Ribbon Communications Inc - Ordinary Shares 10-K 23 Feb 16 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2015	Feb. 16, 2016	Jun. 26, 2015
Document And Entity Information
Entity Registrant Name	SONUS NETWORKS INC
Entity Central Index Key	1,105,472
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		49,479,678
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 376,492,000

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 50,111	$ 41,157
Marketable securities	58,533	64,443
Accounts receivable, net	51,533	62,943
Inventory	23,111	22,114
Deferred income taxes	0	991
Other current assets	11,853	15,239
Total current assets	195,141	206,887
Property and equipment, net	13,620	17,845
Intangible assets, net	26,087	22,594
Goodwill	40,310	39,263
Investments	33,605	42,407
Deferred income taxes	1,879	1,043
Other assets	2,249	2,596
Total assets	312,891	332,635
Current liabilities:
Accounts payable	5,949	7,497
Accrued expenses	31,963	32,149
Current portion of deferred revenue	38,716	36,967
Current portion of long-term liabilities	821	794
Total current liabilities	77,449	77,407
Deferred revenue	7,374	8,009
Deferred income taxes	2,282	1,623
Other long-term liabilities	2,760	5,246
Total liabilities	$ 89,865	$ 92,285
Commitments and Contingencies (Note 21)
Stockholders' equity:
Preferred stock, $0.01 par value; 5,000,000 shares authorized, none issued and outstanding	$ 0	$ 0
Common stock, $0.001 par value; 120,000,000 shares authorized; 49,473,789 shares issued and outstanding at December 31, 2015; 49,357,033 shares issued and outstanding at December 31, 2014	49	49
Additional paid-in capital	1,240,803	1,226,226
Accumulated deficit	(1,023,242)	(991,347)
Accumulated other comprehensive income	5,416	5,422
Total stockholders' equity	223,026	240,350
Total liabilities and stockholders' equity	$ 312,891	$ 332,635

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	1,000,000	1,000,000
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	49,357,033	53,245,218
Common stock, shares outstanding	49,357,033	53,245,218

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue:
Product	$ 141,913	$ 182,455	$ 167,272
Service	107,121	113,871	109,461
Total revenue	249,034	296,326	276,733
Cost of revenue:
Product	50,460	60,284	59,235
Service	36,917	42,637	45,038
Total cost of revenue	87,377	102,921	104,273
Gross profit	161,657	193,405	172,460
Operating expenses:
Research and development	77,908	79,396	69,559
Sales and marketing	72,841	80,141	78,365
General and administrative	39,846	43,937	40,107
Acquisition-related	131	1,558	93
Total operating expenses	192,874	210,657	193,535
Loss from operations	(31,217)	(17,252)	(21,075)
Interest income, net	207	75	405
Other income, net	1,122	2,536	3
Loss before income taxes	(29,888)	(14,641)	(20,667)
Income tax provision	(2,007)	(2,214)	(1,452)
Net loss	$ (31,895)	$ (16,855)	$ (22,119)
Loss per share:
Basic (in dollars per share)	$ (0.64)	$ (0.34)	$ (0.40)
Diluted (in dollars per share)	$ (0.64)	$ (0.34)	$ (0.40)
Shares used to compute loss per share:
Basic (in shares)	49,560	50,245	55,686
Diluted (in shares)	49,560	50,245	55,686

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net loss	$ (31,895)	$ (16,855)	$ (22,119)
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	9	(426)	(672)
Unrealized loss on available-for-sale marketable securities	(15)	(142)	(45)
Less: Reclassification adjustment for gains included in net loss	0	(46)	0
Other comprehensive loss, net of tax	(6)	(614)	(717)
Comprehensive loss, net of tax	$ (31,901)	$ (17,469)	$ (22,836)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance at Dec. 31, 2012	$ 376,046	$ 56	$ 1,321,610	$ (952,373)	$ 6,753
Balance (in shares) at Dec. 31, 2012		56,192,659
Increase (Decrease) in Stockholders' Equity
Issuance of common stock in connection with employee stock purchase plan	2,210		2,210
Issuance of common stock in connection with employee stock purchase plan (in shares)		152,748
Exercise of stock options	2,669	$ 1	2,668
Exercise of stock options (in shares)		260,913
Vesting of restricted stock	1		1
Vesting of restricted stock (in shares)		181,643
Issuance of vested performance-based stock awards	1		1
Issuance of vested performance-based stock awards (in shares)		241,172
Shares of restricted stock returned to the Company under net share settlements to satisfy tax withholding obligations	(1,300)		(1,300)
Shares of restricted stock returned to the Company under net share settlements to satisfy tax withholding obligations (in shares)		(80,939)
Stock-based compensation expense	14,504		14,504
Repurchase of common stock	(59,674)	$ (4)	(59,670)
Repurchase of common stock, shares		(3,702,978)
Assumption of equity awards in connection with acquisition of Network Technologies, Inc.	0
Reclassification of liability to equity for cash bonuses converted to equity awards	631		631
Other comprehensive loss	(717)				(717)
Net loss	(22,119)			(22,119)
Balance at Dec. 31, 2013	312,252	$ 53	1,280,655	(974,492)	6,036
Balance (in shares) at Dec. 31, 2013		53,245,218
Increase (Decrease) in Stockholders' Equity
Issuance of common stock in connection with employee stock purchase plan	2,882		2,882
Issuance of common stock in connection with employee stock purchase plan (in shares)		180,502
Exercise of stock options	10,117	$ 1	$ 10,116
Exercise of stock options (in shares)		806,385
Vesting of restricted stock	0
Vesting of restricted stock (in shares)		428,674
Issuance of vested performance-based stock awards	0
Issuance of vested performance-based stock awards (in shares)		136,526
Shares of restricted stock returned to the Company under net share settlements to satisfy tax withholding obligations	(2,442)		$ (2,442)
Shares of restricted stock returned to the Company under net share settlements to satisfy tax withholding obligations (in shares)		(142,399)
Stock-based compensation expense	23,914		23,914
Repurchase of common stock	(93,224)	$ (5)	(93,219)
Repurchase of common stock, shares		(5,297,873)
Assumption of equity awards in connection with acquisition of Network Technologies, Inc.	1,671
Reclassification of liability to equity for cash bonuses converted to equity awards	2,649		2,649
Other comprehensive loss	(614)				(614)
Net loss	(16,855)			(16,855)
Balance at Dec. 31, 2014	$ 240,350	$ 49	1,226,226	(991,347)	5,422
Balance (in shares) at Dec. 31, 2014	53,245,218	49,357,033
Increase (Decrease) in Stockholders' Equity
Issuance of common stock in connection with employee stock purchase plan	$ 2,378		2,378
Issuance of common stock in connection with employee stock purchase plan (in shares)		233,659
Exercise of stock options	1,757		1,757
Exercise of stock options (in shares)		155,478
Vesting of restricted stock	1	$ 1
Vesting of restricted stock (in shares)		491,739
Issuance of vested performance-based stock awards	0
Issuance of vested performance-based stock awards (in shares)		45,901
Shares of restricted stock returned to the Company under net share settlements to satisfy tax withholding obligations	(2,344)		(2,344)
Shares of restricted stock returned to the Company under net share settlements to satisfy tax withholding obligations (in shares)		(167,634)
Stock-based compensation expense	21,699		21,699
Repurchase of common stock	(7,917)	$ (1)	(7,916)
Repurchase of common stock, shares		(642,387)
Assumption of equity awards in connection with acquisition of Network Technologies, Inc.	0
Reclassification of equity to liability for stock awards converted to cash bonuses	(997)		(997)
Other comprehensive loss	(6)				(6)
Net loss	(31,895)			(31,895)
Balance at Dec. 31, 2015	$ 223,026	$ 49	$ 1,240,803	$ (1,023,242)	$ 5,416
Balance (in shares) at Dec. 31, 2015	49,357,033	49,473,789

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net loss	$ (31,895)	$ (16,855)	$ (22,119)
Adjustments to reconcile net loss to cash flows provided by operating activities:
Depreciation and amortization of property and equipment	11,961	11,488	12,329
Amortization of intangible assets	7,107	4,597	4,546
Stock-based compensation	21,699	23,914	17,873
Impairment of intangible assets	0	0	600
Loss on disposal of property and equipment	112	292	54
Gain sale of domain name	(896)	0	0
Deferred income taxes	752	885	(553)
Changes in operating assets and liabilities:
Accounts receivable	11,369	4,771	3,536
Inventory	(1,001)	5,414	4,150
Other operating assets	4,915	5,077	6,200
Accounts payable	(1,257)	(3,759)	(555)
Accrued expenses and other long-term liabilities	(4,134)	1,657	4,768
Deferred revenue	1,137	(7,439)	3,278
Net cash provided by operating activities	19,869	30,042	34,107
Cash flows from investing activities:
Purchases of property and equipment	(7,792)	(9,541)	(6,949)
Business acquisition, net of cash acquired	(10,897)	(35,022)	0
Divestiture of business	0	2,000	0
Purchases of marketable securities	(54,772)	(112,800)	(182,491)
Sale/maturities of marketable securities	67,980	179,365	196,980
Proceeds from the sale of fixed assets	0	268	0
Proceeds from sale of domain name	896	0	0
Net cash provided by (used in) investing activities	(4,585)	24,270	7,540
Cash flows from financing activities:
Proceeds from sale of common stock in connection with employee stock purchase plan	2,378	2,882	1,888
Proceeds from exercise of stock options	1,757	10,117	2,669
Payment of tax withholding obligations related to net share settlements of restricted stock awards	(2,344)	(2,442)	(1,300)
Repurchase of common stock	(7,917)	(93,224)	(59,674)
Principal payments of capital lease obligations	(76)	(84)	(117)
Payment of debt	0	(2,380)	0
Net cash used in financing activities	(6,202)	(85,131)	(56,534)
Effect of exchange rate changes on cash and cash equivalents	(128)	(447)	(694)
Net increase (decrease) in cash and cash equivalents	8,954	(31,266)	(15,581)
Cash and cash equivalents, beginning of year	41,157	72,423	88,004
Cash and cash equivalents, end of period	50,111	41,157	72,423
Supplemental disclosure of cash flow information:
Interest paid	64	89	89
Income taxes paid	1,430	2,247	1,569
Income tax refunds received	357	94	164
Supplemental disclosure of non-cash investing activities:
Capital expenditures incurred, but not yet paid	375	411	1,446
Property and equipment acquired under capital lease	137	0	113
Business acquisition purchase consideration - assumed equity awards	0	1,671	0
Supplemental disclosure of non-cash financing activities:
Total fair value of restricted stock awards, restricted stock units, performance-based stock awards and performance-based stock units on date vested	$ 9,138	$ 8,425	$ 6,816

NATURE OF THE BUSINESS

NATURE OF THE BUSINESS	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
NATURE OF THE BUSINESS	NATURE OF THE 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 Internet Protocol ("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, network intelligence applications ("VellOS"), which is designed to network-wide security and other cloud network exchange services, media and signaling gateways and network analytics tools. Sonus 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 AND SUMMA

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES BASIS OF PRESENTATION The consolidated financial statements have been prepared in United States dollars, in accordance with accounting principles generally accepted in the United States ("GAAP"). For fiscal years 2015, 2014 and 2013, the Company reported its first, second and third quarters on a 4-4-5 basis, with the quarter ending on the Friday closest to the last day of each third month. In 2015, the Company's first quarter ended on March 27, 2015, the second quarter ended on June 26, 2015 and the third quarter ended on September 25, 2015. In 2014, the Company's first quarter ended on March 28, 2014, the second quarter ended on June 27, 2014 and the third quarter ended on September 26, 2014. In 2013, the Company's first quarter ended on March 29, 2013, the second quarter ended on June 28, 2013 and the third quarter ended on September 27, 2013. Effective January 1, 2016, the Company will report its first, second and third quarters on a month-end basis, such that the Company's first quarter will end on March 31, 2016, the second quarter will end on June 30, 2016 and the third quarter will end on September 30, 2016. The Company's fiscal year will continue to end on December 31. During the preparation of the Company's consolidated financial statements for the three month period ended June 26, 2015, the Company identified an error related to the historical foreign translation of depreciation expense on certain foreign fixed assets that resulted in a historical understatement of expense in prior fiscal years totaling $1.4 million on a cumulative basis. There was no tax effect on these expenses as the amounts were calculated in the appropriate foreign currencies. The Company does not believe this error is material to its previously issued historical consolidated financial statements for any of the periods impacted and, accordingly, has not adjusted its historical financial statements. The Company recorded the cumulative impact of the adjustment in the three months ended June 26, 2015. This adjustment resulted in a one-time $1.4 million overstatement of depreciation expense, which is included in the Company's consolidated statement of operations for the year ended December 31, 2015. The Company does not believe this adjustment is material to its consolidated financial statements for the periods presented. On January 29, 2015, the Company effected a one-for-five reverse stock split of its issued, outstanding and authorized common stock, which became effective on the NASDAQ Global Select Market as of the commencement of trading on January 30, 2015. All references herein to shares outstanding and share issuances have been adjusted to give effect to the aforementioned 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 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 consolidated financial statements for the periods subsequent to the PT Acquisition Date. SIGNIFICANT ACCOUNTING POLICIES Principles of Consolidation The accompanying consolidated financial statements include the accounts of Sonus and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. Use of Estimates and Judgments The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of 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, 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. Business Combinations The Company recognizes identifiable assets acquired and liabilities assumed at their acquisition date fair values. Goodwill as of the acquisition date is measured as the excess of consideration transferred over the net of the acquisition date fair values of the assets acquired and the liabilities assumed and represents the expected future economic benefits arising from other assets acquired in the business combination that are not individually identified and separately recognized. While the Company uses its best estimates and assumptions as part of the purchase price allocation process to accurately value assets acquired and liabilities assumed at the acquisition date, its estimates are inherently uncertain and subject to refinement. As a result, during the measurement period, which may be up to one year from the acquisition date, the Company records adjustments to the assets acquired and liabilities assumed with the corresponding offset to goodwill to the extent that it identifies adjustments to the preliminary purchase price allocation. Upon the conclusion of the measurement period or final determination of the values of assets acquired or liabilities assumed, whichever comes first, any subsequent adjustments are recorded to the consolidated statements of operations. Revenue Recognition The Company recognizes revenue from sales when persuasive evidence of an arrangement exists, delivery has occurred, the sale price is fixed or determinable, and collectability of the related receivable is probable. In instances where customer acceptance is required, revenue is deferred until the acceptance has been achieved. When fees for products or services are not fixed and determinable, the Company defers the recording of receivables, deferred revenue and revenue until such time as the fees become due or are collected. Revenue from maintenance and support services is recognized ratably over the service period. Maintenance revenue is deferred until the associated product is accepted by the customer and all other revenue recognition criteria have been met. Maintenance and support services include telephone support, return and repair support and unspecified rights to product upgrades and enhancements. Revenue from other professional services is typically recognized as the services are delivered if all other revenue recognition criteria have been met. The Company's products typically have both software and non-software components that function together to deliver the products' essential functionality. In addition, hardware sold generally cannot be used apart from the software. Therefore, the Company considers its principal products to be both software and hardware-related. Many of the Company's sales involve multiple element arrangements that include product, maintenance and various professional services. The Company recognizes revenue in accordance with the provisions of Accounting Standards Codification ("ASC") 605-25, Revenue Recognition - Multiple-Element Arrangements ("ASC 605-25") transactions that include both hardware and software components. The Company recognizes revenue from stand-alone software sales under the software revenue recognition guidance in ASC 985-605, Software - Revenue Recognition ("ASC 985-605"). The Company limits the amount of revenue recognized for delivered elements to the amount that is not contingent on the future delivery of products or services, future performance obligations, or subject to customer-specific return or refund privileges. For multiple-element arrangements that include both software-only products and non-software products, the Company allocates the total arrangement consideration to the software-only deliverables as a group and to the individual non-software deliverables based on their relative selling prices. If an undelivered element (such as maintenance and support services) relates to both the software-only and non-software deliverables, the Company bifurcates the consideration allocated to the undelivered element (such as maintenance and support services) into a non-software component and the software-only component using the relative selling price method. The consideration allocated to the non-software and software-only deliverables is recognized in accordance with the guidance as discussed in this note. Under ASC 985-605, revenue for any undelivered elements that are considered not essential to the functionality of the product and for which vendor-specific objective evidence of selling price (“VSOE”) has been established is deferred and recognized upon delivery utilizing the residual method. If the Company has undelivered product for which VSOE has not been established, it defers all revenue on the entire arrangement until VSOE is established or until such elements are delivered, provided that all other revenue recognition criteria are met. If the Company has undelivered services for which VSOE has not been established, the entire arrangement is recognized as revenue over the longest remaining service period from the point in time that all services have commenced and all products have been delivered, provided that all other revenue recognition criteria are met. For transactions that include multiple elements, arrangement consideration is allocated to each element based on the relative selling prices of all of the elements in the arrangement using the fair value hierarchy as required by ASC 605-25. The Company establishes VSOE based upon the price charged when the same element is sold separately or established by management having the relevant pricing authority. The Company has VSOE for its maintenance and support services and certain professional services. When VSOE exists it is used to determine the selling price of a deliverable. The Company has not been able to establish VSOE of any of its products and for certain of its services because the Company has not sold such products or services on a stand-alone basis, has not priced its products or services within a narrow range, or has limited sales history. When VSOE is not established, the Company attempts to establish the selling price of each element based on third-party evidence of selling price (“TPE”). The Company's solution typically differs from that of its peers as there are no similar or interchangeable competitor products or services. The Company's various product, service and maintenance offerings contain a significant level of unique features and functionality and therefore, comparable pricing of competitors' products and services with similar functionality cannot be obtained. Accordingly, the Company is not able to determine TPE for its products or services. When the Company is unable to establish selling price using VSOE or TPE, the Company uses estimated selling price (“ESP”) in its allocation of arrangement consideration for the relevant deliverables. The objective of ESP is to determine the price at which the Company would transact a sale if a product or service was sold on a stand-alone basis. The Company determines ESP for its products and certain services by considering multiple factors including, but not limited to, overall market conditions, including geographic or regional-specific market factors, profit objectives and historical pricing practices for such deliverables. The determination of ESP is a formal process within the Company that includes review and approval by the Company's management. Deferred revenue typically includes customer deposits and amounts associated with partial product shipments and maintenance or service contracts. Deferred revenue expected to be recognized as revenue more than one year subsequent to the balance sheet date is reported as a component of long-term liabilities in the consolidated balance sheets. The Company defers recognition of incremental direct costs, such as cost of goods, third-party installations and commissions, until recognition of the related revenue. Such costs are classified as current assets if the deferred revenue is initially classified as current and noncurrent assets if the related deferred revenue is initially classified as long-term. The Company excludes any taxes assessed by a governmental authority that are directly imposed on a revenue-producing transaction (i.e., sales, use and value added) from its revenue and costs. Reimbursement received for out-of-pocket expenses and shipping costs is recorded as revenue. The Company sells the majority of its products directly to its end customers. For products sold to resellers and distributors, the Company recognizes revenue on a sell-through basis. Financial Instruments The carrying amounts of Sonus' financial instruments, which include cash equivalents, investments, accounts receivable and accounts payable, approximate their fair values. All investments in marketable securities are classified as available-for-sale and are reported at fair value, with unrealized gains and losses excluded from earnings and reported, net of tax, in Accumulated other comprehensive loss, which is a component of stockholders' equity. Unrealized losses that are determined to be other-than-temporary, based on current and expected market conditions, are recognized in earnings. Declines in fair value determined to be credit-related are charged to earnings. The cost of marketable securities sold is determined by the specific identification method. Financial instruments with remaining maturities or that are due within one year from the balance sheet date are classified as current. Financial instruments with remaining maturities or that are payable more than one year from the balance sheet date are classified as noncurrent. Cash and Cash Equivalents Cash equivalents are stated at fair value, with unrealized gains and losses excluded from earnings and reported, net of tax, in Accumulated other comprehensive income (loss). Cash equivalents are liquid securities that have remaining maturities of three months or less at the date of purchase. Restricted Cash The Company classifies as restricted cash all cash pledged as collateral to secure long-term obligations and all cash whose use is otherwise limited by contractual provisions. Restricted cash is recorded within other assets on the consolidated balance sheet. Foreign Currency Translation For foreign subsidiaries where the functional currency is the local currency, assets and liabilities are translated into U.S. dollars at the current exchange rate on the balance sheet date. Revenue and expenses are translated at average rates of exchange prevailing during each period. Translation adjustments for these subsidiaries are included in Accumulated other comprehensive loss. For foreign subsidiaries where the functional currency is the U.S. dollar, monetary assets and liabilities are translated into U.S. dollars at the current exchange rate on the balance sheet date. Nonmonetary assets and liabilities are remeasured into U.S. dollars at historical exchange rates. Revenue and expense items are translated at average rates of exchange prevailing during each period. Realized and unrealized foreign currency gains and losses arising from transactions denominated in currencies other than the subsidiary's functional currency are reflected in earnings with the exception of intercompany transactions considered to be of a long-term investment nature. The components of foreign currency translation gains (losses), which are reported as a component of General and administrative expenses in the consolidated statements of operations, for the years ended December 31, 2015 , 2014 and 2013 are as follows (in thousands): Year ended December 31, 2015 2014 2013 Transaction gains (losses) $ 1,442 $ (420 ) $ (746 ) Remeasurement gains (losses) (1,860 ) 1,980 (164 ) $ (418 ) $ 1,560 $ (910 ) Inventory Inventory is recorded at the lower of cost or market value using the first-in, first-out convention. The Company reduces the carrying value of inventory for those items that are potentially excess, obsolete or slow-moving based on changes in customer demand, technology developments or other economic factors. Sonus writes down evaluation equipment at the time of shipment to its customers, as it is probable that the inventory value will not be realized. Deferred product costs represent deferred cost of revenue for product shipments to customers prior to satisfaction of Sonus' revenue recognition criteria. Such costs are classified as inventory if the related deferred revenue is initially classified as current. Deferred product costs are recorded in Other assets if the related deferred revenue is initially classified as long-term, and remain a component of noncurrent assets until such costs are recognized in the consolidated statement of operations. Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation. Expenditures for maintenance and repairs are charged to expense as incurred. Depreciation is computed using the straight-line method over the estimated useful lives of the related assets, which range from two to five years. Leasehold improvements are amortized over the lesser of the lease term or five years. When an asset is sold or retired, the cost and related accumulated depreciation or amortization are eliminated, and the resulting gain or loss, if any, is recognized in income (loss) from operations in the consolidated statement of operations. The Company reviews property and equipment for impairment in the same manner as intangible assets discussed below. Software development costs associated with internal use software are incurred in three stages of development: the preliminary project stage, the application development stage and the post-implementation stage. Costs incurred during the preliminary project and post-implementation stages are expensed as incurred. Certain qualifying costs incurred during the application development stage are capitalized as property and equipment. Internal use software is amortized on a straight-line basis over its estimated useful life of three years, beginning when the software is ready for its intended use. Intangible Assets and Goodwill Intangible assets are comprised of certain intangible assets arising from the August 24, 2012 acquisition of NET, comprised of developed technology, customer relationships and internal use software, which are amortized over their estimated useful lives of three to five years; the February 19, 2014 acquisition of PT, comprised of developed technology and customer relationships, which are amortized over their estimated useful lives of six to seven years; and the January 2, 2015 acquisition of the SDN Business, which are amortized over their estimated useful lives of seven years. Intangible assets are reviewed for impairment when events or changes in circumstances indicate that their carrying amounts may not be recoverable based upon the estimated undiscounted cash flows. Recoverability of intangible assets with estimated lives and other long-lived assets is measured by a comparison of the carrying amount of an asset or asset group to future net undiscounted cash flows expected to be generated by the asset or asset group. If these comparisons indicate that an asset is not recoverable, the Company will recognize an impairment loss for the amount by which the carrying value of the asset or asset group exceeds the related estimated fair value. Estimated fair value is based on either discounted future operating cash flows or appraised values, depending on the nature of the asset. In the second quarter of 2013, the Company recorded an impairment charge of $0.6 million to write down the carrying value of one of its intellectual property intangible assets to zero. See Note 9 for additional information regarding this expense. Goodwill is recorded when the consideration for an acquisition exceeds the fair value of net tangible and identifiable intangible assets acquired. Goodwill is not amortized, but instead is tested for impairment at least annually or if indicators of potential impairment exist by comparing the fair value of the Company's reporting unit to its carrying value. The Company adopted Accounting Standards Update ("ASU") 2011-08, Intangibles - Goodwill and Other (Topic 350): Testing Goodwill for Impairment ("ASU 2011-08") in fiscal year 2013. ASU 2011-08 permits an entity to first perform a qualitative assessment to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying value. This qualitative assessment included the review of macroeconomic conditions, industry and market considerations, cost factors, overall company financial performance and other related facts and circumstances that could indicate that a more detailed assessment would be required. If it is concluded that it is more likely than not that the fair value is less than the carrying value, then it is necessary to perform the currently prescribed two-step goodwill impairment test. Alternatively, if it is concluded that it is not more likely than not that the fair value exceeds carrying value, the currently prescribed two-step goodwill impairment test is not required. The Company's annual testing for impairment of goodwill is completed as of November 30 of each year. The Company operates as a single operating segment with one reporting unit and consequently evaluates goodwill for impairment based on an evaluation of the fair value of the Company as a whole. The Company performed its qualitative assessments for each of the years ended December 31, 2015, 2014 and 2013 and concluded each year that it was not more likely than not that the fair value of the Company's reporting unit was less than its carrying value. Other Assets Other assets are primarily comprised of the long-term portion of deferred cost of goods sold, prepaid expenses and deposits. Stock-Based Compensation The Company's stock-based compensation cost is measured at the grant date based on the fair value of the award and is recognized as expense over the requisite service period, which generally represents the vesting period, and includes an estimate of the awards that will be forfeited. The Company uses the Black-Scholes valuation model for estimating the fair value on the date of grant of stock options. The fair value of stock option awards is affected by the Company's stock price as well as valuation assumptions, including the volatility of Sonus' stock price, expected term of the option, risk-free interest rate and expected dividends. In 2015, the Company began to grant performance-based stock units ("PSUs") that include a market condition to certain of its executives. The Company uses a Monte Carlo simulation approach to model future stock price movements based upon the risk-free rate of return, the volatility of each entity, and the pair-wise covariance between each entity. These results are then used to calculate the grant date fair values of the PSUs. Research and Development Costs Research and development costs are expensed as incurred. Software Development Costs The costs for the development of new software and substantial enhancements to existing software are expensed as incurred until technological feasibility has been established, at which time any additional costs would be capitalized until the product is available for general release. The Company has determined that technological feasibility is established at the time a working model of the software is completed. The Company's process for developing software is essentially completed concurrently with the establishment of technological feasibility. Accordingly, no costs have been capitalized to date. Concentrations of Credit Risk and Single Source Suppliers The financial instruments that potentially subject Sonus to concentrations of credit risk are cash, cash equivalents, investments and accounts receivable. The Company's cash equivalents and investments were managed by two financial institutions at December 31, 2015 and two financial institutions at December 31, 2014 . Certain components and software licenses from third parties used in Sonus' products are procured from single sources of supply. The failure of a supplier, including a subcontractor, to deliver on schedule could delay or interrupt Sonus' delivery of products and thereby materially adversely affect Sonus' revenues and operating results. Sonus had three contract manufacturers at December 31, 2015 . Failure to manage the activities of these manufacturers or any disruption in these relationships could result in the disruption in the supply of its products and in delays in the fulfillment of the Company's customer orders. Advertising Costs Advertising costs are expensed as incurred and included as a component of Sales and marketing expense in the Company's consolidated statements of operations. Advertising expenses were $0.9 million for the year ended December 31, 2015 , $1.5 million for the year ended December 31, 2014 and $2.7 million for the year ended December 31, 2013 . 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. Loss Contingencies and Reserves Loss Contingencies. Sonus is subject to ongoing business risks arising in the ordinary course of business that affect the estimation process of the carrying value of assets, the recording of liabilities and the possibility of various loss contingencies. An estimated loss contingency is accrued when it is probable that a liability has been incurred or an asset has been impaired and the amount of loss can be reasonably estimated. Sonus regularly evaluates current information available to determine whether such amounts should be adjusted and records changes in estimates in the period they become known. Allowance for Doubtful Accounts. Sonus establishes billing terms at the time it negotiates purchase agreements with its customers. Sonus monitors its outstanding receivables for timely payments and potential collection issues. An allowance for doubtful accounts is estimated based on Sonus' assessment of the collectability of specific customer accounts. Accrual for Royalties. Sonus accrues for royalties for technology that it licenses from vendors based on established royalty rates and usage. In certain cases, Sonus has been contacted by third parties who claim that Sonus' products infringe on certain intellectual property of the third party. Sonus evaluates these claims and accrues amounts only when it is probable that the obligation has been incurred and the amounts are reasonably estimable. Reserve for Litigation and Legal Fees. Sonus is subject to various legal claims. Sonus reserves for legal contingencies and legal fees when it is probable that a loss has been incurred and the amounts are reasonably estimable. Accounting for Income Taxes Deferred tax assets and liabilities are recognized for the expected future consequences of events that have been reflected in the consolidated financial statements. Deferred tax assets and liabilities are determined based on the differences between the book and tax bases of assets and liabilities and operating loss carryforwards, using tax rates expected to be in effect for the years in which the differences are expected to reverse. Such differences arise primarily from stock-based compensation, depreciation, accruals and reserves, acquired intangible assets, deferred revenue, tax credits, net operating loss carryforwards and allowances for accounts receivable. Sonus records valuation allowances to reduce deferred income tax assets to the amount that is more likely than not to be realized. Sonus has not provided for U.S. income taxes on the undistributed earnings of non-U.S. subsidiaries, as the Company plans to permanently reinvest these amounts. Cumulative undistributed foreign earnings were approximately $28 million at December 31, 2015 and approximately $28 million at December 31, 2014 . Generally, the undistributed foreign earnings become subject to U.S. taxation upon the remittance of dividends and under certain other circumstances. The Company has been taxed on certain earnings of its non-U.S. subsidiaries. Previously taxed earnings were approximately $16 million at December 31, 2015 and $15 million at December 31, 2014. Thus, $12 million of the undistributed earnings at December 31, 2015 and $13 million at December 31, 2014 are subject to U.S. income taxes on undistributed earnings. The Company does not believe it is practicable to estimate with reasonable accuracy the hypothetical amount of the unrecognized deferred tax liability on its undistributed foreign earnings given the large number of tax jurisdictions involved and the many factors and assumptions required to estimate the amount of the U.S. federal income tax on the undistributed earnings after reduction for the available foreign tax credits. The Company determines whether it is more likely than not that a tax position will be sustained upon examination. If it is not more likely than not that a position will be sustained, no amount of the benefit attributable to the position is recognized. The tax benefit to be recognized of any tax position that meets the more likely than not recognition threshold is calculated as the largest amount that is more than 50% likely of being realized upon resolution of the contingency. The Company accounts for interest and penalties related to uncertain tax positions as part of its provision for income taxes. In September 2013, the U.S. Department of the Treasury and the Internal Revenue Service released final regulations relating to guidance on applying tax rules to amounts paid to acquire, produce or improve tangible personal property as well as rules for materials and supplies effective for tax years beginning on or after January 1, 2014. The Company has reviewed the regulations and has determined that its current method of accounting is appropriate under the regulations with no change required. Recent Accounting Pronouncements In November 2015, the Financial Accounting Standards Board ("FASB") issued ASU 2015-17, Balance Sheet Classification of Deferred Taxes ("ASU 2015-17"), which requires entities to present deferred tax assets and deferred tax liabilities as noncurrent in the consolidated balance sheet. Netting of deferred tax assets and deferred tax liabilities by tax jurisdiction is still required under ASU 2015-17. The ASU is effective for the Company for its annual reporting of the year ending December 31, 2018 and for interim period reporting beginning January 1, 2019, with early adoption permitted. Companies may adopt ASU 2015-17 either prospectively or retrospectively. The Company has elected to early-adopt ASU 2015-17 prospectively and accordingly, has reclassified its net current deferred tax asset totaling $1.0 million to its noncurrent net deferred tax asset as of December 31, 2015. No prior periods were retrospectively adjusted. In September 2015, the FASB issued ASU 2015-16, Simplifying the Accounting for Measurement-Period Adjustments ("ASU 2015-16"), which eliminates the requirement to restate prior periods to reflect adjustments made to provisional amounts recognized in a business combination. Under ASU 2015-16, an acquirer must recognize adj

BUSINESS ACQUISITONS

BUSINESS ACQUISITONS	12 Months Ended
	Dec. 31, 2015
Business Combinations [Abstract]
Business Acquisitions	BUSINESS ACQUISITIONS Treq Labs, Inc. On the Treq Asset Acquisition Date, the Company acquired from Treq the 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 on the Treq Asset Acquisition Date, and an additional consideration payment of $750,000 on each of July 2, 2015 and 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 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 of common stock ( 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 either initially as of the Treq Asset Acquisition Date or through December 31, 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. The Company finalized its valuation of the identifiable intangible assets in the second quarter of fiscal 2015. Based on the 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 deductible for tax purposes. A summary of the purchase consideration for the SDN Business at December 31, 2015 is as follows (in thousands): Fair value of consideration transferred: Cash, net of cash acquired $ 10,897 Unpaid purchase consideration 750 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 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 began to record amortization expense during the three months ended September 25, 2015 in connection with certain of the in-process research and development intangible assets related to a product that became generally available in the quarter and accordingly, reclassified the asset with a cost basis of $7.5 million to its developed technology intangible assets. The Company will begin to amortize the remaining in-process research and development intangible asset at the time that the related product becomes 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 9 ). The Company has not disclosed the amount of revenue or earnings of the SDN Business since the SDN Business Acquisition Date or pro forma financial information, as these amounts are not significant to the Company's consolidated financial statements. 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 consolidated financial statements starting on the PT Acquisition Date. The Company finalized the valuation of acquired assets, identifiable intangible assets, uncertain tax liabilities and certain accrued liabilities in the fourth quarter of 2014. Based on new information gathered about facts and circumstances that existed as of the PT Acquisition Date related to the valuation of certain acquired assets and assumed liabilities, the Company recorded adjustments which resulted in an increase to goodwill of $0.6 million , a decrease to other current assets of $0.4 million and an increase to other long-term liabilities of $0.2 million in the period subsequent to the PT Acquisition Date. 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 (see Note 15) 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 17,100 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 value the acquired developed technology and customer relationships 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. These intangible assets have a weighted average useful life of 6.8 years (see Note 9 ). The identifiable intangible assets recorded in connection with the PT acquisition are as follows (in thousands): Developed technology $ 13,200 Customer relationships 3,900 $ 17,100 The Company recognized revenue aggregating $14.6 million in the period from the PT Acquisition Date through December 31, 2014. The Company has not disclosed the amount of earnings of PT since the PT Acquisition Date or pro forma financial information, as these amounts are not significant to the Company's consolidated financial statements. 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 , 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 Company incurred $0.4 million of transaction costs, which are included as a component of General and administrative expenses. The results of operations of the MPS business are excluded from the Company's consolidated results for the period subsequent to the MPS Sale Date. 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, and expenses related to cash payments to certain former executives of the acquired businesses under their respective change of control agreements. The amount recorded in the year ended December 31, 2015 relates to professional fees in connection with the acquisition of the SDN Business. Of the amount recorded in the year ended December 31, 2014, $1.3 million relates to the acquisition of PT and $0.3 million relates to professional fees in connection with acquisition of the SDN Business. The amount recorded in the year ended December 31, 2013 relates to the acquisition of PT . The components of acquisition-related costs incurred in the years ended December 31, 2015, 2014 and 2013 are as follows (in thousands): Year ended December 31, 2015 2014 2013 Professional and services fees $ 131 $ 1,309 $ 93 Change of control agreements — 249 — $ 131 $ 1,558 $ 93

EARNINGS (LOSS) PER SHARE

EARNINGS (LOSS) PER SHARE	12 Months Ended
	Dec. 31, 2015
Earnings Per Share [Abstract]
EARNINGS (LOSS) PER SHARE	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): Year ended December 31, 2015 2014 2013 Weighted average shares outstanding—basic 49,560 50,245 55,686 Potential dilutive common shares — — — Weighted average shares outstanding—diluted 49,560 50,245 55,686 Options to purchase the Company's common stock, unvested shares of restricted stock, unvested performance-based stock awards for which the performance conditions have been satisfied but which still have service conditions and shares in connection with future purchases under the Company's Amended and Restated 2000 Employee Stock Purchase Plan, as amended (the "ESPP"), aggregating 8.2 million shares for the year ended December 31, 2015 have not been included in the computation of diluted loss per share because their effect would have been antidilutive. Options to purchase the Company's common stock, unvested shares of restricted stock and unvested performance-based stock awards for which the performance conditions have been satisfied aggregating 8.0 million shares for the year ended December 31, 2014 and 7.1 million shares for the year ended December 31, 2013 have not been included in the computation of diluted loss per share because their effect would have been antidilutive.

CASH EQUIVALENTS AND INVESTMENT

CASH EQUIVALENTS AND INVESTMENTS	12 Months Ended
	Dec. 31, 2015
Investments, All Other Investments [Abstract]
CASH EQUIVALENTS, MARKETABLE SECURITIES AND INVESTMENTS	CASH EQUIVALENTS AND INVESTMENTS The Company invests in debt and equity instruments, primarily U.S. government-backed, municipal and corporate obligations, which management believes to be high quality (investment grade) credit instruments. During the year ended December 31, 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, net, in the Company's consolidated statement of operations for that period. The Company did not realize any gross losses on these sales. The Company did not sell any of its available-for-sale securities during the years ended December 31, 2015 or 2013, and accordingly, no gains or losses were realized in either year. Investments with continuous unrealized losses for one year or greater at December 31, 2015 were nominal; however, since the Company 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 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 December 31, 2015 . The amortized cost, gross unrealized gains and losses and fair value of the Company's cash equivalents and investments at December 31, 2015 and 2014 were comprised of the following (in thousands): December 31, 2015 Amortized cost Unrealized gains Unrealized losses Fair value Cash equivalents $ 7,122 $ — $ — $ 7,122 Short-term investments Municipal obligations $ 3,910 $ — $ (1 ) $ 3,909 U.S. government agency notes 3,450 — (2 ) 3,448 Corporate debt securities 46,736 2 (56 ) 46,682 Commercial paper 3,994 — — 3,994 Certificates of deposit 500 — — 500 $ 58,590 $ 2 $ (59 ) $ 58,533 Investments Municipal obligations $ 2,165 $ — $ (4 ) $ 2,161 U.S. government agency notes 1,999 — (13 ) 1,986 Corporate debt securities 29,541 2 (85 ) 29,458 $ 33,705 $ 2 $ (102 ) $ 33,605 December 31, 2014 Amortized cost Unrealized gains Unrealized losses Fair value Cash equivalents $ 11,653 $ — $ — $ 11,653 Short-term investments 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 that are classified as Investments in the consolidated balance sheet mature after one year but within two years or less from the balance sheet date. Fair Value Hierarchy Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or a liability. The three-tier fair value hierarchy is based on the level of independent, objective evidence surrounding the inputs used to measure fair value. A financial instrument's categorization within the fair value hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The fair value hierarchy is as follows: Level 1. Level 1 applies to assets or liabilities for which there are quoted prices in active markets for identical assets or liabilities. Level 2. Level 2 applies to assets or liabilities for which there are inputs that are directly or indirectly observable in the marketplace, such as quoted prices for similar assets or liabilities in active markets or quoted prices for identical assets or liabilities in markets with insufficient volume or infrequent transactions (less active markets). Level 3. Level 3 applies to assets or liabilities for which there are unobservable inputs to the valuation methodology that are significant to the measurement of the fair value of the assets or liabilities. The following table shows the fair value of the Company's financial assets at December 31, 2015 and 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 consolidated balance sheets (in thousands): Fair value measurements at Total carrying Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) Cash equivalents $ 7,122 $ 7,122 $ — $ — Short-term investments Municipal obligations $ 3,909 $ — $ 3,909 $ — U.S. government agency notes 3,448 — 3,448 — Corporate debt securities 46,682 — 46,682 — Commercial paper 3,994 — 3,994 — Certificates of deposit 500 — 500 — $ 58,533 $ — $ 58,533 $ — Investments Municipal obligations $ 2,161 $ — $ 2,161 $ — U.S. government agency notes 1,986 — 1,986 — Corporate debt securities 29,458 — 29,458 — $ 33,605 $ — $ 33,605 $ — Fair value measurements at Total carrying Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) Cash equivalents $ 11,653 $ 11,653 $ — $ — Short-term investments 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 marketable securities and investments have been valued with the assistance of valuations provided by third-party pricing services, as derived from such services' pricing models. Inputs to the models may include, but are not limited to, reported trades, executable bid and asked prices, broker/dealer quotations, prices or yields of securities with similar characteristics, benchmark curves or information pertaining to the issuer, as well as industry and economic events. The pricing services may use a matrix approach, which considers information regarding securities with similar characteristics to determine the valuation for a security. The Company is ultimately responsible for the consolidated financial statements and underlying estimates. Accordingly, the Company assesses the reasonableness of the valuations provided by the third-party pricing services by reviewing actual trade data, broker/dealer quotes and other similar data, which are obtained from quoted market prices or other sources.

ACCOUNTS RECEIVABLE, NET

ACCOUNTS RECEIVABLE, NET	12 Months Ended
	Dec. 31, 2015
Receivables [Abstract]
ACCOUNTS RECEIVABLE, NET	ACCOUNTS RECEIVABLE, NET Accounts receivable, net, consist of the following (in thousands): December 31, 2015 2014 Accounts receivable, gross $ 51,543 $ 63,001 Allowance for doubtful accounts (10 ) (58 ) Accounts receivable, net $ 51,533 $ 62,943 The activity in the Company's allowance for doubtful accounts is as follows (in thousands): Year ended December 31, Balance at beginning of year Charges to expense Write-offs Balance at end of year 2015 $ 58 $ 17 $ (65 ) $ 10 2014 $ 157 $ 92 $ (191 ) $ 58 2013 $ — $ 415 $ (258 ) $ 157

INVENTORY

INVENTORY	12 Months Ended
	Dec. 31, 2015
Inventory Disclosure [Abstract]
INVENTORY	INVENTORY Inventory consists of the following (in thousands): December 31, 2015 2014 On-hand final assemblies and finished goods inventories $ 17,136 $ 19,285 Deferred cost of goods sold 5,975 2,829 $ 23,111 $ 22,114

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT	PROPERTY AND EQUIPMENT Property and equipment consists of the following (in thousands): December 31, Useful Life 2015 2014 Equipment 3 years $ 63,667 $ 65,703 Software 2-3 years 17,463 17,342 Furniture and fixtures 3-5 years 675 612 Leasehold improvements Shorter of the life of the lease or estimated useful life (1-5 years) 11,615 11,920 93,420 95,577 Less accumulated depreciation and amortization (79,800 ) (77,732 ) Property and equipment, net $ 13,620 $ 17,845 The Company recorded depreciation and amortization expense related to property and equipment of $12.0 million for the year ended December 31, 2015 , $11.5 million for the year ended December 31, 2014 and $12.3 million for the year ended December 31, 2013 . During each of the years ended December 31, 2015 and 2014, the Company disposed of certain property and equipment that was fully depreciated at the time of disposal, which resulted in reductions in both Cost and Accumulated depreciation. Property and equipment under capital leases included in the amounts above are as follows (in thousands): December 31, 2015 2014 Cost $ 137 $ 113 Less accumulated depreciation (9 ) (71 ) Property and equipment under capital leases, net $ 128 $ 42 The net book values of the Company's property and equipment by geographic area are as follows (in thousands): December 31, 2015 2014 United States $ 9,145 $ 12,652 Asia/Pacific 3,098 3,574 Europe 818 765 Other 559 854 $ 13,620 $ 17,845

INTANGIBLE ASSETS AND GOODWILL

INTANGIBLE ASSETS AND GOODWILL	12 Months Ended
	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
INTANGIBLE ASSETS AND GOODWILL	INTANGIBLE ASSETS AND GOODWILL The Company's intangible assets at December 31, 2015 and 2014 consist of the following (in thousands): December 31, 2015 Weighted average amortization period (years) Cost Accumulated amortization Net carrying value In-process research and development * $ 1,600 $ — $ 1,600 Developed technology 6.42 31,280 10,415 20,865 Customer relationships 5.57 10,030 6,408 3,622 Internal use software 3.00 730 730 — 6.19 $ 43,640 $ 17,553 $ 26,087 * An in-process research and development intangible asset has an indefinite life until the product is generally available, at which time such asset is reclassified to developed technology. 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 years ended December 31, 2015 , 2014 and 2013 was as follows (in thousands): Year ended December 31, Statement of operations classification 2015 2014 2013 Intellectual property $ — $ — $ 200 Research and development Developed technology 5,222 2,464 1,999 Cost of revenue - product Customer relationships 1,723 1,889 2,104 Sales and marketing Internal use software 162 244 243 Cost of revenue - product $ 7,107 $ 4,597 $ 4,546 The Company began to record amortization expense during the third quarter of 2015 in connection with certain of the in-process research and development intangible assets related to a product that became generally available in the quarter and accordingly, reclassified the asset with a cost basis of $7.5 million to its developed technology intangible assets and determined that the reclassified asset has an estimated useful life of 7 years. The Company will begin to amortize the remaining in-process research and development intangible asset at the time that the related product becomes generally available. In connection with the preparation of its financial statements for the second quarter of 2013, the Company reviewed its intangible assets and other long-lived assets for impairment indicators. The Company determined that a triggering event had occurred relative to one of its intellectual property intangible assets that had been acquired in 2010. During 2013, the Company discontinued its development of this technology and determined that there were no alternative uses of the technology within either its existing or future product lines. Additionally, based on the age and resulting obsolescence of such technology, the Company concluded that the fair value was nominal based on a discounted cash flow model. As a result, the Company recorded an impairment charge of $0.6 million to write down the carrying value of the asset to zero . This expense is included as a component of research and development expense in the Company's consolidated statements of operations for the year ended December 31, 2013. Estimated future amortization expense for the Company's intangible assets at December 31, 2015 is as follows (in thousands): Years ending December 31, 2016 $ 7,189 2017 7,281 2018 4,644 2019 3,611 2020 2,100 Thereafter 1,262 $ 26,087 Goodwill is recorded when the consideration for an acquisition exceeds the fair value of net tangible and identifiable intangible assets acquired. The changes in the carrying value of the Company's goodwill in the years ended December 31, 2015 and 2014 are as follows (in thousands): Year ended December 31, 2015 2014 Balance at January 1 Goodwill $ 42,369 $ 35,485 Accumulated impairment losses (3,106 ) (3,106 ) 39,263 32,379 Acquisition of SDN Business 1,047 — Acquisition of PT — 8,781 Sale of MPS business — (1,897 ) Balance at December 31 $ 40,310 $ 39,263 The components of the Company's goodwill balances at December 31, 2015 and 2014 are as follows: December 31, 2015 2014 Balance Goodwill $ 43,416 $ 42,369 Accumulated impairment losses (3,106 ) (3,106 ) $ 40,310 $ 39,263

ACCRUED EXPENSES

ACCRUED EXPENSES	12 Months Ended
	Dec. 31, 2015
Payables and Accruals [Abstract]
ACCRUED EXPENSES	ACCRUED EXPENSES Accrued expenses consist of the following (in thousands): December 31, 2015 2014 Employee compensation and related costs $ 22,180 $ 20,042 Other 9,783 12,107 $ 31,963 $ 32,149

RESTRUCTURING ACCRUAL

RESTRUCTURING ACCRUAL	12 Months Ended
	Dec. 31, 2015
Restructuring and Related Activities [Abstract]
RESTRUCTURING ACCRUAL	RESTRUCTURING ACCRUAL The Company has been committed to streamlining operations and reducing operating costs by closing and consolidating certain facilities and reducing its worldwide workforce. The Company recorded restructuring expense aggregating $2.1 million in the year ended December 31, 2015 , $5.6 million in the year ended December 31, 2014 and $5.4 million in the year ended December 31, 2013 . At December 31, 2015 , the Company's accrued restructuring was all classified as current. The portion of restructuring payments due more than one year from the balance sheet date at December 31, 2014 is included in Other long-term liabilities in the Company's consolidated balance sheet as of that date. At December 31, 2014 , the long-term portion of accrued restructuring was $1.9 million and represented future lease payments on restructured facilities. 2015 Restructuring Initiative To better align the Company's cost structure to its then-current revenue expectations, in April 2015, the Company announced a cost reduction review. As part of this review, on April 16, 2015, the Company initiated a restructuring plan to reduce its workforce by approximately 150 positions, or 12.5% of its worldwide workforce (the "2015 Restructuring Initiative"). In connection with the 2015 Restructuring Initiative, the Company recorded $3.8 million of restructuring expense for severance and related costs in the year ended December 31, 2015. A summary of the 2015 Restructuring Initiative accrual for the year ended December 31, 2015 is as follows (in thousands): Balance at Initiatives Cash Balance at Severance $ — $ 3,804 $ (3,055 ) $ 749 The Company expects that the remaining amount accrued under the 2015 Restructuring Initiative will be paid in the second quarter of 2016. 2012 Restructuring Initiative In August 2012, the Company announced that it had committed to a restructuring initiative to streamline operations and reduce operating costs by closing and consolidating certain facilities and reducing its worldwide workforce (the "2012 Restructure Initiative"). The Company regularly reviews its restructuring accruals against expected cash expenditures to determine if adjustments are required. As a result of such reviews, the Company recorded a net credit to restructuring expense aggregating $1.7 million in the year ended December 31, 2015. This amount is comprised of credits of $1.4 million in connection with a settlement with the landlord of the Company's Fremont, California facility to vacate the facility without penalty or future payments, $0.3 million in connection with a settlement with the landlord of the Company's Dulles, Virginia facility for an amount that was lower than had previously been accrued and $0.1 million in connection with changes in the amounts of severance ultimately paid to certain individuals. These credits were partially offset by $0.1 million of incremental expense related to vacating our Rochester, New York facility. A summary of the 2012 Restructuring Initiative accrual activity for the years ended December 31, 2015 and 2014 is as follows (in thousands): Year ended December 31, 2015 Balance at Adjustments for changes in estimate Cash Balance at Severance $ 1,682 $ (67 ) $ (1,615 ) $ — Facilities 3,652 (1,589 ) (2,063 ) — $ 5,334 $ (1,656 ) $ (3,678 ) $ — Year ended December 31, 2014 Balance at Initiatives Cash Balance at Severance $ 1,333 $ 3,615 $ (3,266 ) $ 1,682 Facilities 3,012 1,820 (1,180 ) 3,652 $ 4,345 5,435 $ (4,446 ) $ 5,334 Asset write-offs 190 $ 5,625

DEBT

DEBT	12 Months Ended
	Dec. 31, 2015
Debt Disclosure [Abstract]
DEBT	DEBT Credit Agreement The Company entered into a 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 on June 27, 2014, which agreement was amended by a First Amendment to Credit Agreement on June 26, 2015 (the "Credit Agreement"). The Credit Agreement provides for a revolving credit facility of up to $15 million with a maturity date of June 30, 2016 and provides that the Company may select the interest rates under the credit facility from among the following options: (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 Credit Agreement also provides that the Company 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. and Network Equipment Technologies, Inc. ("NET") (collectively 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 Agreement contains affirmative, negative and financial covenants customary for financings of this type. The negative covenants include limitations on liens, indebtedness, fundamental changes, dispositions, restricted payments, investments, transactions with affiliates, certain restrictive agreements and compliance with sanctions laws and regulations. The amount of cash and cash equivalents of the Loan Parties, subject to certain exclusions, cannot be less than an aggregate amount of $85 million at any time, and that total revenues of the Loan Parties cannot be less than an aggregate of $50 million as of the last day of the Loan Parties' fiscal quarter, computed on a fiscal quarterly basis beginning with the fiscal quarter ending September 25, 2015. The credit facility will become due on June 30, 2016, subject to acceleration upon certain specified events of default, including, without limitation, payment defaults, defaults in the performance of affirmative and negative covenants, the inaccuracy of representations or warranties, bankruptcy and insolvency-related defaults, defaults relating to judgments, and ERISA Event (as defined in the Credit Agreement), the failure to pay specified indebtedness and a change of control default. The Company did not have any amounts outstanding under the Credit Agreement at December 31, 2015 . Assumed Debt - NET Acquisition In December 2007 , NET issued $85.0 million of 3 3/4% Convertible Senior Notes due December 15, 2014 (the "2007 Notes") in a private placement, of which $10.5 million in principal remained outstanding at the NET Acquisition Date, and under which NET remained obligated after the acquisition. The 2007 Notes bore interest at a rate of 3 3/4 % per annum and matured on December 15, 2014 . On August 24, 2012, in connection with the consummation of the acquisition and as provided in the merger agreement, NET entered into a supplemental indenture for the 2007 Notes, which provided, among other things, that, in lieu of being convertible into shares of NET common stock, the 2007 Notes would be convertible into the kind and amount of merger consideration that would have been receivable upon the consummation of the acquisition by a holder of the number of shares of NET common stock issuable upon conversion of such 2007 Notes immediately preceding the effective time of the acquisition. The merger consideration was $1.35 in cash per share of NET common stock. The acquisition of NET by the Company constituted a "fundamental change" under the indenture governing the 2007 Notes, which triggered the distribution of a fundamental change notice to each holder of 2007 Notes, indicating that each such holder had the right to have all or a portion of its 2007 Notes purchased at a price in cash equal to 100% of the principal amount of the 2007 Notes (or portion thereof), plus any accrued and unpaid interest to, but excluding the fundamental change purchase date of October 12, 2012. In response to the fundamental change notice, $8.1 million in aggregate principal amount of 2007 Notes were tendered for purchase. The remaining $2.4 million in aggregate principal amount was paid in full on December 4, 2014 and accordingly, at December 31, 2014, NET's obligations under the 2007 Notes were discharged.

LONG-TERM LIABILITIES

LONG-TERM LIABILITIES	12 Months Ended
	Dec. 31, 2015
Other Liabilities [Abstract]
LONG-TERM LIABILITIES	LONG-TERM LIABILITIES Long-term liabilities consist of the following (in thousands): December 31, 2015 2014 Capital lease obligations $ 131 $ 70 Deferred rent 2,606 3,160 Restructuring 749 5,334 Other 844 1,125 4,330 9,689 Current portion * (1,570 ) (4,443 ) Long-term liabilities, net of current portion $ 2,760 $ 5,246 * Includes $0.7 million at December 31, 2015 and $3.4 million at December 31, 2014 of current accrued restructuring reported as a component of Accrued expenses in the consolidated balance sheets.

COMMON STOCK REPURCHASES AND UN

COMMON STOCK REPURCHASES AND UNDERWRITTEN OFFERING (Notes)	12 Months Ended
	Dec. 31, 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 buyback program does not have a fixed expiration date but may be suspended or discontinued at any time. The buyback program is being funded using the Company's working capital. During the year ended December 31, 2015 , the Company spent $7.9 million , including transaction fees, to repurchase and retire 0.6 million shares of its common stock under the buyback program. During the year ended December 31, 2014 , the Company spent $18.0 million , including transaction fees, to repurchase and retire 1.0 million shares of its common stock under the buyback program. At December 31, 2015 , the Company had $14.9 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

STOCK-BASED COMPENSATION PLANS	12 Months Ended
	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK-BASED COMPENSATION PLANS	STOCK-BASED COMPENSATION PLANS Reverse Stock Split On January 29, 2015, the Company effected a one -for- five reverse stock split of its issued, outstanding and authorized common stock, which became effective on the NASDAQ Global Select Market as of the commencement of trading on January 30, 2015. All references to shares outstanding and share issuances have been adjusted to give effect to the aforementioned reverse stock split. 2007 Stock Incentive Plan The Company's 2007 Stock Incentive Plan (the "2007 Plan") was approved at, and became effective on the date of, the Company's Annual Meeting of Stockholders on November 12, 2007. The 2007 Plan provides for the award of options to purchase the Company's common stock ("stock options"), stock appreciation rights ("SARs"), restricted stock awards ("RSAs"), restricted stock units ("RSUs"), performance-based stock awards ("PSAs"), 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. At its June 2015 Annual Meeting of Stockholders, the Company's stockholders approved amendments to the 2007 Plan to, among other things: • Increase the number of shares available for future grant by 1.4 million shares; and • Revise the rate at which restricted stock, restricted stock units, performance awards and other stock unit awards are counted against the shares of common stock available for issuance under the 2007 Plan from 1.57 shares for every share issued in connection with such award to 1.61 shares for every one share issued in connection with such award. Shares of common stock subject to awards that were granted under the two previous ratios of 1.57 and 1.5 will return to the 2007 Plan upon forfeiture of such awards at the respective previous ratios. At its December 2014 Special Meeting of Stockholders, the Company's stockholders approved amendments to the 2007 Plan to: • Increase the number of shares available for future grant by 2 million shares; • Increase the aggregate number of shares of the Company's common stock authorized for issuance under the 2007 Plan to include: (i) the number of shares of the Company's common stock that are reserved for future issuance under the Company's 2008 Stock Incentive Plan (the "2008 Plan") and the 2012 Amended Performance Technologies, Incorporated Omnibus Incentive Plan (the "2012 Plan," together with the 2008 Plan, the "Acquired Plans") immediately prior to the time this proposal was approved by stockholders (which number was 313,747 shares) and (ii) any shares of the Company's common stock subject to awards that are outstanding under the Acquired Plans immediately prior to the time this proposal was approved by stockholders (which number was 810,064 shares subject to outstanding options and 2,000 restricted shares, for an aggregate of 812,064 shares) that expire, are terminated, canceled, surrendered or forfeited, or are repurchased by the Company at their original issuance price pursuant to a contractual repurchase right under the Acquired Plans. Any shares granted under the 2008 Plan that are returned to the Company will be returned at the fungible rate of 1.25 . The Acquired Plans will no longer be used for new grants; • Increase the maximum number of shares that may be granted to any non-employee director under the 2007 Plan, from 20,000 shares to 40,000 shares per calendar year; and • Revise the rate at which restricted stock, restricted stock units, performance awards and other stock unit awards are counted against the shares of common stock available for issuance under the 2007 Plan from 1.5 shares for every one share issued in connection with such award to 1.57 shares for every one share issued in connection with such award. Shares of common stock subject to awards that were granted under the 1.5 times ratio will return to the 2007 Plan upon forfeiture of such awards at the previous ratio of 1.5 . At its June 2013 annual meeting of stockholders, the Company's stockholders approved an amendment to the 2007 Plan, which increased the number of shares available for future grant by 4.2 million shares. At December 31, 2015 , there were 2.6 million shares available for future issuance under the 2007 Plan. Under the fungible share pool formula, the number of total shares available for future awards under the 2007 Plan would be reduced by the fungible share pool multiple of 1.61 . Accordingly, the total number of shares awarded in the future under the 2007 Plan could be less than the number of shares currently available for issuance. 2008 Stock Incentive Plan In connection with the acquisition of NET, the Company assumed NET's 2008 Equity Incentive Plan (the "NET 2008 Plan"), which provides for the award of stock options, SARs, restricted stock, performance-based awards and RSUs), and the number of shares available for grant under the 2008 Plan were converted to like Sonus equity awards (the "converted awards") using a conversion factor of 0.75 , which was calculated based on the acquisition consideration of $1.35 per share of NET common stock divided by the average of the closing price of Sonus common stock for the ten consecutive days ending with the third trading day that preceded the closing date. This conversion factor was also used to convert the exercise prices of NET stock options to Sonus stock option exercise prices. The converted awards will vest under the same schedules as the respective NET stock options and NET RSUs. The fair values of the NET stock options assumed were estimated using a Black-Scholes option pricing model. The Company recorded $0.9 million as additional purchase consideration for the fair value of the assumed equity awards. The fair value of the assumed awards attributable to future stock-based compensation expense totaled $0.4 million , which was recorded over a weighted average period of approximately eight months. In December 2012, the Company's Board of Directors approved the re-naming of the NET 2008 Plan to the 2008 Stock Incentive Plan (the "2008 Plan"). At December 31, 2015, there were no shares available for future issuance under the 2008 Plan. Under the fungible pool formula, the number of total shares available for future awards under the 2008 Plan would be reduced by the fungible share pool multiple of 1.25 for each share of common stock included in an award other than a stock option or SAR award. At its December 2014 special meeting of stockholders, the Company's stockholders approved moving all shares available for grant under the 2008 Plan to the 2007 Plan and also voted that any outstanding awards under the 2008 Plan that in the future expired, terminated, canceled, surrendered or forfeited, or are repurchased by the Company at their original issuance price pursuant to a contractual repurchase right under the 2008 Plan will be returned to the 2007 Plan. 2012 Stock Incentive Plan In connection with the acquisition of PT, the Company assumed PT's 2012 Amended Performance Technologies, Incorporated Omnibus Incentive Plan, which provides for the award of stock options, SARs, restricted stock, performance-based awards and RSUs to former employees of PT who subsequently became employees of Sonus and Sonus employees hired subsequent to the PT Acquisition Date. The Company also assumed all of the outstanding options to purchase common stock under the Performance Technologies, Incorporated 2003 Omnibus Incentive Plan (the "2003 Plan") and the Performance Technologies, Incorporated 2001 Stock Option Plan (the "2001 Plan"); however, no future equity awards may be granted under either the PT 2003 Plan or the PT 2001 Plan. The options to purchase PT common stock under the 2012 Plan, the 2003 Plan and the 2001 Plan were converted into options to purchase Sonus common stock (the "converted awards"), and the shares of PT common stock available for future grant under the 2012 Plan were converted into shares of Sonus common stock available for future grant, using a conversion factor of 1.23 , which was calculated based on the acquisition consideration of $3.75 per share of PT's common stock divided by the average of the closing price of Sonus' common stock for the ten consecutive days ending with the third trading day that preceded the closing date. This conversion factor was also used to convert the exercise prices of PT stock options to Sonus stock option exercise prices. The converted awards will vest under the same schedules as the respective PT stock options. The fair values of the PT stock options assumed were estimated using a Black-Scholes option pricing model. The Company recorded $1.7 million as additional purchase consideration for the fair value of the assumed equity awards. The fair value of the assumed awards attributable to future stock-based compensation expense totaled $0.9 million , which is being recorded over a weighted average period of approximately one year. At its December 2014 special meeting of stockholders, the Company's stockholders approved moving all shares available for grant under the 2012 Plan to the 2007 Plan and also voted that any outstanding awards under the 2008 Plan that in the future expired, terminated, canceled, surrendered or forfeited, or are repurchased by the Company at their original issuance price pursuant to a contractual repurchase right under the 2012 Plan will be returned to the 2007 Plan. 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 were 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. Under this program, the amount of the 2015 Bonus, if any, for each executive would 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 would be granted to those executives who elected to receive their 2015 Bonus entirely in the form of shares of common stock would 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 would be granted to those executives who elected to receive one-half of their 2015 Bonus in the form of shares of common stock would 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 to 50% of their respective 2015 Bonus earned. Under this program, the 2015 Bonus, if any, would 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 would 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. The Company determined that the grant date criteria for the 2015 Bonus Shares was met on July 2, 2015, and accordingly, recorded stock-based compensation expense based on the grant date fair value of $6.79 per share. Subsequent to that date, in September 2015, the Compensation Committee considered the impact on employee retention and incentive compensation caused by the drop in the price of the Company's common stock since January 2, 2015, and indicated its intent to pay all such executives their 2015 Bonus, if any is earned, in cash. As a result, at September 25, 2015, the Company reclassified the stock-based compensation expense recorded through that date in connection with the 2015 Bonus Shares aggregating $1.0 million from Additional paid-in capital to Accrued expenses. In addition, the Company recorded incremental bonus expense of $1.3 million related to the estimated 2015 Bonus payment, which the Company expects to pay in March 2016. The Company did not record any additional stock-based compensation expense in subsequent periods in connection with the 2015 Bonus Shares, but instead recorded bonus expense through December 31, 2015. In March 2015, the Company granted an aggregate of 131,250 PSUs with both market and service conditions to eight of its executives. 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 that 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. In connection with the separation of one executive from the Company during the fourth quarter of 2015 and in accordance with his employment agreement with the Company, the Company accelerated the vesting of certain unvested stock options and RSAs. In connection with the separation of two executives from the Company during the second quarter of 2015 and in accordance with their respective employment agreements with the Company, the Company accelerated the vesting of certain unvested stock options, RSAs and PSUs. In June 2014, the Company modified the stock options outstanding as of that date that had been granted to its non-employee members of the Board of Directors (the "Board Members") to extend the exercise period to the lesser of three years from the date that a Board Member stepped down from his or her position on the Board of Directors or the remaining contractual life of the respective stock options. In connection with this modification, the Company recorded $0.7 million of incremental stock-based compensation expense in 2014, and this expense is included as a component of General and administrative expense in the Company's consolidated statement of operations for the year ended December 31, 2014. On January 2, 2014, Raymond P. Dolan, the Company's President and Chief Executive Officer ("Mr. Dolan") elected to accept shares of restricted stock in lieu of base salary for the period from January 1, 2014 through December 31, 2014. Accordingly, the Company granted Mr. Dolan restricted stock (the "2014 Dolan Salary Shares") on January 2, 2014, with the number granted calculated by dividing an amount equal to 1.5 times Mr. Dolan's base salary for the period from January 1, 2014 through December 31, 2014 by the closing price of the Company's common stock on the date of grant. The 2014 Dolan Salary Shares vested on December 31, 2014. Effective September 16, 2014, Mr. Dolan's annual base salary was increased from $500,000 to $600,000 . For the remainder of 2014, such increase was prorated and paid in cash and was not subject to any stock-for-cash election. The Company recorded stock-based compensation expense related to the 2014 Dolan Salary Shares ratably for the period of January 1, 2014 through December 31, 2014. In January 2014, 21 of the Company's executives 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"). Each executive could also elect not to participate in this program and to earn his or her 2014 Bonus in the form of cash. The amount of the 2014 Bonus was determined by the Compensation Committee on February 19, 2015. The number of 2014 Bonus Shares that was granted to those executives who elected to receive their 2014 Bonus entirely in the form of shares of common stock was calculated by dividing an amount equal to 1.5 times each executive's 2014 Bonus earned by the closing price of the Company's common stock on January 2, 2014. The number of 2014 Bonus Shares that was granted to those executives who elected to receive one-half of their 2014 Bonus in the form of shares of common stock was calculated by dividing an amount equal to 1.5 times one-half of each executive's 2014 Bonus earned by the closing price of the Company's common stock on January 2, 2014, with the cash portion equal to 50% of their respective 2014 Bonus earned. The 2014 Bonus Shares were granted on February 20, 2015 and vested immediately. Each executive who received the 2014 Bonus Shares was obligated to hold such shares for at least one year, until February 20, 2016. Of the eligible executives, 17 elected to receive their entire 2014 Bonus in shares of common stock and 4 elected to receive 50% of their 2014 Bonus in shares of common stock and 50% in cash. The Company determined that the grant date criteria for accounting purposes for the 2014 Bonus Shares was met on July 9, 2014, and accordingly, has determined that the grant date fair value of the 2014 Bonus Shares is $19.25 per share, the closing price of the Company's common stock on that date, as adjusted to reflect the reverse stock split of the Company's common stock. The Company recorded expense through the grant date of February 20, 2015. In March 2013, 21 executives of the Company elected to receive their fiscal 2013 bonuses (collectively, the "2013 Bonus"), if any were earned, in the form of shares of the Company's common stock (collectively, the "2013 Bonus Shares"). The 2013 Bonus Shares vested immediately, on February 18, 2014, with the number of shares granted calculated by dividing amounts equal to 1.5 times the respective 2013 Bonus amounts earned, as determined by the Compensation Committee, by the closing price of the Company's common stock on the date of grant. The Company recorded stock-based compensation expense for the 2013 Bonus Shares from January 1, 2013 through the grant date of February 18, 2014. In February 2013, the Compensation Committee determined that eight executives of the Company, excluding Mr. Dolan, would receive their bonuses with respect to 2012 in the form of restricted shares of the Company's common stock equal to 100% of their respective target bonus amounts for 2012 (collectively, the "Executive Bonus Shares"). The number of shares granted to each executive was calculated by dividing his/her target bonus amount by the closing price of the Company's common stock on February 15, 2013, the date of grant. The Executive Bonus Shares vested 50% on August 15, 2013 and the remaining 50% vested on February 15, 2014. The Company accrued for the cash payment of bonuses at the expected company-wide cash payout percentage amount at December 31, 2012, which amounts were less than the target bonus amounts for each individual. The Company recorded the expense related to the Executive Bonus Shares as stock-based compensation expense through February 15, 2014. In February 2013, the Compensation Committee took certain actions regarding performance-based stock awards that had been awarded in previous years but for which the grant date criteria had not been met as of December 31, 2012. These actions included determining that a certain number of these performance-based shares would vest as of February 15, 2013 (the “Vested Performance Shares”) and subjecting the remaining performance-based shares (the “Future Performance Shares”) to further performance and service conditions. On July 26, 2013, the Compensation Committee determined that the performance conditions related to the Future Performance Shares had been satisfied based on the Company's performance for the six months ended June 28, 2013 and, accordingly, all of the Future Performance Shares vested contingent upon continued employment with the Company on the vesting dates. The Company recorded the unamortized expense related to the Future Performance Shares based on the vesting dates of the respective awards. The Future Performance Shares were fully vested at December 31, 2015. In August 2012, Mr. Dolan elected to receive his year 2012 target bonus, if earned, in the form of restricted shares (the “Dolan Bonus Shares”). On August 10, 2012, the Company granted Mr. Dolan shares of restricted stock which equaled Mr. Dolan's potential 2012 bonus at the maximum level of achievement ( 150% of Mr. Dolan's annual base salary), divided by the closing price of the Company's common stock on the date of grant. During 2012, the Company recorded stock-based compensation expense for the Dolan Bonus Shares commensurate with the expected achievement level represented by the Company's accrual for its company-wide incentive bonus program, as the performance metrics for each were consistent. 50% of the Dolan Bonus Shares vested on August 15, 2013 and the remaining 50% vested on February 15, 2014. The Company recorded the unamortized expense related to the Dolan Bonus Shares through February 15, 2014. In connection with the separation of three executives from the Company during 2015 and in accordance with their respective employment agreements with the Company, the Company accelerated the vesting of certain unvested stock options, RSAs and PSUs. These RSAs and PSUs are reported as "Vested" in the respective tables below. Stock Options Options are issued to purchase shares of common stock of the Company at prices that are equal to the fair market value of the shares on the date the option is granted. Options generally vest over a period of four years , with 25% of the shares subject to the option vesting on the first anniversary of the grant date and the remaining 75% vesting in equal monthly increments thereafter through the fourth anniversary of the grant date. Options granted under the 2007 Plan generally expire ten years from the date of grant. Options granted under the 2008 Plan generally expire seven years from the date of grant. Options granted under the 2012 Plan generally expire five years from the date of grant. The grant date fair value of options, adjusted for estimated forfeitures, is recognized as expense on a straight-line basis over the requisite service period, which is generally the vesting period. Forfeitures are estimated based on historical experience. The activity related to the Company's outstanding stock options during the year ended December 31, 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 348,380 $ 14.48 Exercised (155,478 ) $ 10.77 Forfeited (588,693 ) $ 16.37 Expired (773,433 ) $ 20.75 Outstanding at December 31, 2015 6,352,208 $ 15.99 6.14 $ 204 Vested or expected to vest at December 31, 2015 6,165,698 $ 15.99 6.08 $ 200 Exercisable at December 31, 2015 4,407,865 $ 15.97 5.32 $ 155 The grant date fair values of options to purchase common stock granted in the years ended December 31, 2015 , 2014 and 2013 were estimated using the Black-Scholes valuation model with the following assumptions: Year ended December 31, 2015 2014 2013 Risk-free interest rate 1.46%-1.75% 1.53%-2.70% 0.82%-1.71% Expected dividends — — — Weighted average volatility 54.3% 60.8% 63.2% Expected life (years) 5.0-6.0 4.5-6.0 4.5-6.0 The risk-free interest rate used is the average U.S. Treasury Constant Maturities Rate for the expected life of the award. The expected dividend yield of zero is based on the fact that the Company has never paid dividends and has no present intention to pay cash dividends. The expected life for stock options is based on a combination of the Company's historical option patterns and expectations of future employee actions. The weighted average grant-date fair values of options granted during the year were $7.30 for the year ended December 31, 2015 , $8.32 for the year ended December 31, 2014 and $7.71 for the year ended December 31, 2013 . The total intrinsic values of options exercised during the year were $0.9 million for the year ended December 31, 2015 , $5.1 million for the year ended December 31, 2014 and $1.3 million for the year ended December 31, 2013 . The Company received cash from option exercises of $1.8 million in the year ended December 31, 2015 , $10.1 million in the year ended December 31, 2014 and $2.7 million in the year ended December 31, 2013 . Restricted Stock Grants - Restricted Stock Awards and Restricted Stock Units The Company's outstanding restricted stock grants consist of both RSAs and RSUs. Holders of unvested RSAs have voting rights and rights to receive dividends, if declared; however, these rights are forfeited if the underlying unvested RSA shares are forfeited. Holders of unvested RSUs do not have such voting and dividend rights. Both RSAs and RSUs generally vest 25% on the first anniversary of the grant date, with the remaining 75% vesting in equal increments semi-annually thereafter. The grant date fair value of restricted stock grants, adjusted for estimated forfeitures, is recognized as expense on a straight-line basis over the requisite service period. The fair value of restricted stock grants is determined based on the market value of the Company's shares on the date of grant. The activity related to the Company's RSAs for the year ended December 31, 2015 is as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2015 370,182 $ 16.74 Granted 1,943,051 $ 14.02 Vested (491,739 ) $ 17.30 Forfeited (308,711 ) $ 14.71 Unvested balance at December 31, 2015 1,512,783 $ 13.48 The activity related to the Company's RSUs for the year ended December 31, 2015 is as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2015 — $ — Granted 120,215 $ 16.05 Vested — $ — Forfeited (24,854 ) $ 16.05 Unvested balance at December 31, 2015 95,361 $ 16.05 The total fair value of restricted stock grant shares vested was $8.5 million in the year ended December 31, 2015 , $6.7 million in the year ended December 31, 2014 and $2.4 million in the year ended December 31, 2013 . Performance-Based Stock Grants - Performance-Based Stock Awards and Performance-Based Stock Units The Company's outstanding performance-based stock grants consist of both PSAs and PSUs. Similar to RSAs, holders of unvested PSAs have voting rights and rights to dividends, if declared; however, these rights are forfeited if the underlying unvested PSA shares are forfeited. Holders of unvested PSUs do not have such voting and dividend rights. The Company begins to record stock-based compensation expense for PSAs at the time that it becomes probable that the respective performance conditions will be achieved. The Company continues to recognize the grant date fair value of PSUs through the vest date of the respective awards so long as it remains probable that the related service conditions will be satisfied. The activity related to the Company's PSAs for the year ended December 31, 2015 is as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2015 34,235 $ 13.60 Granted — $ — Vested (34,235 ) $ 13.60 Forfeited — $ — Unvested balance at December 31, 2015 — $ — The activity related to the Company's PSUs for the year ended December 31, 2015 is as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2015 — $ — Granted 131,250 $ 14.68 Vested (11,666 ) $ 14.18 Forfeited (8,334 ) $ 15.38 Unvested balance at December 31, 2015 111,250 $ 14.68 The total fair value of performance-based stock grant shares vested was $0.6 million in the year ended December 31, 2015 , $1.7 million in the year ended December 31, 2014 and $2.6 million in the year ended December 31, 2013 . ESPP The ESPP is designed to provide eligible employees of the Company and its participating subsidiaries an opportunity to purchase common stock of the Company through accumulated payroll deductions. The ESPP provides for six-month consecutive 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. At December 31, 2015 , 5.0 million shares, the maximum number of shares that may be issued under the ESPP, were authorized and 1.9 million shares were available under the ESPP for future issuance. Stock-Based Compensation The consolidated statements of operations include stock-based compensation for the years ended December 31, 2015 , 2014 and 2013 as follows (in thousands): Year ended December 31, 2015 2014 2013 Product cost of revenue $ 317 $ 337 $ 181 Service cost of revenue 1,524 1,449 1,050 Research and development 5,439 5,759 3,616 Sales and marketing 5,423 5,437 4,780 General and administrative 8,996 10,932 8,246 $ 21,699 $ 23,914 $ 17,873 There is no income tax benefit for employee stock-based compensation expense for the years ended December 31, 2015 , 2014 and 2013 due to the valuation allowance recorded. At December 31, 2015 , there was $32.2 million , net of expected forfeitures, of unrecognized stock-based compensation expense related to unvested stock options, RSAs, RSUs and PSUs. This expense is expected to be recognized over a weighted average period of approximately two years . Common Stock Reserved Common stock reserved for future issuance at December 31, 2015 consists of the following: 2007 Plan 2,560,723 ESPP 1,906,165 4,466,888 The Company's policy is to issue authorized but unissued shares upon the exercise of stock options, grant restricted common stock awards and units and performance-based stock awards and units, and authorize the purchase of shares of the Company's common stock under the ESPP.

EMPLOYEE DEFINED CONTRIBUTION P

EMPLOYEE DEFINED CONTRIBUTION PLAN	12 Months Ended
	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
EMPLOYEE DEFINED CONTRIBUTION PLAN	EMPLOYEE DEFINED CONTRIBUTION PLAN The Company offers a 401(k) savings plan to its employees but does not provide a matching contribution. Accordingly, the Company did not record expense related to its employee defined contribution plan in the years ended December 31, 2015, 2014 and 2013.

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The components of loss from continuing operations before income taxes consist of the following (in thousands): Year ended December 31, 2015 2014 2013 Income (loss) before income taxes: United States $ (29,595 ) $ (16,582 ) $ (21,076 ) Foreign (293 ) 1,941 409 $ (29,888 ) $ (14,641 ) $ (20,667 ) The provision (benefit) for income taxes from continuing operations consists of the following (in thousands): Year ended December 31, 2015 2014 2013 Provision (benefit) for income taxes: Current: Federal $ 60 $ 23 $ 14 State 150 150 150 Foreign 982 926 1,696 Total current 1,192 1,099 1,860 Deferred: Federal (7,069 ) (3,885 ) (1,911 ) State 4,962 (1,656 ) (103 ) Foreign 155 414 (1,081 ) Change in valuation allowance 2,767 6,242 2,687 Total deferred 815 1,115 (408 ) Total $ 2,007 $ 2,214 $ 1,452 A reconciliation of the Company's effective tax rate for continuing operations to the statutory federal rate is as follows: Year ended December 31, 2015 2014 2013 U.S. statutory income tax rate (35.0 )% (35.0 )% (35.0 )% State income taxes, net of federal benefit — (4.9 ) 0.4 Foreign income taxes 3.6 5.1 1.3 Capital loss expiration — — 24.0 Foreign deemed dividends 1.7 11.5 1.8 Stock-based compensation 14.4 12.0 7.6 Tax credits (3.3 ) (14.6 ) (6.1 ) Valuation allowance 24.3 29.8 9.9 Goodwill amortization 2.2 4.8 3.3 Meals and entertainment 0.8 2.5 1.3 Tax gain on sale of acquired assets — 4.2 — Other, net (2.0 ) (0.3 ) (1.5 ) Effective income tax rate 6.7 % 15.1 % 7.0 % The following is a summary of the significant components of deferred income tax assets and liabilities (in thousands): December 31, 2015 2014 Assets: Net operating loss carryforwards $ 76,970 $ 74,717 Research and development tax credits 22,412 24,978 Other tax credits 230 91 Intangible assets 7,128 4,808 Deferred revenue 3,936 1,911 Accrued expenses 8,706 10,619 Inventory 6,103 5,713 Stock-based compensation 13,594 12,913 Other temporary differences 2,623 3,924 141,702 139,674 Valuation allowance (139,823 ) (137,640 ) Total deferred tax assets 1,879 2,034 Liabilities: Purchased intangible assets (2,282 ) (1,623 ) Total deferred tax liabilities (2,282 ) (1,623 ) Total net deferred tax assets $ (403 ) $ 411 Reported as: Deferred income taxes - current assets $ — $ 991 Deferred income taxes - noncurrent assets 1,879 1,043 Deferred income taxes - noncurrent liabilities (2,282 ) (1,623 ) $ (403 ) $ 411 At December 31, 2015 , the Company had cumulative net operating losses ("NOL") of $224.0 million for federal income tax purposes and $103.0 million for state income tax purposes. The federal NOL carryforwards expire at various dates from 2020 through 2034. The state NOL expires at various dates from 2015 through 2035. Of the federal NOL, $145.0 million is attributable to stock option deductions. The Company's federal NOL carryforwards for tax return purposes are $22.4 million greater than its recognized federal NOL for financial reporting purposes, primarily due to excess tax benefits (stock compensation deductions in excess of book compensation costs) not recognized for financial statement purposes until realized. The tax benefit of this loss would be recognized for financial statement purposes in the period in which the tax benefit reduces income taxes payable, which will not be recognized until the Company recognizes a reduction in taxes payable from all other NOL carryforwards. In addition, the Company had $13.6 million of deferred tax assets as of December 31, 2015 related to compensation expenses recognized for financial reporting purposes that are not deductible for tax purposes until options are exercised or shares vest. The ultimate realization of the benefit related to stock options is directly associated with the price of the Company's common stock. Employees will not exercise the underlying options unless the current market price exceeds the option exercise price. The Company also has available federal and state research and development credit carryforwards of approximately $25 million that expire at various dates from 2015 through 2035. In November 2015, the FASB issued ASU 2015-17, which requires entities to present deferred tax assets and deferred tax liabilities as noncurrent in the consolidated balance sheet. The Company has elected to early-adopt ASU 2015-17 and accordingly, has reclassified its net current deferred tax asset totaling $1.0 million to its noncurrent net deferred tax asset as of December 31, 2015. No prior periods were retrospectively adjusted. During 2013, $14.1 million of capital loss carryover resulting from the Company's sale of its Zynetix subsidiary on November 26, 2008 expired. The capital loss was only available to offset capital gains. Because it was not more likely than not that the Company would realize a benefit prior to the expiration of the capital loss carryforward, a full valuation allowance had been established against the $5.5 million tax benefit associated with this capital loss. During 2015 and 2014 , the Company performed an analysis to determine if, based on all available evidence, it considered it more likely than not that some portion or all of the recorded deferred tax assets will not be realized in a future period. As a result of the Company's evaluation, the Company concluded that there was insufficient positive evidence to overcome the more objective negative evidence related to its cumulative losses and other factors. Accordingly, the Company has maintained a valuation allowance against its domestic deferred tax asset amounting to $139.8 million at December 31, 2015 and $137.6 million at December 31, 2014 . A reconciliation of the Company's unrecognized tax benefits is as follows (in thousands): 2015 2014 2013 Unrecognized tax benefits at January 1 $ 8,875 $ 8,861 $ 8,847 Increases related to current year tax positions 13 14 14 Decreases related to prior period tax positions — — — Unrecognized tax benefits at December 31 $ 8,888 $ 8,875 $ 8,861 The Company recorded liabilities for potential penalties and interest of $13,000 for the year ended December 31, 2015 , $14,000 for the year ended December 31, 2014 and $14,000 for the year ended December 31, 2013 . The Company does not expect its unrecognized tax benefits to change materially over the next 12 months. Due to the Company's valuation allowance at December 31, 2015 , none of the Company's unrecognized tax benefits, if recognized, would affect the effective tax rate. The Company and its subsidiaries file income tax returns in the U.S. federal jurisdiction, as well as various state and foreign jurisdictions. Generally, the tax years 2013 through 2015 remain open to examination by the major taxing jurisdictions to which the Company is subject. The Company's federal NOLs generated prior to 2013 could be adjusted on examination even though the year in which the loss was generated is otherwise closed by the statute of limitations. The Company's primary state jurisdiction, Massachusetts, has open periods from 2011 through 2013. The acquisition of NET was accounted for as a nontaxable business combination and the Company carried over the existing tax basis of the acquired assets and liabilities. Deferred taxes were recorded as part of the business combination based on the differences between the tax basis of the acquired assets or liabilities and their reported amounts for financial reporting purposes. The Company concluded that there was insufficient positive evidence to overcome the more objective negative evidence related to cumulative losses and other factors. Accordingly, the Company recorded a valuation allowance against the majority of the acquired deferred tax assets. With respect to the acquisition of NET, during the second quarter of 2013, the Company made an election under Section 338(g) of the Internal Revenue Code to have the acquisition transaction treated as an asset acquisition (i.e., a taxable transaction). The election is not considered part of the business combination and resulted in a step-up in the acquired assets and liabilities to fair market value for tax purposes. During the third quarter of 2013, as a result of the election, the Company reversed all of the deferred taxes related to NET's assets, liabilities and net operating loss carryovers and the related valuation allowance that were recorded in the business combination. The resulting taxable gain from the election was fully offset by NET's operating loss carryovers and no taxes were paid by the Company as a result of the election. The acquisition of PT was accounted for as a taxable business combination and the Company carried over the existing tax basis of the acquired assets and liabilities as the Company did not make the election under Section 338(g) of the Internal Revenue Code to have the transaction treated as an asset acquisition election to step up the basis in the acquired assets and liabilities to fair market value for tax purposes. Deferred taxes were recorded as part of the business combination based on the differences between the tax basis of the acquired assets or liabilities and their reported amounts for financial reporting purposes. The Company concluded that there was insufficient positive evidence to overcome the more objective negative evidence related to cumulative losses and other factors. Accordingly, the Company recorded a valuation allowance against the acquired deferred tax assets. As a result of the change in control of PT, the NOL and credit carryforwards are limited under Internal Revenue Code Section 382. The Company acquired approximately $26 million of federal and state net operating loss carryforwards and federal and state research and development credit carryforwards as a result of the PT acquisition. Under the provisions of the Internal Revenue Code, the net operating losses and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. Net operating losses and tax credit carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership of significant shareholders over a three -year period in excess of 50% , as defined under Sections 382 and 383 of the Internal Revenue Code, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years. The Company has not performed a comprehensive Section 382 study to determine any potential loss limitation with regard to the net operating loss carryforwards and tax credits acquired as a result of the PT acquisition. The acquisition of the SDN Business was a taxable purchase of a business under Section 197 of the Internal Revenue Code. Similar to the NET goodwill, the tax amortization related to the SDN Business goodwill created a deferred tax liability.

MAJOR CUSTOMERS

MAJOR CUSTOMERS	12 Months Ended
	Dec. 31, 2015
Risks and Uncertainties [Abstract]
MAJOR CUSTOMERS	MAJOR CUSTOMERS The following customer contributed 10% or more of the Company's revenue in each of the years ended December 31, 2015, 2014 and 2013 : Year ended December 31, 2015 2014 2013 AT&T 13% 19% 15% There were no other customers that contributed 10% or more of the Company's revenue in any of the years ended December 31, 2015 , 2014 or 2013 . At December 31, 2015 , one customer accounted for 10% or more of the Company's accounts receivable balance, representing approximately 11% of the total balance. At December 31, 2014 , no customer accounted for 10% or more of the Company's accounts receivable balance. The Company performs ongoing credit evaluations of its customers and generally does not require collateral on accounts receivable. The Company maintains an allowance for doubtful accounts and such losses have been within management's expectations.

GEOGRAPHIC AND OPERATING SEGMEN

GEOGRAPHIC AND OPERATING SEGMENT INFORMATION GEOGRAPHIC AND OPERATING SEGMENT INFORMATION	12 Months Ended
	Dec. 31, 2015
Segment Reporting [Abstract]
GEOGRAPHIC INFORMATION	GEOGRAPHIC AND SEGMENT INFORMATION The Company's classification of revenue by geographic area is determined by the location of the Company's customers. The following table summarizes revenue by geographic area as a percentage of total revenue: Year ended December 31, 2015 2014 2013 United States 71 % 71 % 69 % Europe, Middle East and Africa 13 13 12 Japan 10 9 12 Other Asia Pacific 4 5 5 Other 2 2 2 100 % 100 % 100 % The Company's service revenue is comprised of the following (in thousands): Year ended December 31, 2015 2014 2013 Maintenance $ 89,280 $ 90,003 $ 84,698 Professional services 17,841 23,868 24,763 $ 107,121 $ 113,871 $ 109,461

RELATED PARTIES

RELATED PARTIES	12 Months Ended
	Dec. 31, 2015
Related Party Transactions [Abstract]
RELATED PARTIES	RELATED PARTIES H. Brian Thompson, an independent member of the Company's Board of Directors, is the Executive Chairman of GTT Communications, Inc., a leading global cloud networking provider to multinational clients ("GTT"). Howard Janzen is the independent Chairman of the Company's Board of Directors and also serves as an independent director of GTT. In October 2015, GTT completed the acquisition of One Source Networks Inc., a provider of global data, Internet, SIP trunking and managed services ("One Source"). One Source is a customer of the Company. The Company had a well-established and ongoing business relationship with One Source prior to its acquisition by GTT. The Company recognized revenue aggregating approximately $150,000 in the year ended December 31, 2015, pursuant to the terms of a contract between the parties, effective June 28, 2010. The Company believes the terms of this contract are consistent with third-party arrangements that provide similar services. As a matter of corporate governance policy and practice, related party transactions are presented and considered by the Audit Committee of the Company's Board of Directors in accordance with the Company's Related Person Transaction Policy.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Leases The Company leases its facilities under operating leases, which expire at various times through 2020. The Company is responsible for certain real estate taxes, utilities and maintenance costs under these leases. The Company's corporate headquarters is located in a leased facility in Westford, Massachusetts, consisting of 97,500 square feet under a lease that expires in August 2018 . Escalation clauses, free rent and other lease concessions are recognized on a straight-line basis over the minimum lease term. Rent expense was $5.2 million for the year ended December 31, 2015 , $6.1 million for the year ended December 31, 2014 and $5.5 million for the year ended December 31, 2013 . Future minimum payments under operating lease arrangements as of December 31, 2015 are as follows (in thousands): Years ending December 31, 2016 $ 4,111 2017 3,682 2018 2,801 2019 1,565 2020 252 Thereafter — $ 12,411 Litigation and Contingencies On April 6, 2015, Ming Huang, a purported shareholder of the Company, filed a Class Action Complaint (Civil Action No. 3:15-02407), alleging violations of the federal securities laws (the "Complaint") in the United States District Court for the District of New Jersey (the "Court"), against the Company and two of its officers, Raymond P. Dolan, the Company's President and Chief Executive Officer, and Mark T. Greenquist, the Company's Chief Financial Officer (collectively, the "Defendants"). On September 21, 2015, in response to motions subsequently filed with the Court by four other purported shareholders of ours seeking status as lead plaintiff, the Court appointed Richard Sousa as lead plaintiff (the "Plaintiff"). 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 that the Defendants made misleading forward-looking statements concerning the Company's fiscal first quarter of 2015 financial performance. On September 22, 2015, the Company filed a Motion to Transfer this case to the United States District Court for the District of Massachusetts (the "Motion to Transfer"). The Plaintiff filed his opposition to the Motion to Transfer on October 5, 2015, and the Company filed a reply to the Motion to Transfer on October 13, 2015. 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.

QUARTERLY RESULTS (UNAUDITED)

QUARTERLY RESULTS (UNAUDITED)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
QUARTERLY RESULTS (UNAUDITED)	QUARTERLY RESULTS (UNAUDITED) The following tables present the Company's quarterly operating results for the years ended December 31, 2015 and 2014 . The information for each of these quarters is unaudited and has been prepared on the same basis as the audited consolidated financial statements. In the opinion of management, all necessary adjustments, consisting only of normal recurring adjustments, have been included to present fairly the unaudited consolidated quarterly results when read in conjunction with the Company's audited consolidated financial statements and related notes. First Quarter (1) Second Quarter Third Quarter Fourth Quarter (In thousands, except per share data) Fiscal 2015 Revenue $ 50,145 $ 54,701 $ 67,862 $ 76,326 Cost of revenue 20,915 20,287 22,150 24,025 Gross profit $ 29,230 $ 34,414 $ 45,712 $ 52,301 Income (loss) from operations $ (18,866 ) $ (15,049 ) $ (1,362 ) $ 4,060 Net income (loss) $ (19,359 ) $ (15,343 ) $ (1,896 ) $ 4,703 Income (loss) per share (3): Basic $ (0.39 ) $ (0.31 ) $ (0.04 ) $ 0.09 Diluted $ (0.39 ) $ (0.31 ) $ (0.04 ) $ 0.09 Shares used in computing income (loss) per share: Basic 49,423 49,484 49,625 49,685 Diluted 49,423 49,484 49,625 49,906 First Quarter (2) Second Quarter Third Quarter Fourth Quarter (In thousands, except per share data) Fiscal 2014 Revenue $ 70,742 $ 75,570 $ 73,216 $ 76,798 Cost of revenue 24,319 28,282 25,314 25,006 Gross profit $ 46,423 $ 47,288 $ 47,902 $ 51,792 Loss from operations $ (5,791 ) $ (4,801 ) $ (4,715 ) $ (1,945 ) Net income (loss) $ (3,953 ) $ (5,497 ) $ (5,213 ) $ (2,192 ) Loss per share (3): Basic $ (0.07 ) $ (0.11 ) $ (0.11 ) $ (0.04 ) Diluted $ (0.07 ) $ (0.11 ) $ (0.11 ) $ (0.04 ) Shares used in computing loss per share: Basic 53,080 49,424 49,291 49,361 Diluted 53,080 49,424 49,291 49,361 __________________________________ (1) Includes the results of the SDN Business for the period subsequent to January 2, 2015. (2) Includes the results of PT for the period subsequent to February 19, 2014. (3) Income (loss) per share is calculated independently for each of the quarters presented; accordingly, the sum of the quarterly earnings (loss) per share amounts may not equal the total calculated for the year.

BASIS OF PRESENTATION AND SUM30

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Basis of Presentation	BASIS OF PRESENTATION The consolidated financial statements have been prepared in United States dollars, in accordance with accounting principles generally accepted in the United States ("GAAP"). For fiscal years 2015, 2014 and 2013, the Company reported its first, second and third quarters on a 4-4-5 basis, with the quarter ending on the Friday closest to the last day of each third month. In 2015, the Company's first quarter ended on March 27, 2015, the second quarter ended on June 26, 2015 and the third quarter ended on September 25, 2015. In 2014, the Company's first quarter ended on March 28, 2014, the second quarter ended on June 27, 2014 and the third quarter ended on September 26, 2014. In 2013, the Company's first quarter ended on March 29, 2013, the second quarter ended on June 28, 2013 and the third quarter ended on September 27, 2013. Effective January 1, 2016, the Company will report its first, second and third quarters on a month-end basis, such that the Company's first quarter will end on March 31, 2016, the second quarter will end on June 30, 2016 and the third quarter will end on September 30, 2016. The Company's fiscal year will continue to end on December 31. During the preparation of the Company's consolidated financial statements for the three month period ended June 26, 2015, the Company identified an error related to the historical foreign translation of depreciation expense on certain foreign fixed assets that resulted in a historical understatement of expense in prior fiscal years totaling $1.4 million on a cumulative basis. There was no tax effect on these expenses as the amounts were calculated in the appropriate foreign currencies. The Company does not believe this error is material to its previously issued historical consolidated financial statements for any of the periods impacted and, accordingly, has not adjusted its historical financial statements. The Company recorded the cumulative impact of the adjustment in the three months ended June 26, 2015. This adjustment resulted in a one-time $1.4 million overstatement of depreciation expense, which is included in the Company's consolidated statement of operations for the year ended December 31, 2015. The Company does not believe this adjustment is material to its consolidated financial statements for the periods presented. On January 29, 2015, the Company effected a one-for-five reverse stock split of its issued, outstanding and authorized common stock, which became effective on the NASDAQ Global Select Market as of the commencement of trading on January 30, 2015. All references herein to shares outstanding and share issuances have been adjusted to give effect to the aforementioned 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 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 consolidated financial statements for the periods subsequent to the PT Acquisition Date.
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of Sonus and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation.
Use of Estimates and Judgments	Use of Estimates and Judgments The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of 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, 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.
Business Combinations	Business Combinations The Company recognizes identifiable assets acquired and liabilities assumed at their acquisition date fair values. Goodwill as of the acquisition date is measured as the excess of consideration transferred over the net of the acquisition date fair values of the assets acquired and the liabilities assumed and represents the expected future economic benefits arising from other assets acquired in the business combination that are not individually identified and separately recognized. While the Company uses its best estimates and assumptions as part of the purchase price allocation process to accurately value assets acquired and liabilities assumed at the acquisition date, its estimates are inherently uncertain and subject to refinement. As a result, during the measurement period, which may be up to one year from the acquisition date, the Company records adjustments to the assets acquired and liabilities assumed with the corresponding offset to goodwill to the extent that it identifies adjustments to the preliminary purchase price allocation. Upon the conclusion of the measurement period or final determination of the values of assets acquired or liabilities assumed, whichever comes first, any subsequent adjustments are recorded to the consolidated statements of operations.
Revenue Recognition	Revenue Recognition The Company recognizes revenue from sales when persuasive evidence of an arrangement exists, delivery has occurred, the sale price is fixed or determinable, and collectability of the related receivable is probable. In instances where customer acceptance is required, revenue is deferred until the acceptance has been achieved. When fees for products or services are not fixed and determinable, the Company defers the recording of receivables, deferred revenue and revenue until such time as the fees become due or are collected. Revenue from maintenance and support services is recognized ratably over the service period. Maintenance revenue is deferred until the associated product is accepted by the customer and all other revenue recognition criteria have been met. Maintenance and support services include telephone support, return and repair support and unspecified rights to product upgrades and enhancements. Revenue from other professional services is typically recognized as the services are delivered if all other revenue recognition criteria have been met. The Company's products typically have both software and non-software components that function together to deliver the products' essential functionality. In addition, hardware sold generally cannot be used apart from the software. Therefore, the Company considers its principal products to be both software and hardware-related. Many of the Company's sales involve multiple element arrangements that include product, maintenance and various professional services. The Company recognizes revenue in accordance with the provisions of Accounting Standards Codification ("ASC") 605-25, Revenue Recognition - Multiple-Element Arrangements ("ASC 605-25") transactions that include both hardware and software components. The Company recognizes revenue from stand-alone software sales under the software revenue recognition guidance in ASC 985-605, Software - Revenue Recognition ("ASC 985-605"). The Company limits the amount of revenue recognized for delivered elements to the amount that is not contingent on the future delivery of products or services, future performance obligations, or subject to customer-specific return or refund privileges. For multiple-element arrangements that include both software-only products and non-software products, the Company allocates the total arrangement consideration to the software-only deliverables as a group and to the individual non-software deliverables based on their relative selling prices. If an undelivered element (such as maintenance and support services) relates to both the software-only and non-software deliverables, the Company bifurcates the consideration allocated to the undelivered element (such as maintenance and support services) into a non-software component and the software-only component using the relative selling price method. The consideration allocated to the non-software and software-only deliverables is recognized in accordance with the guidance as discussed in this note. Under ASC 985-605, revenue for any undelivered elements that are considered not essential to the functionality of the product and for which vendor-specific objective evidence of selling price (“VSOE”) has been established is deferred and recognized upon delivery utilizing the residual method. If the Company has undelivered product for which VSOE has not been established, it defers all revenue on the entire arrangement until VSOE is established or until such elements are delivered, provided that all other revenue recognition criteria are met. If the Company has undelivered services for which VSOE has not been established, the entire arrangement is recognized as revenue over the longest remaining service period from the point in time that all services have commenced and all products have been delivered, provided that all other revenue recognition criteria are met. For transactions that include multiple elements, arrangement consideration is allocated to each element based on the relative selling prices of all of the elements in the arrangement using the fair value hierarchy as required by ASC 605-25. The Company establishes VSOE based upon the price charged when the same element is sold separately or established by management having the relevant pricing authority. The Company has VSOE for its maintenance and support services and certain professional services. When VSOE exists it is used to determine the selling price of a deliverable. The Company has not been able to establish VSOE of any of its products and for certain of its services because the Company has not sold such products or services on a stand-alone basis, has not priced its products or services within a narrow range, or has limited sales history. When VSOE is not established, the Company attempts to establish the selling price of each element based on third-party evidence of selling price (“TPE”). The Company's solution typically differs from that of its peers as there are no similar or interchangeable competitor products or services. The Company's various product, service and maintenance offerings contain a significant level of unique features and functionality and therefore, comparable pricing of competitors' products and services with similar functionality cannot be obtained. Accordingly, the Company is not able to determine TPE for its products or services. When the Company is unable to establish selling price using VSOE or TPE, the Company uses estimated selling price (“ESP”) in its allocation of arrangement consideration for the relevant deliverables. The objective of ESP is to determine the price at which the Company would transact a sale if a product or service was sold on a stand-alone basis. The Company determines ESP for its products and certain services by considering multiple factors including, but not limited to, overall market conditions, including geographic or regional-specific market factors, profit objectives and historical pricing practices for such deliverables. The determination of ESP is a formal process within the Company that includes review and approval by the Company's management. Deferred revenue typically includes customer deposits and amounts associated with partial product shipments and maintenance or service contracts. Deferred revenue expected to be recognized as revenue more than one year subsequent to the balance sheet date is reported as a component of long-term liabilities in the consolidated balance sheets. The Company defers recognition of incremental direct costs, such as cost of goods, third-party installations and commissions, until recognition of the related revenue. Such costs are classified as current assets if the deferred revenue is initially classified as current and noncurrent assets if the related deferred revenue is initially classified as long-term. The Company excludes any taxes assessed by a governmental authority that are directly imposed on a revenue-producing transaction (i.e., sales, use and value added) from its revenue and costs. Reimbursement received for out-of-pocket expenses and shipping costs is recorded as revenue. The Company sells the majority of its products directly to its end customers. For products sold to resellers and distributors, the Company recognizes revenue on a sell-through basis.
Financial Instruments	Financial Instruments The carrying amounts of Sonus' financial instruments, which include cash equivalents, investments, accounts receivable and accounts payable, approximate their fair values. All investments in marketable securities are classified as available-for-sale and are reported at fair value, with unrealized gains and losses excluded from earnings and reported, net of tax, in Accumulated other comprehensive loss, which is a component of stockholders' equity. Unrealized losses that are determined to be other-than-temporary, based on current and expected market conditions, are recognized in earnings. Declines in fair value determined to be credit-related are charged to earnings. The cost of marketable securities sold is determined by the specific identification method. Financial instruments with remaining maturities or that are due within one year from the balance sheet date are classified as current. Financial instruments with remaining maturities or that are payable more than one year from the balance sheet date are classified as noncurrent.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash equivalents are stated at fair value, with unrealized gains and losses excluded from earnings and reported, net of tax, in Accumulated other comprehensive income (loss). Cash equivalents are liquid securities that have remaining maturities of three months or less at the date of purchase.
Restricted Cash	Restricted Cash The Company classifies as restricted cash all cash pledged as collateral to secure long-term obligations and all cash whose use is otherwise limited by contractual provisions. Restricted cash is recorded within other assets on the consolidated balance sheet.
Foreign Currency Translation	Foreign Currency Translation For foreign subsidiaries where the functional currency is the local currency, assets and liabilities are translated into U.S. dollars at the current exchange rate on the balance sheet date. Revenue and expenses are translated at average rates of exchange prevailing during each period. Translation adjustments for these subsidiaries are included in Accumulated other comprehensive loss. For foreign subsidiaries where the functional currency is the U.S. dollar, monetary assets and liabilities are translated into U.S. dollars at the current exchange rate on the balance sheet date. Nonmonetary assets and liabilities are remeasured into U.S. dollars at historical exchange rates. Revenue and expense items are translated at average rates of exchange prevailing during each period. Realized and unrealized foreign currency gains and losses arising from transactions denominated in currencies other than the subsidiary's functional currency are reflected in earnings with the exception of intercompany transactions considered to be of a long-term investment nature.
Inventory	Inventory Inventory is recorded at the lower of cost or market value using the first-in, first-out convention. The Company reduces the carrying value of inventory for those items that are potentially excess, obsolete or slow-moving based on changes in customer demand, technology developments or other economic factors. Sonus writes down evaluation equipment at the time of shipment to its customers, as it is probable that the inventory value will not be realized. Deferred product costs represent deferred cost of revenue for product shipments to customers prior to satisfaction of Sonus' revenue recognition criteria. Such costs are classified as inventory if the related deferred revenue is initially classified as current. Deferred product costs are recorded in Other assets if the related deferred revenue is initially classified as long-term, and remain a component of noncurrent assets until such costs are recognized in the consolidated statement of operations.
Property and Equipment	Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation. Expenditures for maintenance and repairs are charged to expense as incurred. Depreciation is computed using the straight-line method over the estimated useful lives of the related assets, which range from two to five years. Leasehold improvements are amortized over the lesser of the lease term or five years. When an asset is sold or retired, the cost and related accumulated depreciation or amortization are eliminated, and the resulting gain or loss, if any, is recognized in income (loss) from operations in the consolidated statement of operations. The Company reviews property and equipment for impairment in the same manner as intangible assets discussed below. Software development costs associated with internal use software are incurred in three stages of development: the preliminary project stage, the application development stage and the post-implementation stage. Costs incurred during the preliminary project and post-implementation stages are expensed as incurred. Certain qualifying costs incurred during the application development stage are capitalized as property and equipment. Internal use software is amortized on a straight-line basis over its estimated useful life of three years, beginning when the software is ready for its intended use.
Intangible Assets and Goodwill	Intangible Assets and Goodwill Intangible assets are comprised of certain intangible assets arising from the August 24, 2012 acquisition of NET, comprised of developed technology, customer relationships and internal use software, which are amortized over their estimated useful lives of three to five years; the February 19, 2014 acquisition of PT, comprised of developed technology and customer relationships, which are amortized over their estimated useful lives of six to seven years; and the January 2, 2015 acquisition of the SDN Business, which are amortized over their estimated useful lives of seven years. Intangible assets are reviewed for impairment when events or changes in circumstances indicate that their carrying amounts may not be recoverable based upon the estimated undiscounted cash flows. Recoverability of intangible assets with estimated lives and other long-lived assets is measured by a comparison of the carrying amount of an asset or asset group to future net undiscounted cash flows expected to be generated by the asset or asset group. If these comparisons indicate that an asset is not recoverable, the Company will recognize an impairment loss for the amount by which the carrying value of the asset or asset group exceeds the related estimated fair value. Estimated fair value is based on either discounted future operating cash flows or appraised values, depending on the nature of the asset. In the second quarter of 2013, the Company recorded an impairment charge of $0.6 million to write down the carrying value of one of its intellectual property intangible assets to zero. See Note 9 for additional information regarding this expense. Goodwill is recorded when the consideration for an acquisition exceeds the fair value of net tangible and identifiable intangible assets acquired. Goodwill is not amortized, but instead is tested for impairment at least annually or if indicators of potential impairment exist by comparing the fair value of the Company's reporting unit to its carrying value. The Company adopted Accounting Standards Update ("ASU") 2011-08, Intangibles - Goodwill and Other (Topic 350): Testing Goodwill for Impairment ("ASU 2011-08") in fiscal year 2013. ASU 2011-08 permits an entity to first perform a qualitative assessment to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying value. This qualitative assessment included the review of macroeconomic conditions, industry and market considerations, cost factors, overall company financial performance and other related facts and circumstances that could indicate that a more detailed assessment would be required. If it is concluded that it is more likely than not that the fair value is less than the carrying value, then it is necessary to perform the currently prescribed two-step goodwill impairment test. Alternatively, if it is concluded that it is not more likely than not that the fair value exceeds carrying value, the currently prescribed two-step goodwill impairment test is not required. The Company's annual testing for impairment of goodwill is completed as of November 30 of each year. The Company operates as a single operating segment with one reporting unit and consequently evaluates goodwill for impairment based on an evaluation of the fair value of the Company as a whole. The Company performed its qualitative assessments for each of the years ended December 31, 2015, 2014 and 2013 and concluded each year that it was not more likely than not that the fair value of the Company's reporting unit was less than its carrying value.
Share-Based Compensation	Stock-Based Compensation The Company's stock-based compensation cost is measured at the grant date based on the fair value of the award and is recognized as expense over the requisite service period, which generally represents the vesting period, and includes an estimate of the awards that will be forfeited. The Company uses the Black-Scholes valuation model for estimating the fair value on the date of grant of stock options. The fair value of stock option awards is affected by the Company's stock price as well as valuation assumptions, including the volatility of Sonus' stock price, expected term of the option, risk-free interest rate and expected dividends. In 2015, the Company began to grant performance-based stock units ("PSUs") that include a market condition to certain of its executives. The Company uses a Monte Carlo simulation approach to model future stock price movements based upon the risk-free rate of return, the volatility of each entity, and the pair-wise covariance between each entity. These results are then used to calculate the grant date fair values of the PSUs.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred.
Software Development Costs	Software Development Costs The costs for the development of new software and substantial enhancements to existing software are expensed as incurred until technological feasibility has been established, at which time any additional costs would be capitalized until the product is available for general release. The Company has determined that technological feasibility is established at the time a working model of the software is completed. The Company's process for developing software is essentially completed concurrently with the establishment of technological feasibility. Accordingly, no costs have been capitalized to date.
Advertising Costs	Advertising Costs Advertising costs are expensed as incurred and included as a component of Sales and marketing expense in the Company's consolidated statements of operations.
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.
Loss Contingencies and Reserves	Loss Contingencies and Reserves Loss Contingencies. Sonus is subject to ongoing business risks arising in the ordinary course of business that affect the estimation process of the carrying value of assets, the recording of liabilities and the possibility of various loss contingencies. An estimated loss contingency is accrued when it is probable that a liability has been incurred or an asset has been impaired and the amount of loss can be reasonably estimated. Sonus regularly evaluates current information available to determine whether such amounts should be adjusted and records changes in estimates in the period they become known. Allowance for Doubtful Accounts. Sonus establishes billing terms at the time it negotiates purchase agreements with its customers. Sonus monitors its outstanding receivables for timely payments and potential collection issues. An allowance for doubtful accounts is estimated based on Sonus' assessment of the collectability of specific customer accounts. Accrual for Royalties. Sonus accrues for royalties for technology that it licenses from vendors based on established royalty rates and usage. In certain cases, Sonus has been contacted by third parties who claim that Sonus' products infringe on certain intellectual property of the third party. Sonus evaluates these claims and accrues amounts only when it is probable that the obligation has been incurred and the amounts are reasonably estimable. Reserve for Litigation and Legal Fees. Sonus is subject to various legal claims. Sonus reserves for legal contingencies and legal fees when it is probable that a loss has been incurred and the amounts are reasonably estimable.
Accounting for Income Taxes	Accounting for Income Taxes Deferred tax assets and liabilities are recognized for the expected future consequences of events that have been reflected in the consolidated financial statements. Deferred tax assets and liabilities are determined based on the differences between the book and tax bases of assets and liabilities and operating loss carryforwards, using tax rates expected to be in effect for the years in which the differences are expected to reverse. Such differences arise primarily from stock-based compensation, depreciation, accruals and reserves, acquired intangible assets, deferred revenue, tax credits, net operating loss carryforwards and allowances for accounts receivable. Sonus records valuation allowances to reduce deferred income tax assets to the amount that is more likely than not to be realized. Sonus has not provided for U.S. income taxes on the undistributed earnings of non-U.S. subsidiaries, as the Company plans to permanently reinvest these amounts. Cumulative undistributed foreign earnings were approximately $28 million at December 31, 2015 and approximately $28 million at December 31, 2014 . Generally, the undistributed foreign earnings become subject to U.S. taxation upon the remittance of dividends and under certain other circumstances. The Company has been taxed on certain earnings of its non-U.S. subsidiaries. Previously taxed earnings were approximately $16 million at December 31, 2015 and $15 million at December 31, 2014. Thus, $12 million of the undistributed earnings at December 31, 2015 and $13 million at December 31, 2014 are subject to U.S. income taxes on undistributed earnings. The Company does not believe it is practicable to estimate with reasonable accuracy the hypothetical amount of the unrecognized deferred tax liability on its undistributed foreign earnings given the large number of tax jurisdictions involved and the many factors and assumptions required to estimate the amount of the U.S. federal income tax on the undistributed earnings after reduction for the available foreign tax credits. The Company determines whether it is more likely than not that a tax position will be sustained upon examination. If it is not more likely than not that a position will be sustained, no amount of the benefit attributable to the position is recognized. The tax benefit to be recognized of any tax position that meets the more likely than not recognition threshold is calculated as the largest amount that is more than 50% likely of being realized upon resolution of the contingency. The Company accounts for interest and penalties related to uncertain tax positions as part of its provision for income taxes. In September 2013, the U.S. Department of the Treasury and the Internal Revenue Service released final regulations relating to guidance on applying tax rules to amounts paid to acquire, produce or improve tangible personal property as well as rules for materials and supplies effective for tax years beginning on or after January 1, 2014. The Company has reviewed the regulations and has determined that its current method of accounting is appropriate under the regulations with no change required.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In November 2015, the Financial Accounting Standards Board ("FASB") issued ASU 2015-17, Balance Sheet Classification of Deferred Taxes ("ASU 2015-17"), which requires entities to present deferred tax assets and deferred tax liabilities as noncurrent in the consolidated balance sheet. Netting of deferred tax assets and deferred tax liabilities by tax jurisdiction is still required under ASU 2015-17. The ASU is effective for the Company for its annual reporting of the year ending December 31, 2018 and for interim period reporting beginning January 1, 2019, with early adoption permitted. Companies may adopt ASU 2015-17 either prospectively or retrospectively. The Company has elected to early-adopt ASU 2015-17 prospectively and accordingly, has reclassified its net current deferred tax asset totaling $1.0 million to its noncurrent net deferred tax asset as of December 31, 2015. No prior periods were retrospectively adjusted. In September 2015, the FASB issued ASU 2015-16, Simplifying the Accounting for Measurement-Period Adjustments ("ASU 2015-16"), which eliminates the requirement to restate prior periods to reflect adjustments made to provisional amounts recognized in a business combination. Under ASU 2015-16, an acquirer must recognize adjustments to provisional amounts that are identified during the measurement period in the reporting period in which the adjustment amounts are determined, rather than retrospectively, as had previously been required. ASU 2015-16 also requires acquirers to present separately on the face of the income statement, or disclose in the notes, the portion of the amount recorded in current period earnings by line item that would have been recorded in previous reporting periods if the adjustment to the provisional amounts had been recognized as of the acquisition date. ASU 2015-16 was effective for the Company beginning January 1, 2016. The adoption of ASU 2015-16 is not expected to have a material impact on the Company's consolidated financial statements. In July 2015, the FASB issued ASU 2015-11, Simplifying the Measurement of Inventory ("ASU 2015-11"). ASU 2015-11 simplifies the measurement of inventory by requiring entities to measure most inventory at the lower of cost and net realizable value, replacing the previous requirement to measure most inventory at the lower of cost or market. ASU 2015-11 does not apply to inventories that are measured by using either the last-in, first-out method or the retail inventory method. ASU 2015-11 is effective for the Company for both interim and annual reporting periods beginning January 1, 2017. The adoption of ASU 2015-11 is not expected to have a material impact on the Company's consolidated financial statements. In August 2014, the FASB issued 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 for determining when and how to disclose going concern uncertainties in the financial statements. ASU 2014-15 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 is effective for the Company 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 beginning January 1, 2016. The adoption of ASU 2014-12 is not expected to have a material impact on the Company's consolidated financial statements. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”), which is 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 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 August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date , which defers the original effective date of interim and annual reporting periods by one year. As a result, public entities are not required to apply the new revenue standard until annual reporting periods beginning after December 15, 2017, although early adoption is permitted. The Company is currently assessing the potential impact, which may or may not be material, of the adoption of ASU 2014-09 on its consolidated financial statements. In November 2015, the FASB issued ASU 2015-17, which requires entities to present deferred tax assets and deferred tax liabilities as noncurrent in the consolidated balance sheet. The Company has elected to early-adopt ASU 2015-17 and accordingly, has reclassified its net current deferred tax asset totaling $1.0 million to its noncurrent net deferred tax asset as of December 31, 2015. No prior periods were retrospectively adjusted.

BASIS OF PRESENTATION AND SUM31

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Foreign currency translation	The components of foreign currency translation gains (losses), which are reported as a component of General and administrative expenses in the consolidated statements of operations, for the years ended December 31, 2015 , 2014 and 2013 are as follows (in thousands): Year ended December 31, 2015 2014 2013 Transaction gains (losses) $ 1,442 $ (420 ) $ (746 ) Remeasurement gains (losses) (1,860 ) 1,980 (164 ) $ (418 ) $ 1,560 $ (910 )

BUSINESS ACQUISITONS (Tables)

BUSINESS ACQUISITONS (Tables)	12 Months Ended
	Dec. 31, 2015
Business Acquisition [Line Items]
Schedule of components of acquisition-related costs included in results of operations	The components of acquisition-related costs incurred in the years ended December 31, 2015, 2014 and 2013 are as follows (in thousands): Year ended December 31, 2015 2014 2013 Professional and services fees $ 131 $ 1,309 $ 93 Change of control agreements — 249 — $ 131 $ 1,558 $ 93
PT [Member]
Business Acquisition [Line Items]
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 (see Note 15) 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 17,100 Goodwill 8,781 Current liabilities (2,762 ) Other long-term liabilities (329 ) $ 36,693
Schedule of identifiable intangible assets as of the NET Acquisition Date	The identifiable intangible assets recorded in connection with the PT acquisition are as follows (in thousands): Developed technology $ 13,200 Customer relationships 3,900 $ 17,100
SDN Business [Member]
Business Acquisition [Line Items]
Summary of preliminary allocation of the purchase consideration	A summary of the purchase consideration for the SDN Business at December 31, 2015 is as follows (in thousands): Fair value of consideration transferred: Cash, net of cash acquired $ 10,897 Unpaid purchase consideration 750 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

EARNINGS (LOSS) PER SHARE (Tabl

EARNINGS (LOSS) PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2015
Earnings Per Share [Abstract]
Schedule of calculations of shares used to compute basic and diluted earnings (loss) per share	The calculations of shares used to compute basic and diluted loss per share are as follows (in thousands): Year ended December 31, 2015 2014 2013 Weighted average shares outstanding—basic 49,560 50,245 55,686 Potential dilutive common shares — — — Weighted average shares outstanding—diluted 49,560 50,245 55,686

CASH EQUIVALENTS AND INVESTME34

CASH EQUIVALENTS AND INVESTMENTS (Tables)	12 Months Ended
	Dec. 31, 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	The amortized cost, gross unrealized gains and losses and fair value of the Company's cash equivalents and investments at December 31, 2015 and 2014 were comprised of the following (in thousands): December 31, 2015 Amortized cost Unrealized gains Unrealized losses Fair value Cash equivalents $ 7,122 $ — $ — $ 7,122 Short-term investments Municipal obligations $ 3,910 $ — $ (1 ) $ 3,909 U.S. government agency notes 3,450 — (2 ) 3,448 Corporate debt securities 46,736 2 (56 ) 46,682 Commercial paper 3,994 — — 3,994 Certificates of deposit 500 — — 500 $ 58,590 $ 2 $ (59 ) $ 58,533 Investments Municipal obligations $ 2,165 $ — $ (4 ) $ 2,161 U.S. government agency notes 1,999 — (13 ) 1,986 Corporate debt securities 29,541 2 (85 ) 29,458 $ 33,705 $ 2 $ (102 ) $ 33,605 December 31, 2014 Amortized cost Unrealized gains Unrealized losses Fair value Cash equivalents $ 11,653 $ — $ — $ 11,653 Short-term investments 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	The following table shows the fair value of the Company's financial assets at December 31, 2015 and 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 consolidated balance sheets (in thousands): Fair value measurements at Total carrying Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) Cash equivalents $ 7,122 $ 7,122 $ — $ — Short-term investments Municipal obligations $ 3,909 $ — $ 3,909 $ — U.S. government agency notes 3,448 — 3,448 — Corporate debt securities 46,682 — 46,682 — Commercial paper 3,994 — 3,994 — Certificates of deposit 500 — 500 — $ 58,533 $ — $ 58,533 $ — Investments Municipal obligations $ 2,161 $ — $ 2,161 $ — U.S. government agency notes 1,986 — 1,986 — Corporate debt securities 29,458 — 29,458 — $ 33,605 $ — $ 33,605 $ — Fair value measurements at Total carrying Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) Cash equivalents $ 11,653 $ 11,653 $ — $ — Short-term investments 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 $ —

ACCOUNTS RECEIVABLE, NET (Table

ACCOUNTS RECEIVABLE, NET (Tables)	12 Months Ended
	Dec. 31, 2015
Receivables [Abstract]
Schedule of accounts receivable, net	Accounts receivable, net, consist of the following (in thousands): December 31, 2015 2014 Accounts receivable, gross $ 51,543 $ 63,001 Allowance for doubtful accounts (10 ) (58 ) Accounts receivable, net $ 51,533 $ 62,943
Schedule of allowance for doubtful accounts	The activity in the Company's allowance for doubtful accounts is as follows (in thousands): Year ended December 31, Balance at beginning of year Charges to expense Write-offs Balance at end of year 2015 $ 58 $ 17 $ (65 ) $ 10 2014 $ 157 $ 92 $ (191 ) $ 58 2013 $ — $ 415 $ (258 ) $ 157

INVENTORY (Tables)

INVENTORY (Tables)	12 Months Ended
	Dec. 31, 2015
Inventory Disclosure [Abstract]
Schedule of inventory	Inventory consists of the following (in thousands): December 31, 2015 2014 On-hand final assemblies and finished goods inventories $ 17,136 $ 19,285 Deferred cost of goods sold 5,975 2,829 $ 23,111 $ 22,114

PROPERTY AND EQUIPMENT (Tables)

PROPERTY AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Schedule of property and equipment	Property and equipment under capital leases included in the amounts above are as follows (in thousands): December 31, 2015 2014 Cost $ 137 $ 113 Less accumulated depreciation (9 ) (71 ) Property and equipment under capital leases, net $ 128 $ 42 The net book values of the Company's property and equipment by geographic area are as follows (in thousands): December 31, 2015 2014 United States $ 9,145 $ 12,652 Asia/Pacific 3,098 3,574 Europe 818 765 Other 559 854 $ 13,620 $ 17,845 Property and equipment consists of the following (in thousands): December 31, Useful Life 2015 2014 Equipment 3 years $ 63,667 $ 65,703 Software 2-3 years 17,463 17,342 Furniture and fixtures 3-5 years 675 612 Leasehold improvements Shorter of the life of the lease or estimated useful life (1-5 years) 11,615 11,920 93,420 95,577 Less accumulated depreciation and amortization (79,800 ) (77,732 ) Property and equipment, net $ 13,620 $ 17,845

INTANGIBLE ASSETS AND GOODWILL

INTANGIBLE ASSETS AND GOODWILL (Tables)	12 Months Ended
	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of intangible assets	The Company's intangible assets at December 31, 2015 and 2014 consist of the following (in thousands): December 31, 2015 Weighted average amortization period (years) Cost Accumulated amortization Net carrying value In-process research and development * $ 1,600 $ — $ 1,600 Developed technology 6.42 31,280 10,415 20,865 Customer relationships 5.57 10,030 6,408 3,622 Internal use software 3.00 730 730 — 6.19 $ 43,640 $ 17,553 $ 26,087 * An in-process research and development intangible asset has an indefinite life until the product is generally available, at which time such asset is reclassified to developed technology. 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 years ended December 31, 2015 , 2014 and 2013 was as follows (in thousands): Year ended December 31, Statement of operations classification 2015 2014 2013 Intellectual property $ — $ — $ 200 Research and development Developed technology 5,222 2,464 1,999 Cost of revenue - product Customer relationships 1,723 1,889 2,104 Sales and marketing Internal use software 162 244 243 Cost of revenue - product $ 7,107 $ 4,597 $ 4,546
Schedule of estimated future amortization expense for intangible assets	Estimated future amortization expense for the Company's intangible assets at December 31, 2015 is as follows (in thousands): Years ending December 31, 2016 $ 7,189 2017 7,281 2018 4,644 2019 3,611 2020 2,100 Thereafter 1,262 $ 26,087
Schedule of goodwill	The changes in the carrying value of the Company's goodwill in the years ended December 31, 2015 and 2014 are as follows (in thousands): Year ended December 31, 2015 2014 Balance at January 1 Goodwill $ 42,369 $ 35,485 Accumulated impairment losses (3,106 ) (3,106 ) 39,263 32,379 Acquisition of SDN Business 1,047 — Acquisition of PT — 8,781 Sale of MPS business — (1,897 ) Balance at December 31 $ 40,310 $ 39,263 The components of the Company's goodwill balances at December 31, 2015 and 2014 are as follows: December 31, 2015 2014 Balance Goodwill $ 43,416 $ 42,369 Accumulated impairment losses (3,106 ) (3,106 ) $ 40,310 $ 39,263

ACCRUED EXPENSES (Tables)

ACCRUED EXPENSES (Tables)	12 Months Ended
	Dec. 31, 2015
Payables and Accruals [Abstract]
Schedule of accrued expenses	Accrued expenses consist of the following (in thousands): December 31, 2015 2014 Employee compensation and related costs $ 22,180 $ 20,042 Other 9,783 12,107 $ 31,963 $ 32,149

RESTRUCTURING ACCRUAL (Tables)

RESTRUCTURING ACCRUAL (Tables)	12 Months Ended
	Dec. 31, 2015
Restructuring and Related Activities [Abstract]
Summary of restructuring accrual activity	A summary of the 2015 Restructuring Initiative accrual for the year ended December 31, 2015 is as follows (in thousands): Balance at Initiatives Cash Balance at Severance $ — $ 3,804 $ (3,055 ) $ 749 The Company expects that the remaining amount accrued under the 2015 Restructuring Initiative will be paid in the second quarter of 2016. 2012 Restructuring Initiative In August 2012, the Company announced that it had committed to a restructuring initiative to streamline operations and reduce operating costs by closing and consolidating certain facilities and reducing its worldwide workforce (the "2012 Restructure Initiative"). The Company regularly reviews its restructuring accruals against expected cash expenditures to determine if adjustments are required. As a result of such reviews, the Company recorded a net credit to restructuring expense aggregating $1.7 million in the year ended December 31, 2015. This amount is comprised of credits of $1.4 million in connection with a settlement with the landlord of the Company's Fremont, California facility to vacate the facility without penalty or future payments, $0.3 million in connection with a settlement with the landlord of the Company's Dulles, Virginia facility for an amount that was lower than had previously been accrued and $0.1 million in connection with changes in the amounts of severance ultimately paid to certain individuals. These credits were partially offset by $0.1 million of incremental expense related to vacating our Rochester, New York facility. A summary of the 2012 Restructuring Initiative accrual activity for the years ended December 31, 2015 and 2014 is as follows (in thousands): Year ended December 31, 2015 Balance at Adjustments for changes in estimate Cash Balance at Severance $ 1,682 $ (67 ) $ (1,615 ) $ — Facilities 3,652 (1,589 ) (2,063 ) — $ 5,334 $ (1,656 ) $ (3,678 ) $ — Year ended December 31, 2014 Balance at Initiatives Cash Balance at Severance $ 1,333 $ 3,615 $ (3,266 ) $ 1,682 Facilities 3,012 1,820 (1,180 ) 3,652 $ 4,345 5,435 $ (4,446 ) $ 5,334 Asset write-offs 190 $ 5,625

LONG-TERM LIABILITIES (Tables)

LONG-TERM LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2015
Other Liabilities [Abstract]
Schedule of long-term liabilities	Long-term liabilities consist of the following (in thousands): December 31, 2015 2014 Capital lease obligations $ 131 $ 70 Deferred rent 2,606 3,160 Restructuring 749 5,334 Other 844 1,125 4,330 9,689 Current portion * (1,570 ) (4,443 ) Long-term liabilities, net of current portion $ 2,760 $ 5,246 * Includes $0.7 million at December 31, 2015 and $3.4 million at December 31, 2014 of current accrued restructuring reported as a component of Accrued expenses in the consolidated balance sheets.

STOCK-BASED COMPENSATION PLANS

STOCK-BASED COMPENSATION PLANS (Tables)	12 Months Ended
	Dec. 31, 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 year ended December 31, 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 348,380 $ 14.48 Exercised (155,478 ) $ 10.77 Forfeited (588,693 ) $ 16.37 Expired (773,433 ) $ 20.75 Outstanding at December 31, 2015 6,352,208 $ 15.99 6.14 $ 204 Vested or expected to vest at December 31, 2015 6,165,698 $ 15.99 6.08 $ 200 Exercisable at December 31, 2015 4,407,865 $ 15.97 5.32 $ 155
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 years ended December 31, 2015 , 2014 and 2013 were estimated using the Black-Scholes valuation model with the following assumptions: Year ended December 31, 2015 2014 2013 Risk-free interest rate 1.46%-1.75% 1.53%-2.70% 0.82%-1.71% Expected dividends — — — Weighted average volatility 54.3% 60.8% 63.2% Expected life (years) 5.0-6.0 4.5-6.0 4.5-6.0
Schedule of activity related to unvested restricted stock grants	The activity related to the Company's RSAs for the year ended December 31, 2015 is as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2015 370,182 $ 16.74 Granted 1,943,051 $ 14.02 Vested (491,739 ) $ 17.30 Forfeited (308,711 ) $ 14.71 Unvested balance at December 31, 2015 1,512,783 $ 13.48
Schedule of activity related to performance stock awards	The activity related to the Company's PSAs for the year ended December 31, 2015 is as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2015 34,235 $ 13.60 Granted — $ — Vested (34,235 ) $ 13.60 Forfeited — $ — Unvested balance at December 31, 2015 — $ —
Schedule of stock-based compensation expenses which are included in condensed consolidated statement of operations	The consolidated statements of operations include stock-based compensation for the years ended December 31, 2015 , 2014 and 2013 as follows (in thousands): Year ended December 31, 2015 2014 2013 Product cost of revenue $ 317 $ 337 $ 181 Service cost of revenue 1,524 1,449 1,050 Research and development 5,439 5,759 3,616 Sales and marketing 5,423 5,437 4,780 General and administrative 8,996 10,932 8,246 $ 21,699 $ 23,914 $ 17,873
Schedule of common stock reserved for future issuance	Common stock reserved for future issuance at December 31, 2015 consists of the following: 2007 Plan 2,560,723 ESPP 1,906,165 4,466,888

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Schedule of Income (Loss) Before Taxes	The components of loss from continuing operations before income taxes consist of the following (in thousands): Year ended December 31, 2015 2014 2013 Income (loss) before income taxes: United States $ (29,595 ) $ (16,582 ) $ (21,076 ) Foreign (293 ) 1,941 409 $ (29,888 ) $ (14,641 ) $ (20,667 )
Schedule of Income Tax Expense (Benefit)	The provision (benefit) for income taxes from continuing operations consists of the following (in thousands): Year ended December 31, 2015 2014 2013 Provision (benefit) for income taxes: Current: Federal $ 60 $ 23 $ 14 State 150 150 150 Foreign 982 926 1,696 Total current 1,192 1,099 1,860 Deferred: Federal (7,069 ) (3,885 ) (1,911 ) State 4,962 (1,656 ) (103 ) Foreign 155 414 (1,081 ) Change in valuation allowance 2,767 6,242 2,687 Total deferred 815 1,115 (408 ) Total $ 2,007 $ 2,214 $ 1,452
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation of the Company's effective tax rate for continuing operations to the statutory federal rate is as follows: Year ended December 31, 2015 2014 2013 U.S. statutory income tax rate (35.0 )% (35.0 )% (35.0 )% State income taxes, net of federal benefit — (4.9 ) 0.4 Foreign income taxes 3.6 5.1 1.3 Capital loss expiration — — 24.0 Foreign deemed dividends 1.7 11.5 1.8 Stock-based compensation 14.4 12.0 7.6 Tax credits (3.3 ) (14.6 ) (6.1 ) Valuation allowance 24.3 29.8 9.9 Goodwill amortization 2.2 4.8 3.3 Meals and entertainment 0.8 2.5 1.3 Tax gain on sale of acquired assets — 4.2 — Other, net (2.0 ) (0.3 ) (1.5 ) Effective income tax rate 6.7 % 15.1 % 7.0 %
Summary of Deferred Tax Assets and Liabilities	The following is a summary of the significant components of deferred income tax assets and liabilities (in thousands): December 31, 2015 2014 Assets: Net operating loss carryforwards $ 76,970 $ 74,717 Research and development tax credits 22,412 24,978 Other tax credits 230 91 Intangible assets 7,128 4,808 Deferred revenue 3,936 1,911 Accrued expenses 8,706 10,619 Inventory 6,103 5,713 Stock-based compensation 13,594 12,913 Other temporary differences 2,623 3,924 141,702 139,674 Valuation allowance (139,823 ) (137,640 ) Total deferred tax assets 1,879 2,034 Liabilities: Purchased intangible assets (2,282 ) (1,623 ) Total deferred tax liabilities (2,282 ) (1,623 ) Total net deferred tax assets $ (403 ) $ 411 Reported as: Deferred income taxes - current assets $ — $ 991 Deferred income taxes - noncurrent assets 1,879 1,043 Deferred income taxes - noncurrent liabilities (2,282 ) (1,623 ) $ (403 ) $ 411
Schedule of Unrecognized Tax Benefits	A reconciliation of the Company's unrecognized tax benefits is as follows (in thousands): 2015 2014 2013 Unrecognized tax benefits at January 1 $ 8,875 $ 8,861 $ 8,847 Increases related to current year tax positions 13 14 14 Decreases related to prior period tax positions — — — Unrecognized tax benefits at December 31 $ 8,888 $ 8,875 $ 8,861

MAJOR CUSTOMERS (Tables)

MAJOR CUSTOMERS (Tables)	12 Months Ended
	Dec. 31, 2015
Risks and Uncertainties [Abstract]
Schedule of customers contributing 10% or more of the revenue	The following customer contributed 10% or more of the Company's revenue in each of the years ended December 31, 2015, 2014 and 2013 : Year ended December 31, 2015 2014 2013 AT&T 13% 19% 15%

GEOGRAPHIC AND OPERATING SEGM45

GEOGRAPHIC AND OPERATING SEGMENT INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2015
Segment Reporting [Abstract]
Summary of revenue by geographic area as a percentage of total revenue	The Company's classification of revenue by geographic area is determined by the location of the Company's customers. The following table summarizes revenue by geographic area as a percentage of total revenue: Year ended December 31, 2015 2014 2013 United States 71 % 71 % 69 % Europe, Middle East and Africa 13 13 12 Japan 10 9 12 Other Asia Pacific 4 5 5 Other 2 2 2 100 % 100 % 100 %
Schedule of revenue by type	The Company's service revenue is comprised of the following (in thousands): Year ended December 31, 2015 2014 2013 Maintenance $ 89,280 $ 90,003 $ 84,698 Professional services 17,841 23,868 24,763 $ 107,121 $ 113,871 $ 109,461

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	Future minimum payments under operating lease arrangements as of December 31, 2015 are as follows (in thousands): Years ending December 31, 2016 $ 4,111 2017 3,682 2018 2,801 2019 1,565 2020 252 Thereafter — $ 12,411

QUARTERLY RESULTS (UNAUDITED) (

QUARTERLY RESULTS (UNAUDITED) (Tables)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Schedule of quarterly financial information	The following tables present the Company's quarterly operating results for the years ended December 31, 2015 and 2014 . The information for each of these quarters is unaudited and has been prepared on the same basis as the audited consolidated financial statements. In the opinion of management, all necessary adjustments, consisting only of normal recurring adjustments, have been included to present fairly the unaudited consolidated quarterly results when read in conjunction with the Company's audited consolidated financial statements and related notes. First Quarter (1) Second Quarter Third Quarter Fourth Quarter (In thousands, except per share data) Fiscal 2015 Revenue $ 50,145 $ 54,701 $ 67,862 $ 76,326 Cost of revenue 20,915 20,287 22,150 24,025 Gross profit $ 29,230 $ 34,414 $ 45,712 $ 52,301 Income (loss) from operations $ (18,866 ) $ (15,049 ) $ (1,362 ) $ 4,060 Net income (loss) $ (19,359 ) $ (15,343 ) $ (1,896 ) $ 4,703 Income (loss) per share (3): Basic $ (0.39 ) $ (0.31 ) $ (0.04 ) $ 0.09 Diluted $ (0.39 ) $ (0.31 ) $ (0.04 ) $ 0.09 Shares used in computing income (loss) per share: Basic 49,423 49,484 49,625 49,685 Diluted 49,423 49,484 49,625 49,906 First Quarter (2) Second Quarter Third Quarter Fourth Quarter (In thousands, except per share data) Fiscal 2014 Revenue $ 70,742 $ 75,570 $ 73,216 $ 76,798 Cost of revenue 24,319 28,282 25,314 25,006 Gross profit $ 46,423 $ 47,288 $ 47,902 $ 51,792 Loss from operations $ (5,791 ) $ (4,801 ) $ (4,715 ) $ (1,945 ) Net income (loss) $ (3,953 ) $ (5,497 ) $ (5,213 ) $ (2,192 ) Loss per share (3): Basic $ (0.07 ) $ (0.11 ) $ (0.11 ) $ (0.04 ) Diluted $ (0.07 ) $ (0.11 ) $ (0.11 ) $ (0.04 ) Shares used in computing loss per share: Basic 53,080 49,424 49,291 49,361 Diluted 53,080 49,424 49,291 49,361 __________________________________ (1) Includes the results of the SDN Business for the period subsequent to January 2, 2015. (2) Includes the results of PT for the period subsequent to February 19, 2014. (3) Income (loss) per share is calculated independently for each of the quarters presented; accordingly, the sum of the quarterly earnings (loss) per share amounts may not equal the total calculated for the year.

BASIS OF PRESENTATION AND SUM48

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)	Jan. 30, 2015	Sep. 25, 2015USD ($)	Dec. 31, 2015USD ($)financial_institutionmanufacturersegment	Dec. 31, 2014USD ($)financial_institution	Dec. 31, 2013USD ($)
Property, Plant and Equipment [Line Items]
Weighted average amortization period (years)			6 years 2 months 10 days	5 years 9 months
Impairment of intangible assets			$ 0	$ 0	$ 600,000
Stock split ratio	0.2000
Maximum measurement period from the acquisition date within which company records adjustments to the assets acquired and liabilities assumed			1 year
Number of financial institutions | financial_institution			2	2
Advertising expense			$ 900,000	$ 1,500,000	$ 2,700,000
Number of reportable operating segments | segment			1
Undistributed earnings of foreign subsidiaries			$ 28,000,000	28,000,000
Undistributed earnings of foreign subsidiaries previously taxed			16,000,000	15,000,000
Undistributed earnings of foreign subsidiaries subject to U.S. income taxes			$ 12,000,000	$ 13,000,000
Number of contract manufacturers | manufacturer			3
SDN Business [Member]
Property, Plant and Equipment [Line Items]
Weighted average amortization period (years)			7 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			5 years
Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			3 years
Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			2 years
Minimum [Member] | NET [Member]
Property, Plant and Equipment [Line Items]
Weighted average amortization period (years)			3 years
Minimum [Member] | PT [Member]
Property, Plant and Equipment [Line Items]
Weighted average amortization period (years)			6 years
Minimum [Member] | Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			1 year
Minimum [Member] | Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			2 years
Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			5 years
Maximum [Member] | NET [Member]
Property, Plant and Equipment [Line Items]
Weighted average amortization period (years)			5 years
Maximum [Member] | PT [Member]
Property, Plant and Equipment [Line Items]
Weighted average amortization period (years)			7 years
Maximum [Member] | Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			5 years
Maximum [Member] | Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			3 years
Foreign Translation of Depreciation Expense [Member]
Property, Plant and Equipment [Line Items]
Quantifying Misstatement in Current Year Financial Statements, Amount		$ 1,400,000
Error Correction, Tax Effect		0
Depreciation		$ 1,400,000

BASIS OF PRESENTATION AND SUM49

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Intangible Assets and Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Impairment of intangible assets	$ 0	$ 0	$ 600

BASIS OF PRESENTATION AND SUM50

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Foreign Currency Translation (Details) - General and Administrative Expense [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Foreign Currency Balance [Line Items]
Transaction losses	$ 1,442	$ (420)	$ (746)
Remeasurement gains (losses)	(1,860)	1,980	(164)
Transaction gains (losses)	$ (418)	$ 1,560	$ (910)

BASIS OF PRESENTATION AND SUM51

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred income taxes - current assets	$ 0	$ 991
Deferred income taxes - noncurrent assets	1,879	$ 1,043
New Accounting Pronouncement, Early Adoption, Effect [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred income taxes - current assets	(1,000)
Deferred income taxes - noncurrent assets	$ 1,000

BUSINESS ACQUISITONS - Sale of

BUSINESS ACQUISITONS - Sale of MPS (Details) - USD ($) $ in Thousands	Jun. 20, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Divestiture of business		$ 0	$ 2,000	$ 0
Multi Protocol Server [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Divestiture of business	$ 2,000
Inventory	200
Fixed assets	100
Deferred revenue	200
Goodwill	1,900
Transaction costs	$ 400

BUSINESS ACQUISITONS - (Details

BUSINESS ACQUISITONS - (Details) - USD ($) $ / shares in Units, shares in Millions	Jan. 02, 2015	Feb. 19, 2014	Sep. 25, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jul. 02, 2015	Aug. 24, 2012
Fair value of consideration transferred:
Cash, net of cash acquired					$ 10,897,000	$ 35,022,000	$ 0
Assumption of equity awards in connection with acquisition of Network Technologies, Inc.					0	1,671,000	0
Allocation of the purchase consideration:
Goodwill				$ 39,263,000	40,310,000	39,263,000	32,379,000
Acquisition-Related Costs
Professional Fees					131,000	1,309,000	93,000
Change of Control Agreements					0	249,000	0
Acquisition-related					$ 131,000	$ 1,558,000	$ 93,000
In Process Research and Development [Member]
Allocation of the purchase consideration:
Finite-Lived Intangible Assets, Period Increase (Decrease)			$ (7,500,000)
Treq Labs, Inc [Member]
Acquisition Of Net
Payments to Acquire Business, Net of Cash Acquired, Initial Payment	$ 10,100,000
Business Combination, Consideration Transferred, Liabilities Incurred	$ 750,000
Business Combination, Future Consideration Payment								$ 750,000
Business Combination, Contingent Consideration Arrangements, Shares Authorized in Earn-Out Agreement	3.5
Business Combination, Contingent Consideration, Liability			$ 0
Fair value of consideration transferred:
Cash, net of cash acquired	$ 10,897,000
Fair value of total consideration	11,647,000
Allocation of the purchase consideration:
Assets acquired and liabilities assumed	11,647,000
Treq Labs, Inc [Member] | In Process Research and Development [Member]
Allocation of the purchase consideration:
Intangible assets	9,100,000
Treq Labs, Inc [Member] | Developed technology [Member]
Allocation of the purchase consideration:
Intangible assets	1,500,000
Goodwill	$ 1,047,000
PT [Member]
Acquisition Of Net
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life					6 years 9 months 18 days
Cash consideration per share of the acquired entity (in dollars per share)		$ 3.75
Goodwill, Purchase Accounting Adjustments				600,000
Increase (decrease) to other current assets				(400,000)
Increase (decrease) to other long-term liabilities				$ 200,000
Revenue					$ 14,600,000
Fair value of consideration transferred:
Cash, net of cash acquired		$ 35,022,000
Assumption of equity awards in connection with acquisition of Network Technologies, Inc.		1,671,000
Fair value of total consideration		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
Intangible assets		17,100,000
Goodwill		8,781,000
Current liabilities		(2,762,000)
Other long-term liabilities		(329,000)
Assets acquired and liabilities assumed		36,693,000
Acquisition-Related Costs
Professional Fees					1,300,000
PT [Member] | Developed technology [Member]
Allocation of the purchase consideration:
Intangible assets		13,200,000
PT [Member] | Customer relationships [Member]
Allocation of the purchase consideration:
Intangible assets		$ 3,900,000
NET [Member]
Acquisition Of Net
Cash consideration per share of the acquired entity (in dollars per share)									$ 1.35
SDN Business [Member]
Acquisition-Related Costs
Professional Fees					$ 300,000
Earn-Out Agreement Revenue Level 1 [Member]
Acquisition Of Net
Business Combination, Contingent Consideration Arrangements, Duration of Earn-out Agreement	3 years
Earn-Out Agreement Revenue Level 1 [Member] | Treq Labs, Inc [Member]
Acquisition Of Net
Business Combination, Contingent Consideration Arrangements, Shares Authorized in Earn-Out Agreement	1.3
Business Combination, Contingent Consideration Arrangements, Earn-out Agreement Aggregate Revenue Threshold	$ 60,000,000
Earn-Out Agreement Revenue Level 2 [Member] | Treq Labs, Inc [Member]
Acquisition Of Net
Business Combination, Contingent Consideration Arrangements, Shares Authorized in Earn-Out Agreement	2.2
Business Combination, Contingent Consideration Arrangements, Earn-out Agreement Aggregate Revenue Threshold	$ 150,000,000

EARNINGS (LOSS) PER SHARE - (De

EARNINGS (LOSS) PER SHARE - (Details) - shares shares in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2015	Sep. 25, 2015	Jun. 26, 2015	Mar. 27, 2015	[1]	Dec. 31, 2014	Sep. 26, 2014	Jun. 27, 2014	Mar. 28, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of weighted average shares outstanding from basic to diluted
Weighted average shares outstanding - basic	49,685	49,625	49,484	49,423		49,361	49,291	49,424	53,080	49,560	50,245	55,686
Potential dilutive common shares										0	0	0
Weighted average shares outstanding - diluted	49,906	49,625	49,484	49,423		49,361	49,291	49,424	53,080	49,560	50,245	55,686
Common stock and unvested shares of restricted stock not included because their effect would have been antidilutive (in shares)										8,200	8,000	7,100
[1]	(1)Includes the results of the SDN Business for the period subsequent to January 2, 2015.(2)Includes the results of PT for the period subsequent to February 19, 2014.

CASH EQUIVALENTS AND INVESTME55

CASH EQUIVALENTS AND INVESTMENTS - Narrative (Details) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sale of Available-for-sale Securities	$ 45,900
Available-for-sale Securities, Gross Realized Gains	$ 46

CASH EQUIVALENTS AND INVESTME56

CASH EQUIVALENTS AND INVESTMENTS - Schedule of Activity for Short-Term Investments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 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	$ 7,122	$ 11,653
Cash equivalents, fair value	7,122	11,653
Marketable securities, amortized cost	58,590	64,500
Marketable securities, unrealized gains	2	3
Marketable securities, unrealized losses	(59)	(60)
Marketable securities, fair value	58,533	64,443
Investments, amortized cost	33,705	42,492
Investments, unrealized gains	2	5
Investments, unrealized losses	(102)	(90)
Investments, fair value	$ 33,605	42,407
Minimum [Member]
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Period considered to classify available-for-sale securities as investments	1 year
Maximum [Member]
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Period considered to classify available-for-sale securities as investments	2 years
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	$ 3,910	1,273
Marketable securities, unrealized gains	0	1
Marketable securities, unrealized losses	(1)	(1)
Marketable securities, fair value	3,909	1,273
Investments, amortized cost	2,165	2,702
Investments, unrealized gains	0	1
Investments, unrealized losses	(4)	(3)
Investments, fair value	2,161	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	3,450	4,016
Marketable securities, unrealized gains	0	0
Marketable securities, unrealized losses	(2)	0
Marketable securities, fair value	3,448	4,016
Investments, amortized cost	1,999	2,300
Investments, unrealized gains	0	0
Investments, unrealized losses	(13)	(1)
Investments, fair value	1,986	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	46,736	40,921
Marketable securities, unrealized gains	2	2
Marketable securities, unrealized losses	(56)	(59)
Marketable securities, fair value	46,682	40,864
Investments, amortized cost	29,541	35,897
Investments, unrealized gains	2	4
Investments, unrealized losses	(85)	(86)
Investments, fair value	29,458	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	3,994	9,340
Marketable securities, unrealized gains	0	0
Marketable securities, unrealized losses	0	0
Marketable securities, fair value	3,994	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	500	8,950
Marketable securities, unrealized gains	0	0
Marketable securities, unrealized losses	0	0
Marketable securities, fair value	$ 500	8,950
Investments, amortized cost		500
Investments, unrealized gains		0
Investments, unrealized losses		0
Investments, fair value		$ 500

CASH EQUIVALENTS AND INVESTME57

CASH EQUIVALENTS AND INVESTMENTS - Schedule of Short-Term Investments by Measurement (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	$ 7,122	$ 11,653
Marketable securities, fair value	58,533	64,443
Investments, fair value	33,605	42,407
Quoted prices in active markets (Level 1) [Member]
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	7,122	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	58,533	64,443
Investments, fair value	33,605	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]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	3,909	1,273
Investments, fair value	2,161	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	3,909	1,273
Investments, fair value	2,161	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]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	3,448	4,016
Investments, fair value	1,986	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	3,448	4,016
Investments, fair value	1,986	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]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	46,682	40,864
Investments, fair value	29,458	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	46,682	40,864
Investments, fair value	29,458	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]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	3,994	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	3,994	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]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	500	8,950
Investments, fair value		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
Certificates of deposit [Member] | Significant other observable inputs (Level 2) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	500	8,950
Investments, fair value		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

ACCOUNTS RECEIVABLE, NET - Sche

ACCOUNTS RECEIVABLE, NET - Schedule of Accounts Receivabale, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Receivables [Abstract]
Accounts receivable, gross	$ 51,543	$ 63,001
Allowance for doubtful accounts	(10)	(58)	$ (157)	$ 0
Accounts receivable, net	$ 51,533	$ 62,943

ACCOUNTS RECEIVABLE, NET - Sc59

ACCOUNTS RECEIVABLE, NET - Schedule of Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of year	$ 58	$ 157	$ 0
Charges to expense	17	92	415
Write-offs	(65)	(191)	(258)
Balance at end of year	$ 10	$ 58	$ 157

INVENTORY - (Details)

INVENTORY - (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Inventory Disclosure [Abstract]
On-hand final assemblies and finished goods inventories	$ 17,136	$ 19,285
Deferred cost of goods sold	5,975	2,829
Gross inventory	23,111	22,114
Less current portion	$ (23,111)	$ (22,114)

PROPERTY AND EQUIPMENT - Schedu

PROPERTY AND EQUIPMENT - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 93,420	$ 95,577
Less accumulated depreciation and amortization	(79,800)	(77,732)
Property and equipment, net	$ 13,620	17,845
Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Property and equipment, gross	$ 63,667	65,703
Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Property and equipment, gross	$ 17,463	17,342
Software [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Software [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 675	612
Furniture and Fixtures [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Furniture and Fixtures [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Property and equipment, gross	$ 11,615	$ 11,920
Leasehold Improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	1 year
Leasehold Improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years

PROPERTY AND EQUIPMENT - Narrat

PROPERTY AND EQUIPMENT - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Abstract]
Depreciation and amortization of property and equipment	$ 11,961	$ 11,488	$ 12,329

PROPERTY AND EQUIPMENT - Proper

PROPERTY AND EQUIPMENT - Property and Equipment Under Capital Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Cost	$ 137	$ 113
Less accumulated depreciation	(9)	(71)
Property and equipment under capital leases, net	$ 128	$ 42

PROPERTY AND EQUIPMENT - Prop64

PROPERTY AND EQUIPMENT - Property and Equipment by Geographic Area (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment, net	$ 13,620	$ 17,845
United States [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, net	9,145	12,652
Asia/Pacific [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, net	3,098	3,574
Europe [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, net	818	765
Other [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, net	$ 559	$ 854

INTANGIBLE ASSETS AND GOODWIL65

INTANGIBLE ASSETS AND GOODWILL - (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 25, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Intangible Assets And Goodwill
Weighted average amortization period (years)		6 years 2 months 10 days	5 years 9 months
Cost		$ 43,640	$ 34,049
Accumulated amortization		17,553	11,455
Net carrying value		26,087	22,594
Amortization expense		7,107	4,597	$ 4,546
Impairment of intangible assets		0	0	600
Estimated future amortization expense for intangible assets
2,015		7,189
2,016		7,281
2,017		4,644
2,018		3,611
2,019		2,100
Thereafter		1,262
Total		26,087
Goodwill [Roll Forward]
Goodwill		43,416	42,369	35,485
Accumulated impairment losses		3,106	3,106	3,106
Goodwill at the beginning of the period		39,263	32,379
Goodwill, Written off Related to Sale of Business Unit		0	(1,897)
Goodwill at the end of the period		40,310	$ 39,263	32,379
In Process Research and Development [Member]
Intangible Assets And Goodwill
Finite-Lived Intangible Assets, Period Increase (Decrease)	$ (7,500)
Weighted average amortization period (years)	7 years
Cost		1,600
Accumulated amortization		0
Net carrying value		1,600
Intellectual Property [Member]
Intangible Assets And Goodwill
Weighted average amortization period (years)			5 years
Cost			$ 999
Accumulated amortization			999
Net carrying value			0
Amortization expense		$ 0	$ 0	200
Developed technology [Member]
Intangible Assets And Goodwill
Weighted average amortization period (years)		6 years 5 months 3 days	6 years 2 months 6 days
Cost		$ 31,280	$ 22,280
Accumulated amortization		10,415	5,193
Net carrying value		20,865	17,087
Amortization expense		$ 5,222	$ 2,464	1,999
Customer relationships [Member]
Intangible Assets And Goodwill
Weighted average amortization period (years)		5 years 6 months 27 days	5 years 6 months 27 days
Cost		$ 10,030	$ 10,040
Accumulated amortization		6,408	4,695
Net carrying value		3,622	5,345
Amortization expense		$ 1,723	$ 1,889	2,104
Internal use software [Member]
Intangible Assets And Goodwill
Weighted average amortization period (years)		3 years	3 years
Cost		$ 730	$ 730
Accumulated amortization		730	568
Net carrying value		0	162
Amortization expense		$ 162	244	$ 243
SDN Business [Member]
Intangible Assets And Goodwill
Weighted average amortization period (years)		7 years
Goodwill [Roll Forward]
Acquisition of NET		$ 1,047	0
PT [Member]
Goodwill [Roll Forward]
Acquisition of NET		$ 0	$ 8,781

ACCRUED EXPENSES - (Details)

ACCRUED EXPENSES - (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Employee compensation and related costs	$ 22,180	$ 20,042
Other	9,783	12,107
Total	$ 31,963	$ 32,149

RESTRUCTURING ACCRUAL - (Detail

RESTRUCTURING ACCRUAL - (Details) $ in Thousands	Apr. 16, 2015employees	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		$ 5,334
Balance at the end of the period		749	$ 5,334
Other Long Term Liabilities [Member]
RESTRUCTURING ACCRUAL
Accrued restructuring			1,900
Restructuring Charges [Member]
Restructuring Reserve [Roll Forward]
Restructuring		2,148	5,625	$ 5,411
2015 Restructuring [Member]
RESTRUCTURING ACCRUAL
Number of positions eliminated | employees	150
Number of positions eliminated (percent)	12.50%
2015 Restructuring [Member] | Employee Severance and Facilities [Member]
Restructuring Reserve [Roll Forward]
Restructuring		3,800
2015 Restructuring [Member] | Employee severance [Member]
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		0
Restructuring		3,804
Cash payments		(3,055)
Balance at the end of the period		749	0
2012 Restructuring [Member]
RESTRUCTURING ACCRUAL
Restructuring Reserve, Accrual Adjustment		1,700
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		5,334	4,345
Restructuring		(1,656)	5,435
Cash payments		(3,678)	(4,446)
Balance at the end of the period		0	5,334	4,345
2012 Restructuring [Member] | Employee severance [Member]
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		1,682	1,333
Restructuring		(67)	3,615
Cash payments		(1,615)	(3,266)
Balance at the end of the period		0	1,682	1,333
2012 Restructuring [Member] | Facilities [Member]
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period		3,652	3,012
Restructuring		(1,589)	1,820
Cash payments		(2,063)	(1,180)
Balance at the end of the period		0	3,652	$ 3,012
2012 Restructuring [Member] | Asset write-offs [Member]
Restructuring Reserve [Roll Forward]
Restructuring			190
2012 Restructuring [Member] | Restructuring Charges [Member]
Restructuring Reserve [Roll Forward]
Restructuring			$ 5,625
2012 Restructuring [Member] | Contract Termination [Member] | Fremont, CA [Member]
RESTRUCTURING ACCRUAL
Restructuring Reserve, Accrual Adjustment		1,400
2012 Restructuring [Member] | Contract Termination [Member] | Dulles, VA [Member]
RESTRUCTURING ACCRUAL
Restructuring Reserve, Accrual Adjustment		0
2012 Restructuring [Member] | Contract Termination [Member] | NEW YORK
RESTRUCTURING ACCRUAL
Restructuring Reserve, Accrual Adjustment		0
2012 Restructuring [Member] | Severance [Member]
RESTRUCTURING ACCRUAL
Restructuring Reserve, Accrual Adjustment		$ 0

DEBT - (Details)

DEBT - (Details) - USD ($) $ / shares in Units, $ in Millions	Jun. 27, 2014	Dec. 31, 2007	Dec. 31, 2015	Sep. 26, 2014	Aug. 27, 2012	Aug. 24, 2012
DEBT
Line of Credit Facility, Covenant, Minimum Cash and Cash Equivalent			$ 85
Line of Credit Facility, Covenant, Minimum Revenues			$ 50
NET [Member]
DEBT
Cash consideration per share of the acquired entity (in dollars per share)						$ 1.35
2007 Notes [Member] | NET [Member]
DEBT
Interest rate			3.75%
Amount of debt issued		$ 85
Amount of debt assumed and outstanding at the acquisition date						$ 10.5
Percentage of principal amount at which notes may be required to be repurchased in event of fundamental change			100.00%
Repurchase of aggregate principal amounts					$ 8.1
Aggregate principal amounts remaining outstanding			$ 2.4
Revolving Credit Facility [Member]
DEBT
Line of Credit Facility, Maximum Borrowing Capacity				$ 15
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.15%
London Interbank Offered Rate (LIBOR) [Member] | Revolving Credit Facility [Member]
DEBT
Interest rate				1.50%
Eurodollar [Member] | Revolving Credit Facility [Member]
DEBT
Interest rate				1.00%
Federal Funds Purchased [Member] | Revolving Credit Facility [Member]
DEBT
Interest rate				0.50%
Minimum [Member] | Federal Funds Rate [Member] | Revolving Credit Facility [Member]
DEBT
Basis spread on variable rate			0.50%

LONG-TERM LIABILITIES - Schedul

LONG-TERM LIABILITIES - Schedule of Long-Term Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Other Liabilities [Abstract]
Capital lease obligations	$ 131	$ 70
Deferred rent	2,606	3,160
Restructuring	749	5,334
Other	844	1,125
Long-term liabilities	4,330	9,689
Current portion	(1,570)	(4,443)
Other long-term liabilities	2,760	5,246
Current portion of accrued restructuring	$ 700	$ 3,400

COMMON STOCK REPURCHASES AND 70

COMMON STOCK REPURCHASES AND UNDERWRITTEN OFFERING (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	Mar. 20, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jul. 29, 2013
Class of Stock [Line Items]
Payments for repurchase of common stock	$ 75,300	$ 7,917	$ 93,224	$ 59,674
Remaining authorized purchase amount		14,900
Stock Issued During Period, Shares, New Issues	7,500
Over-allotment Option Period	30 days
Stock Issued During Period, Shares, New Issues, Over-Allotment Option	1,125
Stock Repurchased During Period, Shares	4,300
Stock Repurchased During Period, Price Per Share	$ 17.4410
Transaction Fees	$ 300
Common Stock [Member]
Class of Stock [Line Items]
Authorized amount					$ 100,000
Repurchase and retirement of common stock		$ 7,900
Payments for repurchase of common stock			$ 18,000
Shares repurchased and retired, shares		600	1,000

STOCK-BASED COMPENSATION PLAN71

STOCK-BASED COMPENSATION PLANS - Reverse Stock Split (Details)	Jan. 30, 2015	Dec. 31, 2015$ / sharesshares	Dec. 31, 2014$ / sharesshares
Class of Stock [Line Items]
Stock split ratio	0.2000
Common stock, shares authorized | shares		120,000,000	120,000,000
Common stock, par value (in dollars per share) | $ / shares		$ 0.001	$ 0.001
Subsequent Event [Member]
Class of Stock [Line Items]
Stock split ratio	0.2000

STOCK-BASED COMPENSATION PLAN72

STOCK-BASED COMPENSATION PLANS - 2007 Stock Incentive Plan (Details)	Dec. 02, 2014shares	Dec. 01, 2014shares	Jun. 16, 2010shares	Jun. 30, 2015shares	Dec. 31, 2015shares	Dec. 31, 2014shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)					4,466,888
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares outstanding					1,512,783	370,182
Amended 2007 plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized (in shares)	2,000,000		4,200,000	1,400,000
Maximum shares per employee	40,000	20,000
Conversion factor used to convert a number of shares available for grant into the entity's equity awards				1.61
Shares available for future issuance (in shares)					2,560,723
Options outstanding		810,064
Options and restricted stock outstanding		812,064
Return rate of shares	1.25
Amended 2007 plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares outstanding		2,000
Incentive Plan 2008 and 2012 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)		313,747
Maximum [Member] | Amended 2007 plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Conversion factor used to convert a number of shares available for grant into the entity's equity awards	1.57
Minimum [Member] | Amended 2007 plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Conversion factor used to convert a number of shares available for grant into the entity's equity awards	1.5

STOCK-BASED COMPENSATION PLAN73

STOCK-BASED COMPENSATION PLANS - 2008 and 2012 Stock Incentive Plans (Details) $ / shares in Units, $ in Thousands	Feb. 19, 2014USD ($)$ / shares	Sep. 25, 2015	Nov. 30, 2012	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Aug. 24, 2012$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Business acquisition purchase consideration - assumed equity awards				$ 0	$ 1,671	$ 0
Fair value of the assumed awards attributable to future stock-based compensation expense				$ 32,200
Weighted average period to record stock-based compensation expenses				2 years
2008 plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Conversion factor used to convert a number of shares available for grant into the entity's equity awards				1.25
PT [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Conversion factor used to convert a number of shares available for grant into the entity's equity awards		1.23
Acquisition consideration per share (in dollars per share) | $ / shares	$ 3.75
Assumption of equity awards in connection with acquisition of Network Technologies, Inc.	$ 1,671
Fair value of the assumed awards attributable to future stock-based compensation expense	$ 900
Weighted average period to record stock-based compensation expenses	1 year
NET [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Acquisition consideration per share (in dollars per share) | $ / shares							$ 1.35
NET [Member] | 2008 plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Business acquisition purchase consideration - assumed equity awards				$ 900
Fair value of the assumed awards attributable to future stock-based compensation expense				$ 400
Weighted average period to record stock-based compensation expenses				8 months
NET [Member] | 2008 plan [Member] | Sonus Equity Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Conversion factor used to convert a number of shares available for grant into the entity's equity awards			0.75
Acquisition consideration per share (in dollars per share) | $ / shares							$ 1.35
Number of consecutive trading days used to calculate conversion price of shares				10 days

STOCK-BASED COMPENSATION PLAN74

STOCK-BASED COMPENSATION PLANS - Executive and Board of Directors Equity Arrangements (Details)

Mar. 16, 2015executivesshares

Jul. 09, 2014$ / shares

Jun. 11, 2014

Feb. 15, 2014

Jan. 22, 2014executives

Aug. 15, 2013

Feb. 15, 2013executives

Mar. 29, 2013executives

Sep. 25, 2015$ / shares

Sep. 25, 2015USD ($)executives$ / shares

Dec. 31, 2015USD ($)$ / sharesshares

Dec. 31, 2014$ / shares

Dec. 31, 2013$ / shares

Sep. 16, 2014USD ($)

Sep. 15, 2014USD ($)

Jan. 02, 2014

Aug. 10, 2012

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Incremental stock-based compensation expense | $

$ 700,000

Stock options [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares

$ 7.30

$ 8.32

$ 7.71

Restricted Stock [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Grant-date fair value (in dollars per share) | $ / shares

$ 14.02

Awards granted | shares

1,943,051

Performance Share Units [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Grant-date fair value (in dollars per share) | $ / shares

$ 14.68

Awards granted | shares

131,250

131,250

Share-based Compensation Arrangement by Share-based Payment Award, Number of Executives Granted Shares

8

February 15, 2013 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of Executives

8

February 15, 2013 [Member] | Restricted Stock [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Subscription rate as a percentage of bonus

100.00%

Award vesting percentage

50.00%

2015 Bonus [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of Executives

22

Share-based Compensation by Share-based Payment Award, Stock Percentage of Award

50.00%

Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Salary Base to Calculate Shares Granted

150.00%

Share Price | $ / shares

$ 20.55

$ 20.55

Share-based Compensation by Share-based Payment Award, Cash Percentage of Award

50.00%

Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares

$ 6.79

Adjustments to Additional Paid in Capital, Share-based Compensation, Stock Options, Change in Plan Arrangement | $

$ 1,000,000

2015 Bonus [Member] | Stock options [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of Executives

16

2015 Bonus [Member] | Stock Option and Cash Option [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of Executives

5

2015 Bonus [Member] | Cash Only [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of Executives

1

Board Member [Member] | Stock options [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Exercisable period

3 years

Chief Executive Officer [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Officers' Compensation | $

$ 600,000

$ 500,000

Chief Executive Officer [Member] | Restricted Stock [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Maximum employee subscription rate

150.00%

Chief Executive Officer [Member] | August 10, 2012 [Member] | Restricted Stock [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Maximum employee subscription rate

150.00%

Award vesting percentage

50.00%

50.00%

Executives [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of Executives

21

Grant-date fair value (in dollars per share) | $ / shares

$ 19.25

Executives [Member] | February 18, 2014 [Member] | Restricted Stock [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of Executives

21

Subscription rate as a percentage of bonus

150.00%

Executives [Member] | Bonus 2014 - Entirely in shares [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of Executives

17

Percent of shares awarded for bonus

100.00%

Subscription rate as a percentage of bonus

150.00%

Executives [Member] | Bonus 2014 - Half in shares [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of Executives

4

Percent of shares awarded for bonus

50.00%

Percent of bonus awarded in cash

50.00%

Cash portion of bonus, percent of 2014 Bonus earned

50.00%

Subscription rate as a percentage of bonus

150.00%

Deferred Bonus [Member] | 2015 Bonus [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Deferred Compensation Arrangement with Individual, Compensation Expense | $

$ 1,300,000

STOCK-BASED COMPENSATION PLAN75

STOCK-BASED COMPENSATION PLANS - Other Dislocures (Details) - USD ($) $ / shares in Units, $ in Thousands	Mar. 16, 2015	Dec. 02, 2014	Dec. 01, 2014	Jul. 09, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Oct. 31, 2012
Weighted average exercise price
Granted (in dollars per share)					$ 14.48
Range of assumptions used in estimating fair value of options
Expected dividends					0.00%	0.00%	0.00%
Cash received from the exercise of stock options (in dollars)					$ 1,757	$ 10,117	$ 2,669
Weighted average grant-date fair value
Total fair value of restricted stock awards, restricted stock units, performance-based stock awards and performance-based stock units on date vested					9,138	8,425	6,816
Stock-based compensation (in dollars)					$ 21,699	$ 23,914	$ 17,873
Shares available for future issuance (in shares)					4,466,888
Minimum [Member]
Range of assumptions used in estimating fair value of options
Expected life					4 years 6 months	4 years 6 months	4 years 6 months
Maximum [Member]
Range of assumptions used in estimating fair value of options
Expected life					6 years	6 years	6 years
Product cost of revenue [Member]
Weighted average grant-date fair value
Stock-based compensation (in dollars)					$ 317	$ 337	$ 181
Service cost of revenue [Member]
Weighted average grant-date fair value
Stock-based compensation (in dollars)					1,524	1,449	1,050
Research and development [Member]
Weighted average grant-date fair value
Stock-based compensation (in dollars)					5,439	5,759	3,616
Sales and marketing [Member]
Weighted average grant-date fair value
Stock-based compensation (in dollars)					5,423	5,437	4,780
General and administrative [Member]
Weighted average grant-date fair value
Stock-based compensation (in dollars)					$ 8,996	$ 10,932	$ 8,246
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period					4 years
Number of shares
Outstanding at the beginning of the period (in shares)					7,521,432
Granted (in shares)					348,380
Exercised (in shares)					(155,478)
Forfeited (in shares)					(588,693)
Expired (in shares)					(773,433)
Outstanding at the end of the period (in shares)					6,352,208	7,521,432
Vested or expected to vest at the end of the period (in shares)					6,165,698
Exercisable at the end of the period (in shares)					4,407,865
Weighted average exercise price
Outstanding at the beginning of the period (in dollars per share)					$ 16.47
Exercised (in dollars per share)					10.77
Forfeited (in dollars per share)					16.37
Expired (in dollars per share)					20.75
Outstanding at the end of the period (in dollars per share)					15.99	$ 16.47
Vested or expected to vest at the end of the period (in dollars per share)					15.99
Exercisable at the end of the period (in dollars per share)					$ 15.97
Weighted average remaining contractual life (in years)
Outstanding at the end of the period					6 years 1 month 22 days
Vested or expected to vest at the end of the period					6 years 29 days
Exercisable at the end of the period					5 years 3 months 25 days
Aggregate intrinsic value (in dollars)
Outstanding at the end of the period (in dollars)					$ 204
Vested or expected to vest at the end of the period (in dollars)					200
Exercisable at the end of the period (in dollars)					$ 155
Range of assumptions used in estimating fair value of options
Risk-free interest rates, minimum					1.46%	1.53%	0.82%
Risk-free interest rates, maximum					1.75%	2.70%	1.71%
Weighted average volatility					54.30%	60.80%	63.20%
Weighted average grant date fair value of stock options granted (in dollars per share)					$ 7.30	$ 8.32	$ 7.71
Total intrinsic values of stock options exercised (in dollars)					$ 900	$ 5,100	$ 1,300
Cash received from the exercise of stock options (in dollars)					$ 1,800	$ 10,100	2,700
Restricted Stock [Member]
Change in unvested restricted stock awards
Unvested balance at the beginning of the period (in shares)					370,182
Granted (in shares)					1,943,051
Vested (in shares)					(491,739)
Forfeited (in shares)					(308,711)
Unvested balance at the end of the period (in shares)					1,512,783	370,182
Weighted average grant-date fair value
Unvested balance at the end of the period (in dollars per share)					$ 16.74
Granted (in dollars per share)					14.02
Vested (in dollars per share)					17.30
Forfeited (in dollars per share)					14.71
Unvested balance at end of the period (in dollars per share)					$ 13.48	$ 16.74
Total fair value of restricted stock awards, restricted stock units, performance-based stock awards and performance-based stock units on date vested					$ 8,500	$ 6,700	2,400
Restricted Stock Awards [Member]
Change in unvested restricted stock awards
Unvested balance at the beginning of the period (in shares)					0
Granted (in shares)					120,215
Vested (in shares)					0
Forfeited (in shares)					(24,854)
Unvested balance at the end of the period (in shares)					95,361	0
Weighted average grant-date fair value
Unvested balance at the end of the period (in dollars per share)					$ 0
Granted (in dollars per share)					16.05
Vested (in dollars per share)					0
Forfeited (in dollars per share)					16.05
Unvested balance at end of the period (in dollars per share)					$ 16.05	$ 0
Performance share awards [Member]
Change in unvested restricted stock awards
Unvested balance at the beginning of the period (in shares)					34,235
Granted (in shares)					0
Vested (in shares)					(34,235)
Forfeited (in shares)					0
Unvested balance at the end of the period (in shares)					0	34,235
Weighted average grant-date fair value
Unvested balance at the end of the period (in dollars per share)					$ 13.60
Granted (in dollars per share)					0
Vested (in dollars per share)					13.60
Forfeited (in dollars per share)					0
Unvested balance at end of the period (in dollars per share)					$ 0	$ 13.60
Performance Share Units [Member]
Change in unvested restricted stock awards
Unvested balance at the beginning of the period (in shares)					0
Granted (in shares)	131,250				131,250
Vested (in shares)					(11,666)
Forfeited (in shares)					(8,334)
Unvested balance at the end of the period (in shares)					111,250	0
Weighted average grant-date fair value
Unvested balance at the end of the period (in dollars per share)					$ 0
Granted (in dollars per share)					14.68
Vested (in dollars per share)					14.18
Forfeited (in dollars per share)					15.38
Unvested balance at end of the period (in dollars per share)					$ 14.68	$ 0
Total fair value of restricted stock awards, restricted stock units, performance-based stock awards and performance-based stock units on date vested					$ 600	$ 1,700	$ 2,600
Executives [Member]
Weighted average grant-date fair value
Granted (in dollars per share)				$ 19.25
Amended 2007 plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period					10 years
Number of shares
Outstanding at the beginning of the period (in shares)		810,064
Outstanding at the end of the period (in shares)			810,064
Weighted average grant-date fair value
Maximum shares per employee		40,000	20,000
Shares available for future issuance (in shares)					2,560,723
Amended 2007 plan [Member] | Restricted Stock [Member]
Change in unvested restricted stock awards
Unvested balance at the beginning of the period (in shares)		2,000
Unvested balance at the end of the period (in shares)			2,000
2008 plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period					7 years
2012 plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period					5 years
ESPP [Member]
Weighted average grant-date fair value
Maximum shares per employee					500
Number of shares authorized					5,000,000
Shares available for future issuance (in shares)					1,906,165
Annual Vesting Period [Member] | Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage					25.00%
Annual Vesting Period [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage								25.00%
Monthly Vesting Period [Member] | Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage					75.00%
Semi Annual Vesting Period [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage								75.00%

INCOME TAXES - Schedule of Inco

INCOME TAXES - Schedule of Income (Loss) Before Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loss before income taxes:
United States	$ (29,595)	$ (16,582)	$ (21,076)
Foreign	(293)	1,941	409
Loss before income taxes	$ (29,888)	$ (14,641)	$ (20,667)

INCOME TAXES - Schedule of In77

INCOME TAXES - Schedule of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current:
Federal	$ 60	$ 23	$ 14
State	150	150	150
Foreign	982	926	1,696
Total current	1,192	1,099	1,860
Deferred:
Federal	(7,069)	(3,885)	(1,911)
State	4,962	(1,656)	(103)
Foreign	155	414	(1,081)
Change in valuation allowance	2,767	6,242	2,687
Total deferred	815	1,115	(408)
Total	$ 2,007	$ 2,214	$ 1,452

INCOME TAXES - Schedule of Effe

INCOME TAXES - Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
U.S Statutory income tax rate	(35.00%)	(35.00%)	(35.00%)
State income taxes, net of federal benefit	0.00%	(4.90%)	0.40%
Foreign income taxes	3.60%	5.10%	1.30%
Capital loss expiration	0.00%	0.00%	24.00%
Foreign dividends	1.70%	11.50%	1.80%
Stock-based compensation	14.40%	12.00%	7.60%
Tax credits	(3.30%)	(14.60%)	(6.10%)
Valuation allowance	24.30%	29.80%	9.90%
Goodwill amortization	2.20%	4.80%	3.30%
Meals and entertainment	0.80%	2.50%	1.30%
Tax gain on acquired assets	0.00%	4.20%	0.00%
Other, net	(2.00%)	(0.30%)	(1.50%)
Effective income tax rate	6.70%	15.10%	7.00%

INCOME TAXES - Summary of Defer

INCOME TAXES - Summary of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Assets:
Net operating loss carryforwards	$ 76,970	$ 74,717
Research and development tax credits	22,412	24,978
Other tax credits	230	91
Intangible assets	7,128	4,808
Deferred revenue	3,936	1,911
Accrued expenses	8,706	10,619
Inventory	6,103	5,713
Stock-based compensation	13,594	12,913
Other temporary differences	2,623	3,924
Deferred tax assets, gross	141,702	139,674
Valuation allowance	(139,823)	(137,640)
Total deferred tax assets	1,879	2,034
Liabilities:
Purchased intangible assets	(2,282)	(1,623)
Total deferred tax liabilities	(2,282)	(1,623)
Total net deferred tax assets	(403)	411
Deferred income taxes - current assets	0	991
Deferred income taxes - noncurrent assets	1,879	1,043
Deferred income taxes - noncurrent liabilities	$ (2,282)	$ (1,623)

INCOME TAXES - Operating Loss N

INCOME TAXES - Operating Loss Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Feb. 19, 2014
Operating Loss Carryforwards [Line Items]
Significant change in shareholder ownership, period of change	3 years
Significant change in shareholder ownership, benchmark of change percentage	50.00%
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 224
Portion of operating loss carryforwards for stock option deductions	145
Operating carryforward not recognized	22.4
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 103
PT [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards and tax credit carryforwards, acquired		$ 26

INCOME TAXES - Tax Carryforward

INCOME TAXES - Tax Carryforward Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Nov. 26, 2008
Tax Carryforward [Line Items]
Deferred tax assets, stock-based compensation	$ 13,594,000	$ 12,913,000
Tax credit carryforward	25,000,000
Deferred income taxes - current assets	0	991,000
Deferred income taxes - noncurrent assets	1,879,000	1,043,000
Deferred tax assets, valuation allowance	139,823,000	137,640,000
Income tax penalties and interest accrued		14,000	$ 14,000
Increases related to current year tax positions	13,000	$ 14,000	$ 14,000
New Accounting Pronouncement, Early Adoption, Effect [Member]
Tax Carryforward [Line Items]
Deferred income taxes - current assets	(1,000,000)
Deferred income taxes - noncurrent assets	1,000,000
Zynetix [Member] | Capital Loss Carryforward [Member]
Tax Carryforward [Line Items]
Tax credit carryforward				$ 14,100,000
Deferred tax asset, capital loss carryforwards	$ 5,500,000

INCOME TAXES - Schedule of Unre

INCOME TAXES - Schedule of Unrecognized Tax Benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at the beginning of the period	$ 8,875,000	$ 8,861,000	$ 8,847,000
Increases related to current year tax positions	13,000	14,000	14,000
Decreases related to prior period tax positions	0	0	0
Unrecognized tax benefits at the end of the period	$ 8,888,000	$ 8,875,000	$ 8,861,000

MAJOR CUSTOMERS - (Details)

MAJOR CUSTOMERS - (Details) - Customer [Member] - customer	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue [Member] | AT&T [Member]
MAJOR CUSTOMERS
Concentration risk, percentage	13.00%	19.00%	15.00%
Accounts receivable balance [Member]
MAJOR CUSTOMERS
Concentration risk, percentage	11.00%
Number of major customers	1	0

GEOGRAPHIC AND OPERATING SEGM84

GEOGRAPHIC AND OPERATING SEGMENT INFORMATION - Summary of Revenue by Geographic Area as a Percentage of Total Revenue (Details) - Revenue [Member] - Geographical area [Member]	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue by geographic area and by customer
Percentage of total revenue	100.00%	100.00%	100.00%
United States [Member]
Revenue by geographic area and by customer
Percentage of total revenue	71.00%	71.00%	69.00%
Europe, Middle East and Africa [Member]
Revenue by geographic area and by customer
Percentage of total revenue	13.00%	13.00%	12.00%
Japan [Member]
Revenue by geographic area and by customer
Percentage of total revenue	10.00%	9.00%	12.00%
Other Asia Pacific [Member]
Revenue by geographic area and by customer
Percentage of total revenue	4.00%	5.00%	5.00%
Other [Member]
Revenue by geographic area and by customer
Percentage of total revenue	2.00%	2.00%	2.00%

GEOGRAPHIC AND OPERATING SEGM85

GEOGRAPHIC AND OPERATING SEGMENT INFORMATION - Summary by Product and Type of Service (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue from External Customer [Line Items]
Service	$ 107,121	$ 113,871	$ 109,461
Services, Maintenance [Member]
Revenue from External Customer [Line Items]
Service	89,280	90,003	84,698
Services, Professional services [Member]
Revenue from External Customer [Line Items]
Service	$ 17,841	$ 23,868	$ 24,763

RELATED PARTIES (Details)

RELATED PARTIES (Details)	12 Months Ended
	Dec. 31, 2015USD ($)
Related Party [Member] | GTT Communications, Inc [Member]
Related Party Transaction [Line Items]
Revenue from related party	$ 150,000

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Leases Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)ft²	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Commitments and Contingencies Disclosure [Abstract]
Area of leased facility (in sqft) | ft²	97,500
Rent expense	$ 5,200	$ 6,100	$ 5,500
Years ending December 31,
2,015	4,111
2,016	3,682
2,017	2,801
2,018	1,565
2,019	252
Thereafter	0
Operating lease, future minimum payments	$ 12,411

QUARTERLY RESULTS (UNAUDITED) -

QUARTERLY RESULTS (UNAUDITED) - (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2015		Sep. 25, 2015		Jun. 26, 2015		Mar. 27, 2015	[1]	Dec. 31, 2014		Sep. 26, 2014		Jun. 27, 2014		Mar. 28, 2014		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 76,326		$ 67,862		$ 54,701		$ 50,145		$ 76,798		$ 73,216		$ 75,570		$ 70,742		$ 249,034	$ 296,326	$ 276,733
Cost of revenue	24,025		22,150		20,287		20,915		25,006		25,314		28,282		24,319		87,377	102,921	104,273
Gross profit	52,301		45,712		34,414		29,230		51,792		47,902		47,288		46,423		161,657	193,405	172,460
Income (loss) from operations	4,060		(1,362)		(15,049)		(18,866)		(1,945)		(4,715)		(4,801)		(5,791)		(31,217)	(17,252)	(21,075)
Net loss	$ 4,703		$ (1,896)		$ (15,343)		$ (19,359)		$ (2,192)		$ (5,213)		$ (5,497)		$ (3,953)		$ (31,895)	$ (16,855)	$ (22,119)
Loss per share:
Basic (in dollars per share)	$ 0.09	[2]	$ (0.04)	[2]	$ (0.31)	[2]	$ (0.39)	[2]	$ (0.04)	[2]	$ (0.11)	[2]	$ (0.11)	[2]	$ (0.07)	[2]	$ (0.64)	$ (0.34)	$ (0.40)
Diluted (in dollars per share)	$ 0.09	[2]	$ (0.04)	[2]	$ (0.31)	[2]	$ (0.39)	[2]	$ (0.04)	[2]	$ (0.11)	[2]	$ (0.11)	[2]	$ (0.07)	[2]	$ (0.64)	$ (0.34)	$ (0.40)
Shares used in computing loss per share:
Basic (in shares)	49,685		49,625		49,484		49,423		49,361		49,291		49,424		53,080		49,560	50,245	55,686
Diluted (in shares)	49,906		49,625		49,484		49,423		49,361		49,291		49,424		53,080		49,560	50,245	55,686
[1]	(1)Includes the results of the SDN Business for the period subsequent to January 2, 2015.(2)Includes the results of PT for the period subsequent to February 19, 2014.
[2]	Income (loss) per share is calculated independently for each of the quarters presented; accordingly, the sum of the quarterly earnings (loss) per share amounts may not equal the total calculated for the year.