Ribbon Communications Inc - Ordinary Shares 10-Q 27 Apr 17 2017 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2017	Apr. 21, 2017
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-Q
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		49,522,648

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 31,931	$ 31,923
Marketable securities	59,680	61,836
Accounts receivable, net of allowance for doubtful accounts of $10 at both March 31, 2017 and December 31, 2016	39,616	53,862
Inventory	17,671	18,283
Other current assets	12,988	12,010
Total current assets	161,886	177,914
Property and equipment, net	10,954	11,741
Intangible assets, net	27,938	30,197
Goodwill	49,891	49,393
Investments	37,193	32,371
Deferred income taxes	1,578	1,542
Other assets	4,914	4,901
Total assets	294,354	308,059
Current liabilities:
Accounts payable	5,988	6,525
Accrued expenses	15,786	25,886
Current portion of deferred revenue	46,430	43,504
Current portion of long-term liabilities	1,172	1,154
Total current liabilities	69,376	77,069
Deferred revenue	8,142	7,188
Deferred income taxes	3,255	3,047
Other long-term liabilities	1,566	1,633
Total liabilities	82,339	88,937
Commitments and contingencies (Note 15)
Stockholders' equity:
Preferred stock, $0.01 par value per share; 5,000,000 shares authorized, none issued and outstanding	0	0
Common stock, $0.001 par value per share; 120,000,000 shares authorized; 49,297,373 shares issued and outstanding at March 31, 2017; 49,041,881 shares issued and outstanding at December 31, 2016	49	49
Additional paid-in capital	1,254,155	1,250,744
Accumulated deficit	(1,047,820)	(1,037,174)
Accumulated other comprehensive income	5,631	5,503
Total stockholders' equity	212,015	219,122
Total liabilities and stockholders' equity	$ 294,354	$ 308,059

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 10	$ 10
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	49,297,373	49,041,881
Common stock, shares outstanding	49,297,373	49,041,881

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenue:
Product	$ 25,395	$ 34,769
Service	27,973	24,382
Total revenue	53,368	59,151
Cost of revenue:
Product	9,753	11,536
Service	9,867	9,212
Total cost of revenue	19,620	20,748
Gross profit	33,748	38,403
Operating expenses:
Research and development	20,209	17,318
Sales and marketing	14,676	16,595
General and administrative	9,019	8,371
Acquisition-related	56	0
Restructuring	570	0
Total operating expenses	44,530	42,284
Loss from operations	(10,782)	(3,881)
Interest income, net	258	164
Other income, net	1	103
Loss before income taxes	(10,523)	(3,614)
Income tax provision	(123)	(1,040)
Net loss	$ (10,646)	$ (4,654)
Loss per share:
Basic (in dollars per share)	$ (0.22)	$ (0.09)
Diluted (in dollars per share)	$ (0.22)	$ (0.09)
Shares used to compute loss per share:
Basic (in shares)	49,114	49,484
Diluted (in shares)	49,114	49,484

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Net loss	$ (10,646)	$ (4,654)
Other comprehensive income, net of tax:
Foreign currency translation adjustments	125	173
Unrealized gain on available-for sale marketable securities, net of tax	3	235
Reclassification adjustment for realized losses included in net loss	0	18
Other comprehensive income, net of tax	128	426
Comprehensive loss, net of tax	$ (10,518)	$ (4,228)

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities:
Net loss	$ (10,646)	$ (4,654)
Adjustments to reconcile net loss to cash flows provided by operating activities:
Depreciation and amortization of property and equipment	1,823	1,981
Amortization of intangible assets	2,259	1,946
Stock-based compensation	3,263	4,415
Loss on disposal of property and equipment	0	14
Deferred income taxes	238	418
Changes in operating assets and liabilities:
Accounts receivable	14,324	17,267
Inventory	315	(1,237)
Other operating assets	(405)	(3,531)
Accounts payable	(651)	(1,592)
Accrued expenses and other long-term liabilities	(10,530)	(13,855)
Deferred revenue	3,614	2,142
Net cash provided by operating activities	3,604	3,314
Cash flows from investing activities:
Purchases of property and equipment	(998)	(952)
Business acquisition, net of cash acquired	0	(750)
Purchases of marketable securities	(18,632)	(29,574)
Maturities/sales of marketable securities	15,693	21,867
Net cash (used in) provided by investing activities	(3,937)	(9,409)
Cash flows from financing activities:
Proceeds from sale of common stock in connection with employee stock purchase plan	593	632
Proceeds from exercise of stock options	51	5
Payment of tax withholding obligations related to net share settlements of restricted stock awards	(496)	(786)
Repurchase of common stock	0	(1,456)
Principal payments of capital lease obligations	(10)	(14)
Net cash provided by (used in) financing activities	138	(1,619)
Effect of exchange rate changes on cash and cash equivalents	203	252
Net increase (decrease) in cash and cash equivalents	8	(7,462)
Cash and cash equivalents, beginning of year	31,923	50,111
Cash and cash equivalents, end of period	31,931	42,649
Supplemental disclosure of cash flow information:
Interest paid	66	9
Income taxes paid	490	248
Income tax refunds received	80	165
Supplemental disclosure of non-cash investing activities:
Capital expenditures incurred, but not yet paid	318	248
Property and equipment acquired under capital lease	$ 0	$ 36

BASIS OF PRESENTATION

BASIS OF PRESENTATION	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
BASIS OF PRESENTATION	BASIS OF PRESENTATION Business Sonus Networks, Inc. (“Sonus” or the “Company”) is a leading provider of networked solutions for communications service providers (e.g., telecommunications, wireless and cable service providers) and enterprises to help them secure and unify their real-time communications infrastructures. Sonus helps many of the world's leading communications service providers and enterprises embrace the next generation of Session Initiation Protocol ("SIP") and 4G/LTE (Long-Term Evolution)-based solutions, including Voice over IP ("VoIP"), Voice over WiFi ("VoWiFi"), 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") and VoWiFi solutions, which are supported by a global services team with experience in the design, deployment and maintenance of the world's largest IP networks. Sonus' communications solutions provide a secure way for its customers to link and leverage multivendor, multiprotocol communications systems and applications across their networks, around the world and in a rapidly changing ecosystem of IP-enabled devices such as smartphones and tablets. Sonus' solutions help realize the intended value and benefits of UC platforms by allowing disparate communications environments, commonplace in most enterprises today, to work seamlessly together. Likewise, Sonus' solutions facilitate the evolution to cloud-based delivery of UC solutions. Basis of Presentation In the opinion of management, the accompanying unaudited condensed consolidated financial statements include all adjustments, consisting only of normal recurring items, necessary for their fair presentation with accounting principles generally accepted in the United States of America ("GAAP") and with the rules and regulations of the U.S. Securities and Exchange Commission ("SEC"). Interim results are not necessarily indicative of results for a full year or any future interim period. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the Company's Annual Report on Form 10-K for the year ended December 31, 2016 (the "Annual Report"), which was filed with the SEC on February 27, 2017. Significant Accounting Policies The Company's significant accounting policies are disclosed in Note 2 to the Consolidated Financial Statements included in the Annual Report. There were no material changes to the significant accounting policies during the three months ended March 31, 2017 . Principles of Consolidation The condensed consolidated financial statements include the accounts of Sonus and its wholly-owned subsidiaries. Intercompany transactions and balances have been eliminated in consolidation. Use of Estimates and Judgments The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting periods. Significant estimates and judgments relied upon in preparing these consolidated financial statements include accounting for business combinations, revenue recognition for multiple element arrangements, inventory valuations, assumptions used to determine the fair value of stock-based compensation, intangible assets and goodwill valuations, including impairments, legal contingencies and recoverability of Sonus' net deferred tax assets and the related valuation allowances. Sonus regularly assesses these estimates and records changes in estimates in the period in which they become known. Sonus bases its estimates on historical experience and various other assumptions that it believes to be reasonable under the circumstances. Actual results could differ from those estimates. Fair Value of Financial Instruments The carrying amounts of the Company's financial instruments, which include cash equivalents, marketable securities, investments, accounts receivable, accounts payable and other long-term liabilities, approximate their fair values. Operating Segments The Company operates in a single segment. Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker in making decisions regarding resource allocation and assessing performance. To date, the chief operating decision maker has made such decisions and assessed performance at the company level, as one segment. The Company's chief operating decision maker is its President and Chief Executive Officer. Recent Accounting Pronouncements In January 2017, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment ("ASU 2017-04"), which removes the requirement to compare the implied fair value of goodwill with its carrying amount as part of step two of the goodwill impairment test. As a result, under ASU 2017-04, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount and should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. In addition, ASU 2017-04 clarifies the requirements for excluding and allocating foreign currency translation adjustments to reporting units in connection with an entity's testing of reporting units for goodwill impairment; clarifies that an entity should consider income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable; and makes minor changes to other related guidance within the Accounting Standards Codification ("ASC"). ASU 2017-04 is effective prospectively for the Company beginning January 15, 2020, with early adoption permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company elected to early-adopt ASU 2017-04 as of January 1, 2017; such early adoption did not have a material impact on the Company's consolidated financial results. In October 2016, the FASB issued ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory ("ASU 2016-16"), which removes the prohibition in ASC 740, Income Taxes, against the immediate recognition of the current and deferred income tax effects of intra-entity transfers of assets other than inventory. ASU 2016-16 is intended to reduce the complexity of GAAP and diversity in practice related to the tax consequences of certain types of intra-entity asset transfers, particularly those involving intellectual property. ASU 2016-16 is effective for the Company beginning January 1, 2019 for both interim and annual reporting periods. The Company does not believe that the adoption of ASU 2016-16 will have a material impact on its consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments ("ASU 2016-15"), which amends the guidance in ASC 230 on the classification of certain cash receipts and payments in the statement of cash flows. The primary purpose of ASU 2016-15 is to reduce the diversity in practice that has resulted from the lack of consistent principles on this topic. ASU 2016-15 adds or clarifies guidance on eight cash flow issues, including debt prepayment or debt extinguishment costs, settlement of zero-coupon debt instruments or certain other debt instruments, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies, distributions received from equity method investees, beneficial interests in securitization transactions and separately identifiable cash flows and application of the predominance principle. ASU 2016-15 is effective for the Company beginning January 1, 2018 for both interim and annual reporting periods, with early adoption permitted. Entities must apply the guidance retrospectively to all periods presented but may apply it prospectively from the earliest date practicable if retrospective application would be impracticable. The Company does not expect the adoption of ASU 2016-15 will have a material impact on its consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instrument s ("ASU 2016-13"), which adds an impairment model that is based on expected losses rather than incurred losses. Under ASU 2016-13, an entity recognizes as an allowance its estimate of expected credit losses, which the FASB believes will result in more timely recognition of such losses. ASU 2016-13 is effective for the Company beginning January 1, 2020 for both interim and annual reporting periods, with early adoption permitted. The Company does not expect the adoption of ASU 2016-13 will have a material impact on its consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting ("ASU 2016-09"), which simplifies several aspects of the accounting for employee share-based payment transactions, including the accounting for income taxes, forfeitures and statutory tax withholding requirements, as well as classification in the statement of cash flows. ASU 2016-09 became effective for the Company beginning January 1, 2017 for both interim and annual reporting periods. Under ASU 2016-09, the Company will now recognize unrealized excess tax benefits. Due to the Company's full valuation allowance on its federal and state income taxes, the adoption of ASU 2016-09 did not have a material impact on the Company's accounting for income taxes. Without the valuation allowance, the Company would have recognized an increased deferred tax asset approximating $5 million . The Company has elected to continue to apply forfeiture rates to its expense attribution related to stock options, restricted stock awards and restricted stock units, as the Company believes that such continued application results in more accurate expense attribution over the life of these equity grants. The adoption of ASU 2016-09 did not have a material impact on the Company's consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) Section A - Leases: Amendments to the FASB Accounting Standards Codification ("ASU 2016-02"), its new standard on accounting for leases. ASU 2016-02 introduces a lessee model that brings most leases onto the balance sheet. The new standard also aligns many of the underlying principles of the new lessor model with those in ASC 606, the FASB's new revenue recognition standard (i.e., those related to evaluating when profit can be recognized). Furthermore, ASU 2016-02 addresses other concerns related to the current leases model. For example, ASU 2016-02 eliminates the current GAAP requirement for an entity to use bright-line tests in determining lease classification. ASU 2016-02 is effective for the Company for both interim and annual periods beginning January 1, 2019. The Company is currently assessing the potential impact of the adoption of ASU 2016-02 on its consolidated financial statements. In July 2015, the FASB issued ASU 2015-11, Simplifying the Measurement of Inventory ("ASU 2015-11"), which 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 became effective for the Company for both interim and annual reporting periods beginning January 1, 2017. The adoption of ASU 2015-11 did not 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"), which provides guidelines for determining when and how to disclose going concern uncertainties in the financial statements. The new standard requires management to perform interim and annual assessments of an entity's ability to continue as a going concern within one year of the date the financial statements are issued. An entity must provide certain disclosures if conditions or events raise substantial doubt about the entity's ability to continue as a going concern. ASU 2014-15 was effective for the Company beginning January 1, 2017. The adoption of ASU 2014-15 did not 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”), its final standard on revenue from contracts with customers, along with additional ASUs which, among other things, clarified the implementation of the new revenue guidance and delayed the adoption by one year, to January 1, 2018 (collectively, the "New Revenue Standard"). The New Revenue Standard outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. The core principle of the revenue model is that an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In applying the revenue model to contracts within its scope, an entity identifies the contract(s) with a customer, identifies the performance obligations in the contract, determines the transaction price, allocates the transaction price to the performance obligations in the contract and recognizes revenue when (or as) the entity satisfies a performance obligation. The New Revenue Standard applies to all contracts with customers that are within the scope of other topics in the ASC. Certain of the New Revenue Standard'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. The Company continues to assess the potential impact of the adoption of the New Revenue Standard on its consolidated financial statements, and currently believes that such adoption will, in general, accelerate the recognition of revenue (i.e., more revenue will be recognized upon delivery than is currently recognized ratably or upon payment) compared to the current standards in effect, in particular, sales of software-only products and sales to customers currently accounted for on a cash basis. The Company currently expects to adopt the New Revenue Standard using the modified retrospective option.

BUSINESS ACQUISITION

BUSINESS ACQUISITION	3 Months Ended
	Mar. 31, 2017
Business Combinations [Abstract]
BUSINESS ACQUISITIONS	BUSINESS ACQUISITION On September 26, 2017 (the "Taqua Acquisition Date"), the Company acquired Taqua, LLC ("Taqua"), a leading supplier of IP communications systems, applications and services to mobile and fixed operators. Taqua enables the transformation of software-based service provider networks to deliver next-generation voice, video and messaging services, including VoIP, VoWiFi and Voice over Long-Term Evolution ("VoLTE"). The acquisition of Taqua has, among other things, accelerated the Company's mobile strategy by adding a Virtualized Mobile Core ("VMC") Platform and an IP Multimedia Subsystem ("IMS") Service Core and expanded the Company's fixed portfolio by adding a Class 5 Softswitch (the T7000) for network transformation projects and a Multimedia Controller used in IP Peering applications (the T7100), both of which are complementary to Sonus' current product offerings. In consideration for the acquisition of Taqua, Sonus paid $19.9 million in cash to the sellers on the Taqua Acquisition Date, net of cash acquired. The Company also entered into an Earn-Out Agreement, dated as of September 26, 2016, with Taqua Holdings, LLC and Jeffrey L. Brawner, the seller representative in the transaction, under which there is the potential for additional cash payments of up to $65.0 million in the aggregate to the sellers if certain annual revenue thresholds are exceeded as measured annually through 2020. The Company had initially recorded $10.0 million of contingent consideration as of the Taqua Acquisition Date, with the estimate based on historical sales and probability weighted cash flows related to forecasted sales. During the fourth quarter of 2016, the Company reassessed the historical and updated forecasted sales and accordingly, reversed the previous estimated contingent consideration such that as of both March 31, 2017 and December 31, 2016, no incremental contingent consideration was recorded. The transaction has been accounted for as a business combination and the financial results of Taqua have been included in the Company's condensed consolidated financial statements for the period subsequent to its acquisition. As of March 31, 2017, the valuation of acquired assets, identifiable intangible assets and certain accrued liabilities is preliminary. The Company is still in the process of investigating the facts and circumstances existing as of the Taqua Acquisition Date in order to finalize its valuation, particularly, short-term assets and liabilities, including accounts receivable, inventory and accrued expenses, and intangible assets. During both the first quarter of 2017 and the fourth quarter of 2016, the Company recorded changes to the initial preliminary purchase price allocation. The primary adjustments in the first quarter of 2017 were a $0.4 million increase to current liabilities and a $0.1 million increase to noncurrent liabilities. The primary adjustments recorded in the fourth quarter of 2016 were the reversal of the $10.0 million of previously recorded contingent consideration discussed above, a reduction of $12.1 million to the developed technology intangible asset and an increase of $5.5 million to the customer relationship intangible assets. These adjustments, as well as other immaterial adjustments to the balance sheet accounts, resulted in a net reduction to goodwill of $2.2 million since September 30, 2016. Based on this updated preliminary purchase price allocation, the Company recorded $9.6 million of goodwill, which is primarily due to expected synergies between the combined companies and expanded market opportunities resulting from the expanded product offering portfolio. The goodwill is deductible for tax purposes. The Company expects to finalize the valuation of the assets acquired and liabilities assumed in the second quarter of 2017. A summary of the preliminary allocation of the purchase consideration for Taqua is as follows (in thousands): Fair value of consideration transferred: Cash, net of cash acquired $ 19,919 Fair value of assets acquired and liabilities assumed: Current assets $ 3,347 Property and equipment 1,478 Intangible assets: Developed technology 2,100 Customer relationships 9,510 Goodwill 9,581 Other noncurrent assets 23 Current liabilities (5,435 ) Long-term liabilities (685 ) $ 19,919 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 relationship intangible assets. The preliminary 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 is amortizing the identifiable intangible assets in relation to the expected cash flows from the individual intangible assets over their respective useful lives (see Note 6 ). The Company has not provided pro forma financial information, as the historical amount are not significant to the Company's consolidated financial statements. 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, as well as cash payments to certain employees of acquired companies in connection with change of control agreements. The Company recorded $56,000 of acquisition-related expenses in the three months ended March 31, 2017 related to professional fees in connection with the acquisition of Taqua. The Company did not record acquisition-related expenses in the three months ended March 31, 2016.

EARNINGS (LOSS) PER SHARE

EARNINGS (LOSS) PER SHARE	3 Months Ended
	Mar. 31, 2017
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): Three months ended March 31, March 31, Weighted average shares outstanding—basic 49,114 49,484 Potential dilutive common shares — — Weighted average shares outstanding—diluted 49,114 49,484 Options to purchase the Company's common stock, unvested shares of restricted stock, unvested shares of performance-based stock and shares in connection with future purchases under the Company's Amended and Restated 2000 Employee Stock Purchase Plan, as amended (the "ESPP"), totaling 8.4 million shares for the three months ended March 31, 2017 and 7.7 million shares for the three months ended March 31, 2016 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	3 Months Ended
	Mar. 31, 2017
Investments, All Other Investments [Abstract]
CASH EQUIVALENTS, MARKETABLE SECURITIES AND INVESTMENTS	CASH EQUIVALENTS AND INVESTMENTS The Company invests in debt instruments, primarily U.S. government-backed, municipal and corporate obligations, which management believes to be high quality (investment grade) credit instruments. During the three months ended March 31, 2016, the Company sold $3.8 million of its available-for-sale securities and recognized gross losses aggregating $18,000 , which is included as a component of Other income, net, in the Company's condensed consolidated statement of operations for that period. The Company did not sell any of its available-for-sale securities in the three months ended March 31, 2017. Investments with continuous unrealized losses for one year or greater at March 31, 2017 were nominal. Since the Company currently does not intend to sell these securities and does not believe it will be required to sell any securities before they recover in value, it does not believe these declines are other-than-temporary. On a quarterly basis, the Company reviews its marketable securities and investments to determine if there have been any events that could create a credit impairment. Based on its reviews, the Company does not believe that any impairment existed with its current holdings at March 31, 2017 . The amortized cost, gross unrealized gains and losses and fair value of the Company's marketable debt securities and investments at March 31, 2017 and December 31, 2016 were comprised of the following (in thousands): March 31, 2017 Amortized cost Unrealized gains Unrealized losses Fair value Cash equivalents $ 4,822 $ — $ — $ 4,822 Marketable securities Municipal obligations $ 2,672 $ — $ (1 ) $ 2,671 U.S. government agency notes 20,880 — (21 ) 20,859 Corporate debt securities 35,696 2 (39 ) 35,659 Certificates of deposit 491 — — 491 $ 59,739 $ 2 $ (61 ) $ 59,680 Investments U.S. government agency notes $ 17,609 $ 6 $ (41 ) $ 17,574 Corporate debt securities 14,550 2 (29 ) 14,523 Certificates of deposit 5,096 — — 5,096 $ 37,255 $ 8 $ (70 ) $ 37,193 December 31, 2016 Amortized cost Unrealized gains Unrealized losses Fair value Cash equivalents $ 6,619 $ — $ — $ 6,619 Marketable securities Municipal obligations $ 3,264 $ — $ (3 ) $ 3,261 U.S. government agency notes 16,477 3 (3 ) 16,477 Corporate debt securities 41,893 4 (45 ) 41,852 Certificates of deposit 246 — — 246 $ 61,880 $ 7 $ (51 ) $ 61,836 Investments U.S. government agency notes $ 19,473 $ 3 $ (39 ) $ 19,437 Corporate debt securities 10,520 — (44 ) 10,476 Certificates of deposit 2,458 — — 2,458 $ 32,451 $ 3 $ (83 ) $ 32,371 The Company's available-for-sale debt securities classified as Investments in the condensed consolidated balance sheets at March 31, 2017 and December 31, 2016 had maturity dates after one year but within approximately two years or less from the balance sheet date. Fair Value Hierarchy Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or a liability. The three-tier fair value hierarchy is based on the level of independent, objective evidence surrounding the inputs used to measure fair value. A financial instrument's categorization within the fair value hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The fair value hierarchy is as follows: Level 1. Level 1 applies to assets or liabilities for which there are quoted prices in active markets for identical assets or liabilities. Level 2. Level 2 applies to assets or liabilities for which there are inputs that are directly or indirectly observable in the marketplace, such as quoted prices for similar assets or liabilities in active markets or quoted prices for identical assets or liabilities in markets with insufficient volume or infrequent transactions (less active markets). Level 3. Level 3 applies to assets or liabilities for which there are unobservable inputs to the valuation methodology that are significant to the measurement of the fair value of the assets or liabilities. The following table shows the fair value of the Company's financial assets at March 31, 2017 and December 31, 2016 . These financial assets are comprised of the Company's available-for-sale debt securities and reported under the captions Cash and cash equivalents, Marketable securities and Investments in the condensed consolidated balance sheets (in thousands): Fair value measurements at Total carrying Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) Cash equivalents $ 4,822 $ 4,822 $ — $ — Marketable securities Municipal obligations $ 2,671 $ — $ 2,671 $ — U.S. government agency notes 20,859 — 20,859 — Corporate debt securities 35,659 — 35,659 — Certificates of deposit 491 — 491 — $ 59,680 $ — $ 59,680 $ — Investments U.S. government agency notes $ 17,574 $ — $ 17,574 $ — Corporate debt securities 14,523 — 14,523 — Certificates of deposit 5,096 — 5,096 — $ 37,193 $ — $ 37,193 $ — 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 $ 6,619 $ 6,619 $ — $ — Marketable securities Municipal obligations $ 3,261 $ — $ 3,261 $ — U.S. government agency notes 16,477 — 16,477 — Corporate debt securities 41,852 — 41,852 — Certificates of deposit 246 — 246 — $ 61,836 $ — $ 61,836 $ — Investments U.S. government agency notes $ 19,437 $ — $ 19,437 $ — Corporate debt securities 10,476 — 10,476 — Certificates of deposit 2,458 — 2,458 — $ 32,371 $ — $ 32,371 $ — The Company's marketable securities and investments have been valued with the assistance of valuations provided by third-party pricing services, as derived from such services' pricing models. Inputs to the models may include, but are not limited to, reported trades, executable bid and asked prices, broker/dealer quotations, prices or yields of securities with similar characteristics, benchmark curves or information pertaining to the issuer, as well as industry and economic events. The pricing services may use a matrix approach, which considers information regarding securities with similar characteristics to determine the valuation for a security. The Company is ultimately responsible for the condensed consolidated financial statements and underlying estimates. Accordingly, the Company assesses the reasonableness of the valuations provided by the third-party pricing services by reviewing actual trade data, broker/dealer quotes and other similar data, which are obtained from quoted market prices or other sources.

INVENTORY

INVENTORY	3 Months Ended
	Mar. 31, 2017
Inventory Disclosure [Abstract]
INVENTORY	INVENTORY Inventory at March 31, 2017 and December 31, 2016 consists of the following (in thousands): March 31, December 31, On-hand final assemblies and finished goods inventories $ 16,554 $ 15,346 Deferred cost of goods sold 2,717 4,237 19,271 19,583 Less current portion (17,671 ) (18,283 ) Noncurrent portion (included in Other assets) $ 1,600 $ 1,300

INTANGIBLE ASSETS AND GOODWILL

INTANGIBLE ASSETS AND GOODWILL	3 Months Ended
	Mar. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
INTANGIBLE ASSETS AND GOODWILL	INTANGIBLE ASSETS AND GOODWILL The Company's intangible assets at March 31, 2017 and December 31, 2016 consist of the following (dollars in thousands): March 31, 2017 Weighted average amortization period (years) Cost Accumulated amortization Net carrying value Developed technology 6.54 $ 34,980 $ 18,019 $ 16,961 Customer relationships 5.78 19,540 8,563 10,977 Internal use software 3.00 730 730 — 6.23 $ 55,250 $ 27,312 $ 27,938 December 31, 2016 Weighted average amortization period (years) Cost Accumulated amortization Net carrying value Developed technology 6.54 $ 34,980 $ 16,453 $ 18,527 Customer relationships 5.78 19,540 7,870 11,670 Internal use software 3.00 730 730 — 6.23 $ 55,250 $ 25,053 $ 30,197 Amortization expense for intangible assets for the three months ended March 31, 2017 and 2016 was as follows (in thousands): Three months ended Statement of operations classification March 31, March 31, Developed technology $ 1,566 $ 1,627 Cost of revenue - product Customer relationships 693 319 Sales and marketing $ 2,259 $ 1,946 Estimated future amortization expense for the Company's intangible assets at March 31, 2017 is as follows (in thousands): Years ending December 31, Remainder of 2017 $ 6,878 2018 6,615 2019 5,608 2020 4,166 2021 2,395 Thereafter 2,276 $ 27,938 The changes in the carrying value of the Company's goodwill in the three months ended March 31, 2017 were as follows (in thousands): Balance at January 1, 2017 Goodwill $ 52,499 Accumulated impairment losses (3,106 ) 49,393 Purchase accounting adjustments - Taqua 498 Balance at March 31, 2017 $ 49,891 Balance at March 31, 2017 Goodwill $ 52,997 Accumulated impairment losses (3,106 ) $ 49,891 There were no changes in the carrying value of the Company's goodwill in the three months ended March 31, 2016 .

ACCRUED EXPENSES

ACCRUED EXPENSES	3 Months Ended
	Mar. 31, 2017
Payables and Accruals [Abstract]
ACCRUED EXPENSES	ACCRUED EXPENSES Accrued expenses at March 31, 2017 and December 31, 2016 consist of the following (in thousands): March 31, December 31, Employee compensation and related costs $ 9,200 $ 15,879 Other 6,586 10,007 $ 15,786 $ 25,886

RESTRUCTURING ACCRUAL

RESTRUCTURING ACCRUAL	3 Months Ended
	Mar. 31, 2017
Restructuring and Related Activities [Abstract]
RESTRUCTURING ACCRUAL	RESTRUCTURING ACCRUAL 2016 Restructuring Initiative In July 2016, the Company announced a program to further accelerate its investment in new technologies as the communications industry migrates to a cloud-based architecture (the "2016 Restructuring Initiative"). The Company expects to record between $3 million and $4 million of restructuring expense in the aggregate in connection with this action, resulting in expected annual savings of approximately $6 million to $8 million . To date, the Company has recorded $1.7 million of restructuring expense in the aggregate in connection with this initiative and expects to record the remaining $1.3 million to $2.3 million by the end of the third quarter of 2017. The Company intends to utilize the majority of these savings to shift headcount toward new strategic initiatives, such as new products and an expanded go-to-market footprint in selected geographies and discrete vertical markets. In connection with this restructuring initiative, the Company recorded $0.2 million of restructuring expense in the three months ended March 31, 2017. A summary of the 2016 Restructuring Initiative accrual activity for the three months ended March 31, 2017 is as follows (in thousands): Balance at Initiatives Adjustments for changes in estimate Cash Balance at Severance $ 497 $ 236 $ (26 ) $ (420 ) $ 287 The Company expects that the amounts accrued under the 2016 Restructuring Initiative will be paid by end of the fourth quarter of 2017. Taqua Restructuring Initiative In connection with the acquisition of Taqua, the Company's management approved a restructuring plan in the third quarter of 2016 to eliminate certain redundant positions within the combined companies. On October 24, 2016, the Audit Committee of the Company's Board of Directors approved a broader Taqua restructuring plan related to headcount and redundant facilities (both restructuring plans, the "Taqua Restructuring Initiative"). In connection with this initiative, the Company recorded $0.4 million of restructuring expense in the three months ended March 31, 2017. The Company anticipates it will record additional future expense in connection with this initiative for headcount and redundant facilities aggregating approximately $1 million through the third quarter of 2017. A summary of the Taqua Restructuring Initiative accrual activity for the three months ended March 31, 2017 is as follows (in thousands): Balance at Initiatives Adjustments for changes in estimate Cash Balance at Severance $ 384 $ 39 $ (49 ) $ (365 ) $ 9 Facilities 218 370 — (94 ) 494 $ 602 $ 409 $ (49 ) $ (459 ) $ 503 2015 Restructuring Initiative To better align the Company's cost structure to its current revenue expectations, in April 2015, the Company announced a cost reduction review and restructuring initiative (the "2015 Restructuring Initiative"). A summary of the 2015 Restructuring Initiative accrual activity for the three months ended March 31, 2017 is as follows (in thousands): Balance at Initiatives Adjustments for changes in estimate Cash Balance at Severance $ 168 $ — $ — $ (168 ) $ — Balance Sheet Classification At March 31, 2017 , the Company's restructuring accruals aggregated $0.8 million , of which approximately $0.2 million was included in Other long-term liabilities and represented future lease payments on restructured facilities. At December 31, 2016 , the Company's restructuring accruals aggregated $1.3 million , of which approximately $62,000 was included in Other long-term liabilities and represented future lease payments on restructured facilities. The remainder of the restructuring accruals at both March 31, 2017 and December 31, 2016 are included in Accrued expenses in the condensed consolidated balance sheets.

DEBT

DEBT	3 Months Ended
	Mar. 31, 2017
Debt Disclosure [Abstract]
DEBT	DEBT 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 (the "Credit Agreement"), which agreement was amended by a First Amendment to Credit Agreement on June 26, 2015 (the "First Amendment") and further amended by a Second Amendment to Credit Agreement on June 13, 2016 (the "Second Amendment" and collectively with the Credit Agreement and the First Amendment, the "Amended Credit Agreement"). Certain terms of the Credit Agreement have been amended by the Second Amendment, including, among other things: (i) an increase of the commitments from $15 million to $20 million ; (ii) an extension of the maturity date from June 30, 2016 to June 30, 2017; (iii) a reduction to the aggregate amount of cash and cash equivalents that the Loan Parties (as defined below) are required to hold at any time from $85 million to $50 million ; and (iv) a reduction of the commitment fee on the unused commitments available for borrowing from 0.15% to 0.1125% . The Amended Credit Agreement provides that the Company may select the interest rates under the credit facility from among the following options: (i) 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 (ii) 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 obligations of the Company under the Amended Credit Agreement are guaranteed by Sonus International, Inc., Sonus Federal, Inc., Network Equipment Technologies, Inc. ("NET") and Taqua (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 Amended 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 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. The credit facility will become due on June 30, 2017, 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 of warranties, bankruptcy and insolvency-related defaults, defaults relating to judgments, an ERISA Event (as defined in the Amended Credit Agreement), the failure to pay specified indebtedness and a change of control default. The Company did not have any amounts outstanding under the Amended Credit Agreement at either March 31, 2017 or December 31, 2016 .

COMMON STOCK REPURCHASES (Notes

COMMON STOCK REPURCHASES (Notes)	3 Months Ended
	Mar. 31, 2017
Equity [Abstract]
COMMON STOCK REPURCHASES	COMMON STOCK REPURCHASES On July 29, 2013, the Company announced that its Board of Directors had authorized a stock buyback program to repurchase up to $100 million of the Company's common stock from time to time on the open market or in privately negotiated transactions. The timing and amount of any shares repurchased will be determined by the Company's management based on its evaluation of market conditions and other factors. The Company may elect to implement a 10b5-1 repurchase program, which would permit shares to be repurchased when the Company might otherwise be precluded from doing so under insider trading laws. The Company has not implemented such a 10b5-1 repurchase program to date. The stock buyback program may be suspended or discontinued at any time. The stock buyback program is funded with the Company's working capital. The Company did not repurchase any shares during the three months ended March 31, 2017 . During the three months ended March 31, 2016 , the Company spent $1.5 million , including transaction fees, to repurchase and retire 0.2 million shares of its common stock under the stock buyback program. At March 31, 2017 , the Company had $5.4 million remaining under the stock buyback program for future repurchases.

STOCK-BASED COMPENSATION PLANS

STOCK-BASED COMPENSATION PLANS	3 Months Ended
	Mar. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK-BASED COMPENSATION PLANS	STOCK-BASED COMPENSATION PLANS Amended and Restated Stock Incentive Plan The Company's Amended and Restated Stock Incentive Plan, as amended (the "Plan"), provides for the award of options to purchase the Company's common stock ("stock options"), stock appreciation rights ("SARs"), restricted common stock awards ("RSAs"), restricted common stock units ("RSUs"), performance-based stock awards ("PSAs"), performance-based stock units ("PSUs") and other stock-based awards to employees, officers, directors (including those directors who are not employees or officers of the Company), consultants and advisors of the Company and its subsidiaries. Executive Equity Arrangements On March 31, 2017, the Company granted an aggregate of 165,000 PSUs with both market and service conditions to five of its executives (the "2017 PSUs"). The terms of the 2017 PSUs are such that up to one-third of the shares subject to the 2017 PSUs will vest on each of the first, second and third anniversaries of the date of grant (collectively, the "2017 PSU 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 fiscal year, measured by the Compensation Committee after each of the 2017, 2018 and 2019 fiscal years, respectively (as used in this paragraph, 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 2017 PSUs that fail to be earned will be forfeited. The 2017 PSUs include a market condition that required the use of a Monte Carlo simulation approach to model future stock price movements based upon the risk-free rate of return, the 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 2017 PSUs. Because the 2017 PSUs have market conditions, the Company is required to record expense for the 2017 PSUs through the final 2017 PSU Vesting Date of March 31, 2020, regardless of the number of shares that are ultimately earned. On April 1, 2016, the Company granted an aggregate of 131,250 PSUs with both market and service conditions to six of its executives (the "2016 PSUs"). The terms of the 2016 PSUs are such that up to one-third of the shares subject to the 2016 PSUs will vest on each of the first, second and third anniversaries of the date of grant (collectively, the "2016 PSU Vesting Dates") to the extent of achievement of the Company's TSR compared to the TSR of the companies included in the NASDAQ Telecommunications Index for the same fiscal year, measured by the Compensation Committee of the Company's Board of Directors (the "Compensation Committee") after each of the 2016, 2017 and 2018 fiscal years, respectively (as used in this paragraph, 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 2016 PSUs that fail to be earned will be forfeited. The 2016 PSUs include a market condition that required the use of a Monte Carlo simulation approach to model future stock price movements based upon the risk-free rate of return, the 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 2016 PSUs. Because the 2016 PSUs have market conditions, the Company is required to record expense for the 2016 PSUs through the final 2016 PSU Vesting Date of April 1, 2019, regardless of the number of shares that are ultimately earned. In February 2017, the Compensation Committee determined that the performance metrics for the 2016 PSUs for the 2016 Performance Period had been achieved at the 90.4% level, and accordingly, 24,106 shares in the aggregate were released to the four executives holding such outstanding grants on March 16, 2017. The unearned shares relating to the 2016 Performance Period, aggregating 2,560 shares, were forfeited on March 16, 2017. These amounts are included in the performance-based units table below. On March 16, 2015, the Company granted an aggregate of 131,250 PSUs with both market and service conditions to eight of its executives (the "2015 PSUs"). In 2015, subsequent to the grant date, two executives separated from the Company and, in accordance with their respective employment agreements with the Company, the Company accelerated the vesting of certain unvested 2015 PSUs. The terms of the 2015 PSUs are such that up to one-third of the shares subject to the 2015 PSUs will vest on each of the first, second and third anniversaries of the date of grant (collectively, the "2015 PSU Vesting Dates") to the extent of achievement of the Company's 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 (as used in this paragraph, 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 2015 PSUs that fail to be earned will be forfeited. The 2015 PSUs include a market condition that required the use of a Monte Carlo simulation approach to calculate the grant date fair values of the 2015 PSUs. Because the 2015 PSUs have market conditions, the Company is required to record expense for the 2015 PSUs through the final 2015 PSU Vesting Date of March 16, 2018, regardless of the number of shares that are ultimately earned, if any. In February 2017, the Compensation Committee determined that the performance metrics for the 2015 PSUs for the 2016 Performance Period had been achieved at the 76.0% level, and accordingly, 23,750 shares in the aggregate were released to the four executives holding such outstanding grants on April 1, 2017. The unearned shares relating to the 2016 Performance Period, aggregating 7,500 shares, were forfeited on April 1, 2017. These amounts are included in the performance-based units table below. Stock Options The activity related to the Company's outstanding stock options for the three months ended March 31, 2017 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, 2017 5,610,106 $ 15.73 Granted 3,920 $ 6.10 Exercised (13,430 ) $ 3.80 Forfeited (22,483 ) $ 13.91 Expired (50,425 ) $ 21.50 Outstanding at March 31, 2017 5,527,688 $ 15.70 5.08 $ 98 Vested or expected to vest at March 31, 2017 5,480,151 $ 15.73 5.05 $ 97 Exercisable at March 31, 2017 4,890,476 $ 15.79 4.75 $ 92 The grant date fair values of options to purchase common stock granted in the three months ended March 31, 2017 were estimated using the Black-Scholes valuation model with the following assumptions: Three months ended March 31, Risk-free interest rate 1.95% Expected dividends — Weighted average volatility 51.3% Expected life (years) 5.0 Additional information regarding the Company's stock options for the three months ended March 31, 2017 is as follows: Three months ended March 31, Weighted average grant date fair value of stock options granted $ 2.81 Total intrinsic value of stock options exercised (in thousands) $ 37 Cash received from the exercise of stock options (in thousands) $ 51 Restricted Stock Awards and Units The activity related to the Company's RSAs for the three months ended March 31, 2017 is as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2017 2,030,028 $ 9.69 Granted 518,560 $ 6.58 Vested (164,629 ) $ 13.98 Forfeited (7,092 ) $ 16.60 Unvested balance at March 31, 2017 2,376,867 $ 8.70 The activity related to the Company's RSUs for the three months ended March 31, 2017 is as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2017 110,219 $ 11.95 Granted — $ — Vested (11,185 ) $ 16.05 Forfeited (10,750 ) $ 8.12 Unvested balance at March 31, 2017 88,284 $ 11.89 The total fair value of shares of restricted stock granted under RSAs and RSUs that vested during the three months ended March 31, 2017 was $2.5 million . Performance-Based Stock Units The activity related to the Company's PSUs for the three months ended March 31, 2017 is as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2017 147,085 $ 12.11 Granted 165,000 $ 8.41 Vested (24,106 ) $ 15.37 Forfeited (2,560 ) $ 15.37 Unvested balance at March 31, 2017 285,419 $ 9.67 The total fair value of shares of restricted stock granted under PSUs that vested during the three months ended March 31, 2017 was $0.4 million . The Company did not have outstanding PSAs during the three months ended March 31, 2017 or at December 31, 2016. Employee Stock Purchase Plan The Company's ESPP provides for six -month offering periods with the purchase price of the stock equal to 85% of the lesser of the market price on the first or last day of the offering period. The maximum number of shares of common stock an employee may purchase during each offering period is 500 , subject to certain adjustments pursuant to the ESPP. S tock-Based Compensation The condensed consolidated statements of operations include stock-based compensation for the three months ended March 31, 2017 and 2016 as follows (in thousands): Three months ended March 31, March 31, Product cost of revenue $ 99 $ 71 Service cost of revenue 317 332 Research and development 1,317 1,179 Sales and marketing (88 ) 1,020 General and administrative 1,618 1,813 $ 3,263 $ 4,415 The $0.1 million credit amount reported as sales and marketing stock-based compensation expense for the three months ended March 31, 2017 is comprised of $0.9 million of stock-based compensation expense, net of the reversal of $1.0 million of incremental expense to correct an error in 2016 related to the acceleration of certain stock awards held by an executive who separated from the Company in 2016. Management had reviewed and considered the impact of the error and determined that it was not material to the Company's consolidated financial results for the third and fourth quarters of 2016, as well as the 2016 fiscal year. Management has also determined that the correction of this error is not material to the results of operations for the three months ended March 31, 2017. There is no income tax benefit for employee stock-based compensation expense for the three months ended March 31, 2017 or March 31, 2016 due to the valuation allowance recorded. At March 31, 2017 , there was $21.7 million , net of expected forfeitures, of unrecognized stock-based compensation expense related to unvested stock options, awards, units and ESPP shares. This expense is expected to be recognized over a weighted average period of approximately two years .

MAJOR CUSTOMERS

MAJOR CUSTOMERS	3 Months Ended
	Mar. 31, 2017
Risks and Uncertainties [Abstract]
MAJOR CUSTOMERS	MAJOR CUSTOMERS The following customers contributed 10% or more of the Company's revenue in at least one of the three month periods ended March 31, 2017 and March 31, 2016 : Three months ended March 31, March 31, Verizon Communications 17% * Level 3 Communications * 19% AT&T Inc. * 11% _______________________ * Represents less than 10% of revenue At March 31, 2017 , one customer accounted for 10% or more of the Company's accounts receivable balance, representing approximately 14% of the Company's accounts receivable balance. At December 31, 2016 , 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 INFORMATION

GEOGRAPHIC INFORMATION	3 Months Ended
	Mar. 31, 2017
Segment Reporting [Abstract]
GEOGRAPHIC INFORMATION	GEOGRAPHIC INFORMATION The Company's classification of revenue by geographic area is determined by the location to which the product is shipped or where the services are performed. The following table summarizes revenue by geographic area as a percentage of total revenue: Three months ended March 31, March 31, United States 67 % 68 % Europe, Middle East and Africa 12 13 Japan 14 13 Other Asia Pacific 4 4 Other 3 2 100 % 100 % International revenue, both as a percentage of total revenue and absolute dollars, may vary from one period to the next, and accordingly, historical data may not be indicative of future periods.

INCOME TAXES

INCOME TAXES	3 Months Ended
	Mar. 31, 2017
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The Company's income tax provisions for the three months ended March 31, 2017 and 2016 reflect the Company's estimates of the effective rates expected to be applicable for the respective full years, adjusted for any discrete events, which are recorded in the period that they occur. These estimates are reevaluated each quarter based on the Company's estimated tax expense for the full year. The estimated effective rates for the three months ended March 31, 2017 and 2016 do not include any benefit for the Company's domestic losses, as the Company has concluded that a valuation allowance on any domestic benefit is required. Included in the Company's provision for the three months ended March 31, 2016 is a discrete charge of $0.7 million related to an uncertain tax position of the Company's subsidiary in France.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS 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 "District of New Jersey"), 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 former Chief Financial Officer (collectively, the "Defendants"). On September 21, 2015, in response to motions subsequently filed with the District of New Jersey by four other purported shareholders of the Company seeking status as lead plaintiff, the District of New Jersey 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 (the “Motion to Transfer”) this case to the United States District Court for the District of Massachusetts (the "District of Massachusetts"). On March 21, 2016, the District of New Jersey granted the Company's Motion to Transfer. Thus, this case will now be litigated in the District of Massachusetts (Civil Action No. 1:16-cv-10657-GAO). On May 4, 2016, the Plaintiff filed an amended complaint (the "Amended Complaint"), which is now the operative complaint in this litigation. On June 20, 2016, the Company and the other Defendants filed a Motion to Dismiss the Amended Complaint (the "Motion to Dismiss") and on July 25, 2016, the Plaintiff filed an opposition to the Motion to Dismiss. The Company filed its reply to the Plaintiff's opposition to the Motion to Dismiss on August 15, 2016. The Company filed its reply to the Plaintiff's opposition to the Motion to Dismiss on August 15, 2016. A hearing on the Motion to Dismiss was held on February 28, 2017, and the parties are now awaiting a decision from the District of Massachusetts. The Company believes that the Defendants have meritorious defenses to the allegations made in the Amended Complaint and does not expect the results of this suit to have a material effect on its business or consolidated financial statements. The Company is also fully cooperating with an SEC inquiry regarding the development and issuance of the Company's first quarter 2015 revenue and earnings guidance. At this time, it is not possible to predict the outcome of the SEC's inquiry, including whether or not any proceedings will be initiated or, if so, when or how the matter will be resolved and therefore an estimate of the possible range of loss, if any, cannot be made. In addition, the Company is often a party to disputes and legal proceedings that it considers routine and incidental to its business. Management does not expect the results of any of these actions to have a material effect on the Company's business or consolidated financial statements.

BASIS OF PRESENTATION (Policies

BASIS OF PRESENTATION (Policies)	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation In the opinion of management, the accompanying unaudited condensed consolidated financial statements include all adjustments, consisting only of normal recurring items, necessary for their fair presentation with accounting principles generally accepted in the United States of America ("GAAP") and with the rules and regulations of the U.S. Securities and Exchange Commission ("SEC"). Interim results are not necessarily indicative of results for a full year or any future interim period. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the Company's Annual Report on Form 10-K for the year ended December 31, 2016 (the "Annual Report"), which was filed with the SEC on February 27, 2017.
Principles of Consolidation	Principles of Consolidation The condensed consolidated financial statements include the accounts of Sonus and its wholly-owned subsidiaries. Intercompany transactions and balances have been eliminated in consolidation.
Use of Estimates and Judgments	Use of Estimates and Judgments The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting periods. Significant estimates and judgments relied upon in preparing these consolidated financial statements include accounting for business combinations, revenue recognition for multiple element arrangements, inventory valuations, assumptions used to determine the fair value of stock-based compensation, intangible assets and goodwill valuations, including impairments, legal contingencies and recoverability of Sonus' net deferred tax assets and the related valuation allowances. Sonus regularly assesses these estimates and records changes in estimates in the period in which they become known. Sonus bases its estimates on historical experience and various other assumptions that it believes to be reasonable under the circumstances. Actual results could differ from those estimates.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of the Company's financial instruments, which include cash equivalents, marketable securities, investments, accounts receivable, accounts payable and other long-term liabilities, approximate their fair values.
Operating Segments	Operating Segments The Company operates in a single segment. Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker in making decisions regarding resource allocation and assessing performance. To date, the chief operating decision maker has made such decisions and assessed performance at the company level, as one segment. The Company's chief operating decision maker is its President and Chief Executive Officer.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In January 2017, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment ("ASU 2017-04"), which removes the requirement to compare the implied fair value of goodwill with its carrying amount as part of step two of the goodwill impairment test. As a result, under ASU 2017-04, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount and should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. In addition, ASU 2017-04 clarifies the requirements for excluding and allocating foreign currency translation adjustments to reporting units in connection with an entity's testing of reporting units for goodwill impairment; clarifies that an entity should consider income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable; and makes minor changes to other related guidance within the Accounting Standards Codification ("ASC"). ASU 2017-04 is effective prospectively for the Company beginning January 15, 2020, with early adoption permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company elected to early-adopt ASU 2017-04 as of January 1, 2017; such early adoption did not have a material impact on the Company's consolidated financial results. In October 2016, the FASB issued ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory ("ASU 2016-16"), which removes the prohibition in ASC 740, Income Taxes, against the immediate recognition of the current and deferred income tax effects of intra-entity transfers of assets other than inventory. ASU 2016-16 is intended to reduce the complexity of GAAP and diversity in practice related to the tax consequences of certain types of intra-entity asset transfers, particularly those involving intellectual property. ASU 2016-16 is effective for the Company beginning January 1, 2019 for both interim and annual reporting periods. The Company does not believe that the adoption of ASU 2016-16 will have a material impact on its consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments ("ASU 2016-15"), which amends the guidance in ASC 230 on the classification of certain cash receipts and payments in the statement of cash flows. The primary purpose of ASU 2016-15 is to reduce the diversity in practice that has resulted from the lack of consistent principles on this topic. ASU 2016-15 adds or clarifies guidance on eight cash flow issues, including debt prepayment or debt extinguishment costs, settlement of zero-coupon debt instruments or certain other debt instruments, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies, distributions received from equity method investees, beneficial interests in securitization transactions and separately identifiable cash flows and application of the predominance principle. ASU 2016-15 is effective for the Company beginning January 1, 2018 for both interim and annual reporting periods, with early adoption permitted. Entities must apply the guidance retrospectively to all periods presented but may apply it prospectively from the earliest date practicable if retrospective application would be impracticable. The Company does not expect the adoption of ASU 2016-15 will have a material impact on its consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instrument s ("ASU 2016-13"), which adds an impairment model that is based on expected losses rather than incurred losses. Under ASU 2016-13, an entity recognizes as an allowance its estimate of expected credit losses, which the FASB believes will result in more timely recognition of such losses. ASU 2016-13 is effective for the Company beginning January 1, 2020 for both interim and annual reporting periods, with early adoption permitted. The Company does not expect the adoption of ASU 2016-13 will have a material impact on its consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting ("ASU 2016-09"), which simplifies several aspects of the accounting for employee share-based payment transactions, including the accounting for income taxes, forfeitures and statutory tax withholding requirements, as well as classification in the statement of cash flows. ASU 2016-09 became effective for the Company beginning January 1, 2017 for both interim and annual reporting periods. Under ASU 2016-09, the Company will now recognize unrealized excess tax benefits. Due to the Company's full valuation allowance on its federal and state income taxes, the adoption of ASU 2016-09 did not have a material impact on the Company's accounting for income taxes. Without the valuation allowance, the Company would have recognized an increased deferred tax asset approximating $5 million . The Company has elected to continue to apply forfeiture rates to its expense attribution related to stock options, restricted stock awards and restricted stock units, as the Company believes that such continued application results in more accurate expense attribution over the life of these equity grants. The adoption of ASU 2016-09 did not have a material impact on the Company's consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) Section A - Leases: Amendments to the FASB Accounting Standards Codification ("ASU 2016-02"), its new standard on accounting for leases. ASU 2016-02 introduces a lessee model that brings most leases onto the balance sheet. The new standard also aligns many of the underlying principles of the new lessor model with those in ASC 606, the FASB's new revenue recognition standard (i.e., those related to evaluating when profit can be recognized). Furthermore, ASU 2016-02 addresses other concerns related to the current leases model. For example, ASU 2016-02 eliminates the current GAAP requirement for an entity to use bright-line tests in determining lease classification. ASU 2016-02 is effective for the Company for both interim and annual periods beginning January 1, 2019. The Company is currently assessing the potential impact of the adoption of ASU 2016-02 on its consolidated financial statements. In July 2015, the FASB issued ASU 2015-11, Simplifying the Measurement of Inventory ("ASU 2015-11"), which 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 became effective for the Company for both interim and annual reporting periods beginning January 1, 2017. The adoption of ASU 2015-11 did not 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"), which provides guidelines for determining when and how to disclose going concern uncertainties in the financial statements. The new standard requires management to perform interim and annual assessments of an entity's ability to continue as a going concern within one year of the date the financial statements are issued. An entity must provide certain disclosures if conditions or events raise substantial doubt about the entity's ability to continue as a going concern. ASU 2014-15 was effective for the Company beginning January 1, 2017. The adoption of ASU 2014-15 did not 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”), its final standard on revenue from contracts with customers, along with additional ASUs which, among other things, clarified the implementation of the new revenue guidance and delayed the adoption by one year, to January 1, 2018 (collectively, the "New Revenue Standard"). The New Revenue Standard outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. The core principle of the revenue model is that an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In applying the revenue model to contracts within its scope, an entity identifies the contract(s) with a customer, identifies the performance obligations in the contract, determines the transaction price, allocates the transaction price to the performance obligations in the contract and recognizes revenue when (or as) the entity satisfies a performance obligation. The New Revenue Standard applies to all contracts with customers that are within the scope of other topics in the ASC. Certain of the New Revenue Standard'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. The Company continues to assess the potential impact of the adoption of the New Revenue Standard on its consolidated financial statements, and currently believes that such adoption will, in general, accelerate the recognition of revenue (i.e., more revenue will be recognized upon delivery than is currently recognized ratably or upon payment) compared to the current standards in effect, in particular, sales of software-only products and sales to customers currently accounted for on a cash basis. The Company currently expects to adopt the New Revenue Standard using the modified retrospective option.

BUSINESS ACQUISITION (Tables)

BUSINESS ACQUISITION (Tables)	3 Months Ended
	Mar. 31, 2017
Business Combinations [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	A summary of the preliminary allocation of the purchase consideration for Taqua is as follows (in thousands): Fair value of consideration transferred: Cash, net of cash acquired $ 19,919 Fair value of assets acquired and liabilities assumed: Current assets $ 3,347 Property and equipment 1,478 Intangible assets: Developed technology 2,100 Customer relationships 9,510 Goodwill 9,581 Other noncurrent assets 23 Current liabilities (5,435 ) Long-term liabilities (685 ) $ 19,919

EARNINGS (LOSS) PER SHARE (Tabl

EARNINGS (LOSS) PER SHARE (Tables)	3 Months Ended
	Mar. 31, 2017
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): Three months ended March 31, March 31, Weighted average shares outstanding—basic 49,114 49,484 Potential dilutive common shares — — Weighted average shares outstanding—diluted 49,114 49,484

CASH EQUIVALENTS AND INVESTME25

CASH EQUIVALENTS AND INVESTMENTS (Tables)	3 Months Ended
	Mar. 31, 2017
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 marketable debt securities and investments at March 31, 2017 and December 31, 2016 were comprised of the following (in thousands): March 31, 2017 Amortized cost Unrealized gains Unrealized losses Fair value Cash equivalents $ 4,822 $ — $ — $ 4,822 Marketable securities Municipal obligations $ 2,672 $ — $ (1 ) $ 2,671 U.S. government agency notes 20,880 — (21 ) 20,859 Corporate debt securities 35,696 2 (39 ) 35,659 Certificates of deposit 491 — — 491 $ 59,739 $ 2 $ (61 ) $ 59,680 Investments U.S. government agency notes $ 17,609 $ 6 $ (41 ) $ 17,574 Corporate debt securities 14,550 2 (29 ) 14,523 Certificates of deposit 5,096 — — 5,096 $ 37,255 $ 8 $ (70 ) $ 37,193 December 31, 2016 Amortized cost Unrealized gains Unrealized losses Fair value Cash equivalents $ 6,619 $ — $ — $ 6,619 Marketable securities Municipal obligations $ 3,264 $ — $ (3 ) $ 3,261 U.S. government agency notes 16,477 3 (3 ) 16,477 Corporate debt securities 41,893 4 (45 ) 41,852 Certificates of deposit 246 — — 246 $ 61,880 $ 7 $ (51 ) $ 61,836 Investments U.S. government agency notes $ 19,473 $ 3 $ (39 ) $ 19,437 Corporate debt securities 10,520 — (44 ) 10,476 Certificates of deposit 2,458 — — 2,458 $ 32,451 $ 3 $ (83 ) $ 32,371
Schedule of fair value of financial assets	The following table shows the fair value of the Company's financial assets at March 31, 2017 and December 31, 2016 . These financial assets are comprised of the Company's available-for-sale debt securities and reported under the captions Cash and cash equivalents, Marketable securities and Investments in the condensed consolidated balance sheets (in thousands): Fair value measurements at Total carrying Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) Cash equivalents $ 4,822 $ 4,822 $ — $ — Marketable securities Municipal obligations $ 2,671 $ — $ 2,671 $ — U.S. government agency notes 20,859 — 20,859 — Corporate debt securities 35,659 — 35,659 — Certificates of deposit 491 — 491 — $ 59,680 $ — $ 59,680 $ — Investments U.S. government agency notes $ 17,574 $ — $ 17,574 $ — Corporate debt securities 14,523 — 14,523 — Certificates of deposit 5,096 — 5,096 — $ 37,193 $ — $ 37,193 $ — 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 $ 6,619 $ 6,619 $ — $ — Marketable securities Municipal obligations $ 3,261 $ — $ 3,261 $ — U.S. government agency notes 16,477 — 16,477 — Corporate debt securities 41,852 — 41,852 — Certificates of deposit 246 — 246 — $ 61,836 $ — $ 61,836 $ — Investments U.S. government agency notes $ 19,437 $ — $ 19,437 $ — Corporate debt securities 10,476 — 10,476 — Certificates of deposit 2,458 — 2,458 — $ 32,371 $ — $ 32,371 $ —

INVENTORY (Tables)

INVENTORY (Tables)	3 Months Ended
	Mar. 31, 2017
Inventory Disclosure [Abstract]
Schedule of inventory	Inventory at March 31, 2017 and December 31, 2016 consists of the following (in thousands): March 31, December 31, On-hand final assemblies and finished goods inventories $ 16,554 $ 15,346 Deferred cost of goods sold 2,717 4,237 19,271 19,583 Less current portion (17,671 ) (18,283 ) Noncurrent portion (included in Other assets) $ 1,600 $ 1,300

INTANGIBLE ASSETS AND GOODWILL

INTANGIBLE ASSETS AND GOODWILL (Tables)	3 Months Ended
	Mar. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of intangible assets	The Company's intangible assets at March 31, 2017 and December 31, 2016 consist of the following (dollars in thousands): March 31, 2017 Weighted average amortization period (years) Cost Accumulated amortization Net carrying value Developed technology 6.54 $ 34,980 $ 18,019 $ 16,961 Customer relationships 5.78 19,540 8,563 10,977 Internal use software 3.00 730 730 — 6.23 $ 55,250 $ 27,312 $ 27,938 December 31, 2016 Weighted average amortization period (years) Cost Accumulated amortization Net carrying value Developed technology 6.54 $ 34,980 $ 16,453 $ 18,527 Customer relationships 5.78 19,540 7,870 11,670 Internal use software 3.00 730 730 — 6.23 $ 55,250 $ 25,053 $ 30,197
Schedule of amortization expense related to intangible assets	Amortization expense for intangible assets for the three months ended March 31, 2017 and 2016 was as follows (in thousands): Three months ended Statement of operations classification March 31, March 31, Developed technology $ 1,566 $ 1,627 Cost of revenue - product Customer relationships 693 319 Sales and marketing $ 2,259 $ 1,946
Schedule of estimated future amortization expense for intangible assets	Estimated future amortization expense for the Company's intangible assets at March 31, 2017 is as follows (in thousands): Years ending December 31, Remainder of 2017 $ 6,878 2018 6,615 2019 5,608 2020 4,166 2021 2,395 Thereafter 2,276 $ 27,938
Schedule of goodwill	The changes in the carrying value of the Company's goodwill in the three months ended March 31, 2017 were as follows (in thousands): Balance at January 1, 2017 Goodwill $ 52,499 Accumulated impairment losses (3,106 ) 49,393 Purchase accounting adjustments - Taqua 498 Balance at March 31, 2017 $ 49,891 Balance at March 31, 2017 Goodwill $ 52,997 Accumulated impairment losses (3,106 ) $ 49,891

ACCRUED EXPENSES (Tables)

ACCRUED EXPENSES (Tables)	3 Months Ended
	Mar. 31, 2017
Payables and Accruals [Abstract]
Schedule of accrued expenses	Accrued expenses at March 31, 2017 and December 31, 2016 consist of the following (in thousands): March 31, December 31, Employee compensation and related costs $ 9,200 $ 15,879 Other 6,586 10,007 $ 15,786 $ 25,886

RESTRUCTURING ACCRUAL (Tables)

RESTRUCTURING ACCRUAL (Tables)	3 Months Ended
	Mar. 31, 2017
Restructuring and Related Activities [Abstract]
Summary of restructuring accrual activity	A summary of the 2016 Restructuring Initiative accrual activity for the three months ended March 31, 2017 is as follows (in thousands): Balance at Initiatives Adjustments for changes in estimate Cash Balance at Severance $ 497 $ 236 $ (26 ) $ (420 ) $ 287 A summary of the Taqua Restructuring Initiative accrual activity for the three months ended March 31, 2017 is as follows (in thousands): Balance at Initiatives Adjustments for changes in estimate Cash Balance at Severance $ 384 $ 39 $ (49 ) $ (365 ) $ 9 Facilities 218 370 — (94 ) 494 $ 602 $ 409 $ (49 ) $ (459 ) $ 503 A summary of the 2015 Restructuring Initiative accrual activity for the three months ended March 31, 2017 is as follows (in thousands): Balance at Initiatives Adjustments for changes in estimate Cash Balance at Severance $ 168 $ — $ — $ (168 ) $ —

STOCK-BASED COMPENSATION PLANS

STOCK-BASED COMPENSATION PLANS (Tables)	3 Months Ended
	Mar. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of activity related to outstanding stock options	The activity related to the Company's outstanding stock options for the three months ended March 31, 2017 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, 2017 5,610,106 $ 15.73 Granted 3,920 $ 6.10 Exercised (13,430 ) $ 3.80 Forfeited (22,483 ) $ 13.91 Expired (50,425 ) $ 21.50 Outstanding at March 31, 2017 5,527,688 $ 15.70 5.08 $ 98 Vested or expected to vest at March 31, 2017 5,480,151 $ 15.73 5.05 $ 97 Exercisable at March 31, 2017 4,890,476 $ 15.79 4.75 $ 92
Schedule of assumptions used to estimate the fair value of options at the date of grant using the Black-Scholes option pricing model	The grant date fair values of options to purchase common stock granted in the three months ended March 31, 2017 were estimated using the Black-Scholes valuation model with the following assumptions: Three months ended March 31, Risk-free interest rate 1.95% Expected dividends — Weighted average volatility 51.3% Expected life (years) 5.0
Schedule of stock options, additional information	Additional information regarding the Company's stock options for the three months ended March 31, 2017 is as follows: Three months ended March 31, Weighted average grant date fair value of stock options granted $ 2.81 Total intrinsic value of stock options exercised (in thousands) $ 37 Cash received from the exercise of stock options (in thousands) $ 51
Schedule of activity related to unvested restricted stock grants	The activity related to the Company's RSAs for the three months ended March 31, 2017 is as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2017 2,030,028 $ 9.69 Granted 518,560 $ 6.58 Vested (164,629 ) $ 13.98 Forfeited (7,092 ) $ 16.60 Unvested balance at March 31, 2017 2,376,867 $ 8.70 The activity related to the Company's RSUs for the three months ended March 31, 2017 is as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2017 110,219 $ 11.95 Granted — $ — Vested (11,185 ) $ 16.05 Forfeited (10,750 ) $ 8.12 Unvested balance at March 31, 2017 88,284 $ 11.89
Schedule of activity related to performance stock awards	The activity related to the Company's PSUs for the three months ended March 31, 2017 is as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2017 147,085 $ 12.11 Granted 165,000 $ 8.41 Vested (24,106 ) $ 15.37 Forfeited (2,560 ) $ 15.37 Unvested balance at March 31, 2017 285,419 $ 9.67
Schedule of stock-based compensation expenses which are included in condensed consolidated statement of operations	The condensed consolidated statements of operations include stock-based compensation for the three months ended March 31, 2017 and 2016 as follows (in thousands): Three months ended March 31, March 31, Product cost of revenue $ 99 $ 71 Service cost of revenue 317 332 Research and development 1,317 1,179 Sales and marketing (88 ) 1,020 General and administrative 1,618 1,813 $ 3,263 $ 4,415

MAJOR CUSTOMERS (Tables)

MAJOR CUSTOMERS (Tables)	3 Months Ended
	Mar. 31, 2017
Risks and Uncertainties [Abstract]
Schedule of customers contributing 10% or more of the revenue	The following customers contributed 10% or more of the Company's revenue in at least one of the three month periods ended March 31, 2017 and March 31, 2016 : Three months ended March 31, March 31, Verizon Communications 17% * Level 3 Communications * 19% AT&T Inc. * 11% _______________________ * Represents less than 10% of revenue

GEOGRAPHIC INFORMATION (Tables)

GEOGRAPHIC INFORMATION (Tables)	3 Months Ended
	Mar. 31, 2017
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 to which the product is shipped or where the services are performed. The following table summarizes revenue by geographic area as a percentage of total revenue: Three months ended March 31, March 31, United States 67 % 68 % Europe, Middle East and Africa 12 13 Japan 14 13 Other Asia Pacific 4 4 Other 3 2 100 % 100 %

BASIS OF PRESENTATION - Narrati

BASIS OF PRESENTATION - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017USD ($)segment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Number of reportable operating segments | segment	1
Accounting Standards Update 2016-09 [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Increased deferred tax asset | $	$ 5

BUSINESS ACQUISITION - Narrativ

BUSINESS ACQUISITION - Narrative Taqua LLC Acquisition (Details) - USD ($) $ in Thousands	Sep. 26, 2016	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2014
Business Acquisition [Line Items]
Cash, net of cash acquired		$ 0		$ 750
Goodwill		49,891	$ 49,393
Acquisition-related expenses		56		$ 0
Taqua, LLC [Member]
Business Acquisition [Line Items]
Cash, net of cash acquired	$ 19,919
Contingent consideration estimate	10,000
Goodwill	9,581
Increase to current liabilities		400
Increase to noncurrent liabilities		$ 100
Reversal of previously recorded contingent consideration			10,000
Reduction to goodwill			2,200
Acquisition-related expenses					$ 56
Taqua, LLC [Member] | Developed technology [Member]
Business Acquisition [Line Items]
Increase (decrease) in intangible assets			(12,100)
Taqua, LLC [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Increase (decrease) in intangible assets			$ 5,500
Maximum [Member] | Taqua, LLC [Member]
Business Acquisition [Line Items]
Contingent consideration estimate	$ 65,000

BUSINESS ACQUISITION - Summary

BUSINESS ACQUISITION - Summary of Taquq LLC Acquisition (Details) - USD ($) $ in Thousands	Sep. 26, 2016	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Business Acquisition [Line Items]
Cash, net of cash acquired		$ 0	$ 750
Current assets	$ 3,347
Goodwill		$ 49,891		$ 49,393
Taqua, LLC [Member]
Business Acquisition [Line Items]
Cash, net of cash acquired	19,919
Property and equipment	1,478
Goodwill	9,581
Other noncurrent assets	23
Current liabilities	(5,435)
Long-term liabilities	(685)
Total Assets and Liabilities, Net	19,919
Developed technology [Member] | Taqua, LLC [Member]
Business Acquisition [Line Items]
Intangible assets	2,100
Customer Relationships [Member] | Taqua, LLC [Member]
Business Acquisition [Line Items]
Intangible assets	$ 9,510

EARNINGS (LOSS) PER SHARE - (De

EARNINGS (LOSS) PER SHARE - (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Reconciliation of weighted average shares outstanding from basic to diluted
Weighted average shares outstanding - basic	49,114	49,484
Potential dilutive common shares	0	0
Weighted average shares outstanding - diluted	49,114	49,484
Common stock and unvested shares of restricted stock not included because their effect would have been antidilutive (in shares)	8,400	7,700

CASH EQUIVALENTS AND INVESTME37

CASH EQUIVALENTS AND INVESTMENTS - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities sold		$ 3,800
Available-for-sale securities, gross realized gains		$ 18
Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Period considered to classify available-for-sale securities as investments	1 year
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Period considered to classify available-for-sale securities as investments	2 years

CASH EQUIVALENTS AND INVESTME38

CASH EQUIVALENTS AND INVESTMENTS - Schedule of Activity for Short-Term Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Cash equivalents, amortized cost	$ 4,822	$ 6,619
Cash equivalents, fair value	4,822	6,619
Marketable securities, amortized cost	59,739	61,880
Marketable securities, unrealized gains	2	7
Marketable securities, unrealized losses	(61)	(51)
Marketable securities, fair value	59,680	61,836
Investments, amortized cost	37,255	32,451
Investments, unrealized gains	8	3
Investments, unrealized losses	(70)	(83)
Investments, fair value	37,193	32,371
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	2,672	3,264
Marketable securities, unrealized gains	0	0
Marketable securities, unrealized losses	(1)	(3)
Marketable securities, fair value	2,671	3,261
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	20,880	16,477
Marketable securities, unrealized gains	0	3
Marketable securities, unrealized losses	(21)	(3)
Marketable securities, fair value	20,859	16,477
Investments, amortized cost	17,609	19,473
Investments, unrealized gains	6	3
Investments, unrealized losses	(41)	(39)
Investments, fair value	17,574	19,437
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	35,696	41,893
Marketable securities, unrealized gains	2	4
Marketable securities, unrealized losses	(39)	(45)
Marketable securities, fair value	35,659	41,852
Investments, amortized cost	14,550	10,520
Investments, unrealized gains	2	0
Investments, unrealized losses	(29)	(44)
Investments, fair value	14,523	10,476
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	491	246
Marketable securities, unrealized gains	0	0
Marketable securities, unrealized losses	0	0
Marketable securities, fair value	491	246
Investments, amortized cost	5,096	2,458
Investments, unrealized gains	0	0
Investments, unrealized losses	0	0
Investments, fair value	$ 5,096	$ 2,458

CASH EQUIVALENTS AND INVESTME39

CASH EQUIVALENTS AND INVESTMENTS - Schedule of Short-Term Investments by Measurement (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	$ 4,822	$ 6,619
Marketable securities, fair value	59,680	61,836
Investments, fair value	37,193	32,371
Total carrying value [Member]
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	4,822	6,619
Marketable securities, fair value	59,680	61,836
Investments, fair value	37,193	32,371
Quoted prices in active markets (Level 1) [Member]
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	4,822	6,619
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	59,680	61,836
Investments, fair value	37,193	32,371
Significant unobservable inputs (Level 3) [Member]
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	0	0
Marketable securities, fair value	0	0
Investments, fair value	0	0
Municipal obligations [Member] | Total carrying value [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	2,671	3,261
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
Municipal obligations [Member] | Significant other observable inputs (Level 2) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	2,671	3,261
Municipal obligations [Member] | Significant unobservable inputs (Level 3) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
U.S. government agency notes [Member] | Total carrying value [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	20,859	16,477
Investments, fair value	17,574	19,437
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	20,859	16,477
Investments, fair value	17,574	19,437
U.S. government agency notes [Member] | Significant unobservable inputs (Level 3) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value	0	0
Corporate debt securities [Member] | Total carrying value [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	35,659	41,852
Investments, fair value	14,523	10,476
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	35,659	41,852
Investments, fair value	14,523	10,476
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
Certificates of deposit [Member] | Total carrying value [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	491	246
Investments, fair value	5,096	2,458
Certificates of deposit [Member] | Quoted prices in active markets (Level 1) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value	0	0
Certificates of deposit [Member] | Significant other observable inputs (Level 2) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	491	246
Investments, fair value	5,096	2,458
Certificates of deposit [Member] | Significant unobservable inputs (Level 3) [Member]
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value	$ 0	$ 0

INVENTORY - (Details)

INVENTORY - (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
On-hand final assemblies and finished goods inventories	$ 16,554	$ 15,346
Deferred cost of goods sold	2,717	4,237
Gross inventory	19,271	19,583
Less current portion	(17,671)	(18,283)
Inventory, Noncurrent	$ 1,600	$ 1,300

INTANGIBLE ASSETS AND GOODWIL41

INTANGIBLE ASSETS AND GOODWILL - (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Intangible Assets And Goodwill
Weighted average amortization period (years)	6 years 2 months 22 days		6 years 2 months 22 days
Cost	$ 55,250		$ 55,250
Accumulated amortization	27,312		25,053
Net carrying value	27,938		$ 30,197
Amortization expense	2,259	$ 1,946
Estimated future amortization expense for intangible assets
Remainder of 2017	6,878
2,018	6,615
2,019	5,608
2,020	4,166
2,021	2,395
Thereafter	2,276
Total	$ 27,938
Developed technology [Member]
Intangible Assets And Goodwill
Weighted average amortization period (years)	6 years 6 months 15 days		6 years 6 months 15 days
Cost	$ 34,980		$ 34,980
Accumulated amortization	18,019		16,453
Net carrying value	16,961		$ 18,527
Amortization expense	$ 1,566	1,627
Customer Relationships [Member]
Intangible Assets And Goodwill
Weighted average amortization period (years)	5 years 9 months 12 days		5 years 9 months 12 days
Cost	$ 19,540		$ 19,540
Accumulated amortization	8,563		7,870
Net carrying value	10,977		$ 11,670
Amortization expense	$ 693	$ 319
Internal use software [Member]
Intangible Assets And Goodwill
Weighted average amortization period (years)	3 years		3 years
Cost	$ 730		$ 730
Accumulated amortization	730		730
Net carrying value	$ 0		$ 0

INTANGIBLE ASSETS AND GOODWIL42

INTANGIBLE ASSETS AND GOODWILL - (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 26, 2016
Goodwill [Roll Forward]
Goodwill		$ 52,997	$ 52,499
Accumulated impairment losses		(3,106)	(3,106)
Goodwill, beginning of period	$ 49,891	$ 49,891	$ 49,393
Goodwill, end of period	49,891
Taqua, LLC [Member]
Goodwill [Roll Forward]
Goodwill, beginning of period				$ 9,581
Acquisition	$ 498

ACCRUED EXPENSES - (Details)

ACCRUED EXPENSES - (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Employee compensation and related costs	$ 9,200	$ 15,879
Other	6,586	10,007
Total	$ 15,786	$ 25,886

RESTRUCTURING ACCRUAL - Narrati

RESTRUCTURING ACCRUAL - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring	$ 570	$ 0
Restructuring reserve	800		$ 800	$ 1,300
Other Noncurrent Liabilities [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	200		200	62
2016 Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring	200		1,700
Taqua Restructuring Incentive [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring	409
Restructuring reserve	503		503	$ 602
Minimum [Member] | 2016 Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expense expected to be recorded	3,000		3,000
Expected annual savings	6,000		6,000
Expected cost remaining	1,300		1,300
Minimum [Member] | Taqua Restructuring Incentive [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expense expected to be recorded	1,000		1,000
Maximum [Member] | 2016 Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expense expected to be recorded	4,000		4,000
Expected annual savings	8,000		8,000
Expected cost remaining	2,300		2,300
Maximum [Member] | Taqua Restructuring Incentive [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expense expected to be recorded	$ 2,000		$ 2,000

RESTRUCTURING ACCRUAL - Rollfor

RESTRUCTURING ACCRUAL - Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	$ 1,300
Initiatives charged to expense	570	$ 0
Balance at the end of the period	800		$ 800
2016 Restructuring [Member]
Restructuring Reserve [Roll Forward]
Initiatives charged to expense	200		1,700
Taqua Restructuring Incentive [Member]
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	602
Initiatives charged to expense	409
Adjustments for changes in estimate	(49)
Cash payments	(459)
Balance at the end of the period	503		503
Employee Severance [Member] | 2016 Restructuring [Member]
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	497
Initiatives charged to expense	236
Adjustments for changes in estimate	(26)
Cash payments	(420)
Balance at the end of the period	287		287
Employee Severance [Member] | Taqua Restructuring Incentive [Member]
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	384
Initiatives charged to expense	39
Adjustments for changes in estimate	(49)
Cash payments	(365)
Balance at the end of the period	9		9
Employee Severance [Member] | 2015 Restructuring [Member]
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	168
Initiatives charged to expense	0
Adjustments for changes in estimate	0
Cash payments	(168)
Balance at the end of the period	0		0
Facility Closing [Member] | Taqua Restructuring Incentive [Member]
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	218
Initiatives charged to expense	370
Adjustments for changes in estimate	0
Cash payments	(94)
Balance at the end of the period	$ 494		$ 494

DEBT - (Details)

DEBT - (Details) - USD ($)	Jun. 13, 2016	Mar. 31, 2017	Mar. 31, 2016
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 20,000,000		$ 15,000,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Covenant terms, minimum cash and cash equivalents	$ 50,000,000		$ 85,000,000
Unused commitment fee percentage	0.1125%		0.15%
Covenant terms, minimum total revenues		$ 50,000,000
Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate (as a percent)	1.50%
Revolving Credit Facility [Member] | Federal Funds Purchased [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate (as a percent)	0.50%
Revolving Credit Facility [Member] | Eurodollar [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate (as a percent)	1.00%

COMMON STOCK REPURCHASES (Detai

COMMON STOCK REPURCHASES (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Jul. 29, 2013
Class of Stock [Line Items]
Payments for repurchase of common stock	$ 0	$ 1,456,000
Stock repurchased and retired during period (in shares)	0	200,000
Remaining authorized repurchase amount	$ 5,400,000
Common Stock [Member]
Class of Stock [Line Items]
Stock buyback program authorized amount			$ 100,000,000
Stock Buyback Program [Member]
Class of Stock [Line Items]
Payments for repurchase of common stock		$ 1,500,000

STOCK-BASED COMPENSATION PLAN48

STOCK-BASED COMPENSATION PLANS - (Details)	Apr. 01, 2017$ / sharesshares	Mar. 31, 2017USD ($)executive$ / sharesshares	Mar. 16, 2017shares	Apr. 01, 2016executiveshares	Mar. 16, 2015executiveshares	Feb. 28, 2017executiveshares	Mar. 31, 2017USD ($)$ / sharesshares	Mar. 31, 2016USD ($)	Dec. 31, 2015executive
Range of assumptions used in estimating fair value of options
Cash received from the exercise of stock options (in dollars) | $							$ 51,000	$ 5,000
Weighted average grant-date fair value
Stock-based compensation (in dollars) | $							3,263,000	4,415,000
Tax benefit from stock based compensation expense | $							0	0
Fair value of the assumed awards attributable to future stock-based compensation expense | $		$ 21,700,000					$ 21,700,000
Expected period for unrecognized expense							2 years
Product cost of revenue [Member]
Weighted average grant-date fair value
Stock-based compensation (in dollars) | $							$ 99,000	71,000
Service cost of revenue [Member]
Weighted average grant-date fair value
Stock-based compensation (in dollars) | $							317,000	332,000
Research and development [Member]
Weighted average grant-date fair value
Stock-based compensation (in dollars) | $							1,317,000	1,179,000
Sales and marketing [Member]
Weighted average grant-date fair value
Stock-based compensation (in dollars) | $							(88,000)	1,020,000
General and Administrative Expense [Member]
Weighted average grant-date fair value
Stock-based compensation (in dollars) | $							$ 1,618,000	$ 1,813,000
Performance Share Units [Member]
Change in unvested restricted stock awards
Unvested balance at the beginning of the period (in shares)	285,419						147,085
Granted (in shares)							165,000
Vested (in shares)							(24,106)
Forfeited (in shares)							(2,560)
Unvested balance at the end of the period (in shares)		285,419					285,419
Weighted average grant-date fair value
Unvested balance at the end of the period (in dollars per share) | $ / shares	$ 9.67						$ 12.11
Granted (in dollars per share) | $ / shares							8.41
Vested (in dollars per share) | $ / shares							15.37
Forfeited (in dollars per share) | $ / shares							15.37
Unvested balance at end of the period (in dollars per share) | $ / shares		$ 9.67					$ 9.67
Total fair value (in dollars) | $							$ 400,000
Stock Options [Member]
Number of shares
Outstanding at the beginning of the period (in shares)	5,527,688						5,610,106
Granted (in shares)							3,920
Exercised (in shares)							(13,430)
Forfeited (in shares)							(22,483)
Expired (in shares)							(50,425)
Outstanding at the end of the period (in shares)		5,527,688					5,527,688
Vested or expected to vest at the end of the period (in shares)		5,480,151					5,480,151
Exercisable at the end of the period (in shares)		4,890,476					4,890,476
Weighted average exercise price
Outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 15.70						$ 15.73
Granted (in dollars per share) | $ / shares							6.10
Exercised (in dollars per share) | $ / shares							3.80
Forfeited (in dollars per share) | $ / shares							13.91
Expired (in dollars per share) | $ / shares							21.50
Outstanding at the end of the period (in dollars per share) | $ / shares		$ 15.70					15.70
Vested or expected to vest at the end of the period (in dollars per share) | $ / shares		15.73					15.73
Exercisable at the end of the period (in dollars per share) | $ / shares		$ 15.79					$ 15.79
Weighted average remaining contractual life (in years)
Outstanding at the end of the period							5 years 1 month
Vested or expected to vest at the end of the period							5 years 20 days
Exercisable at the end of the period							4 years 9 months 1 day
Aggregate intrinsic value (in dollars)
Outstanding at the end of the period (in dollars) | $		$ 98,000					$ 98,000
Vested or expected to vest at the end of the period (in dollars) | $		97,000					97,000
Exercisable at the end of the period (in dollars) | $		$ 92,000					$ 92,000
Range of assumptions used in estimating fair value of options
Risk-free interest rate							1.95%
Expected dividends							0.00%
Weighted average volatility							51.30%
Expected life							5 years
Weighted average grant date fair value of stock options granted (in dollars per share) | $ / shares							$ 2.81
Total intrinsic values of stock options exercised (in dollars) | $							$ 37,000
Cash received from the exercise of stock options (in dollars) | $							$ 51,000
Restricted stock awards [Member]
Change in unvested restricted stock awards
Unvested balance at the beginning of the period (in shares)	2,376,867						2,030,028
Granted (in shares)							518,560
Vested (in shares)							(164,629)
Forfeited (in shares)							(7,092)
Unvested balance at the end of the period (in shares)		2,376,867					2,376,867
Weighted average grant-date fair value
Unvested balance at the end of the period (in dollars per share) | $ / shares	$ 8.70						$ 9.69
Granted (in dollars per share) | $ / shares							6.58
Vested (in dollars per share) | $ / shares							13.98
Forfeited (in dollars per share) | $ / shares							16.60
Unvested balance at end of the period (in dollars per share) | $ / shares		$ 8.70					$ 8.70
Total fair value (in dollars) | $							$ 2,500,000
Restricted Stock Units (RSUs) [Member]
Change in unvested restricted stock awards
Unvested balance at the beginning of the period (in shares)	88,284						110,219
Granted (in shares)							0
Vested (in shares)							(11,185)
Forfeited (in shares)							(10,750)
Unvested balance at the end of the period (in shares)		88,284					88,284
Weighted average grant-date fair value
Unvested balance at the end of the period (in dollars per share) | $ / shares	$ 11.89						$ 11.95
Granted (in dollars per share) | $ / shares							0
Vested (in dollars per share) | $ / shares							16.05
Forfeited (in dollars per share) | $ / shares							8.12
Unvested balance at end of the period (in dollars per share) | $ / shares		$ 11.89					$ 11.89
Employee Stock [Member]
Weighted average grant-date fair value
Offering period							6 months
Purchase price of common stock (percentage)							85.00%
Maximum number of shares purchasable per employee							500
2017 Performance Share Units [Member] | Performance Share Units [Member]
Stock-based compensation
Number of executives granted shares | executive		5
Change in unvested restricted stock awards
Granted (in shares)		165,000
2017 Performance Share Units [Member] | Performance Share Units [Member] | Share-based Compensation Award, Tranche One [Member]
Stock-based compensation
Vesting percentage		33.33%
2017 Performance Share Units [Member] | Performance Share Units [Member] | Share-based Compensation Award, Tranche Two [Member]
Stock-based compensation
Vesting percentage		33.33%
2017 Performance Share Units [Member] | Performance Share Units [Member] | Share-based Compensation Award, Tranche Three [Member]
Stock-based compensation
Vesting percentage		33.33%
2016 Performance Share Units [Member] | Performance Share Units [Member]
Stock-based compensation
Number of executives granted shares | executive				6		4
Percent of performance metrics achieved						90.40%
Change in unvested restricted stock awards
Granted (in shares)				131,250
Vested (in shares)						(24,106)
Forfeited (in shares)			(2,560)
2016 Performance Share Units [Member] | Performance Share Units [Member] | Share-based Compensation Award, Tranche One [Member]
Stock-based compensation
Vesting percentage				33.33%
2016 Performance Share Units [Member] | Performance Share Units [Member] | Share-based Compensation Award, Tranche Two [Member]
Stock-based compensation
Vesting percentage				33.33%
2016 Performance Share Units [Member] | Performance Share Units [Member] | Share-based Compensation Award, Tranche Three [Member]
Stock-based compensation
Vesting percentage				33.33%
2015 Performance Share Units [Member] | Performance Share Units [Member]
Stock-based compensation
Number of executives granted shares | executive					8	4			2
Percent of performance metrics achieved						76.00%
Change in unvested restricted stock awards
Granted (in shares)					131,250
Vested (in shares)						(23,750)
Forfeited (in shares)	(7,500)
2015 Performance Share Units [Member] | Performance Share Units [Member] | Share-based Compensation Award, Tranche One [Member]
Stock-based compensation
Vesting percentage					33.33%
2015 Performance Share Units [Member] | Performance Share Units [Member] | Share-based Compensation Award, Tranche Two [Member]
Stock-based compensation
Vesting percentage					33.33%
2015 Performance Share Units [Member] | Performance Share Units [Member] | Share-based Compensation Award, Tranche Three [Member]
Stock-based compensation
Vesting percentage					33.33%
Scenario, Previously Reported [Member] | Sales and marketing [Member]
Weighted average grant-date fair value
Stock-based compensation (in dollars) | $							$ 900,000
Restatement Adjustment [Member] | Sales and marketing [Member]
Weighted average grant-date fair value
Stock-based compensation (in dollars) | $							$ (1,000,000)

MAJOR CUSTOMERS - (Details)

MAJOR CUSTOMERS - (Details) - customer	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Revenue [Member] | Less than [Member]
MAJOR CUSTOMERS
Threshold percentage	10.00%
Revenue [Member] | Customer [Member] | Verizon Communications[Member]
MAJOR CUSTOMERS
Concentration risk, percentage	17.00%
Revenue [Member] | Customer [Member] | Level 3 Communications [Member]
MAJOR CUSTOMERS
Concentration risk, percentage		19.00%
Revenue [Member] | Customer [Member] | AT&T [Member]
MAJOR CUSTOMERS
Concentration risk, percentage		11.00%
Accounts receivable balance [Member]
MAJOR CUSTOMERS
Threshold percentage	10.00%
Accounts receivable balance [Member] | Customer [Member]
MAJOR CUSTOMERS
Concentration risk, percentage	14.00%
Number of major customers	1		0

GEOGRAPHIC INFORMATION - Summar

GEOGRAPHIC INFORMATION - Summary of Revenue by Geographic Area as a Percentage of Total Revenue (Details) - Revenue [Member] - Geographical area [Member]	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenue by geographic area and by customer
Percentage of total revenue	100.00%	100.00%
United States [Member]
Revenue by geographic area and by customer
Percentage of total revenue	67.00%	68.00%
Europe, Middle East and Africa [Member]
Revenue by geographic area and by customer
Percentage of total revenue	12.00%	13.00%
Japan [Member]
Revenue by geographic area and by customer
Percentage of total revenue	14.00%	13.00%
Other Asia Pacific [Member]
Revenue by geographic area and by customer
Percentage of total revenue	4.00%	4.00%
Other [Member]
Revenue by geographic area and by customer
Percentage of total revenue	3.00%	2.00%

INCOME TAXES - (Details)

INCOME TAXES - (Details) $ in Millions	3 Months Ended
	Mar. 31, 2016USD ($)
Income Tax Disclosure [Abstract]
Discrete charge related to an uncertain tax position	$ 0.7

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details)	Sep. 21, 2015shareholder	Apr. 06, 2015officer
Commitments and Contingencies Disclosure [Abstract]
Number of officers listed as defendants | officer		2
Number of shareholders seeking plaintiff status | shareholder	4