The condensed consolidated financial statements include the accounts of Sonus 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, 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 Sonus' net deferred tax assets and the related valuation allowances. Sonus regularly assesses these estimates and records changes in estimates in the period in which they become known. Sonus 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. Fair Value of Financial Instruments The carrying amounts of the Company's financial instruments, which include cash equivalents, marketable securities, investments, accounts receivable, accounts payable, convertible subordinated debt and other long-term liabilities, approximate their fair values. Operating Segments The Company operates in a single segment. Operating segments are identified as components of an enterprise about which separate discrete financial information is available 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. Recent Accounting Pronouncements In August 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2014-15, Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern ("ASU 2014-15"). ASU 2014-15 provides guidelines determining when and how to disclose going concern uncertainties in the financial statements. The new standard requires management to perform interim and annual assessments of an entity's ability to continue as a going concern within one year of the date the financial statements are issued. An entity must provide certain disclosures if conditions or events raise substantial doubt about the entity's ability to continue as a going concern. ASU 2014-15 applies to all entities and is effective for annual periods ending after December 15, 2016, and interim periods thereafter, with early adoption permitted. The adoption of ASU 2014-15 is not expected to have a material impact on the Company's consolidated financial statements. In June 2014, the FASB issued ASU 2014-12, Compensation - Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period (a consensus of the FASB Emerging Issues Task Force) (“ASU 2014-12”). ASU 2014-12 clarifies that entities should treat performance targets that can be met after the requisite service period of a share-based payment award as performance conditions that affect vesting. Therefore, an entity would not record compensation expense (measured as of the grant date without taking into account the effect of the performance target) related to an award for which transfer to the employee is contingent upon the entity’s satisfaction of a performance target until it becomes probable that the performance target will be met. ASU 2014-12 does not contain any new disclosure requirements. ASU 2014-12 was effective for the Company on January 1, 2015. The adoption of ASU 2014-12 did not have a material impact on the Company's condensed consolidated financial statements. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”) its final standard on revenue from contracts with customers. ASU 2014-09 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. ASU 2014-09 applies to all contracts with customers that are within the scope of other topics in the FASB Accounting Standards Codification ("ASC"). Certain of ASU 2014-09’s provisions also apply to transfers of nonfinancial assets, including in-substance nonfinancial assets that are not an output of an entity’s ordinary activities (i.e., property plant and equipment; real estate; or intangible assets). Existing accounting guidance applicable to these transfers has been amended or superseded. In April 2015, the FASB tentatively decided to defer the original effective date of interim and annual reporting periods beginning after December 15, 2015 by one year. As a result, public entities would not be required to apply the new revenue standard until annual reporting periods beginning after December 15, 2017. The Company is currently assessing the potential impact of the adoption of ASU 2014-09 on its condensed consolidated financial statements. In April 2014, the FASB issued ASU 2014-08, Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity (“ASU 2014-08”), which amends the definition of discontinued operations in ASC 205-20 and requires entities to provide additional disclosures about discontinued operations as well as disposal transactions that do not meet the discontinued operations criteria. The new guidance eliminates the previous criteria that the operations and cash flows of the component that have been (or will be) eliminated from the ongoing operations of the entity as a result of the disposal transaction. The new guidance also eliminates the previous criteria that the entity will not have any significant continuing involvement in the operations of the component after the disposal transaction. Instead, ASU 2014-08 requires discontinued operations treatment for disposals of a component or group of components that represents a strategic shift that has or will have a major impact on an entity’s operations or financial results. ASU 2014-08 requires entities to reclassify assets and liabilities of a discontinued operation for all comparative periods presented in the statement of financial position. In addition, ASU 2014-08 requires that an entity disclose in its statement of cash flows, for all periods presented, either: (1) operating and investing cash flows or (2) depreciation and amortization, capital expenditures and significant operating and investing non-cash items related to the discontinued operation. ASU 2014-08 was effective prospectively for all disposals (except disposals classified as held for sale before the adoption date) or components initially classified as held for sale in periods beginning on or after December 15, 2014. The adoption of ASU 2014-08 did not have a material impact on the Company's condensed consolidated financial statements.

BUSINESS ACQUISITIONS

3 Months Ended

Mar. 27, 2015

Business Combinations [Abstract]

BUSINESS ACQUISITIONS

Treq Labs, Inc.

On the Treq Asset Acquisition Date, the Company acquired from Treq its SDN Business.. The SDN Business provides solutions that optimize networks for voice, video and UC for both enterprise and service provider customers. The Company believes that the acquisition of the SDN Business will accelerate Sonus' delivery of its SDN strategy. In consideration for the acquisition of the SDN Business, Sonus paid $10.1 million in cash at the Treq Asset Acquisition Date, with an additional consideration payment of $750,000 due on July 2, 2015 and a second additional consideration payment of $750,000 due on January 4, 2016. The Company also entered into an Earn-Out Agreement, dated as of January 2, 2015, with Treq and Karl F. May, the seller representative in the transaction (the "Earn-Out Agreement"), under which the Company has agreed to issue up to an aggregate of 1.3 million shares of common stock over a three-year period subsequent to the Treq Asset Acquisition Date if aggregate revenue thresholds of at least $60 million are achieved by the SDN Business during that period, and up to an aggregate of an additional 2.2 million shares (3.5 million shares in total) if aggregate revenue thresholds of at least $150 million are achieved by the SDN Business during that period. If the initial revenue thresholds are not met, no shares will be issued. Based on historical and forecasted sales, no incremental contingent consideration was recorded initially as of the Treq Asset Acquisition Date or through March 27, 2015. Any shares issued pursuant to the Earn-Out Agreement will be issued in reliance on the exemption from registration available under Section 4(a)(2) of the Securities Act of 1933, as amended (the "Securities Act") and will be subsequently registered for resale under the Securities Act by the Company.

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

As of March 27, 2015, the valuation of the identifiable intangible assets remained preliminary. The Company is in the process of finalizing its valuation, which it plans to complete in the second quarter of fiscal 2015. Based on the preliminary purchase price allocation, the Company recorded $1.0 million of goodwill, primarily due to expected synergies between the combined companies and expanded market opportunities. The goodwill is not deductible for tax purposes.

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



Fair value of consideration transferred:
Cash, net of cash acquired	$	10,147
Unpaid purchase consideration	1,500
Fair value of total consideration	$	11,647
Fair value of assets acquired and liabilities assumed:
Intangible assets:
In-process research and development	$	9,100
Developed technology	1,500
Goodwill	1,047
	$	11,647

The valuation of the acquired intangible assets is inherently subjective and relies on significant unobservable inputs. The Company used an income approach to preliminarily value the acquired in-process research and development and developed technology 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 technology attrition and revenue growth projections. The Company will begin to amortize the in-process research and development intangible asset at the time that the related products become generally available. Once the products become generally available, the Company will amortize the identifiable intangible assets in relation to the expected cash flows from the individual intangible assets over their respective useful lives (see Note 6).

The actual results of the SDN Business for the period since the Treq Asset Acquisition Date were not material to the Company's financial results. The Company has not provided pro forma information as the results of the SDN Business are not material to the Company's financial results.

Performance Technologies, Incorporated

On the PT Acquisition Date, the Company acquired all of the outstanding common stock of PT for cash consideration of $35.0 million, or $3.75 per share of PT common stock. This acquisition has enabled Sonus to expand its solutions portfolio with signaling technology and acquire expertise to enable mobile service providers to offer new real-time multimedia services through their mobile infrastructure. Delivering these services across the LTE next-generation mobile networks will require adoption of the next-generation signaling technology known in the industry as Diameter Signal. The acquisition of PT has allowed Sonus to diversify its product portfolio with an integrated, virtualized Diameter and SIP-based solution and deliver strategic value to service providers seeking to offer new multimedia services through mobile, cloud-based, real-time communications.

The transaction has been accounted for as a business combination and the financial results of PT have been included in the Company's condensed consolidated financial statements starting on the PT Acquisition Date.

The Company finalized the valuation of acquired assets, identifiable intangible assets and certain accrued liabilities in the fourth quarter of 2014. The Company recorded $8.8 million of goodwill, primarily due to expected synergies between the combined companies and expanded market opportunities. The goodwill is not deductible for tax purposes.

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



Fair value of consideration transferred:
Cash, net of cash acquired	$	35,022
Fair value of equity awards assumed	1,671
Fair value of total consideration	$	36,693
Fair value of assets acquired and liabilities assumed:
Marketable securities	$	2,315
Other current assets	9,337
Property and equipment	2,251
Intangible assets:
Developed technology	13,200
Customer relationships	3,900
Goodwill	8,781
Current liabilities	(2,762		)
Other long-term liabilities	(329		)
	$	36,693

The valuation of the acquired intangible assets is inherently subjective and relies on significant unobservable inputs. The Company used an income approach to preliminarily value the acquired customer relationships and developed technology 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 contract renewal, technology attrition and revenue growth projections. The Company is amortizing the identifiable intangible assets in relation to the expected cash flows from the individual intangible assets over their respective useful lives (see Note 6).

The Company has not provided pro forma information as the results of PT are not material to the Company's financial results.

Acquisition-Related Expenses

Acquisition-related expenses include those expenses related to acquisitions that would otherwise not have been incurred by the Company. These expenses include professional and services fees, such as legal, audit, consulting, paying agent and other fees. These expenses also include cash payments to certain former PT executives under their respective PT change of control agreements. The amount recorded in the three months ended March 27, 2015 relates to professional fees in connection with the acquisition of the SDN Business. The amount recorded in the three months ended March 28, 2014 represents professional and services fees and expenses related to cash payments to certain former PT executives under their respective PT change of control agreements in connection with the PT acquisition.

The components of acquisition-related costs included in the Company's results of operations for the three months ended March 27, 2015 and March 28, 2014 are as follows (in thousands):



	Three months ended
	March 27, 2015		March 28, 2014
Professional and services fees	$	107	$	1,057
Change of control agreements	—		249
	$	107	$	1,306

Sale of Multi-Protocol Server Business

On June 20, 2014 (the "MPS Sale Date"), the Company sold its PT Multi-Protocol Server ("MPS") business for $2.0 million to an affiliate of Sunhillo Corporation, comprised of $0.2 million of inventory, $0.1 million of fixed assets, $0.2 million of deferred revenue and $1.9 million of PT goodwill allocable to the MPS business. The Company had acquired the MPS business in connection with the acquisition of PT. The results of operations of the MPS business are excluded from the Company's condensed consolidated results after the MPS Sale Date.

EARNINGS (LOSS) PER SHARE

3 Months Ended

Mar. 27, 2015

Earnings Per Share [Abstract]

EARNINGS (LOSS) PER SHARE

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

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



	Three months ended
	March 27, 2015	March 28, 2014
Weighted average shares outstanding—basic	49,423	53,080
Potential dilutive common shares	—	—
Weighted average shares outstanding—diluted	49,423	53,080

Options to purchase the Company's common stock, unvested shares of restricted stock, unvested performance-based stock awards and shares in connection with future purchases under the Company's Amended and Restated 2000 Employee Stock Purchase Plan, as amended (the "ESPP"), aggregating 9.4 million shares for the three months ended March 27, 2015 and 9.1 million shares for the three months ended March 28, 2014 have not been included in the computation of diluted loss per share because their effect would have been antidilutive.

CASH EQUIVALENTS AND INVESTMENTS

3 Months Ended

Mar. 27, 2015

Investments, All Other Investments [Abstract]

CASH EQUIVALENTS, MARKETABLE SECURITIES AND INVESTMENTS

CASH EQUIVALENTS 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.

During the three months ended March 28, 2014, the Company sold $45.9 million of its available-for-sale securities and realized gross gains aggregating $46,000, which are included as a component of Other income (expense), net, in the Company's condensed consolidated statement of operations for that period. The Company did not realize any gross losses on these sales. In addition, $41.7 million of the Company's available-for-sale securities matured during the three months ended March 28, 2014 and were redeemed upon maturity. The Company did not sell any of its available-for-sale securities during the three months ended March 27, 2015.

Investments with continuous unrealized losses for one year or greater at March 27, 2015 were nominal. Since the Company currently does not intend to sell these securities and does not believe it will be required to sell any securities before they recover in value, it does not believe these declines are other-than-temporary.

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 27, 2015.

The amortized cost, gross unrealized gains and losses and fair value of the Company's marketable debt securities and investments at March 27, 2015 and December 31, 2014 were comprised of the following (in thousands):



	March 27, 2015
	Amortized cost		Unrealized gains		Unrealized losses			Fair value
Cash equivalents	$	1,391	$	—	$	—		$	1,391

Marketable securities
Municipal obligations	$	1,523	$	1	$	—		$	1,524
U.S. government agency notes	4,154		1		—			4,155
Corporate debt securities	45,325		4		(40		)	45,289
Commercial paper	8,190		—		—			8,190
Certificates of deposit	6,550		—		—			6,550
	$	65,742	$	6	$	(40	)	$	65,708
Investments
Municipal obligations	$	2,197	$	3	$	(1	)	$	2,199
U.S. government agency notes	2,300		2		—			2,302
Corporate debt securities	24,051		14		(21		)	24,044
Certificates of deposit	500		—		—			500
	$	29,048	$	19	$	(22	)	$	29,045



	December 31, 2014
	Amortized cost		Unrealized gains		Unrealized losses			Fair value
Cash equivalents	$	11,653	$	—	$	—		$	11,653

Marketable securities
Municipal obligations	$	1,273	$	1	$	(1	)	$	1,273
U.S. government agency notes	4,016		—		—			4,016
Corporate debt securities	40,921		2		(59		)	40,864
Commercial paper	9,340		—		—			9,340
Certificates of deposit	8,950		—		—			8,950
	$	64,500	$	3	$	(60	)	$	64,443
Investments
Municipal obligations	$	2,702	$	1	$	(3	)	$	2,700
U.S. government agency notes	2,300		—		(1		)	2,299
Corporate debt securities	35,897		4		(86		)	35,815
Commercial paper	1,093		—		—			1,093
Certificates of deposit	500		—		—			500
	$	42,492	$	5	$	(90	)	$	42,407

The Company's available-for-sale debt securities classified as Investments in the condensed consolidated balance sheets at March 27, 2015 and December 31, 2014 had maturity dates 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 27, 2015 and December 31, 2014. These financial assets are comprised of the Company's available-for-sale debt securities and reported under the captions Cash and cash equivalents, Short-term investments and Investments in the condensed consolidated balance sheets (in thousands):



			Fair value measurements at March 27, 2015 using:
	Total carrying value at March 27, 2015		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
Cash equivalents	$	1,391	$	1,391	$	—	$	—

Marketable securities
Municipal obligations	$	1,524	$	—	$	1,524	$	—
U.S. government agency notes	4,155		—		4,155		—
Corporate debt securities	45,289		—		45,289		—
Commercial paper	8,190		—		8,190		—
Certificates of deposit	6,550		—		6,550		—
	$	65,708	$	—	$	65,708	$	—
Investments
Municipal obligations	$	2,199	$	—	$	2,199	$	—
U.S. government agency notes	2,302		—		2,302		—
Corporate debt securities	24,044		—		24,044		—
Certificates of deposit	500		—		500		—
	$	29,045	$	—	$	29,045	$	—



			Fair value measurements at December 31, 2014 using:
	Total carrying value at December 31, 2014		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
Cash equivalents	$	11,653	$	11,653	$	—	$	—

Marketable securities
Municipal obligations	$	1,273	$	—	$	1,273	$	—
U.S. government agency notes	4,016		—		4,016		—
Corporate debt securities	40,864		—		40,864		—
Commercial paper	9,340		—		9,340		—
Certificates of deposit	8,950		—		8,950		—
	$	64,443	$	—	$	64,443	$	—
Investments
Municipal obligations	$	2,700	$	—	$	2,700	$	—
U.S. government agency notes	2,299		—		2,299		—
Corporate debt securities	35,815		—		35,815		—
Commercial paper	1,093		—		1,093		—
Certificates of deposit	500		—		500		—
	$	42,407	$	—	$	42,407	$	—

The Company's 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.

INTANGIBLE ASSETS AND GOODWILL

3 Months Ended

Mar. 27, 2015

Goodwill and Intangible Assets Disclosure [Abstract]

INTANGIBLE ASSETS AND GOODWILL

The Company's intangible assets at March 27, 2015 and December 31, 2014 consist of the following (dollars in thousands):



March 27, 2015	Weighted average amortization period (years)	Cost		Accumulated amortization		Net carrying value
In-process research and development	7.00	$	9,100	$	—	$	9,100
Intellectual property	5.00	999		999		—
Developed technology	6.24	23,780		6,300		17,480
Customer relationships	5.57	10,040		5,174		4,866
Internal use software	3.00	730		629		101
	6.05	$	44,649	$	13,102	$	31,547



December 31, 2014	Weighted average amortization period (years)	Cost		Accumulated amortization		Net carrying value
Intellectual property	5.00	$	999	$	999	$	—
Developed technology	6.18	22,280		5,193		17,087
Customer relationships	5.57	10,040		4,695		5,345
Internal use software	3.00	730		568		162
	5.75	$	34,049	$	11,455	$	22,594

Amortization expense for intangible assets for the three months ended March 27, 2015 and March 28, 2014 was as follows (in thousands):



	Three months ended				Statement of operations classification
	March 27, 2015		March 28, 2014		Statement of operations classification
Developed technology	$	1,107	$	570	Cost of revenue - product
Customer relationships	479		398		Sales and marketing
Internal use software	61		61		Cost of revenue - product
	$	1,647	$	1,029

The Company did not record amortization expense in connection with the in-process research and development intangible asset because the related products were not yet generally available. The Company will begin to amortize the in-process research and development intangible asset at the time that the related products become generally available and will amortize the identifiable intangible assets in relation to the expected cash flows from the individual intangible assets over their respective useful lives; the Company will begin to amortize this intangible asset at the time that the related products become generally available, which the Company expects will occur in the second and fourth quarters of 2015. Estimated future amortization expense for the Company's intangible assets at March 27, 2015 is as follows (in thousands):



Years ending December 31,
Remainder of 2015	$	5,895
2016	7,001
2017	7,338
2018	4,589
2019	3,554
Thereafter	3,170
	$	31,547

The changes in the carrying value of the Company's goodwill in the three months ended March 27, 2015 and March 28, 2014 were as follows (in thousands):




Balance at January 1, 2015
Goodwill	$	42,369
Accumulated impairment losses	(3,106		)
	39,263
Acquisition of SDN Business	1,047
Balance at March 27, 2015	$	40,310

Balance at March 27, 2015
Goodwill	$	43,416
Accumulated impairment losses	(3,106		)
	$	40,310




Balance at January 1, 2014
Goodwill	$	35,485
Accumulated impairment losses	(3,106		)
	32,379
Acquisition of PT	8,193
Balance at March 28, 2014	$	40,572

Balance at March 28, 2014
Goodwill	$	43,678
Accumulated impairment losses	(3,106		)
	$	40,572

RESTRUCTURING ACCRUAL

3 Months Ended

Mar. 27, 2015

Restructuring and Related Activities [Abstract]

RESTRUCTURING ACCRUAL

The Company recorded a credit of $0.3 million to restructuring expense in the three months ended March 27, 2015 that it had previously accrued in connection with its earlier restructuring initiative. The reversal of approximately $272,000 for facilities was recorded in connection with the settlement with the landlord of the Company's Dulles, Virginia facility for an amount that was lower than had previously been accrued. The Company also reversed approximately $67,000 in connection with changes in the amounts of severance ultimately paid to certain individuals.

The Company recorded $1.2 million of restructuring expense in the three months ended March 28, 2014 for severance and related costs in connection with reducing its workforce.

The table below summarizes the restructuring accrual activity for the three months ended March 27, 2015 (in thousands):



	Balance at January 1, 2015		Adjustments for changes in estimate			Cash payments			Balance at March 27, 2015
Severance	$	1,682	$	(67	)	$	(1,290	)	$	325
Facilities	3,652		(272		)	(1,135		)	2,245
	$	5,334	$	(339	)	$	(2,425	)	$	2,570

The Company expects to complete the restructuring payments related to severance in the fourth quarter of fiscal 2015 and the payments related to facilities in fiscal 2016. The current portion of the restructuring accrual is included as a component of Accrued expenses in the Company's condensed consolidated balance sheets. The portion of restructuring payments due more than one year from the balance sheet date is included in Other long-term liabilities in the Company's condensed consolidated balance sheets. The long-term portions of accrued restructuring were $0.9 million at March 27, 2015 and $1.9 million at December 31, 2014.

DEBT	3 Months Ended
DEBT	Mar. 27, 2015
Debt Disclosure [Abstract]
DEBT	DEBT On June 27, 2014, the Company entered into a credit agreement (the "Credit Agreement") by and among the Company, 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. The Credit Agreement provides for a revolving credit facility of up to $40 million and provides that the Company may select the interest rates under the credit facility equal to (1) the Eurodollar Rate (which is defined as the rate per annum equal to the London Interbank Offered Rate plus 1.5% per annum) for a Eurodollar Rate Loan; and (2) the highest of (a) the Federal Funds Rate plus 1/2 of 1%, (b) the rate of interest in effect on the borrowing date as publicly announced from time to time by Bank of America as its prime rate, and (c) the monthly Eurodollar Rate plus 1%. The Company will pay a 0.15% commitment fee on the unused commitments available for borrowing. The obligations of the Company under the Credit Agreement are guaranteed by Sonus International, Inc., Sonus Federal, Inc., Network Equipment Technologies, Inc. ("NET") and PT (collectively, together with the Company, the "Loan Parties") pursuant to a Master Continuing Guaranty and are secured by the assets of the Loan Parties pursuant to a Security and Pledge Agreement. The credit facility will become due on June 27, 2015, subject to acceleration upon certain specified events of default. The Company did not have any amounts outstanding under the Credit Agreement at March 27, 2015.

COMMON STOCK REPURCHASES AND UNDERWRITTEN OFFERING (Notes)	3 Months Ended
	Mar. 27, 2015
Equity [Abstract]
COMMON STOCK REPURCHASES AND UNDERWRITTEN OFFERING	COMMON STOCK REPURCHASES AND UNDERWRITTEN OFFERING Stock Buyback Program On July 29, 2013, the Company announced that its Board of Directors had authorized a stock buyback program to repurchase up to $100 million of the Company's common stock from time to time on the open market or in privately negotiated transactions. The timing and amount of any shares repurchased will be determined by the Company's management based on its evaluation of market conditions and other factors. The Company may elect to implement a 10b5-1 repurchase program, which would permit shares to be repurchased when the Company might otherwise be precluded from doing so under insider trading laws. The Company has not implemented such a 10b5-1 repurchase program to date. The stock buyback program may be suspended or discontinued at any time. The stock buyback program is being funded using the Company's working capital. During the three months ended March 27, 2015, the Company spent $6.1 million, including transaction fees, to repurchase and retire 0.4 million shares of its common stock under the stock buyback program. During the three months ended March 28, 2014, the Company spent $0.1 million, including transaction fees, to repurchase and retire 7,700 shares of its common stock under the stock buyback program. At March 27, 2015, the Company had $16.8 million remaining under the stock buyback program for future repurchases. Underwritten Offering On March 20, 2014, the Company announced the commencement of an underwritten public offering of 7.5 million shares of its common stock on behalf of Galahad Securities Limited and its affiliated entities (collectively, the "Legatum Group"). The underwriter of the offering was granted a 30-day option to purchase up to 1.125 million additional shares from the Legatum Group. The Legatum Group received all the proceeds from the underwritten offering; no shares in the underwritten offering were sold by Sonus or any of its officers or directors. Sonus purchased 4.3 million shares of its common stock from the underwriter for $17.4410 per share, the price equal to the price paid by the underwriter to the Legatum Group in the underwritten offering, for a total of $75.3 million, including transaction fees of $0.3 million. This repurchase was not completed under the Company's stock buyback program. Sonus funded the share repurchase with cash on hand. The repurchased shares were retired upon completion of the transaction.

STOCK-BASED COMPENSATION PLANS

3 Months Ended

Mar. 27, 2015

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

STOCK-BASED COMPENSATION PLANS

Stock Incentive Plan

The Company's 2007 Stock Incentive Plan, as amended (the "2007 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 and Board of Directors Equity Arrangements

In connection with the Company's annual incentive program, 22 executives of the Company were given the choice to receive all or half of their fiscal year 2015 bonuses (the "2015 Bonus"), if any are earned, in the form of shares of the Company's common stock (the "2015 Bonus Shares"). Each executive could also elect not to participate in this program and to earn his or her 2015 Bonus, if any, in the form of cash. The amount of the 2015 Bonus, if any, for each executive shall be determined by the Compensation Committee of the Board of Directors of the Company (the "Compensation Committee"). The number of shares of the Company's common stock that will be granted to those executives who elected to receive their 2015 Bonus entirely in the form of shares of common stock will be calculated by dividing an amount equal to 1.5 times each executive's 2015 Bonus earned by $20.55, the closing price of the Company's common stock on January 2, 2015. The number of shares of the Company's common stock that will be granted to those executives who elected to receive one-half of their 2015 Bonus in the form of shares of common stock will be calculated by dividing an amount equal to 1.5 times one-half of each executive's 2015 Bonus earned by $20.55, with the cash portion equal 50% of their respective 2015 Bonus earned. The 2015 Bonus, if any, will be granted and/or paid on a date concurrent with the timing of the payout of bonuses under the Company-wide incentive bonus program and will be fully vested on the date of grant. Of the eligible executives, 16 elected to receive their entire 2015 Bonus in shares of common stock, five elected to receive 50% of their 2015 Bonus in shares of common stock and 50% in cash and one elected not to participate and instead to receive his entire 2015 Bonus in cash. As of March 27, 2015, the Company determined that the grant date criteria for the 2015 Bonus Shares had not been met; accordingly, the Company is marking to market the 2015 Bonus Shares expected to be earned and recording expense based on the aggregate fair value of the 2015 Bonus Shares at March 27, 2015. The Company did not record expense related to the 2015 Bonus Shares in the three months ended March 27, 2015 as it did not believe that any 2015 Bonus Shares would be earned. Since the 2015 Bonus Shares will not be granted until the date of the 2015 Bonus payment, there are no shares related to the 2015 Bonus reported in the restricted stock grant table below.

On January 22, 2014, 21 executives of the Company were given the choice to receive all or half of their fiscal year 2014 bonuses (the "2014 Bonus"), if any were earned, in the form of shares of the Company's common stock (the "2014 Bonus Shares"). Of the eligible executives, 17 elected to receive their entire 2014 Bonus in shares of common stock, while 4 elected to receive 50% of their 2014 Bonus in shares of common stock and 50% in cash. The 2014 Bonus Shares were granted on February 20, 2015 and vested immediately. The Company granted approximately 266,000 2014 Bonus Shares, with the number of shares granted calculated by dividing amounts equal to 1.5 times each executive's 2014 Bonus earned, as determined by the Compensation Committee, by $15.40, the closing price of the Company's common stock on January 2, 2014. The Company recorded stock-based compensation expense for the 2014 Bonus Shares from January 1, 2014 through the grant date. These shares are reported as both "Granted" and "Vested" in the RSA table below.

On March 16, 2015, the Company granted 131,250 PSUs in the aggregate to eight of its executives with both market and service conditions. The terms of the PSUs are such that up to one-third of the shares subject to the PSUs will vest on each of the first, second and third anniversaries of the date of grant (collectively, the "Vesting Dates") to the extent of achievement of the Company's total shareholder return ("TSR") compared to the TSR of the companies included in the NASDAQ Telecommunications Index for the same Performance Period, measured by the Compensation Committee at the end of each of the 2015, 2016 and 2017 fiscal years, respectively (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. The PSUs include a market condition which requires the use of a Monte Carlo simulation approach to model future stock price movements based upon the risk-free rate of return, the volatility of each entity, and the pair-wise covariance between each entity. These results were then used to calculate the grant date fair values of the PSUs. The Company is recording expense for the PSUs through the final Vesting Date of March 16, 2018. The PSUs are reported as "Granted" in the performance-based awards table below.

Stock Options

The activity related to the Company's outstanding stock options during the three months ended March 27, 2015 is as follows:



	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (in thousands)
Outstanding at January 1, 2015	7,521,432		$	16.47
Granted	279,930		$	16.28
Exercised	(143,320	)	$	11.19
Forfeited	(82,773	)	$	15.85
Expired	(43,013	)	$	24.12
Outstanding at March 27, 2015	7,532,256		$	16.53	6.79	$	317
Vested or expected to vest at March 27, 2015	7,083,866		$	16.52	6.68	$	310
Exercisable at March 27, 2015	4,175,385		$	16.88	5.47	$	263

The grant date fair values of options to purchase common stock granted in the three months ended March 27, 2015 were estimated using the Black-Scholes valuation model with the following assumptions:



		Three months ended
		March 27, 2015
Risk-free interest rate		1.46% - 1.74%
Expected dividends		—
Weighted average volatility		54.3%
Expected life (years)		5.0 - 6.0

Additional information regarding the Company's stock options for the three months ended March 27, 2015 is as follows:



	Three months ended
	March 27, 2015
Weighted average grant date fair value of stock options granted	$	8.25
Total intrinsic value of stock options exercised (in thousands)	$	902
Cash received from the exercise of stock options (in thousands)	$	1,687

Restricted Stock Awards and Units

The activity related to the Company's RSAs for the three months ended March 27, 2015 is as follows:



	Shares		Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2015	370,182		$	16.74
Granted	1,411,099		$	16.45
Vested	(287,176	)	$	17.76
Forfeited	(950	)	$	16.05
Unvested balance at March 27, 2015	1,493,155		$	16.28

The activity related to the Company's unvested RSUs for the three months ended March 27, 2015 is as follows:



	Shares	Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2015	—	$	—
Granted	120,215	$	16.05
Vested	—	$	—
Forfeited	—	$	—
Unvested balance at March 27, 2015	120,215	$	16.05

The total fair value of shares of restricted stock that vested during the three months ended March 27, 2015 was $5.1 million.

Performance-Based Stock Awards and Units

The activity related to the Company's PSAs for the three months ended March 27, 2015 is as follows:



	Shares		Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2015	34,235		$	13.60
Granted	—		$	—
Vested	(28,610	)	$	13.60
Forfeited	—		$	—
Unvested balance at March 27, 2015	5,625		$	13.60

The activity related to the Company's PSUs for the three months ended March 27, 2015 is as follows:



	Shares		Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2015	—	—	$	—
Granted	131,250	14.68	$	14.68
Vested	—	—	$	—
Forfeited	—	—	$	—
Unvested balance at March 27, 2015	131,250	14.68	$	14.68

Employee Stock Purchase Plan

The Company's 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.

Stock-Based Compensation

The condensed consolidated statements of operations include stock-based compensation for the three months ended March 27, 2015 and March 28, 2014 as follows (in thousands):



	Three months ended
	March 27, 2015		March 28, 2014
Product cost of revenue	$	74	$	79
Service cost of revenue	380		279
Research and development	1,358		1,313
Sales and marketing	1,016		1,249
General and administrative	1,992		2,854
	$	4,820	$	5,774

There is no income tax benefit for employee stock-based compensation expense for the three months ended March 27, 2015 or March 28, 2014 due to the valuation allowance recorded.

At March 27, 2015, there was $44.7 million, net of expected forfeitures, of unrecognized stock-based compensation expense related to unvested stock options, awards and units. This expense is expected to be recognized over a weighted average period of approximately three years.

COMMITMENTS AND CONTINGENCIES	3 Months Ended
COMMITMENTS AND CONTINGENCIES	Mar. 27, 2015
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES On April 6, 2015, Ming Huang, a purported shareholder of the Company (the “Plaintiff”), filed a Class Action Complaint alleging violations of the federal securities laws (the “Complaint”) in the United States District Court for the District of New Jersey (Civil Action No. 3:15-02407), against Sonus and two of its officers, Raymond P. Dolan, the Company’s President and Chief Executive Officer, and Mark Greenquist, the Company’s Chief Financial Officer (the “Defendants”). The Plaintiff claims to represent purchasers of the Company’s common stock during the period from October 23, 2014 to March 24, 2015 and seeks unspecified damages. The principal allegation contained in the Complaint is the claim that the Defendants made misleading forward-looking statements concerning the Company’s fiscal first quarter 2015 financial performance. The Company believes that the Defendants have meritorious defenses to the allegations made in the Complaint and does not expect the results of this suit to have a material 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. 27, 2015
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"). 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, 2014 (the "Annual Report") filed with the SEC on February 25, 2015. We effected a one-for-five reverse stock split of our issued, outstanding and authorized common stock, which became effective as of the commencement of trading on the NASDAQ Global Select Market on January 30, 2015. Unless otherwise indicated, all references herein to shares outstanding and share issuances have been adjusted to give effect to our January 2015 reverse stock split. On January 2, 2015 (the "Treq Asset Acquisition Date"), the Company acquired from Treq Labs, Inc. ("Treq") certain assets related to Treq's business of designing, developing, marketing, selling, servicing and maintaining software defined networking ("SDN") technology, SDN controller software and SDN management software (the "SDN Business"). The financial results of the SDN Business are included in the Company's condensed consolidated financial statements starting on the Treq Asset Acquisition Date. On February 19, 2014 (the "PT Acquisition Date"), the Company completed the acquisition of Performance Technologies, Incorporated ("PT"). The financial results of PT are included in the Company's condensed consolidated financial statements starting on the PT Acquisition Date.
Principles of Consolidation	Principles of Consolidation The condensed consolidated financial statements include the accounts of Sonus 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, 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 Sonus' net deferred tax assets and the related valuation allowances. Sonus regularly assesses these estimates and records changes in estimates in the period in which they become known. Sonus 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.
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, accounts payable, convertible subordinated debt and other long-term liabilities, approximate their fair values.
Operating Segments	Operating Segments The Company operates in a single segment. Operating segments are identified as components of an enterprise about which separate discrete financial information is available 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.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In August 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2014-15, Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern ("ASU 2014-15"). ASU 2014-15 provides guidelines determining when and how to disclose going concern uncertainties in the financial statements. The new standard requires management to perform interim and annual assessments of an entity's ability to continue as a going concern within one year of the date the financial statements are issued. An entity must provide certain disclosures if conditions or events raise substantial doubt about the entity's ability to continue as a going concern. ASU 2014-15 applies to all entities and is effective for annual periods ending after December 15, 2016, and interim periods thereafter, with early adoption permitted. The adoption of ASU 2014-15 is not expected to have a material impact on the Company's consolidated financial statements. In June 2014, the FASB issued ASU 2014-12, Compensation - Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period (a consensus of the FASB Emerging Issues Task Force) (“ASU 2014-12”). ASU 2014-12 clarifies that entities should treat performance targets that can be met after the requisite service period of a share-based payment award as performance conditions that affect vesting. Therefore, an entity would not record compensation expense (measured as of the grant date without taking into account the effect of the performance target) related to an award for which transfer to the employee is contingent upon the entity’s satisfaction of a performance target until it becomes probable that the performance target will be met. ASU 2014-12 does not contain any new disclosure requirements. ASU 2014-12 was effective for the Company on January 1, 2015. The adoption of ASU 2014-12 did not have a material impact on the Company's condensed consolidated financial statements. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”) its final standard on revenue from contracts with customers. ASU 2014-09 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. ASU 2014-09 applies to all contracts with customers that are within the scope of other topics in the FASB Accounting Standards Codification ("ASC"). Certain of ASU 2014-09’s provisions also apply to transfers of nonfinancial assets, including in-substance nonfinancial assets that are not an output of an entity’s ordinary activities (i.e., property plant and equipment; real estate; or intangible assets). Existing accounting guidance applicable to these transfers has been amended or superseded. In April 2015, the FASB tentatively decided to defer the original effective date of interim and annual reporting periods beginning after December 15, 2015 by one year. As a result, public entities would not be required to apply the new revenue standard until annual reporting periods beginning after December 15, 2017. The Company is currently assessing the potential impact of the adoption of ASU 2014-09 on its condensed consolidated financial statements. In April 2014, the FASB issued ASU 2014-08, Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity (“ASU 2014-08”), which amends the definition of discontinued operations in ASC 205-20 and requires entities to provide additional disclosures about discontinued operations as well as disposal transactions that do not meet the discontinued operations criteria. The new guidance eliminates the previous criteria that the operations and cash flows of the component that have been (or will be) eliminated from the ongoing operations of the entity as a result of the disposal transaction. The new guidance also eliminates the previous criteria that the entity will not have any significant continuing involvement in the operations of the component after the disposal transaction. Instead, ASU 2014-08 requires discontinued operations treatment for disposals of a component or group of components that represents a strategic shift that has or will have a major impact on an entity’s operations or financial results. ASU 2014-08 requires entities to reclassify assets and liabilities of a discontinued operation for all comparative periods presented in the statement of financial position. In addition, ASU 2014-08 requires that an entity disclose in its statement of cash flows, for all periods presented, either: (1) operating and investing cash flows or (2) depreciation and amortization, capital expenditures and significant operating and investing non-cash items related to the discontinued operation. ASU 2014-08 was effective prospectively for all disposals (except disposals classified as held for sale before the adoption date) or components initially classified as held for sale in periods beginning on or after December 15, 2014. The adoption of ASU 2014-08 did not have a material impact on the Company's condensed consolidated financial statements.

BUSINESS ACQUISITIONS (Tables)

3 Months Ended

Mar. 27, 2015

Business Combinations [Abstract]

Summary of preliminary allocation of the purchase consideration

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



Fair value of consideration transferred:
Cash, net of cash acquired	$	35,022
Fair value of equity awards assumed	1,671
Fair value of total consideration	$	36,693
Fair value of assets acquired and liabilities assumed:
Marketable securities	$	2,315
Other current assets	9,337
Property and equipment	2,251
Intangible assets:
Developed technology	13,200
Customer relationships	3,900
Goodwill	8,781
Current liabilities	(2,762		)
Other long-term liabilities	(329		)
	$	36,693

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



Fair value of consideration transferred:
Cash, net of cash acquired	$	10,147
Unpaid purchase consideration	1,500
Fair value of total consideration	$	11,647
Fair value of assets acquired and liabilities assumed:
Intangible assets:
In-process research and development	$	9,100
Developed technology	1,500
Goodwill	1,047
	$	11,647

Schedule of Components of Acquisition Related Costs

The components of acquisition-related costs included in the Company's results of operations for the three months ended March 27, 2015 and March 28, 2014 are as follows (in thousands):



	Three months ended
	March 27, 2015		March 28, 2014
Professional and services fees	$	107	$	1,057
Change of control agreements	—		249
	$	107	$	1,306

CASH EQUIVALENTS AND INVESTMENTS (Tables)

3 Months Ended

Mar. 27, 2015

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 27, 2015
	Amortized cost		Unrealized gains		Unrealized losses			Fair value
Cash equivalents	$	1,391	$	—	$	—		$	1,391

Marketable securities
Municipal obligations	$	1,523	$	1	$	—		$	1,524
U.S. government agency notes	4,154		1		—			4,155
Corporate debt securities	45,325		4		(40		)	45,289
Commercial paper	8,190		—		—			8,190
Certificates of deposit	6,550		—		—			6,550
	$	65,742	$	6	$	(40	)	$	65,708
Investments
Municipal obligations	$	2,197	$	3	$	(1	)	$	2,199
U.S. government agency notes	2,300		2		—			2,302
Corporate debt securities	24,051		14		(21		)	24,044
Certificates of deposit	500		—		—			500
	$	29,048	$	19	$	(22	)	$	29,045



	December 31, 2014
	Amortized cost		Unrealized gains		Unrealized losses			Fair value
Cash equivalents	$	11,653	$	—	$	—		$	11,653

Marketable securities
Municipal obligations	$	1,273	$	1	$	(1	)	$	1,273
U.S. government agency notes	4,016		—		—			4,016
Corporate debt securities	40,921		2		(59		)	40,864
Commercial paper	9,340		—		—			9,340
Certificates of deposit	8,950		—		—			8,950
	$	64,500	$	3	$	(60	)	$	64,443
Investments
Municipal obligations	$	2,702	$	1	$	(3	)	$	2,700
U.S. government agency notes	2,300		—		(1		)	2,299
Corporate debt securities	35,897		4		(86		)	35,815
Commercial paper	1,093		—		—			1,093
Certificates of deposit	500		—		—			500
	$	42,492	$	5	$	(90	)	$	42,407

Schedule of fair value of financial assets



			Fair value measurements at March 27, 2015 using:
	Total carrying value at March 27, 2015		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
Cash equivalents	$	1,391	$	1,391	$	—	$	—

Marketable securities
Municipal obligations	$	1,524	$	—	$	1,524	$	—
U.S. government agency notes	4,155		—		4,155		—
Corporate debt securities	45,289		—		45,289		—
Commercial paper	8,190		—		8,190		—
Certificates of deposit	6,550		—		6,550		—
	$	65,708	$	—	$	65,708	$	—
Investments
Municipal obligations	$	2,199	$	—	$	2,199	$	—
U.S. government agency notes	2,302		—		2,302		—
Corporate debt securities	24,044		—		24,044		—
Certificates of deposit	500		—		500		—
	$	29,045	$	—	$	29,045	$	—



			Fair value measurements at December 31, 2014 using:
	Total carrying value at December 31, 2014		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
Cash equivalents	$	11,653	$	11,653	$	—	$	—

Marketable securities
Municipal obligations	$	1,273	$	—	$	1,273	$	—
U.S. government agency notes	4,016		—		4,016		—
Corporate debt securities	40,864		—		40,864		—
Commercial paper	9,340		—		9,340		—
Certificates of deposit	8,950		—		8,950		—
	$	64,443	$	—	$	64,443	$	—
Investments
Municipal obligations	$	2,700	$	—	$	2,700	$	—
U.S. government agency notes	2,299		—		2,299		—
Corporate debt securities	35,815		—		35,815		—
Commercial paper	1,093		—		1,093		—
Certificates of deposit	500		—		500		—
	$	42,407	$	—	$	42,407	$	—

INTANGIBLE ASSETS AND GOODWILL (Tables)

3 Months Ended

Mar. 27, 2015

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of intangible assets

The Company's intangible assets at March 27, 2015 and December 31, 2014 consist of the following (dollars in thousands):



March 27, 2015	Weighted average amortization period (years)	Cost		Accumulated amortization		Net carrying value
In-process research and development	7.00	$	9,100	$	—	$	9,100
Intellectual property	5.00	999		999		—
Developed technology	6.24	23,780		6,300		17,480
Customer relationships	5.57	10,040		5,174		4,866
Internal use software	3.00	730		629		101
	6.05	$	44,649	$	13,102	$	31,547



December 31, 2014	Weighted average amortization period (years)	Cost		Accumulated amortization		Net carrying value
Intellectual property	5.00	$	999	$	999	$	—
Developed technology	6.18	22,280		5,193		17,087
Customer relationships	5.57	10,040		4,695		5,345
Internal use software	3.00	730		568		162
	5.75	$	34,049	$	11,455	$	22,594

Schedule of amortization expense related to intangible assets

Amortization expense for intangible assets for the three months ended March 27, 2015 and March 28, 2014 was as follows (in thousands):



	Three months ended				Statement of operations classification
	March 27, 2015		March 28, 2014		Statement of operations classification
Developed technology	$	1,107	$	570	Cost of revenue - product
Customer relationships	479		398		Sales and marketing
Internal use software	61		61		Cost of revenue - product
	$	1,647	$	1,029

Schedule of estimated future amortization expense for intangible assets

Estimated future amortization expense for the Company's intangible assets at March 27, 2015 is as follows (in thousands):



Years ending December 31,
Remainder of 2015	$	5,895
2016	7,001
2017	7,338
2018	4,589
2019	3,554
Thereafter	3,170
	$	31,547

Schedule of goodwill

The changes in the carrying value of the Company's goodwill in the three months ended March 27, 2015 and March 28, 2014 were as follows (in thousands):




Balance at January 1, 2015
Goodwill	$	42,369
Accumulated impairment losses	(3,106		)
	39,263
Acquisition of SDN Business	1,047
Balance at March 27, 2015	$	40,310

Balance at March 27, 2015
Goodwill	$	43,416
Accumulated impairment losses	(3,106		)
	$	40,310




Balance at January 1, 2014
Goodwill	$	35,485
Accumulated impairment losses	(3,106		)
	32,379
Acquisition of PT	8,193
Balance at March 28, 2014	$	40,572

Balance at March 28, 2014
Goodwill	$	43,678
Accumulated impairment losses	(3,106		)
	$	40,572

STOCK-BASED COMPENSATION PLANS (Tables)

3 Months Ended

Mar. 27, 2015

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 during the three months ended March 27, 2015 is as follows:



	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (in thousands)
Outstanding at January 1, 2015	7,521,432		$	16.47
Granted	279,930		$	16.28
Exercised	(143,320	)	$	11.19
Forfeited	(82,773	)	$	15.85
Expired	(43,013	)	$	24.12
Outstanding at March 27, 2015	7,532,256		$	16.53	6.79	$	317
Vested or expected to vest at March 27, 2015	7,083,866		$	16.52	6.68	$	310
Exercisable at March 27, 2015	4,175,385		$	16.88	5.47	$	263

Schedule of assumptions used to estimate the fair value of options at the date of grant using the Black-Scholes option pricing model

The grant date fair values of options to purchase common stock granted in the three months ended March 27, 2015 were estimated using the Black-Scholes valuation model with the following assumptions:



		Three months ended
		March 27, 2015
Risk-free interest rate		1.46% - 1.74%
Expected dividends		—
Weighted average volatility		54.3%
Expected life (years)		5.0 - 6.0

Schedule of stock options, additional information

Additional information regarding the Company's stock options for the three months ended March 27, 2015 is as follows:



	Three months ended
	March 27, 2015
Weighted average grant date fair value of stock options granted	$	8.25
Total intrinsic value of stock options exercised (in thousands)	$	902
Cash received from the exercise of stock options (in thousands)	$	1,687

Schedule of activity related to unvested restricted stock grants

The activity related to the Company's RSAs for the three months ended March 27, 2015 is as follows:



	Shares		Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2015	370,182		$	16.74
Granted	1,411,099		$	16.45
Vested	(287,176	)	$	17.76
Forfeited	(950	)	$	16.05
Unvested balance at March 27, 2015	1,493,155		$	16.28

Schedule of activity related to performance stock awards

The activity related to the Company's PSAs for the three months ended March 27, 2015 is as follows:



	Shares		Weighted Average Grant Date Fair Value
Unvested balance at January 1, 2015	34,235		$	13.60
Granted	—		$	—
Vested	(28,610	)	$	13.60
Forfeited	—		$	—
Unvested balance at March 27, 2015	5,625		$	13.60

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 27, 2015 and March 28, 2014 as follows (in thousands):



	Three months ended
	March 27, 2015		March 28, 2014
Product cost of revenue	$	74	$	79
Service cost of revenue	380		279
Research and development	1,358		1,313
Sales and marketing	1,016		1,249
General and administrative	1,992		2,854
	$	4,820	$	5,774

BUSINESS ACQUISITIONS - (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended				0 Months Ended			0 Months Ended	3 Months Ended								0 Months Ended
	Mar. 27, 2015	Mar. 28, 2014	Dec. 31, 2014	Dec. 31, 2013	Jan. 02, 2015 Treq Labs, Inc [Member]	Jan. 02, 2015 Treq Labs, Inc [Member]	Feb. 19, 2014 Treq Labs, Inc [Member]	Feb. 19, 2014 PT [Member]	Mar. 27, 2015 PT [Member]	Mar. 28, 2014 PT [Member]	Jan. 02, 2015 In Process Research and Development [Member] Treq Labs, Inc [Member]	Jan. 02, 2015 Developed Technology Rights [Member] Treq Labs, Inc [Member]	Feb. 19, 2014 Developed Technology Rights [Member] PT [Member]	Feb. 19, 2014 Customer relationships [Member] PT [Member]	Jan. 04, 2016 Scenario, Forecast [Member] Treq Labs, Inc [Member]	Jul. 02, 2015 Scenario, Forecast [Member] Treq Labs, Inc [Member]	Jan. 02, 2015 Earn-Out Agreement Revenue Level 1 [Member]	Jan. 02, 2015 Earn-Out Agreement Revenue Level 1 [Member] Treq Labs, Inc [Member]	Jan. 02, 2015 Earn-Out Agreement Revenue Level 2 [Member] Treq Labs, Inc [Member]
Acquisition Of Net
Cash consideration								$ 35,000,000
Cash consideration per share of the acquired entity (in dollars per share)								$ 3.75
Future consideration payment															750,000	750,000
Shares authorized in earn-out agreement					3.5													1.3	2.2
Duration of earn-out agreement																	3 years
Earn-out agreement aggregate revenue threshold																		60,000,000	150,000,000
Fair value of consideration transferred:
Cash, net of cash acquired	10,147,000	34,010,000			10,147,000			35,022,000
Business Combination, Consideration Transferred, Liabilities Incurred					1,500,000
Assumption of equity awards in connection with acquisition of Network Technologies, Inc.								1,671,000
Fair value of total consideration					11,647,000			36,693,000
Allocation of the purchase consideration:
Marketable securities							2,315,000
Other current assets								9,337,000
Property and equipment								2,251,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill											9,100,000	1,500,000	13,200,000	3,900,000
Goodwill	40,310,000	40,572,000	39,263,000	32,379,000				8,781,000				1,047,000
Current liabilities								(2,762,000)
Other long-term liabilities								(329,000)
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net						11,647,000		36,693,000
Professional Fees									107,000	1,057,000
Change of Control Agreements									0	249,000
Acquisition-related	$ 107,000	$ 1,306,000							$ 107,000	$ 1,306,000

BUSINESS ACQUISITIONS - Sale of MPS (Details) (Multi Protocol Server [Member], USD $) In Millions, unless otherwise specified	0 Months Ended	3 Months Ended
	Jun. 20, 2014	Mar. 27, 2015	Jun. 20, 2014
Multi Protocol Server [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Divestiture of business		$ 2.0
Inventory			(0.2)
Fixed assets			(0.1)
Deferred revenue	0.2
Goodwill			$ (1.9)

EARNINGS (LOSS) PER SHARE - (Details)	3 Months Ended
EARNINGS (LOSS) PER SHARE - (Details)	Mar. 27, 2015	Mar. 28, 2014
Reconciliation of weighted average shares outstanding from basic to diluted
Weighted average shares outstanding - basic	49,423,000	53,080,000
Potential dilutive common shares	0	0
Weighted average shares outstanding - diluted	49,423,000	53,080,000
Common stock and unvested shares of restricted stock not included because their effect would have been antidilutive (in shares)	9,400,000	9,100,000

CASH EQUIVALENTS AND INVESTMENTS - Narrative (Details) (USD $)	3 Months Ended
	Mar. 27, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities sold	$ 45,900,000
Available-for-sale securities, gross realized gains	46,000
Proceeds from maturities of available-for-sale securities	$ 41,700,000
Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Period considered to classify available-for-sale securities as investments	1 year
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Period considered to classify available-for-sale securities as investments	2 years

CASH EQUIVALENTS AND INVESTMENTS - Schedule of Activity for Short-Term Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 27, 2015	Dec. 31, 2014
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Cash equivalents, amortized cost	$ 1,391	$ 11,653
Cash equivalents, fair value	1,391	11,653
Marketable securities, amortized cost	65,742	64,500
Marketable securities, unrealized gains	6	3
Marketable securities, unrealized losses	(40)	(60)
Marketable securities, fair value	65,708	64,443
Investments, amortized cost	29,048	42,492
Investments, unrealized gains	19	5
Investments, unrealized losses	(22)	(90)
Investments, fair value	29,045	42,407
Municipal obligations [Member]
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Marketable securities, amortized cost	1,523	1,273
Marketable securities, unrealized gains	1	1
Marketable securities, unrealized losses	0	(1)
Marketable securities, fair value	1,524	1,273
Investments, amortized cost	2,197	2,702
Investments, unrealized gains	3	1
Investments, unrealized losses	(1)	(3)
Investments, fair value	2,199	2,700
U.S. government agency notes [Member]
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Marketable securities, amortized cost	4,154	4,016
Marketable securities, unrealized gains	1	0
Marketable securities, unrealized losses	0	0
Marketable securities, fair value	4,155	4,016
Investments, amortized cost	2,300	2,300
Investments, unrealized gains	2	0
Investments, unrealized losses	0	(1)
Investments, fair value	2,302	2,299
Corporate debt securities [Member]
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Marketable securities, amortized cost	45,325	40,921
Marketable securities, unrealized gains	4	2
Marketable securities, unrealized losses	(40)	(59)
Marketable securities, fair value	45,289	40,864
Investments, amortized cost	24,051	35,897
Investments, unrealized gains	14	4
Investments, unrealized losses	(21)	(86)
Investments, fair value	24,044	35,815
Commercial paper [Member]
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Marketable securities, amortized cost	8,190	9,340
Marketable securities, unrealized gains	0	0
Marketable securities, unrealized losses	0	0
Marketable securities, fair value	8,190	9,340
Investments, amortized cost		1,093
Investments, unrealized gains		0
Investments, unrealized losses		0
Investments, fair value		1,093
Certificates of deposit [Member]
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Marketable securities, amortized cost	6,550	8,950
Marketable securities, unrealized gains	0	0
Marketable securities, unrealized losses	0	0
Marketable securities, fair value	6,550	8,950
Investments, amortized cost	500	500
Investments, unrealized gains	0	0
Investments, unrealized losses	0	0
Investments, fair value	$ 500	$ 500

CASH EQUIVALENTS AND INVESTMENTS - Schedule of Short-Term Investments by Measurement (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 27, 2015	Dec. 31, 2014
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	$ 1,391	$ 11,653
Marketable securities, fair value	65,708	64,443
Investments, fair value	29,045	42,407
Total carrying value [Member]
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	1,391	11,653
Marketable securities, fair value	65,708	64,443
Investments, fair value	29,045	42,407
Quoted prices in active markets (Level 1) [Member]
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	1,391	11,653
Marketable securities, fair value	0	0
Investments, fair value	0	0
Significant other observable inputs (Level 2) [Member]
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	0	0
Marketable securities, fair value	65,708	64,443
Investments, fair value	29,045	42,407
Significant unobservable inputs (Level 3) [Member]
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
Municipal obligations [Member] \| Total carrying value [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	1,524	1,273
Investments, fair value	2,199	2,700
Municipal obligations [Member] \| Quoted prices in active markets (Level 1) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value	0	0
Municipal obligations [Member] \| Significant other observable inputs (Level 2) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	1,524	1,273
Investments, fair value	2,199	2,700
Municipal obligations [Member] \| Significant unobservable inputs (Level 3) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value	0	0
U.S. government agency notes [Member] \| Total carrying value [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	4,155	4,016
Investments, fair value	2,302	2,299
U.S. government agency notes [Member] \| Quoted prices in active markets (Level 1) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value	0	0
U.S. government agency notes [Member] \| Significant other observable inputs (Level 2) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	4,155	4,016
Investments, fair value	2,302	2,299
U.S. government agency notes [Member] \| Significant unobservable inputs (Level 3) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value	0	0
Corporate debt securities [Member] \| Total carrying value [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	45,289	40,864
Investments, fair value	24,044	35,815
Corporate debt securities [Member] \| Quoted prices in active markets (Level 1) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value	0	0
Corporate debt securities [Member] \| Significant other observable inputs (Level 2) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	45,289	40,864
Investments, fair value	24,044	35,815
Corporate debt securities [Member] \| Significant unobservable inputs (Level 3) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value	0	0
Commercial paper [Member] \| Total carrying value [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	8,190	9,340
Investments, fair value		1,093
Commercial paper [Member] \| Quoted prices in active markets (Level 1) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value		0
Commercial paper [Member] \| Significant other observable inputs (Level 2) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	8,190	9,340
Investments, fair value		1,093
Commercial paper [Member] \| Significant unobservable inputs (Level 3) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value		0
Certificates of deposit [Member] \| Total carrying value [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	6,550	8,950
Investments, fair value	500	500
Certificates of deposit [Member] \| Quoted prices in active markets (Level 1) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value	0	0
Certificates of deposit [Member] \| Significant other observable inputs (Level 2) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	6,550	8,950
Investments, fair value	500	500
Certificates of deposit [Member] \| Significant unobservable inputs (Level 3) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value	$ 0	$ 0

INVENTORY - (Details) (USD $) In Thousands, unless otherwise specified	Mar. 27, 2015	Dec. 31, 2014
Inventory Disclosure [Abstract]
On-hand final assemblies and finished goods inventories	$ 22,312	$ 19,285
Deferred cost of goods sold	2,835	2,829
Gross inventory	25,147	22,114
Less current portion	$ (25,147)	$ (22,114)

INTANGIBLE ASSETS AND GOODWILL - (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 27, 2015	Mar. 28, 2014	Dec. 31, 2014	Dec. 31, 2013
Intangible Assets And Goodwill
Goodwill, Gross	$ 43,416	$ 43,678	$ 42,369	$ 35,485
Goodwill, Impaired, Accumulated Impairment Loss	3,106	3,106	3,106	3,106
Weighted average amortization period (years)	6 years 0 months 18 days		5 years 9 months 0 days
Cost	44,649		34,049
Accumulated amortization	13,102		11,455
Net carrying value	31,547		22,594
Amortization expense	1,647	1,029
Estimated future amortization expense for intangible assets
Remainder of 2014	5,895
2015	7,001
2016	7,338
2017	4,589
2018	3,554
Thereafter	3,170
Total	31,547
In Process Research and Development [Member]
Intangible Assets And Goodwill
Weighted average amortization period (years)	7 years
Cost	9,100
Accumulated amortization	0
Net carrying value	9,100
Intellectual Property [Member]
Intangible Assets And Goodwill
Weighted average amortization period (years)	5 years		5 years
Cost	999		999
Accumulated amortization	999		999
Net carrying value	0		0
Developed technology [Member]
Intangible Assets And Goodwill
Weighted average amortization period (years)	6 years 2 months 28 days		6 years 2 months 6 days
Cost	23,780		22,280
Accumulated amortization	6,300		5,193
Net carrying value	17,480		17,087
Amortization expense	1,107	570
Customer relationships [Member]
Intangible Assets And Goodwill
Weighted average amortization period (years)	5 years 6 months 26 days		5 years 6 months 24 days
Cost	10,040		10,040
Accumulated amortization	5,174		4,695
Net carrying value	4,866		5,345
Amortization expense	479	398
Internal use software [Member]
Intangible Assets And Goodwill
Weighted average amortization period (years)	3 years		3 years
Cost	730		730
Accumulated amortization	629		568
Net carrying value	101		162
Amortization expense	$ 61	$ 61

INTANGIBLE ASSETS AND GOODWILL - (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 27, 2015	Mar. 28, 2014	Dec. 31, 2014	Dec. 31, 2013
Goodwill [Roll Forward]
Goodwill	$ 43,416	$ 43,678	$ 42,369	$ 35,485
Accumulated impairment losses	(3,106)	(3,106)	(3,106)	(3,106)
Goodwill, beginning of period	40,310	40,572	39,263	32,379
Acquisition of SDN Business	1,047	8,193
Goodwill, end of period	$ 40,310	$ 40,572	$ 39,263	$ 32,379

RESTRUCTURING ACCRUAL - (Details) (USD $)	3 Months Ended
RESTRUCTURING ACCRUAL - (Details) (USD $)	Mar. 27, 2015	Mar. 28, 2014	Dec. 31, 2014
RESTRUCTURING ACCRUAL
Accrued restructuring	$ 900,000		$ 1,900,000
Restructuring accrual activity
Restructuring	(339,000)	1,169,000
Proceeds from settlement with landlord	272,000
Reversal of severance costs	(67,000)
Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	1,682,000
Adjustments for changes in estimate	(67,000)
Cash payments	(1,290,000)
Balance at the end of the period	325,000
Facilities [Member]
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	3,652,000
Adjustments for changes in estimate	(272,000)
Cash payments	(1,135,000)
Balance at the end of the period	2,245,000
Employee Severance and Facilities [Member]
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	5,334,000
Adjustments for changes in estimate	(339,000)
Cash payments	(2,425,000)
Balance at the end of the period	$ 2,570,000

DEBT - (Details) (Revolving Credit Facility [Member], USD $)	0 Months Ended
	Jun. 27, 2014
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 40,000,000
Unused commitment fee percentage	0.15%
London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Interest rate	1.50%
Federal Funds Purchased [Member]
Line of Credit Facility [Line Items]
Interest rate	0.50%
Eurodollar [Member]
Line of Credit Facility [Line Items]
Interest rate	1.00%

COMMON STOCK REPURCHASES AND UNDERWRITTEN OFFERING (Details) (USD $)	0 Months Ended	3 Months Ended					3 Months Ended
	Mar. 20, 2014	Mar. 27, 2015	Mar. 28, 2014	Mar. 20, 2014	Jan. 02, 2014	Jul. 29, 2013 Common Stock [Member]	Mar. 27, 2015 Stock Buyback Program [Member]	Mar. 28, 2014 Stock Buyback Program [Member]
Class of Stock [Line Items]
Stock buyback program authorized amount						$ 100,000,000
Payments for repurchase of common stock	75,300,000	6,084,000	75,385,000				6,100,000	100,000
Stock repurchased and retired during period	4,300,000	400,000	7,700
Share Price		$ 20.55		$ 17.4410	$ 15.40
Remaining authorized repurchase amount		16,800,000		1,125,000
Stock issued during period	7,500,000
Over-allotment Option Period	30 days
Transaction Fees	$ 300,000

STOCK-BASED COMPENSATION PLANS - (Details) (USD $)	0 Months Ended	3 Months Ended				3 Months Ended												0 Months Ended	3 Months Ended							1 Months Ended
STOCK-BASED COMPENSATION PLANS - (Details) (USD $)	Jan. 22, 2014 executives	Mar. 27, 2015 executives	Mar. 28, 2014	Mar. 20, 2014	Jan. 02, 2014	Mar. 27, 2015 Product cost of revenue [Member]	Mar. 28, 2014 Product cost of revenue [Member]	Mar. 27, 2015 Service cost of revenue [Member]	Mar. 28, 2014 Service cost of revenue [Member]	Mar. 27, 2015 Research and development [Member]	Mar. 28, 2014 Research and development [Member]	Mar. 27, 2015 Sales and marketing [Member]	Mar. 28, 2014 Sales and marketing [Member]	Mar. 27, 2015 General and Administrative Expense [Member]	Mar. 28, 2014 General and Administrative Expense [Member]	Mar. 27, 2015 Minimum [Member]	Mar. 27, 2015 Maximum [Member]	Feb. 19, 2014 PT [Member]	Mar. 27, 2015 Stock options [Member] executives	Mar. 27, 2015 Stock Option and Cash Option [Member] executives	Mar. 27, 2015 Cash Only [Member] executives	Mar. 27, 2015 Restricted stock awards [Member]	Mar. 27, 2015 Restricted Stock Units (RSUs) [Member]	Mar. 27, 2015 Performance share awards [Member]	Mar. 27, 2015 Performance Share Units [Member]	Mar. 28, 2014 Employee Stock [Member]
Stock-based compensation
Share-based Compensation by Share-based Payment Award, Offering Period																										6 months
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent																										85.00%
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable																		$ 1,671,000
Number of executives	21	22																	16	5	1
Number of Executives Electing to Receive Cash Bonus	4
Share-based Compensation by Share-based Payment Award, Stock Percentage of Award	50.00%	50.00%
Share-based Compensation by Share-based Payment Award, Cash Percentage of Award	50.00%	50.00%
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Salary Base to Calculate Shares Granted	150.00%	150.00%
Share Price		$ 20.55		$ 17.4410	$ 15.40
Number of Executives Electing to Receive Stock Bonus	17
Business Acquisition, Share Price																		$ 3.75
Total fair value (in dollars)																						5,100,000
Stock-based compensation (in dollars)		4,820,000	5,774,000			74,000	79,000	380,000	279,000	1,358,000	1,313,000	1,016,000	1,249,000	1,992,000	2,854,000
Fair value of the assumed awards attributable to future stock-based compensation expense		44,700,000
Expected period for unrecognized expense		3 years
Stock-based compensation		4,820,000	5,774,000
Number of shares
Outstanding at the beginning of the period (in shares)																			7,521,432
Granted (in shares)	266,000																		279,930
Exercised (in shares)																			(143,320)
Forfeited (in shares)																			(82,773)
Expired (in shares)																			(43,013)
Outstanding at the end of the period (in shares)																			7,532,256
Vested or expected to vest at the end of the period (in shares)																			7,083,866
Exercisable at the end of the period (in shares)																			4,175,385
Weighted average exercise price
Outstanding at the beginning of the period (in dollars per share)																			$ 16.47
Granted (in dollars per share)																			$ 16.28
Exercised (in dollars per share)																			$ 11.19
Forfeited (in dollars per share)																			$ 15.85
Expired (in dollars per share)																			$ 24.12
Outstanding at the end of the period (in dollars per share)																			$ 16.53
Vested or expected to vest at the end of the period (in dollars per share)																			$ 16.52
Exercisable at the end of the period (in dollars per share)																			$ 16.88
Weighted average remaining contractual life (in years)
Outstanding at the end of the period																			6 years 9 months 15 days
Vested or expected to vest at the end of the period																			6 years 8 months 4 days
Exercisable at the end of the period																			5 years 5 months 20 days
Aggregate intrinsic value (in dollars)
Outstanding at the end of the period (in dollars)																			317,000
Vested or expected to vest at the end of the period (in dollars)																			310,000
Exercisable at the end of the period (in dollars)																			263,000
Range of assumptions used in estimating fair value of options
Risk-free interest rates, minimum																			1.46%
Risk-free interest rates, maximum																			1.74%
Expected dividends																			0.00%
Weighted average volatility																			54.30%
Expected life																5 years	6 years
Weighted average grant date fair value of stock options granted (in dollars per share)																			$ 8.25
Total intrinsic values of stock options exercised (in dollars)																			902,000
Cash received from the exercise of stock options (in dollars)		$ 1,687,000	$ 3,444,000																$ 1,687,000
Change in unvested restricted stock awards
Unvested balance at the beginning of the period (in shares)																						370,182	0	34,235	0
Granted (in shares)																						1,411,099	120,215	0	131,250
Vested (in shares)																						(287,176)	0	(28,610)	0
Forfeited (in shares)																						(950)	0	0	0
Unvested balance at the end of the period (in shares)																						1,493,155	120,215	5,625	131,250
Weighted average grant-date fair value
Unvested balance at the end of the period (in dollars per share)																						$ 16.74	$ 0.00	$ 13.60	$ 0.00
Granted (in dollars per share)																						$ 16.45	$ 16.05	$ 0.00	$ 14.68
Vested (in dollars per share)																						$ 17.76	$ 0.00	$ 13.60	$ 0.00
Forfeited (in dollars per share)																						$ 16.05	$ 0.00	$ 0.00	$ 0.00
Unvested balance at end of the period (in dollars per share)																						$ 16.28	$ 16.05	$ 13.60	$ 14.68

MAJOR CUSTOMERS - (Details)	3 Months Ended
MAJOR CUSTOMERS - (Details)	Mar. 27, 2015 customer	Dec. 31, 2014 customer
Revenue [Member] \| Less than [Member]
MAJOR CUSTOMERS
Threshold percentage	10.00%
Revenue [Member] \| Customer [Member] \| Verizon [Member]
MAJOR CUSTOMERS
Concentration risk, percentage	15.00%
Revenue [Member] \| Customer [Member] \| Softbank Corporation [Member]
MAJOR CUSTOMERS
Concentration risk, percentage	11.00%
Revenue [Member] \| Customer [Member] \| AT&T [Member]
MAJOR CUSTOMERS
Concentration risk, percentage	28.00%
Accounts receivable balance [Member]
MAJOR CUSTOMERS
Threshold percentage	10.00%
Accounts receivable balance [Member] \| Customer [Member]
MAJOR CUSTOMERS
Concentration risk, percentage	26.00%
Number of major customers	2	0

SUBSEQUENT EVENTS (Details) (USD $) In Millions, unless otherwise specified		0 Months Ended
	Mar. 27, 2015	Apr. 16, 2015 Subsequent Event [Member] employees	Apr. 21, 2015 Subsequent Event [Member]
Subsequent Event [Line Items]
Expected number of positions eliminated		150
Expected percentage of positions eliminated		12.50%
Expected cost			$ 5
Expected future payments in the three months ended June 26, 2015			4.5
Expected future payments during the three months ended September 25, 2015	$ 0.5

INCOME TAXES	3 Months Ended
INCOME TAXES	Mar. 27, 2015
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The Company's income tax provisions for the three months ended March 27, 2015 and March 28, 2014 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 27, 2015 and March 28, 2014 do not include any benefit for the Company's domestic losses, as the Company has concluded that a valuation allowance on any domestic benefit is required.

SUBSEQUENT EVENTS	3 Months Ended
SUBSEQUENT EVENTS	Mar. 27, 2015
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS As part of the Company's recently announced cost reduction review, on April 16, 2015, the Company initiated a restructuring plan that will reduce its workforce by approximately 150 positions, or approximately 12.5% of the Company's worldwide workforce. The Company expects to record approximately $5 million of restructuring expense for severance and related costs in the three months ending June 26, 2015. The Company expects that of this amount, $4.5 million will be paid in the three months ending June 26, 2015 and the remainder will be paid in the three months ending September 25, 2015.

BASIS OF PRESENTATION - Narrative (Details)	0 Months Ended	3 Months Ended
BASIS OF PRESENTATION - Narrative (Details)	Jan. 30, 2015	Mar. 27, 2015 segment
Accounting Policies [Abstract]
Stock split, conversion ratio	0.2
Number of reportable operating segments		1

ACCRUED EXPENSES - (Details) (USD $) In Thousands, unless otherwise specified	Mar. 27, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Employee compensation and related costs	$ 10,246	$ 20,042
Other	12,008	12,107
Total	$ 22,254	$ 32,149

GEOGRAPHIC INFORMATION - Summary of Revenue by Geographic Area as a Percentage of Total Revenue (Details) (Revenue [Member], Geographical area [Member])	3 Months Ended
	Mar. 27, 2015	Mar. 28, 2014
Revenue by geographic area and by customer
Percentage of total revenue	100.00%	100.00%
United States [Member]
Revenue by geographic area and by customer
Percentage of total revenue	62.00%	73.00%
Europe, Middle East and Africa [Member]
Revenue by geographic area and by customer
Percentage of total revenue	14.00%	13.00%
Japan [Member]
Revenue by geographic area and by customer
Percentage of total revenue	18.00%	8.00%
Other Asia Pacific [Member]
Revenue by geographic area and by customer
Percentage of total revenue	4.00%	3.00%
Other [Member]
Revenue by geographic area and by customer
Percentage of total revenue	2.00%	3.00%