Ribbon Communications (RBBN) 10-Q 31 Oct 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 23, 2018
Document And Entity Information
Entity Registrant Name	RIBBON COMMUNICATIONS INC.
Entity Central Index Key	1,708,055
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		106,519,406

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 35,984	$ 57,073
Marketable securities	7,284	17,224
Accounts receivable, net	150,677	165,156
Inventory	21,724	21,303
Other current assets	19,830	21,463
Total current assets	235,499	282,219
Property and equipment, net	25,960	24,780
Intangible assets, net	263,393	244,414
Goodwill	382,493	335,716
Investments	0	9,031
Deferred income taxes	8,212	8,434
Other assets	8,496	6,289
Total assets	924,053	910,883
Current liabilities:
Revolving credit facility	58,000	20,000
Accounts payable	43,215	45,851
Accrued expenses and other	74,610	76,380
Deferred revenue	82,489	100,571
Total current liabilities	258,314	242,802
Long-term debt, related party	23,500	22,500
Deferred revenue, net of current	15,985	14,184
Deferred income taxes	3,869	2,787
Other long-term liabilities	32,023	13,189
Total liabilities	333,691	295,462
Commitments and contingencies (Note 15)
Stockholders' equity:
Preferred stock, $0.01 par value per share; 10,000,000 shares authorized, none issued and outstanding	0	0
Common stock, $0.0001 par value per share; 240,000,000 shares authorized; 106,512,530 shares issued and outstanding at September 30, 2018; 101,752,856 shares issued and outstanding at December 31, 2017	11	10
Additional paid-in capital	1,722,116	1,684,768
Accumulated deficit	(1,134,957)	(1,072,426)
Accumulated other comprehensive income	3,192	3,069
Total stockholders' equity	590,362	615,421
Total liabilities and stockholders' equity	$ 924,053	$ 910,883

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	240,000,000	240,000,000
Common stock, shares issued (in shares)	106,512,530	101,752,856
Common stock, shares outstanding (in shares)	106,512,530	101,752,856

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue:
Total revenue	$ 152,468	$ 74,629	$ 411,009	$ 183,730
Cost of revenue:
Total cost of revenue	70,234	20,082	198,391	59,033
Gross profit	82,234	54,547	212,618	124,697
Operating expenses:
Research and development	34,403	20,798	109,056	61,071
Sales and marketing	31,488	17,454	94,152	47,850
General and administrative	15,942	10,833	46,571	27,993
Acquisition- and integration-related	5,570	1,543	14,262	6,278
Restructuring	2,397	0	15,162	1,071
Total operating expenses	89,800	50,628	279,203	144,263
(Loss) income from operations	(7,566)	3,919	(66,585)	(19,566)
Interest (expense) income, net	(1,420)	260	(2,754)	772
Other (expense) income, net	(1,254)	1	(3,058)	577
(Loss) income before income taxes	(10,240)	4,180	(72,397)	(18,217)
Income tax benefit (provision)	82	(727)	(2,587)	(1,321)
Net (loss) income	$ (10,158)	$ 3,453	$ (74,984)	$ (19,538)
(Loss) earnings per share
Basic (in dollars per share)	$ (0.10)	$ 0.07	$ (0.73)	$ (0.39)
Diluted (in dollars per share)	$ (0.10)	$ 0.07	$ (0.73)	$ (0.39)
Shares used to compute (loss) earnings per share:
Basic (in shares)	104,918	49,753	103,009	49,472
Diluted (in shares)	104,918	50,131	103,009	49,472
Product
Revenue:
Total revenue	$ 77,283	$ 44,120	$ 191,937	$ 98,305
Cost of revenue:
Total cost of revenue	38,891	9,708	102,183	28,748
Service
Revenue:
Total revenue	75,185	30,509	219,072	85,425
Cost of revenue:
Total cost of revenue	$ 31,343	$ 10,374	$ 96,208	$ 30,285

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (10,158)	$ 3,453	$ (74,984)	$ (19,538)
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	(80)	(13)	(43)	102
Unrealized gain on available-for sale marketable securities, net of reclassification adjustments for realized amounts	23	43	(10)	12
Employee retirement benefits	156	0	156	0
Other comprehensive income, net of tax	99	30	103	114
Comprehensive (loss) income	$ (10,059)	$ 3,483	$ (74,881)	$ (19,424)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net loss	$ (74,984)	$ (19,538)
Adjustments to reconcile net loss to cash flows (used in) provided by operating activities:
Depreciation and amortization of property and equipment	8,270	5,255
Amortization of intangible assets	37,721	6,845
Stock-based compensation	7,421	11,387
Deferred income taxes	(39)	687
Foreign exchange losses	3,066	15
Other	0	(566)
Changes in operating assets and liabilities:
Accounts receivable	24,550	2,360
Inventory	2,783	1,806
Other operating assets	2,796	(560)
Accounts payable	(7,679)	384
Accrued expenses and other long-term liabilities	(20,033)	(3,028)
Deferred revenue	(7,413)	4,000
Net cash (used in) provided by operating activities	(23,541)	9,047
Cash flows from investing activities:
Purchases of property and equipment	(5,950)	(3,265)
Business acquisitions, net of cash acquired	(46,389)	0
Purchases of marketable securities	0	(28,731)
Sale/maturities of marketable securities	18,919	41,964
Proceeds from the sale of intangible assets	0	576
Net cash (used in) provided by investing activities	(33,420)	10,544
Cash flows from financing activities:
Borrowings under revolving line of credit	142,500	0
Principal payments on revolving line of credit	(104,500)	0
Principal payments of capital lease obligations	(436)	(30)
Payment of debt issuance costs	(624)	0
Proceeds from the sale of common stock in connection with employee stock purchase plan and exercise of stock options	43	1,401
Payment of tax withholding obligations related to net share settlements of restricted stock awards	(830)	(1,904)
Net cash provided by (used in) financing activities	36,153	(533)
Effect of exchange rate changes on cash and cash equivalents	(281)	299
Net (decrease) increase in cash and cash equivalents	(21,089)	19,357
Cash and cash equivalents, beginning of year	57,073	31,923
Cash and cash equivalents, end of period	35,984	51,280
Supplemental disclosure of cash flow information:
Interest paid	1,568	84
Income taxes paid	4,047	1,198
Income tax refunds received	426	91
Supplemental disclosure of non-cash investing activities:
Capital expenditures incurred, but not yet paid	344	301
Property and equipment acquired under capital lease	1,218	0
Acquisition purchase consideration - deferred payments	30,000	0
Shares of common stock issued as purchase consideration	30,000	0
Acquisition purchase consideration - assumed equity awards	747	0
Supplemental disclosure of non-cash financing activities:
Total fair value of restricted stock awards, restricted stock units and performance-based stock units on date vested	$ 5,462	$ 6,225

BASIS OF PRESENTATION

BASIS OF PRESENTATION	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
BASIS OF PRESENTATION	BASIS OF PRESENTATION Business Ribbon is a leading provider of network communications solutions to telecommunications, wireless and cable service providers and enterprises of all sizes across industry verticals. With over 1,000 customers around the globe, including some of the largest telecommunications service providers and enterprises in the world, Ribbon enables service providers and enterprises to modernize their communications networks and provide secure real-time communications ("RTC") solutions to their customers and employees. By securing and enabling reliable and scalable Internet Protocol ("IP") networks, Ribbon helps service providers and enterprises adopt the next generation of software-based virtualized and cloud communications technologies to drive new, incremental revenue while protecting their existing revenue streams. Ribbon's solutions provide a secure way for its customers to connect and leverage multivendor, multiprotocol communications systems and applications across their networks and the cloud, around the world and in a rapidly changing ecosystem of IP-enabled devices such as smartphones and tablets. In addition, Ribbon's solutions secure the evolution to cloud-based delivery of unified communications ("UC") solutions - both for service providers transforming to a cloud-based network and for enterprises using cloud-based UC. Ribbon goes to market through both direct sales and indirect channels globally, leveraging the assistance of resellers, and provides ongoing support to its customers through a global services team with experience in design, deployment and maintenance of some of the world's largest IP networks. The Merger with GENBAND (see Note 2 ) was completed in October 2017. As a result of the Merger, Ribbon believes it is better positioned to enable network transformations to IP and to cloud-based networks for service providers and enterprise customers worldwide, with a broader and deeper sales footprint, increased ability to invest in growth, more efficient and effective research and development, and a comprehensive RTC product offering. Basis of Presentation In the opinion of management, the accompanying unaudited condensed consolidated financial statements include all adjustments, consisting only of normal recurring items, necessary for their fair presentation with accounting principles generally accepted in the United States of America ("GAAP") and with the rules and regulations of the U.S. Securities and Exchange Commission ("SEC"). On October 27, 2017 (the "Merger Date"), Sonus Networks, Inc. ("Sonus") consummated an acquisition as specified in an Agreement and Plan of Merger (the "Merger Agreement") with Solstice Sapphire Investments, Inc. ("NewCo") and certain of its wholly-owned subsidiaries, GENBAND Holdings Company, GENBAND Inc. and GENBAND II, Inc. (collectively, "GENBAND") pursuant to which, following a series of merger transactions (collectively, the "Merger"), Sonus and GENBAND each became a wholly-owned subsidiary of NewCo, with Sonus deemed the acquirer in the transaction for accounting purposes. Subsequently, on November 28, 2017, the Company changed its name to "Ribbon Communications Inc." The condensed consolidated financial statements of the Company represent the consolidated financial statements of Sonus, prior to the Merger Date, and the condensed consolidated financial statements of Ribbon, on and after the Merger Date. The financial results of GENBAND are included in Ribbon's condensed consolidated financial statements beginning on the Merger Date. On August 3, 2018 (the "Edgewater Acquisition Date"), the Company completed the acquisition of Edgewater Networks, Inc. (“Edgewater”). The financial results of Edgewater are included in the Company's condensed consolidated financial statements for the period subsequent to the Edgewater Acquisition Date. Interim results are not necessarily indicative of results for a full year or any future interim period. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the Company's Annual Report on Form 10-K for the year ended December 31, 2017 (the "Annual Report"), which was filed with the SEC on March 8, 2018. Significant Accounting Policies The Company's significant accounting policies are disclosed in Note 2 to the Consolidated Financial Statements included in the Annual Report. There were no material changes to the significant accounting policies during the nine months ended September 30, 2018 , apart from the Company's accounting policy related to revenue recognition, as discussed below. Effective January 1, 2018, the Company adopted Accounting Standards Codification ("ASC") 606, Revenue from Contracts with Customers ("ASC 606" or the "New Revenue Standard"), the new standard on revenue from contracts with customers, which codified Accounting Standards Update ("ASU") 2014-09, Revenue from Contracts with Customers ("ASU 2014-09"). As a result, the Company changed its accounting policy for revenue recognition to ensure compliance with ASC 606, which is described below and in Note 10 . Revenue Recognition Policy The Company derives revenues from two primary sources: products and services. Product revenue includes the Company's hardware and software that function together to deliver the products' essential functionality. Software and hardware are also sold on a standalone basis. Services include customer support (software updates, upgrades and technical support), consulting, design services, installation services and training. Generally, contracts with customers contain multiple performance obligations, consisting of products and services. For these contracts, the Company accounts for individual performance obligations separately if they are considered distinct. When an arrangement contains more than one performance obligation, the Company will generally allocate the transaction price to each performance obligation on a relative standalone selling price basis. The best evidence of a standalone selling price is the observable price of a good or service when the entity sells that good or service separately in similar circumstances and to similar customers. If the good or service is not sold separately, an entity must estimate the standalone selling price by using an approach that maximizes the use of observable inputs. Acceptable estimation methods include but are not limited to: (1) adjusted market assessment; (2) expected cost plus a margin; and (3) a residual approach (when the standalone selling price is not directly observable and is either highly variable or uncertain). The Company's software licenses typically provide a perpetual right to use the Company's software. The Company also sells term-based software licenses that expire and Software-as-a-Service ("SaaS")-based software which are referred to as subscription arrangements. The Company does not customize its software nor are installation services required, as the customer has a right to utilize internal resources or a third-party service company. The software and hardware are delivered before related services are provided and are functional without professional services or customer support. The Company has concluded that its software licenses are functional intellectual property that are distinct, as the user can benefit from the software on its own. The product revenue is typically recognized upon transfer of control or when the software is made available for download, as this is the point that the user of the software can direct the use of, and obtain substantially all of the remaining benefits from, the functional intellectual property. The Company does not recognize software revenue related to the renewal of subscription software licenses earlier than the beginning of the subscription period. Hardware product is generally sold with software to provide the customer solution. Services revenue includes revenue from customer support and other professional services. The Company offers warranties on its products. Certain of the Company's warranties are considered to be assurance-type in nature and do not cover anything beyond ensuring that the product is functioning as intended. Based on the guidance in Accounting Standards Codification ("ASC") 606, assurance-type warranties do not represent separate performance obligations. The Company also sells separately-priced maintenance service contracts which qualify as service-type warranties and represent separate performance obligations. The Company does not allow and has no history of accepting product returns. Customer support includes software updates on a when-and-if-available basis, telephone support, integrated web-based support and bug fixes or patches. The Company sells its customer support contracts at a percentage of list or net product price related to the support. Customer support revenue is recognized ratably over the term of the customer support agreement, which is typically one year. The Company's professional services include consulting, technical support, resident engineer services, design services and installation services. Because control transfers over time, revenue is recognized based on progress toward completion of the performance obligation. The method to measure progress toward completion requires judgment and is based on the nature of the products or services to be provided. The Company generally uses the input method to measure progress for its contracts because it believes such method best depicts the transfer of assets to the customer, which occurs as the Company incurs costs for the contracts. Under the cost-to-cost measure of progress, the progress toward completion is measured based on the ratio of costs incurred to date to the total estimated costs at completion of the performance obligation. When the measure of progress is based upon expended labor, progress toward completion is measured as the ratio of labor time expended to date vs the total estimated labor time required to complete the performance obligation. Revenue is recorded proportionally as costs are incurred or labor is expended. Costs to fulfill these obligations include internal labor as well as subcontractor costs. Customer training includes courses offered by the Company. The related revenue is typically recognized as the training services are performed. Principles of Consolidation The condensed consolidated financial statements include the accounts of Ribbon and its wholly-owned subsidiaries. Intercompany transactions and balances have been eliminated in consolidation. Use of Estimates and Judgments The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting periods. Significant estimates and judgments relied upon in preparing these consolidated financial statements include accounting for business combinations; revenue recognition for multiple element arrangements, including determining the standalone selling prices of performance obligations; inventory valuations; assumptions used to determine the fair value of stock-based compensation; intangible assets and goodwill valuations, including impairments; legal contingencies; and recoverability of Ribbon's net deferred tax assets and the related valuation allowances. Ribbon regularly assesses these estimates and records changes in estimates in the period in which they become known. Ribbon bases its estimates on historical experience and various other assumptions that it believes to be reasonable under the circumstances. Actual results could differ from those estimates. Reclassifications Certain reclassifications have been made to the previously issued financial statements to conform to the current period presentation, none of which affected net loss as previously reported. Fair Value of Financial Instruments The carrying amounts of the Company's financial instruments, which include cash equivalents; marketable securities; investments; accounts receivable; revolving credit facility; accounts payable; long-term debt, related party; and other long-term liabilities; approximate their fair values. Operating Segments The Company operates in a single segment, as the chief operating decision maker makes decisions and assesses performance at the company level. Operating segments are identified as components of an enterprise about which separate discrete financial information is utilized for evaluation by the chief operating decision maker in making decisions regarding resource allocation and assessing performance. To date, the chief operating decision maker has made such decisions and assessed performance at the company level, as one segment. The Company's chief operating decision maker is its President and Chief Executive Officer. Foreign Currency Translation As part of ongoing merger integration activities, the Company conducted an assessment of the functional currencies of its foreign subsidiaries. The Company concluded that the U.S. dollar is the appropriate functional currency for the majority of the former GENBAND foreign subsidiaries, based on its assessment of underlying factors. As such, the functional currency was changed to the U.S. dollar effective January 1, 2018. Recent Accounting Pronouncements In February 2018, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income ("ASU 2018-02"), which amends ASC 220, Income Statement - Reporting Comprehensive Income , to allow a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act and requires entities to provide certain disclosures regarding stranded tax effects. ASU 2018-02 is effective for the Company beginning January 1, 2019, with early adoption permitted. The Company is currently assessing the potential impact of the adoption of ASU 2018-02 on its consolidated financial statements. In August 2018, the FASB issued ASU 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”), which provides guidance on implementation costs incurred in a cloud computing arrangement (“CCA”) that is a service contract. ASU 2018-15 amends ASC 350, Intangibles - Goodwill and Other (“ASC 350”) to include in its scope implementation costs of a CCA that is a service contract and clarifies that a customer should apply the guidance in ASC 350-40 to determine which implementation costs should be capitalized in such a CCA. ASU 2018-15 is effective for the Company beginning January 1, 2020. The Company is currently assessing the potential impact of the adoption of ASU 2018-15 on our consolidated financial statements. In May 2017, the FASB issued ASU 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting ("ASU 2017-09"), which amends the scope of modification accounting for share-based payment arrangements such that an entity would not apply modification accounting if the fair value, vesting conditions and classification of the awards are the same immediately before and after the modification. ASU 2017-09 became effective for the Company beginning January 1, 2018 for both interim and annual reporting periods. The adoption of ASU 2017-09 did not have a material impact on the Company's condensed consolidated financial statements. In March 2017, the FASB issued ASU 2017-07, Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Post Retirement Benefit Cost ("ASU 2017-07"). ASU 2017-07 amends the requirements in ASC 715 to require entities to disaggregate the current-service-cost component from the other components of net benefit cost (the "other components") and include it with other current compensation costs for related employees, present the other components elsewhere in the income statement and outside of income from operations if such a subtotal is presented and disclose the income statement lines that contain the other components if they are not presented on appropriately described separate lines. ASU 2017-07 became effective for the Company beginning January 1, 2018 for both interim and annual reporting periods. The adoption of ASU 2017-07 did not have a material impact on the Company's condensed consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments ("ASU 2016-15"), which adds or clarifies guidance on eight cash flow issues, including debt prepayment or debt extinguishment costs, settlement of zero-coupon debt instruments or certain other debt instruments, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies, distributions received from equity method investees, beneficial interests in securitization transactions and separately identifiable cash flows and application of the predominance principle. ASU 2016-15 became effective for the Company beginning January 1, 2018 for both interim and annual reporting periods. Entities must apply the guidance retrospectively to all periods presented but may apply it prospectively from the earliest date practicable if retrospective application would be impracticable. The adoption of ASU 2016-15 did not have a material impact on the Company's condensed consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) Section A - Leases: Amendments to the FASB Accounting Standards Codification ("ASU 2016-02"), its new standard on accounting for leases. ASU 2016-02 introduces a lessee model that brings most leases onto the balance sheet. ASU 2016-02 eliminates the current GAAP requirement for an entity to use bright-line tests in determining lease classification. ASU 2016-02 is effective for the Company for both interim and annual periods beginning January 1, 2019. Upon adoption of ASU 2016-02, the Company will recognize lease obligations for the right to use these assets in connection with its existing lease agreements. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements ("ASU 2018-11") and ASU 2018-10, Codification Improvements to Topic 842, Leases , both of which provided improvements to certain aspects of the guidance in ASC 842, Lease s. In January 2018, the FASB issued ASU 2018-01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842 , which provided additional clarification and implementation guidance. The Company has elected to use the alternative transition method as described in ASU 2018-11, which allows entities to initially apply ASU 2016-02 at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings, with no subsequent adjustments to prior period lease costs for comparability. The Company has essentially completed the lease assessment phase of implementation and is currently reviewing the contracts within its lease portfolio in order to quantify the impact of adoption on its consolidated balance sheet as of January 1, 2019. The Company expects to quantify such amounts to be recognized on the balance sheet by the end of the fourth quarter of 2018. In addition, the FASB has issued the following accounting pronouncements, none of which the Company believes will have a material impact on its consolidated financial statements: In August 2018, the FASB issued ASU 2018-14, Compensation - Retirement Benefits - Defined Benefit Plans - General (Subtopic 715-20): Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans (“ASU 2018-14”), which amends ASC 715, Compensation - Retirement Benefits (“ASC 715”) to add, remove and clarify disclosure requirements related to defined benefit pension and other postretirement plans. ASU 2018-14 is effective for the Company beginning January 1, 2020. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”), which changes the fair value measurement requirements of ASC 820, Fair Value Measurement (“ASC 820”). ASU 2018-13 is effective for the Company beginning January 1, 2020 for both interim and annual reporting. In July 2018, the FASB issued ASU 2018-09, Codification Improvements (“ASU 2018-09”), which contains amendments to clarify, correct errors in or make minor improvements to the Codification. ASU 2018-09 makes improvements to multiple topics, including but not limited to comprehensive income, debt, income taxes related to both stock-based compensation and business combinations, fair value measurement and defined contribution benefit plans. ASU 2018-09 is effective for the Company beginning January 1, 2019. In June 2018, the FASB issued ASU 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting ("ASU 2018-07"), which expands the scope of ASC 718, Compensation - Stock Compensation ("ASC 718"), to include all share-based payment arrangements related to the acquisition of goods and services from both nonemployees and employees. As a result, most of the guidance in ASC 718 associated with employee share-based payments, including most of its requirements related to classification and measurement, applies to nonemployee share-based payment arrangements. ASU 2018-07 is effective for the Company beginning January 1, 2019, although early adoption is permitted. In October 2016, the FASB issued ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory ("ASU 2016-16"), which removes the prohibition in ASC 740, Income Taxes, against the immediate recognition of the current and deferred income tax effects of intra-entity transfers of assets other than inventory. ASU 2016-16 is effective for the Company beginning January 1, 2019 for both interim and annual reporting periods. 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.

BUSINESS ACQUISITIONS

BUSINESS ACQUISITIONS	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
BUSINESS ACQUISITIONS	BUSINESS ACQUISITIONS Edgewater Networks, Inc. On the Edgewater Acquisition Date, the Company completed its acquisition of Edgewater, a private company headquartered in San Jose, California (the "Edgewater Acquisition"). The Edgewater Acquisition was completed in accordance with the terms and conditions of the Agreement and Plan of Merger, dated as of June 24, 2018, by and among Ribbon, Merger Sub, Edgewater and Shareholder Representative Services LLC, a Colorado limited liability company, solely in its capacity as the initial holder representative (the "Edgewater Merger Agreement”). Edgewater is a market leader in Network Edge Orchestration for the small and medium enterprise ("SME") and UC market. The Company believes that the acquisition of Edgewater will allow it to offer its global customer base a complete core-to-edge product portfolio, end-to-end service assurance and analytics solutions, and a fully integrated software-defined wide-area network ("SD-WAN") service. As consideration for the Edgewater Acquisition, Ribbon paid, in the aggregate, $46.4 million of cash, net of cash acquired, and issued 4.2 million shares of Ribbon common stock to Edgewater's selling shareholders and holders of vested in-the-money options and warrants to acquire common stock of Edgewater (the "Edgewater Selling Stakeholders") on the Edgewater Acquisition Date. Pursuant to the Edgewater Merger Agreement and subject to the terms and conditions contained therein, Ribbon has agreed to pay the Edgewater Selling Stakeholders an additional $30 million of cash, $15 million of which is to be paid 6 months from the closing date and the other $15 million of which is to be paid as early as 9 months from the closing date and no later than 18 months from the closing date (the exact timing of which will depend on the amount of revenue generated from the sales of Edgewater products in 2018). The current portion of this deferred purchase consideration is included as a component of Accrued expenses and other, and the noncurrent portion is included as a component of Other long-term liabilities in the Company's condensed consolidated balance sheet as of September 30, 2018. The Edgewater Acquisition has been accounted for as a business combination and the financial results of Edgewater have been included in the Company's consolidated financial statements for the period subsequent to its acquisition. As of September 30, 2018, the valuation of acquired assets, identifiable intangible assets and certain assumed liabilities was preliminary. The Company is still in the process of investigating the facts and circumstances existing as of the Edgewater Acquisition Date in order to finalize its valuation. The Company expects to finalize the valuation of the assets acquired and liabilities assumed by the second quarter of 2019. A summary of the preliminary allocation of the purchase consideration for Edgewater is as follows (in thousands): Fair value of consideration transferred: Cash consideration: Cash paid to Edgewater Selling Stakeholders $ 51,162 Less cash acquired (4,773 ) Net cash consideration 46,389 Unpaid cash consideration 30,000 Fair value of Ribbon stock issued 30,000 Fair value of equity awards assumed (see Note 11) 747 Fair value of total consideration $ 107,136 Fair value of assets acquired and liabilities assumed: Current assets, net of cash acquired $ 16,837 Property and equipment 380 Intangible assets: Developed technology 29,500 Customer relationships 26,100 Trade names 1,100 Goodwill 46,777 Other noncurrent assets 103 Deferred revenue (2,749 ) Other current liabilities (9,402 ) Deferred revenue, net of current (669 ) Other long-term liabilities (841 ) $ 107,136 The valuation of the acquired intangible assets is inherently subjective and relies on significant unobservable inputs. The Company used an income approach to value the acquired developed technology, customer relationships and trade name intangible assets. The valuation for each of these intangible assets was based on estimated projections of expected cash flows to be generated by the assets, discounted to the present value at discount rates commensurate with perceived risk. The valuation assumptions take into consideration the Company's estimates of customer attrition, technology obsolescence and revenue growth projections. The Company is amortizing the identifiable intangible assets in relation to the expected cash flows from the individual intangible assets over their respective useful lives, which have a weighted average life of 8.3 years (see Note 6 ). Goodwill resulting from the transaction is primarily due to expected synergies between the combined companies and is not deductible for tax purposes. The Company's revenue for both the three and nine months ended September 30, 2018 included approximately $10 million of revenue attributable to Edgewater since the Edgewater Acquisition Date. The Company has not provided pro forma financial information, as the historical amounts are not significant to the Company's consolidated financial statements. GENBAND Merger On October 27, 2017, Sonus consummated an acquisition as specified in the Merger Agreement with NewCo and GENBAND such that, following the Merger, Sonus and GENBAND each became a wholly-owned subsidiary of NewCo, with Sonus deemed the acquirer in the transaction for accounting purposes. On November 28, 2017, the Company changed its name to "Ribbon Communications Inc." Prior to the Merger, GENBAND was a Cayman Islands exempted company limited by shares that was formed on April 7, 2010. Through its wholly owned operating subsidiaries, GENBAND created rapid communications and applications for service providers, enterprises, independent software vendors, system integrators and developers globally. A majority of GENBAND's shares were held by JPMorgan Chase & Co. and managed by One Equity Partners ("OEP"). GENBAND shares were not listed on an exchange or quoted on any automated services, and there was no established trading market for GENBAND shares. The Company believes that Sonus' and GENBAND's complementary products, solutions and strategies position the combined company to deliver comprehensive solutions to service providers and enterprises migrating to a virtualized all-IP environment in an expanded customer and global footprint. Pursuant to the Merger Agreement, NewCo issued 50.9 million shares of Sonus common stock to the GENBAND equity holders, with the number of shares issued in the aggregate to the GENBAND equity holders equal to the number of shares of Sonus common stock outstanding immediately prior to the closing date of the Merger, such that former stockholders of Sonus would own approximately 50% , and former shareholders of GENBAND would own approximately 50% , of the shares of NewCo common stock issued and outstanding immediately following the consummation of the Merger. In addition, NewCo repaid GENBAND’s long-term debt, including both principal and unpaid interest, to a related party of GENBAND totaling $48 million and repaid GENBAND’s management fees due to an affiliate of OEP totaling $10.3 million . NewCo also issued a promissory note for $22.5 million to certain GENBAND equity holders (the "Promissory Note"). NewCo assumed the liability under GENBAND's revolving credit facility with Silicon Valley Bank, which had outstanding borrowings and letters of credit totaling $17.9 million and $2.9 million , respectively, at October 27, 2017. At October 27, 2017, the outstanding borrowings had an average interest rate of 4.67% . The Merger has been accounted for as a business combination and the financial results of GENBAND have been included in the Company's consolidated financial statements for the period subsequent to its acquisition. As of September 30, 2018, the valuation of acquired assets, identifiable intangible assets and certain assumed liabilities was final. A summary of the final allocation of the purchase consideration for GENBAND is as follows (in thousands): Fair value of consideration transferred: Cash consideration: Repayment of GENBAND long-term debt and accrued interest, related party $ 47,973 Payment of GENBAND management fees due to majority shareholder 10,302 Less cash acquired (15,324 ) Net cash consideration 42,951 Fair value of Sonus stock issued 413,982 Promissory note issued to GENBAND equity holders 22,500 Fair value of total consideration $ 479,433 Fair value of assets acquired and liabilities assumed: Current assets, net of cash acquired $ 99,126 Property and equipment 16,770 Intangible assets: In-process research and development 5,600 Developed technology 129,000 Customer relationships 101,300 Trade names 900 Goodwill 285,825 Other noncurrent assets 6,732 Revolving credit facility (17,930 ) Deferred revenue (32,390 ) Other current liabilities (80,023 ) Deferred revenue, net of current (6,804 ) Other long-term liabilities (28,673 ) $ 479,433 The valuation of the acquired intangible assets is inherently subjective and relies on significant unobservable inputs. The Company used an income approach to value the acquired developed technology, customer relationships and trade name intangible assets. The valuation for each of these intangible assets was based on estimated projections of expected cash flows to be generated by the assets, discounted to the present value at discount rates commensurate with perceived risk. The valuation assumptions take into consideration the Company's estimates of customer attrition, technology obsolescence and revenue growth projections. The Company will reclassify its in-process research and development intangible asset to developed technology intangible asset in the period that the related product becomes generally available and begin to record amortization expense for the developed technology intangible asset at that time. The Company is amortizing the identifiable intangible assets in relation to the expected cash flows from the individual intangible assets over their respective useful lives, which have a weighted average life of 8.3 years (see Note 6 ). Goodwill resulting from the transaction is primarily due to expected synergies between the combined companies and is not deductible for tax purposes. Pro Forma Results The following unaudited pro forma information presents the condensed combined results of operations of Sonus and GENBAND for the three and nine months ended September 30, 2017 as if the Merger had been completed on January 1, 2017, with adjustments to give effect to pro forma events that are directly attributable to the Merger. These pro forma adjustments include a reduction of historical GENBAND revenue for the fair value adjustment related to acquired deferred revenue, an increase in amortization expense for the acquired identifiable intangible assets, a decrease in historical GENBAND interest expense reflecting the extinguishment of certain of GENBAND's debt as a result of the Merger, net of the interest expense recorded in connection with the Promissory Note issued to certain GENBAND equity holders as part of the purchase consideration and the elimination of revenue and costs related to sales transactions between Sonus and GENBAND. The unaudited pro forma results do not reflect any operating efficiencies or potential cost savings that may result from the consolidation of the operations of Sonus and GENBAND. Accordingly, these unaudited pro forma results are presented for illustrative purposes and are not intended to represent or be indicative of the actual results of operations of the combined company that would have been achieved had the Merger occurred at the beginning of the period presented, nor are they intended to represent or be indicative of future results of operations (in thousands, except per share amounts): Three months ended September 30, 2017 Nine months ended September 30, 2017 Revenue $ 147,608 $ 419,749 Net loss $ (22,148 ) $ (105,666 ) Loss per share $ (0.22 ) $ (1.04 ) Acquisition- and Integration-Related Expenses Acquisition- and integration-related expenses include those expenses related to acquisitions that would otherwise not have been incurred by the Company. The acquisition-related expenses include professional and services fees such as legal, audit, consulting, paying agent and other fees, and expenses related to cash payments to certain former executives of the acquired businesses in connection with their employment agreements. These amounts include costs related to the Merger and the Edgewater Acquisition, as well as nominal amounts related to acquisitive activities. The integration-related expenses recorded in both the three and nine months ended September 30, 2018 represent incremental costs related to combining Sonus and GENBAND, such as third-party consulting and other services related to merging the two separate companies' systems and processes. The acquisition-related amounts recorded in both the three and nine months ended September 30, 2017 relate to professional fees incurred in connection with the Company's September 2016 acquisition of Taqua, LLC. The Company's acquisition- and integration-related expenses for the three and nine months ended September 30, 2018 and 2017 were as follows (in thousands): Three months ended Nine months ended September 30, September 30, September 30, September 30, Professional and services fees (acquisition-related) $ 2,905 $ 1,543 $ 5,314 $ 6,278 Management bonuses (acquisition-related) — — 1,972 — Integration-related expenses 2,665 — 6,976 — $ 5,570 $ 1,543 $ 14,262 $ 6,278

EARNINGS (LOSS) PER SHARE

EARNINGS (LOSS) PER SHARE	9 Months Ended
	Sep. 30, 2018
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 earnings per share is determined by using the weighted average number of common and dilutive common equivalent shares outstanding during the period unless the effect is antidilutive. The calculations of shares used to compute loss per share were as follows (in thousands): Three months ended Nine months ended September 30, September 30, September 30, September 30, Weighted average shares outstanding—basic 104,918 49,753 103,009 49,472 Potential dilutive common shares — 378 — — Weighted average shares outstanding—diluted 104,918 50,131 103,009 49,472 Options to purchase the Company's common stock and unvested shares of restricted and performance-based stock and stock units aggregating 3.5 million have not been included in the computation of diluted loss per share for the three and nine months ended September 30, 2018 because their effect would have been antidilutive. The Company has excluded 5.2 million weighted shares underlying options to purchase shares of the Company's common stock from the computation of diluted earnings per share for the three months ended September 30, 2017, because the options' exercise prices were greater than the average market price for the common stock and their effect would have been antidilutive. Options to purchase the Company's common stock and unvested shares of restricted and performance-based stock and stock units totaling 7.4 million shares for the nine months ended September 30, 2017 have not been included in the computation of diluted loss per share because their effect would have been antidilutive.

CASH EQUIVALENTS, MARKETABLE SE

CASH EQUIVALENTS, MARKETABLE SECURITIES AND INVESTMENTS	9 Months Ended
	Sep. 30, 2018
Investments, All Other Investments [Abstract]
CASH EQUIVALENTS AND INVESTMENTS	CASH EQUIVALENTS, MARKETABLE SECURITIES AND INVESTMENTS The Company invests in debt instruments, primarily U.S. government-backed, municipal and corporate obligations, which management believes to be high quality (investment grade) credit instruments. The Company sold $12.5 million of its available-for sale securities in both the three and nine months ended September 30, 2018, primarily to provide cash for acquisition-related payments in connection with the Edgewater Acquisition and to support integration-related and restructuring activities in connection with the Merger. The Company recognized nominal gross gains and approximately $20,000 of gross losses from the sales of these securities. The Company did not sell any of its available-for-sale securities during the three or nine months ended September 30, 2017. At September 30, 2018, the Company did not hold any investments that matured beyond one year. 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 September 30, 2018 . The amortized cost, gross unrealized gains and losses and fair value of the Company's marketable debt securities and investments at September 30, 2018 and December 31, 2017 were comprised of the following (in thousands): September 30, 2018 Amortized cost Unrealized gains Unrealized losses Fair value Cash equivalents $ 427 $ — $ — $ 427 Marketable securities U.S. government agency notes $ 3,997 $ — $ (17 ) $ 3,980 Corporate debt securities 3,317 — (13 ) 3,304 $ 7,314 $ — $ (30 ) $ 7,284 December 31, 2017 Amortized cost Unrealized gains Unrealized losses Fair value Cash equivalents $ 1,254 $ — $ — $ 1,254 Marketable securities U.S. government agency notes $ 4,091 $ — $ (19 ) $ 4,072 Corporate debt securities 8,048 — (31 ) 8,017 Certificates of deposit 5,135 — — 5,135 $ 17,274 $ — $ (50 ) $ 17,224 Investments U.S. government agency notes $ 3,992 $ — $ (28 ) $ 3,964 Corporate debt securities 3,908 — (24 ) 3,884 Certificates of deposit 1,183 — — 1,183 $ 9,083 $ — $ (52 ) $ 9,031 The Company's available-for-sale debt securities classified as Investments in the condensed consolidated balance sheet at December 31, 2017 mature after one year but within two years or less from the balance sheet date. The Company did not have any available-for-sale debt securities classified as Investments at September 30, 2018. 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 September 30, 2018 and December 31, 2017 . These financial assets are comprised of the Company's available-for-sale debt securities and reported under the captions Cash and cash equivalents, Marketable securities and Investments in the condensed consolidated balance sheets (in thousands): Fair value measurements at Total carrying Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) Cash equivalents $ 427 $ 427 $ — $ — Marketable securities U.S. government agency notes $ 3,980 $ — $ 3,980 $ — Corporate debt securities 3,304 — 3,304 — $ 7,284 $ — $ 7,284 $ — 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 $ 1,254 $ 1,254 $ — $ — Marketable securities U.S. government agency notes $ 4,072 $ — $ 4,072 $ — Corporate debt securities 8,017 — 8,017 — Certificates of deposit 5,135 — 5,135 — $ 17,224 $ — $ 17,224 $ — Investments U.S. government agency notes $ 3,964 $ — $ 3,964 $ — Corporate debt securities 3,884 — 3,884 — Certificates of deposit 1,183 — 1,183 — $ 9,031 $ — $ 9,031 $ — The Company's marketable securities and investments have been valued with the assistance of valuations provided by third-party pricing services, as derived from such services' pricing models. Inputs to the models may include, but are not limited to, reported trades, executable bid and asked prices, broker/dealer quotations, prices or yields of securities with similar characteristics, benchmark curves or information pertaining to the issuer, as well as industry and economic events. The pricing services may use a matrix approach, which considers information regarding securities with similar characteristics to determine the valuation for a security. The Company is ultimately responsible for the condensed consolidated financial statements and underlying estimates. Accordingly, the Company assesses the reasonableness of the valuations provided by the third-party pricing services by reviewing actual trade data, broker/dealer quotes and other similar data, which are obtained from quoted market prices or other sources.

INVENTORY

INVENTORY	9 Months Ended
	Sep. 30, 2018
Inventory Disclosure [Abstract]
INVENTORY	INVENTORY Inventory at September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, December 31, On-hand final assemblies and finished goods inventories $ 19,371 $ 18,374 Deferred cost of goods sold 3,707 4,569 23,078 22,943 Less noncurrent portion (included in other assets) (1,354 ) (1,640 ) Current portion $ 21,724 $ 21,303

INTANGIBLE ASSETS AND GOODWILL

INTANGIBLE ASSETS AND GOODWILL	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
INTANGIBLE ASSETS AND GOODWILL	INTANGIBLE ASSETS AND GOODWILL The Company's intangible assets at September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, 2018 Weighted average amortization period (years) Cost Accumulated amortization Net carrying value In-process research and development * $ 5,600 $ — $ 5,600 Developed technology 6.91 182,880 53,666 129,214 Customer relationships 9.44 146,940 19,896 127,044 Trade names 3.00 2,000 465 1,535 Internal use software 3.00 730 730 — 7.86 $ 338,150 $ 74,757 $ 263,393 December 31, 2017 Weighted average amortization period (years) Cost Accumulated amortization Net carrying value In-process research and development * $ 5,600 $ — $ 5,600 Developed technology 6.90 153,380 24,211 129,169 Customer relationships 9.32 120,840 12,015 108,825 Trade names 3.00 900 80 820 Internal use software 3.00 730 730 — 7.77 $ 281,450 $ 37,036 $ 244,414 * An in-process research and development intangible asset has an indefinite life until the product is generally available, at which time such asset is typically reclassified to developed technology. Amortization expense for intangible assets for the three and nine months ended September 30, 2018 and 2017 was as follows (in thousands): Three months ended Nine months ended Statement of operations classification September 30, September 30, September 30, September 30, Developed technology $ 10,593 $ 1,602 $ 29,455 $ 4,769 Cost of revenue - product Customer relationships 2,695 691 7,881 2,076 Sales and marketing Trade names 160 — 385 — Sales and marketing $ 13,448 $ 2,293 $ 37,721 $ 6,845 Estimated future amortization expense for the Company's intangible assets at September 30, 2018 was as follows (in thousands): Years ending December 31, Remainder of 2018 $ 12,003 2019 47,411 2020 46,552 2021 40,571 2022 34,156 Thereafter 82,700 $ 263,393 The changes in the carrying value of the Company's goodwill in the nine months ended September 30, 2018 and 2017 were as follows (in thousands): Balance at January 1 2018 2017 Goodwill $ 338,822 $ 52,499 Accumulated impairment losses (3,106 ) (3,106 ) 335,716 49,393 Acquisition of Edgewater 46,777 — Purchase accounting adjustments - acquisition of Taqua, LLC — 498 Balance at September 30 $ 382,493 $ 49,891 Balance at September 30 Goodwill $ 385,599 $ 52,997 Accumulated impairment losses (3,106 ) (3,106 ) $ 382,493 $ 49,891

ACCRUED EXPENSES

ACCRUED EXPENSES	9 Months Ended
	Sep. 30, 2018
Payables and Accruals [Abstract]
ACCRUED EXPENSES	ACCRUED EXPENSES Accrued expenses at September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, December 31, Employee compensation and related costs $ 33,174 $ 37,782 Professional fees 8,997 13,743 Deferred purchase consideration - Edgewater 15,000 — Other 17,439 24,855 $ 74,610 $ 76,380

RESTRUCTURING ACCRUALS

RESTRUCTURING ACCRUALS	9 Months Ended
	Sep. 30, 2018
Restructuring and Related Activities [Abstract]
RESTRUCTURING ACCRUALS	RESTRUCTURING ACCRUALS The Company recorded restructuring expense aggregating $2.4 million in the three months ended September 30, 2018 and did not record restructuring expense in the three months ended September 30, 2017. The Company recorded restructuring expense aggregating $15.2 million in the nine months ended September 30, 2018 and $1.1 million in the nine months ended September 30, 2017. Merger Restructuring Initiative In connection with the Merger, the Company's management approved a restructuring plan in the fourth quarter of 2017 to eliminate certain redundant positions and facilities within the combined companies (the "Merger Restructuring Initiative"). In connection with this initiative, the Company recorded $8.5 million of restructuring expense in the fourth quarter of 2017 for severance and related costs for approximately 120 employees. The Company recorded $14.3 million in the nine months ended September 30, 2018, comprised of $2.5 million in the three months ended September 30, 2018, $5.3 million in the three months ended June 30, 2018 and $6.5 million in the three months ended March 31, 2018. The amount recorded in the three months ended September 30, 2018 related to severance and related costs for approximately 30 employees. The amounts recorded in the three months ended June 30, 2018 included $5.1 million for severance and related costs for approximately 140 employees and $0.2 million related to a U.S. facility. The amount recorded in the three months ended March 31, 2018 represented severance and related costs for approximately 115 employees. The Company anticipates it will record additional future expense in connection with this initiative for headcount and redundant facilities aggregating approximately $1 million as it continues to combine the two businesses and benefit from operational synergies. The Company expects that the amount accrued at September 30, 2018 for severance will be paid by the end of the end of the first half of 2019 and that the payments related to the expected additional future expense will be completed in 2019. A summary of the Merger Restructuring Initiative accrual activity for the nine months ended September 30, 2018 is as follows (in thousands): Balance at Initiatives Adjustments for changes in estimate Cash Balance at Severance $ 7,595 $ 14,121 $ (5 ) $ (18,928 ) $ 2,783 Facilities — 193 — (70 ) 123 $ 7,595 $ 14,314 $ (5 ) $ (18,998 ) $ 2,906 Assumed Restructuring Initiative The Company assumed GENBAND's previously recorded restructuring liability, totaling $4.1 million , on the Merger Date (the "GENBAND Restructuring Initiative"). Of this amount, $3.7 million related to severance and related costs and $0.4 million related to facilities. The Company reversed $0.1 million of facilities accrual in the three months ended September 30, 2018 and net adjustments aggregating $0.9 million of expense in the nine months ended September 30, 2018 for changes in estimated costs previously accrued. The additional expense for severance relates to higher-than-previously-anticipated amounts due to certain international employees. The net additional expense for facilities relates to changes in sub-lease income assumptions for a facility previously restructured under this plan. The Company does not expect to record additional expense in connection with this initiative except for any additional adjustments for changes in estimated costs. The Company expects that the payments related to this assumed liability will be completed in 2018. A summary of the GENBAND Restructuring Initiative accrual activity for the nine months ended September 30, 2018 is as follows (in thousands): Balance at Initiatives Adjustments for changes in estimate Cash Balance at Severance $ 1,916 $ — $ 487 $ (2,358 ) $ 45 Facilities 205 — 366 (401 ) 170 $ 2,121 $ — $ 853 $ (2,759 ) $ 215 2016 Restructuring Initiative In July 2016, the Company announced a program (the "2016 Restructuring Initiative") to further accelerate its investment in new technologies, as the communications industry migrates to a cloud-based architecture and as the Company pursues new strategic initiatives, such as new products and an expanded go-to-market footprint in selected geographies and discrete vertical markets. The Company recorded $2.0 million of restructuring expense in the aggregate in connection with this initiative, comprised of $1.9 million for severance and related costs and $0.1 million to abandon its facility in Rochester, New York (the "Rochester Facility"). In connection with the 2016 Restructuring Initiative, the Company recorded $0.5 million of restructuring expense in the nine months ended September 30, 2017, comprised of $0.4 million for severance and related costs and $0.1 million related to the Rochester Facility. The actions under the 2016 Restructuring Initiative have been implemented and accordingly, the Company does not expect to record additional expense in connection with this initiative. The amounts accrued for severance and related costs had been fully paid by the end of the third quarter of 2017. The Company expects that the amounts accrued for facilities will be paid by the end of October 2019, when the lease on the Rochester Facility expires. A summary of the 2016 Restructuring Initiative accrual activity for the nine months ended September 30, 2018 is as follows (in thousands): Balance at Initiatives Adjustments for changes in estimate Cash Balance at Facilities $ 95 $ — $ — $ (25 ) $ 70 Taqua Restructuring Initiative In connection with the acquisition of Taqua, the Company's management approved a restructuring plan in the third quarter of 2016 to eliminate certain redundant positions within the combined companies. On October 24, 2016, the Audit Committee of the Company's Board of Directors approved a broader Taqua restructuring plan related to headcount and redundant facilities (both restructuring plans, the "Taqua Restructuring Initiative"). The Company recorded $1.8 million of restructuring expense in the aggregate in connection with this initiative, comprised of $1.2 million for severance and related costs and $0.6 million related to the elimination of redundant facilities. The actions under the Taqua Restructuring Initiative have been implemented and accordingly, the Company does not expect to record additional expense in connection with this initiative. The amounts accrued for severance and related costs had been fully paid by the end of the third quarter of 2017. The Company expects that the amounts accrued for facilities will be paid by the end of 2018. In connection with the Taqua Restructuring Initiative, the Company recorded $0.6 million of restructuring expense in the nine months ended September 30, 2017, comprised of $0.2 million for severance and related costs and $0.4 million for redundant facilities. A summary of the Taqua Restructuring Initiative accrual activity for the nine months ended September 30, 2018 is as follows (in thousands): Balance at Initiatives Adjustments for changes in estimate Cash Balance at Facilities $ 365 $ — $ — $ (255 ) $ 110 Balance Sheet Classification The current portions of accrued restructuring are included as a component of Accrued expenses and the long-term portions of accrued restructuring are included as a component of Other long-term liabilities in the condensed consolidated balance sheets. The current portions of accrued restructuring totaled $3.2 million at September 30, 2018 and $10.0 million at December 31, 2017. The long-term portions of accrued restructuring totaled $0.1 million at September 30, 2018 and $0.2 million at December 31, 2017 . The long-term amounts represent future lease payments on restructured facilities.

DEBT

DEBT	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
DEBT	DEBT Assumed Senior Secured Credit Agreement On the Merger Date and in connection with the Merger, the Company assumed GENBAND's Senior Secured Credit Agreement with Silicon Valley Bank ("SVB") (the "Prior Credit Agreement"), which had outstanding borrowings and letters of credit totaling $17.9 million and $2.9 million , respectively, and an average interest rate of 4.67% . GENBAND had entered into the Prior Credit Agreement with SVB effective July 1, 2016, with two of its operating subsidiaries as borrowers and GENBAND as the guarantor. The Prior Credit Agreement had a maturity date of July 1, 2019 and provided for revolving loans, including letters of credit and swingline loans, not to exceed $50 million in total, with potential further increases of $75 million available for a total revolving line of credit of up to $125 million . The Prior Credit Agreement was superseded by a Senior Secured Credit Facilities Credit Agreement, as amended, which was entered into on December 21, 2017 and is discussed below. Senior Secured Credit Facility On December 21, 2017, the Company entered into a Senior Secured Credit Facilities Credit Agreement (as amended, the “Credit Facility”), by and among the Company, as a guarantor, Sonus Networks, Inc., as the borrower (“Borrower”), SVB, as administrative agent (in such capacity, the “Administrative Agent”), issuing lender, swingline lender and lead arranger and the lenders party thereto (each referred to individually as a “Lender”, and collectively, the “Lenders”), which refinanced the Prior Credit Agreement. The Credit Facility includes $100 million of commitments, the full amount of which is available for revolving loans, a $15 million sublimit that is available for letters of credit and a $15 million sublimit that is available for swingline loans. The Credit Facility is scheduled to mature in December 2021, subject to a springing maturity if, on or before July 14, 2020, the existing Promissory Note issued to certain shareholders is not converted or extended to March 2022 or later. The Credit Facility includes procedures for additional financial institutions to become lenders or for any existing lender to increase its commitment under the facility, subject to an available increase of $50 million for all incremental commitments under the Credit Facility. On June 24, 2018, the Company amended the Credit Facility to, among other things, permit the Edgewater Acquisition and related transactions. The indebtedness and other obligations under the Credit Facility are unconditionally guaranteed on a senior secured basis by the Company and GENBAND US LLC, a wholly-owned domestic subsidiary of the Company (collectively, the “Guarantors”) and each other material US domestic subsidiary of the Company. The Credit Facility is secured by first-priority liens on substantially all of the assets of the Borrower and the Guarantors, including the Company. The Credit Facility requires periodic interest payments on any outstanding borrowings under the facility. The Borrower may prepay all revolving loans under the Credit Facility at any time without premium or penalty (other than customary LIBOR breakage costs), subject to certain notice requirements. Revolving loans under the Credit Facility bear interest at the Borrower’s option at either the Eurodollar (LIBOR) rate plus a margin ranging from 2.50% to 3.00% per year or the base rate (the highest of the Federal Funds rate plus 0.50% , or the prime rate announced from time to time in The Wall Street Journal) plus a margin ranging from 1.50% to 2.00% per year (such margins being referred to as the “Applicable Margin”). The Applicable Margin varies depending on the Company’s consolidated leverage ratio (as defined in the Credit Facility). The base rate and the LIBOR rate are each subject to a zero percent floor. The Borrower is charged a commitment fee ranging from 0.25% to 0.40% per year on the daily amount of the unused portions of the commitments under the Credit Facility. Additionally, with respect to all letters of credit outstanding under the Credit Facility, the Borrower is charged a fronting fee of 0.125% per year and an outstanding letter of credit fee equal to the Applicable Margin for base rate loans ranging from 1.50% to 2.00% times the amount of the outstanding letters of credit. The Credit Facility requires compliance with financial covenants of a minimum consolidated quick ratio, minimum consolidated interest coverage ratio and maximum consolidated leverage ratio, all of which are defined in the Credit Facility and tested on a quarterly basis. In addition, the Credit Facility contains various covenants that, among other restrictions, limit the Company’s and its subsidiaries’ ability to enter into certain types of transactions, including, but not limited to: incurring or assuming indebtedness, making acquisitions or engaging in mergers, making investments, repurchasing equity and paying dividends, selling or otherwise transferring assets, changing the nature of its business and amending or making prepayments on certain junior debt. The Company was in compliance with all covenants of the Credit Facility as of September 30, 2018 and December 31, 2017 . The Credit Facility contains events of default that are customary for a secured credit facility. If an event of default relating to bankruptcy or other insolvency events with respect to a borrower occurs, all obligations under the Credit Facility will immediately become due and payable. If any other event of default exists under the Credit Facility, the lenders may accelerate the maturity of the obligations outstanding under the Credit Facility and exercise other rights and remedies, including charging a default rate of interest equal to 2.00% per year above the rate that would otherwise be applicable. In addition, if any event of default exists under the Credit Facility, the lenders may commence foreclosure or other actions against the collateral. If any default exists under the Credit Facility, or if the Borrower is unable to make any of the representations and warranties as stated in the Credit Facility at the applicable time, the Borrower will be unable to borrow funds or have letters of credit issued under the Credit Facility, which, depending on the circumstances prevailing at that time, could have a material adverse effect on the Borrower’s liquidity and working capital. At September 30, 2018 , the Company had an outstanding debt balance of $58.0 million at an average interest rate of 5.26% and $2.6 million of outstanding letters of credit at an average interest rate of 1.75% under the Credit Facility. At December 31, 2017, the Company had an outstanding debt balance of $20.0 million at an interest rate of 4.51% and $2.9 million of outstanding letters of credit at an average interest rate of 2.00% under the Credit Facility. Promissory Note In connection with the Merger, on October 27, 2017, the Company issued the Promissory Note for $22.5 million to certain of GENBAND's equity holders. The Promissory Note does not amortize, and the principal thereon is payable in full on the third anniversary of its execution. Interest on the Promissory Note is payable quarterly in arrears and accrued at a rate of 7.5% per year for the first six months after issuance, and thereafter at a rate of 10% per year. The failure to make any payment under the Promissory Note when due and, with respect to payment of any interest, the continuation of such failure for a period of thirty days thereafter, constitutes an event of default under the Promissory Note. If an event of default occurs under the Promissory Note, the payees may declare the entire balance of the Promissory Note due and payable (including principal and accrued and unpaid interest) within five business days of the payees' notification to the Company of such acceleration. Interest that is not paid on the interest payment date will increase the principal amount of the Promissory Note. At September 30, 2018, the Promissory Note balance was $23.5 million , comprised of $22.5 million of principal plus $1.0 million of interest converted to principal.

REVENUE RECOGNITION

REVENUE RECOGNITION	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
REVENUE RECOGNITION	REVENUE RECOGNITION In May 2014, the FASB issued ASU 2014-09, which, among other things, clarified the implementation of the new revenue guidance and delayed the adoption by one year, to January 1, 2018. The New Revenue Standard outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. The core principle of the revenue model is that an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In applying the revenue model to contracts within its scope, an entity identifies the contract(s) with a customer, identifies the performance obligations in the contract, determines the transaction price, allocates the transaction price to the performance obligations in the contract and recognizes revenue when (or as) the entity satisfies a performance obligation. Effective January 1, 2018, the Company adopted the New Revenue Standard using the modified retrospective option and identified the necessary changes to its policies, processes, systems and controls. Under the modified retrospective method, the Company is applying the New Revenue Standard to all contracts not yet completed as of January 1, 2018, recognizing in beginning Accumulated deficit an adjustment for the cumulative effect of the change and providing additional disclosures comparing results to those as if the Company was still following the previous accounting standards. Under ASC 605, the Company concluded it did not have vendor-specific objective evidence ("VSOE") for certain elements in software bundled arrangements, which resulted in revenue being recognized ratably over the longest performance period. The majority of the transition adjustment related to these arrangements. In connection with the adoption of ASC 606, as of January 1, 2018, the Company recorded an adjustment to decrease Accumulated deficit by approximately $12 million and capitalized certain commission costs resulting directly from securing contracts which were previously expensed. Significant Judgments The Company's contracts with customers often include promises to transfer multiple products and services to the customer. Determining whether products and services are considered distinct performance obligations that should be accounted for separately versus together may require significant judgment. Judgment is required to determine the standalone selling price for each distinct performance obligation. In instances where SSP is not directly observable, such as when the Company does not sell the product or service separately, the Company determines the SSP using information that may include market conditions and other observable inputs. The Company typically has more than one SSP for individual products and services due to the stratification of those products and services by customers and circumstances. In these instances, the Company may use information such as the size of the customer and geographic region in determining the SSP. Deferred Revenue Deferred revenue represents amounts collected from or invoiced to customers in excess of revenue recognized. This results primarily from the billing of annual customer support agreements where the revenue is recognized over the term of the agreement. The value of deferred revenue will increase or decrease based on the timing of invoices and recognition of revenue. Disaggregation of Revenue The Company disaggregates its revenue from contracts with customers based on the nature of the products and services and the geographic regions in which each customer is domiciled. The Company's revenue for the three and nine months ended September 30, 2018 and 2017 was disaggregated as follows: Three months ended September 30, 2018 Product revenue Service revenue (maintenance) Service revenue (professional services) Total revenue United States $ 49,699 $ 34,065 $ 9,040 $ 92,804 Europe, Middle East and Africa 10,380 11,504 2,169 24,053 Japan 3,588 2,882 503 6,973 Other Asia Pacific 6,959 3,551 906 11,416 Other 6,657 8,154 2,411 17,222 $ 77,283 $ 60,156 $ 15,029 $ 152,468 Three months ended September 30, 2017 Product revenue Service revenue (maintenance) Service revenue (professional services) Total revenue United States $ 35,126 $ 16,745 $ 4,263 $ 56,134 Europe, Middle East and Africa 3,072 2,960 272 6,304 Japan 3,376 2,489 1,552 7,417 Other Asia Pacific 1,771 992 47 2,810 Other 775 1,070 119 1,964 $ 44,120 $ 24,256 $ 6,253 $ 74,629 Nine months ended September 30, 2018 Product revenue Service revenue (maintenance) Service revenue (professional services) Total revenue United States $ 109,977 $ 98,354 $ 25,535 $ 233,866 Europe, Middle East and Africa 29,807 35,550 8,157 73,514 Japan 16,128 8,431 2,296 26,855 Other Asia Pacific 21,970 8,905 3,185 34,060 Other 14,055 23,049 5,610 42,714 $ 191,937 $ 174,289 $ 44,783 $ 411,009 Nine months ended September 30, 2017 Product revenue Service revenue (maintenance) Service revenue (professional services) Total revenue United States $ 72,123 $ 48,502 $ 10,116 $ 130,741 Europe, Middle East and Africa 10,295 8,006 1,456 19,757 Japan 8,569 7,536 3,768 19,873 Other Asia Pacific 4,180 2,920 383 7,483 Other 3,138 2,234 504 5,876 $ 98,305 $ 69,198 $ 16,227 $ 183,730 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. The Company's product revenue from its direct sales program and from indirect sales through its channel partner program for the three and nine months ended September 30, 2018 and 2017 was as follows (in thousands): Three months ended Nine months ended September 30, September 30, September 30, September 30, Indirect sales through channel program $ 26,309 $ 10,704 $ 42,151 $ 28,063 Direct sales 50,974 33,416 149,786 70,242 $ 77,283 $ 44,120 $ 191,937 $ 98,305 The Company's product revenue from sales to enterprise customers and from sales to service provider customers for the three and nine months ended September 30, 2018 and 2017 was as follows (in thousands): Three months ended Nine months ended September 30, September 30, September 30, September 30, Sales to enterprise customers $ 23,581 $ 9,602 $ 37,534 $ 23,903 Sales to service provider customers 53,702 34,518 154,403 74,402 $ 77,283 $ 44,120 $ 191,937 $ 98,305 Revenue Contract Balances The timing of revenue recognition, billings and cash collections results in billed accounts receivable, unbilled receivables (contract assets) and customer advances and deposits (contract liabilities) in the Company's condensed consolidated balance sheets. Amounts are billed as work progresses in accordance with agreed-upon contractual terms, either at periodic intervals or upon achievement of contractual milestones. Billing may occur subsequent to revenue recognition, resulting in contract assets. The Company may receive advances or deposits from its customers before revenue is recognized, resulting in contract liabilities which are classified as deferred revenue. These assets and liabilities are reported in the Company's condensed consolidated balance sheets on a contract-by-contract basis as of the end of each reporting period. Deposits are liquidated when revenue is recognized. Changes in the contract asset and liability balances during the nine-month period ended September 30, 2018 were not materially impacted by any other factors. Nearly all of the Company's deferred revenue balance is related to services revenue, primarily customer support contracts. Unbilled receivables stem primarily from engagements where services have been performed; however, billing cannot occur until services are completed. In some arrangements, the Company allows customers to pay for term-based software licenses and products over the term of the software license. The Company also sells SaaS-based software under subscription arrangements, with payment terms over the term of the SaaS agreement. Amounts recognized as revenue in excess of amounts billed are recorded as unbilled receivables. Unbilled receivables that are anticipated to be invoiced in the next twelve months are included in Accounts receivable on the Company's condensed consolidated balance sheets. The changes in the Company's accounts receivable, unbilled receivables and deferred revenue balances for the nine months ended September 30, 2018 were as follows (in thousands): Accounts receivable Unbilled accounts receivable Deferred revenue (current) Deferred revenue (long-term) Balance at January 1, 2018 $ 149,122 $ 16,034 $ 100,571 $ 14,184 Increase (decrease), net (13,317 ) (1,162 ) (18,082 ) 1,801 Balance at September 30, 2018 $ 135,805 $ 14,872 $ 82,489 $ 15,985 The decrease in accounts receivable was primarily the result of lower billings in the current year period compared with the Company's typically higher billings at year-end. The decrease in deferred revenue was primarily due to the ratable amortization of annual customer support renewals. The Company recognized $18.4 million and $79.1 million , respectively, of revenue in the three and nine months ended September 30, 2018 that was recorded as deferred revenue at December 31, 2017. Of the Company's deferred revenue reported as long-term in its condensed consolidated balance sheet at September 30, 2018, the Company expects that approximately $3 million will be recognized as revenue in 2019, approximately $9 million will be recognized as revenue in 2020 and approximately $4 million will be recognized as revenue in 2021 and beyond. Deferred Commissions Cost Sales commissions earned by the Company's employees are considered incremental and recoverable costs of obtaining a contract with a customer. Under ASC 605, the costs associated with obtaining a customer contract were expensed in the period the revenue was earned. Under ASC 606, these payments have been deferred on our condensed consolidated balance sheet and amortized over the expected life of the customer contract. Adoption of ASC 606 Under the modified retrospective method, the Company applied ASC 606 to those contracts which were not completed as of January 1, 2018. Results for reporting periods beginning January 1, 2018 are presented under ASC 606, which prior period amounts have not been adjusted and will continue to be reported in accordance with the Company's historical accounting treatment under ASC 605, Revenue Recognition ("ASC 605"). The Company recorded a net reduction to Accumulated deficit of approximately $12 million at January 1, 2018 due to the cumulative impact of adopting ASC 606, primarily related to software orders with non-VSOE services revenue. Had the Company continued to recognize revenue under ASC 605, the Company would have recognized approximately $8 million and approximately $9 million less revenue in the three and nine months ended September 30, 2018, respectively. Incremental costs that would have been recognized had the Company continued to recognize revenue under ASC 605 would not have been material to the Company's consolidated results of operations. The Company's typical performance obligations include the following: Performance Obligation When Performance Obligation is Typically Satisfied When Payment is Typically Due Software and Product Revenue Software licenses (perpetual or term) Upon transfer of control; typically, when made available for download (point in time) Within 30 days of invoicing except for term licenses which may be paid for over time Software licenses (subscription) Upon activation of hosted site (over time) Within 30 days of invoicing Hardware When control of the appliances passes to the customer; typically, upon delivery (point in time) Generally, within 30 days of invoicing Software upgrades Upon transfer of control; typically, when made available for download (point in time) Generally, within 30 days of invoicing Customer Support Revenue Customer support Ratably over the course of the support contract (over time) At the beginning of the contract period Professional Services Other professional services (excluding education services) As work is performed (over time) Within 30 days of invoicing (upon completion of services) Training When the class is taught (point in time) Within 30 days of services being performed

STOCK-BASED COMPENSATION PLANS

STOCK-BASED COMPENSATION PLANS	9 Months Ended
	Sep. 30, 2018
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. 2002 Stock Option Plan In connection with the Edgewater Acquisition, the Company assumed Edgewater's Amended and Restated 2002 Stock Option Plan (the "Edgewater Plan") to the extent of the shares underlying the options outstanding under the Edgewater Plan as of the Edgewater Acquisition Date (the "Edgewater Options"). The Edgewater Options were converted to like Ribbon stock options (the "Ribbon Replacement Options") using a conversion factor of 0.17 , which was calculated based on the acquisition consideration of $1.20 per share of Edgewater common stock divided by the weighted average of the closing price of Ribbon common stock for the ten consecutive days, ending with the trading day that preceded the Edgewater Acquisition Date. This conversion factor was also used to convert the exercise prices of Edgewater Options to Ribbon Replacement Option exercise prices. The Ribbon Replacement Options will vest under the same schedules as the respective Edgewater Options. The fair values of the Edgewater Options assumed were estimated using a Black-Scholes option pricing model. The Company recorded $0.7 million as additional purchase consideration for the fair value of the assumed Edgewater Options. The fair value of the Ribbon Replacement Options attributable to future service totaled $1.0 million , which will be recognized over a weighted average period of approximately two years. Executive Equity Arrangements - PSUs In addition to granting RSAs and RSUs to its executives and certain of its employees, the Company also grants PSUs to certain of its executives. In May 2018, the Company granted its President and Chief Executive Officer Franklin (Fritz) Hobbs ("Mr. Hobbs"), 195,000 PSUs with both performance and service conditions (the "Hobbs PSUs"). Of the 195,000 Hobbs PSUs, one-half will vest based on the achievement of two separate metrics related to the Company's 2018 financial performance (the "Hobbs Performance Conditions"). The Company's achievement of the Hobbs Performance Conditions (and the shares of Company common stock to vest as a result thereof) will be measured on a linear sliding scale in relation to specific threshold, target and stretch performance conditions. The number of shares of common stock to be received upon vesting of the Hobbs PSUs will in no event exceed 150% of the Hobbs PSUs. The Company is recording stock-based compensation expense for the Hobbs PSUs based on its assessment of the probability that each performance condition will be achieved and the level, if any, of such achievement. Upon the determination by the Compensation Committee of the Board of Directors (the "Compensation Committee") of the number of shares that will be received upon vesting of the Hobbs PSUs, such number of shares will become fixed and the unamortized expense recorded through the remainder of the service period that ends December 31, 2020. The Company recorded stock-based compensation expense approximating $154,000 in the three months ended September 30, 2018 and $194,000 in the nine months ended September 30, 2018 in connection with the Hobbs PSUs. From 2015 through 2017, the Company granted PSUs with both market and service conditions to certain of its executives. The terms of each PSU grant are such that up to one-third of the shares subject to the respective PSU grant will vest, if at all, on each of the respective first, second and third anniversaries of the date of grant, depending on the Company's total shareholder return ("TSR") compared with 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 fiscal years as defined by each grant (each, a "Performance Period"). The shares determined to be earned will vest on the anniversary of the grant date following each Performance Period. Shares subject to the PSUs that fail to be earned will be forfeited. The PSUs that included a market condition required the use of a Monte Carlo simulation approach to model future stock price movements based upon the risk-free rate of return, the date of return, the volatility of each entity and the pair-wise covariance between each entity. These results were then used to calculate the grant date fair values of the respective PSUs. The Company is required to record expense for the PSUs with market conditions through their respective final vesting dates, regardless of the number of shares that are ultimately earned. On March 31, 2017, the Company granted an aggregate of 165,000 PSUs with both market and service conditions to five of its executives (the "2017 PSUs"). In March 2018, the Compensation Committee determined that the performance metrics for the 2017 PSUs for the 2017 Performance Period had been achieved at the 130% level and accordingly, 33,584 shares in the aggregate were released to the three executives holding such outstanding grants, comprised of 25,834 shares, representing the 100% achievement target, granted on March 31, 2017 and 7,750 shares, representing the 30% achievement over target, granted on March 31, 2018. The grant of the additional shares and the release of the earned shares, both of which occurred on March 31, 2018, are included in the PSU table below. On April 1, 2016, the Company granted an aggregate of 131,250 PSUs with both market and service conditions to six of its executives (the "2016 PSUs"). In March 2018, the Compensation Committee determined that the performance metrics for the 2016 PSUs for the 2017 Performance Period had been achieved at the 130% level, and accordingly, 16,250 shares in the aggregate were released to the two executives holding such outstanding grants, comprised of 12,500 shares, representing the 100% achievement target, granted on April 1, 2016 and 3,750 shares, representing the 30% achievement over target, granted on April 1, 2018. The grant of the additional shares and the release of the earned shares, both of which occurred on April 1, 2018, are included in PSU 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 March 2018, the Compensation Committee determined that the performance metrics for the 2015 PSUs for the 2017 Performance Period had been achieved at the 112% level, and accordingly, 7,934 shares in the aggregate were released to the two executives holding such outstanding grants, comprised of 7,084 shares, representing the 100% achievement target, granted on March 16, 2015 and 850 shares, representing the 12% achievement over target, granted on March 16, 2018. The grant of the additional shares and the release of the earned shares, both of which occurred on March 16, 2018, are included in the PSU table below. Stock Options The activity related to the Company's outstanding stock options for the nine months ended September 30, 2018 was as follows: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (years) Aggregate Intrinsic Value (in thousands) Outstanding at January 1, 2018 435,187 $ 14.71 Granted — $ — Edgewater outstanding options converted to Ribbon options 312,452 $ 1.97 Exercised (8,653 ) $ 4.97 Forfeited — $ — Expired (109,486 ) $ 14.40 Outstanding at September 30, 2018 629,500 $ 8.57 6.12 $ 1,538 Vested or expected to vest at September 30, 2018 589,719 $ 9.01 5.96 $ 1,352 Exercisable at September 30, 2018 344,653 $ 14.01 4.41 $ 161 The Company did not grant any stock options in the nine months ended September 30, 2018. Additional information regarding the Company's stock options for the three and nine months ended September 30, 2018 was as follows: Three months ended Nine months ended September 30, September 30, Total intrinsic value of stock options exercised (in thousands) $ 13 $ 21 Cash received from the exercise of stock options (in thousands) $ 33 $ 43 Restricted Stock Awards and Units The activity related to the Company's RSAs for the nine months ended September 30, 2018 was as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2018 1,696,582 $ 7.68 Granted 1,123,956 $ 6.90 Vested (752,085 ) $ 8.46 Forfeited (270,075 ) $ 7.36 Unvested balance at September 30, 2018 1,798,378 $ 6.91 The activity related to the Company's RSUs for the nine months ended September 30, 2018 was as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2018 17,932 $ 6.99 Granted 899,500 $ 6.27 Vested (17,110 ) $ 7.00 Forfeited (41,822 ) $ 6.72 Unvested balance at September 30, 2018 858,500 $ 6.25 The total fair value of shares of restricted stock granted under RSAs and RSUs that vested during the nine months ended September 30, 2018 was $6.5 million . Performance-Based Stock Units The activity related to the Company's PSUs for the nine months ended September 30, 2018 was as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2018 60,834 $ 9.65 Granted 207,350 $ 5.78 Vested (57,768 ) $ 9.90 Forfeited — $ — Unvested at September 30, 2018 210,416 $ 5.77 The total fair value of shares of restricted stock granted under PSUs that vested during the nine months ended September 30, 2018 was $0.6 million . Employee Stock Purchase Plan The Company's Amended and Restated 2000 Employee Stock Purchase Plan ("ESPP") is designed to provide eligible employees of the Company and its participating subsidiaries an opportunity to purchase common stock of the Company through accumulated payroll deductions. The ESPP provides for six -month offering periods with the purchase price of the stock equal to 85% of the lesser of the market price on the first or last day of the offering period. The maximum number of shares of common stock an employee may purchase during each offering period is 500 , subject to certain adjustments pursuant to the ESPP. In May 2017, the Compensation Committee determined to suspend all offering periods under the ESPP effective September 1, 2017 and until such time after the closing of the then-pending merger with GENBAND as the Compensation Committee determines is best in its sole discretion. In September 2018, at the recommendation of the Compensation Committee, the Board determined to re-instate all offering periods under the ESPP, effective December 1, 2018. Stock-Based Compensation The condensed consolidated statements of operations include stock-based compensation for the three and nine months ended September 30, 2018 and 2017 as follows (in thousands): Three months ended Nine months ended September 30, September 30, September 30, September 30, Product cost of revenue $ 21 $ 75 $ 91 $ 261 Service cost of revenue 65 199 264 777 Research and development 313 1,095 1,364 3,650 Sales and marketing 585 871 1,944 1,690 General and administrative 1,532 1,647 3,758 5,009 $ 2,516 $ 3,887 $ 7,421 $ 11,387 There is no income tax benefit for employee stock-based compensation expense for the nine months ended September 30, 2018 or September 30, 2017 due to the valuation allowance recorded. At September 30, 2018 , there was $12.6 million , net of expected forfeitures, of unrecognized stock-based compensation expense related to unvested stock options, awards and units. This expense is expected to be recognized over a weighted average period of approximately two years .

MAJOR CUSTOMERS

MAJOR CUSTOMERS	9 Months Ended
	Sep. 30, 2018
Risks and Uncertainties [Abstract]
MAJOR CUSTOMERS	MAJOR CUSTOMERS The following customers contributed 10% or more of the Company's revenue in the three and nine months ended September 30, 2018 and 2017 : Three months ended Nine months ended September 30, September 30, September 30, September 30, Verizon Communications Inc. 13% 16% 15% 15% AT&T Inc. 12% 11% 10% 10% There were no other customers that contributed 10% or more of the Company's revenue in the three or nine months ended September 30, 2018 or 2017. At September 30, 2018 , two customers accounted for 10% or more of the Company's accounts receivable balance, representing approximately 25% in the aggregate of the Company's total accounts receivable. At December 31, 2017 , two customers accounted for 10% or more of the Company's accounts receivable balance, representing approximately 31% in the aggregate of total accounts receivable. The Company performs ongoing credit evaluations of its customers and generally does not require collateral on accounts receivable. The Company maintains an allowance for doubtful accounts and such losses have been within management's expectations.

RELATED PARTY TRANSACTIONS

RELATED PARTY TRANSACTIONS	9 Months Ended
	Sep. 30, 2018
Related Party Transactions [Abstract]
RELATED PARTY TRANSACTIONS	RELATED PARTY TRANSACTIONS As a portion of the consideration for the Merger, on October 27, 2017, the Company issued a Promissory Note for $22.5 million to certain of GENBAND's equity holders who, following the Merger, owned greater than five percent of the Company's outstanding shares. As described in Note 9 above, the Promissory Note does not amortize, and the principal thereon is payable in full on the third anniversary of its execution. Interest on the Promissory Note is payable quarterly in arrears and accrued at a rate of 7.5% per year for the first six months after issuance, and thereafter at a rate of 10% per year. Of the unpaid interest on the Promissory Note at September 30, 2018, $1.0 million was converted to principal and included as a component of Long-term debt, related party, and $0.4 million was included as a component of Accrued expenses and other in the Company's condensed consolidated balance sheets. The failure to make any payment under the Promissory Note when due and, with respect to payment of any interest, the continuation of such failure for a period of thirty days thereafter, constitutes an event of default under the Promissory Note. If an event of default occurs under the Promissory Note, the payees may declare the entire balance of the promissory note due and payable (including principal and accrued and unpaid interest) within five business days of the payees' notification to the Company of such acceleration.

INCOME TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The Company's income tax provisions for the nine months ended September 30, 2018 and 2017 reflect the Company's estimates of the effective rates expected to be applicable for the respective full years, adjusted for any discrete events, which are recorded in the period that they occur. These estimates are reevaluated each quarter based on the Company's estimated tax expense for the full year. The estimated effective rates for the nine months ended September 30, 2018 and 2017 do not include any benefit for the Company's domestic or Ireland losses, as the Company has concluded that a valuation allowance on any domestic or Ireland benefit is required. On December 22, 2017, the U.S. government enacted comprehensive tax legislation commonly referred to as the Tax Cuts and Jobs Act (the "Tax Act"). The Tax Act makes broad and complex changes to the U.S. tax code, including, but not limited to: reducing the U.S. federal corporate tax rate from 35% to 21%; requiring companies to pay a one-time transition tax on certain unrepatriated earnings of foreign subsidiaries; generally eliminating U.S. federal income taxes on dividends from foreign subsidiaries; requiring a current inclusion in U.S. federal taxable income of certain earnings (the Global Intangible Low-taxed Income ("GILTI")) of controlled foreign corporations; eliminating the corporate alternative minimum tax ("AMT") and changing how existing AMT credits can be realized; creating the base erosion anti-abuse tax ("BEAT"); creating a new limitation on deductible interest expense; changing rules related to uses and limitations of net operating loss carryforwards created in tax years beginning after December 31, 2017; providing a tax deduction for foreign derived intangible income ("FDII"); and changing rules related to deductibility of compensation for certain officers. The impact of certain effects of the Tax Act was provisionally recognized in the period in which the new legislation was enacted per guidance in Staff Accounting Bulletin 118, which allows for a measurement period to complete the accounting for certain elements of the tax reform. The Company has previously provided for a provisional impact related to remeasured deferred tax assets based on the new federal income tax rate of 21%. The Company has also previously provided for the provisional impact related to the Tax Act's change to the federal NOL and AMT carryovers. The total estimated impact of $4.8 million was reflected in the Company's net loss and increased the tax benefit for the year ended December 31, 2017. During the nine months ended September 30, 2018, the Company recorded an adjustment that reduced the benefit of the provisional impact relating to the change in its deferred tax assets by $0.2 million as a result of the new federal tax rate of 21%. The Company will continue to refine its calculations as additional analysis is completed and expects to complete the accounting for the impact of the Tax Act within the measurement period. The Company cannot currently predict with certainty how the Tax Act will affect its financial position or results of operations.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES The Company fully cooperated with an SEC inquiry regarding the development and issuance of Sonus’ first quarter 2015 revenue and earnings guidance. The Company and the SEC reached an agreement to resolve this matter and on August 7, 2018, the SEC issued a Cease and Desist Order (the "Order"). As part of the Order, the findings of which the Company neither admitted to nor denied, the Company agreed to pay a $1.9 million civil penalty and agreed not to violate the securities laws in the future. The Company recorded $1.9 million in the year ended December 31, 2017 for potential fines in connection with this investigation and has paid such amount to the SEC. The Company is involved in five lawsuits with Metaswitch Networks Ltd., Metaswitch Networks Corp. and Metaswitch Inc. (collectively, “Metaswitch”). In all five of the lawsuits, the Company is the plaintiff and, in three of the lawsuits, the Company is also a counterclaim defendant. On January 21, 2014, GENBAND and the Company’s indirectly-owned subsidiary, GENBAND US LLC, filed a complaint in the Eastern District of Texas, Marshall Division, alleging that Metaswitch infringed certain patents owned by GENBAND. Following unsuccessful mediation, a trial took place and on January 15, 2016, and the jury awarded approximately $8.2 million in past royalty damages to GENBAND, which neither GENBAND nor the Company has recorded. On September 29, 2016, the district court confirmed the jury verdict following motions from both parties. On March 22, 2018, the district court entered final judgment awarding GENBAND $8.9 million in royalties for damages through January 15, 2016 at rates set by the district court, excluding pre and post-judgment interest and costs. On April 10, 2018, the clerk of the court set the awarded costs at $0.4 million. On April 19, 2018, Metaswitch filed a notice of appeal on the judgment with United States Court of Appeals for the Federal Circuit, and filed its appeal brief on July 6, 2018. On April 18, 2018, Sonus filed a complaint in the Eastern District of Texas, Marshall Division, alleging that Metaswitch is continuing to infringe the patents from the first lawsuit above through sales of Metaswitch's allegedly "redesigned" products. This suit seeks a finding that Metaswitch's infringement is willful. This suit also alleges false advertising and seeks damages resulting from allegedly false and misleading statements Metaswitch made regarding the first lawsuit. The district court has set trial for September 9, 2019. Through Sonus and GENBAND US LLC, the Company is involved as plaintiff and counterclaim defendant in a lawsuit with Metaswitch regarding claims that Metaswitch misappropriated trade secrets of GENBAND. This case is pending in state court in Dallas County, Texas, and stems from claims originally brought in a patent lawsuit between GENBAND and Metaswitch. The state court action was filed on March 28, 2017. Metaswitch filed its answer on April 21, 2017, in which it asserted counterclaims against GENBAND. On July 11, 2018, Metaswitch filed its fifth amended answer and counterclaims against GENBAND. The Texas state court has set a special setting for a trial for this case on April 22, 2019. Through Sonus, the Company is also involved as plaintiff and counterclaim defendant in two patent infringement lawsuits with Metaswitch asserting the infringement of a total of ten patents that came into the Company from Sonus. Sonus filed these two lawsuits in the Eastern District of Texas, Marshall Division, on March 8, 2018. Metaswitch filed its answers on May 15, 2018, in which it asserted counterclaims against Sonus, including alleged infringement by the Company and Sonus of a total of ten patents. The district court has set trials for these cases to occur on February 18, 2020 and June 15, 2020. At this time, it is not possible to predict the outcome of the litigation matters with Metaswitch, but the Company does not expect the results of any of these actions to have a material adverse effect on its business or consolidated financial statements. In addition, the Company is often a party to disputes and legal proceedings that it considers routine and incidental to its business. Management does not expect the results of any of these actions to have a material effect on the Company's business or consolidated financial statements.

BASIS OF PRESENTATION (Policies

BASIS OF PRESENTATION (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation In the opinion of management, the accompanying unaudited condensed consolidated financial statements include all adjustments, consisting only of normal recurring items, necessary for their fair presentation with accounting principles generally accepted in the United States of America ("GAAP") and with the rules and regulations of the U.S. Securities and Exchange Commission ("SEC"). On October 27, 2017 (the "Merger Date"), Sonus Networks, Inc. ("Sonus") consummated an acquisition as specified in an Agreement and Plan of Merger (the "Merger Agreement") with Solstice Sapphire Investments, Inc. ("NewCo") and certain of its wholly-owned subsidiaries, GENBAND Holdings Company, GENBAND Inc. and GENBAND II, Inc. (collectively, "GENBAND") pursuant to which, following a series of merger transactions (collectively, the "Merger"), Sonus and GENBAND each became a wholly-owned subsidiary of NewCo, with Sonus deemed the acquirer in the transaction for accounting purposes. Subsequently, on November 28, 2017, the Company changed its name to "Ribbon Communications Inc." The condensed consolidated financial statements of the Company represent the consolidated financial statements of Sonus, prior to the Merger Date, and the condensed consolidated financial statements of Ribbon, on and after the Merger Date. The financial results of GENBAND are included in Ribbon's condensed consolidated financial statements beginning on the Merger Date. On August 3, 2018 (the "Edgewater Acquisition Date"), the Company completed the acquisition of Edgewater Networks, Inc. (“Edgewater”). The financial results of Edgewater are included in the Company's condensed consolidated financial statements for the period subsequent to the Edgewater Acquisition Date. Interim results are not necessarily indicative of results for a full year or any future interim period. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the Company's Annual Report on Form 10-K for the year ended December 31, 2017 (the "Annual Report"), which was filed with the SEC on March 8, 2018.
Revenue Recognition Policy	Revenue Recognition Policy The Company derives revenues from two primary sources: products and services. Product revenue includes the Company's hardware and software that function together to deliver the products' essential functionality. Software and hardware are also sold on a standalone basis. Services include customer support (software updates, upgrades and technical support), consulting, design services, installation services and training. Generally, contracts with customers contain multiple performance obligations, consisting of products and services. For these contracts, the Company accounts for individual performance obligations separately if they are considered distinct. When an arrangement contains more than one performance obligation, the Company will generally allocate the transaction price to each performance obligation on a relative standalone selling price basis. The best evidence of a standalone selling price is the observable price of a good or service when the entity sells that good or service separately in similar circumstances and to similar customers. If the good or service is not sold separately, an entity must estimate the standalone selling price by using an approach that maximizes the use of observable inputs. Acceptable estimation methods include but are not limited to: (1) adjusted market assessment; (2) expected cost plus a margin; and (3) a residual approach (when the standalone selling price is not directly observable and is either highly variable or uncertain). The Company's software licenses typically provide a perpetual right to use the Company's software. The Company also sells term-based software licenses that expire and Software-as-a-Service ("SaaS")-based software which are referred to as subscription arrangements. The Company does not customize its software nor are installation services required, as the customer has a right to utilize internal resources or a third-party service company. The software and hardware are delivered before related services are provided and are functional without professional services or customer support. The Company has concluded that its software licenses are functional intellectual property that are distinct, as the user can benefit from the software on its own. The product revenue is typically recognized upon transfer of control or when the software is made available for download, as this is the point that the user of the software can direct the use of, and obtain substantially all of the remaining benefits from, the functional intellectual property. The Company does not recognize software revenue related to the renewal of subscription software licenses earlier than the beginning of the subscription period. Hardware product is generally sold with software to provide the customer solution. Services revenue includes revenue from customer support and other professional services. The Company offers warranties on its products. Certain of the Company's warranties are considered to be assurance-type in nature and do not cover anything beyond ensuring that the product is functioning as intended. Based on the guidance in Accounting Standards Codification ("ASC") 606, assurance-type warranties do not represent separate performance obligations. The Company also sells separately-priced maintenance service contracts which qualify as service-type warranties and represent separate performance obligations. The Company does not allow and has no history of accepting product returns. Customer support includes software updates on a when-and-if-available basis, telephone support, integrated web-based support and bug fixes or patches. The Company sells its customer support contracts at a percentage of list or net product price related to the support. Customer support revenue is recognized ratably over the term of the customer support agreement, which is typically one year. The Company's professional services include consulting, technical support, resident engineer services, design services and installation services. Because control transfers over time, revenue is recognized based on progress toward completion of the performance obligation. The method to measure progress toward completion requires judgment and is based on the nature of the products or services to be provided. The Company generally uses the input method to measure progress for its contracts because it believes such method best depicts the transfer of assets to the customer, which occurs as the Company incurs costs for the contracts. Under the cost-to-cost measure of progress, the progress toward completion is measured based on the ratio of costs incurred to date to the total estimated costs at completion of the performance obligation. When the measure of progress is based upon expended labor, progress toward completion is measured as the ratio of labor time expended to date vs the total estimated labor time required to complete the performance obligation. Revenue is recorded proportionally as costs are incurred or labor is expended. Costs to fulfill these obligations include internal labor as well as subcontractor costs. Customer training includes courses offered by the Company. The related revenue is typically recognized as the training services are performed.
Principles of Consolidation	Principles of Consolidation The condensed consolidated financial statements include the accounts of Ribbon and its wholly-owned subsidiaries. Intercompany transactions and balances have been eliminated in consolidation.
Use of Estimates and Judgments	Use of Estimates and Judgments The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting periods. Significant estimates and judgments relied upon in preparing these consolidated financial statements include accounting for business combinations; revenue recognition for multiple element arrangements, including determining the standalone selling prices of performance obligations; inventory valuations; assumptions used to determine the fair value of stock-based compensation; intangible assets and goodwill valuations, including impairments; legal contingencies; and recoverability of Ribbon's net deferred tax assets and the related valuation allowances. Ribbon regularly assesses these estimates and records changes in estimates in the period in which they become known. Ribbon bases its estimates on historical experience and various other assumptions that it believes to be reasonable under the circumstances. Actual results could differ from those estimates.
Reclassifications	Reclassifications Certain reclassifications have been made to the previously issued financial statements to conform to the current period presentation, none of which affected net loss as previously reported.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of the Company's financial instruments, which include cash equivalents; marketable securities; investments; accounts receivable; revolving credit facility; accounts payable; long-term debt, related party; and other long-term liabilities; approximate their fair values.
Operating Segments	Operating Segments The Company operates in a single segment, as the chief operating decision maker makes decisions and assesses performance at the company level. Operating segments are identified as components of an enterprise about which separate discrete financial information is utilized for evaluation by the chief operating decision maker in making decisions regarding resource allocation and assessing performance. To date, the chief operating decision maker has made such decisions and assessed performance at the company level, as one segment. The Company's chief operating decision maker is its President and Chief Executive Officer.
Foreign Currency Translations	Foreign Currency Translation As part of ongoing merger integration activities, the Company conducted an assessment of the functional currencies of its foreign subsidiaries. The Company concluded that the U.S. dollar is the appropriate functional currency for the majority of the former GENBAND foreign subsidiaries, based on its assessment of underlying factors. As such, the functional currency was changed to the U.S. dollar effective January 1, 2018.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2018, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income ("ASU 2018-02"), which amends ASC 220, Income Statement - Reporting Comprehensive Income , to allow a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act and requires entities to provide certain disclosures regarding stranded tax effects. ASU 2018-02 is effective for the Company beginning January 1, 2019, with early adoption permitted. The Company is currently assessing the potential impact of the adoption of ASU 2018-02 on its consolidated financial statements. In August 2018, the FASB issued ASU 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”), which provides guidance on implementation costs incurred in a cloud computing arrangement (“CCA”) that is a service contract. ASU 2018-15 amends ASC 350, Intangibles - Goodwill and Other (“ASC 350”) to include in its scope implementation costs of a CCA that is a service contract and clarifies that a customer should apply the guidance in ASC 350-40 to determine which implementation costs should be capitalized in such a CCA. ASU 2018-15 is effective for the Company beginning January 1, 2020. The Company is currently assessing the potential impact of the adoption of ASU 2018-15 on our consolidated financial statements. In May 2017, the FASB issued ASU 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting ("ASU 2017-09"), which amends the scope of modification accounting for share-based payment arrangements such that an entity would not apply modification accounting if the fair value, vesting conditions and classification of the awards are the same immediately before and after the modification. ASU 2017-09 became effective for the Company beginning January 1, 2018 for both interim and annual reporting periods. The adoption of ASU 2017-09 did not have a material impact on the Company's condensed consolidated financial statements. In March 2017, the FASB issued ASU 2017-07, Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Post Retirement Benefit Cost ("ASU 2017-07"). ASU 2017-07 amends the requirements in ASC 715 to require entities to disaggregate the current-service-cost component from the other components of net benefit cost (the "other components") and include it with other current compensation costs for related employees, present the other components elsewhere in the income statement and outside of income from operations if such a subtotal is presented and disclose the income statement lines that contain the other components if they are not presented on appropriately described separate lines. ASU 2017-07 became effective for the Company beginning January 1, 2018 for both interim and annual reporting periods. The adoption of ASU 2017-07 did not have a material impact on the Company's condensed consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments ("ASU 2016-15"), which adds or clarifies guidance on eight cash flow issues, including debt prepayment or debt extinguishment costs, settlement of zero-coupon debt instruments or certain other debt instruments, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies, distributions received from equity method investees, beneficial interests in securitization transactions and separately identifiable cash flows and application of the predominance principle. ASU 2016-15 became effective for the Company beginning January 1, 2018 for both interim and annual reporting periods. Entities must apply the guidance retrospectively to all periods presented but may apply it prospectively from the earliest date practicable if retrospective application would be impracticable. The adoption of ASU 2016-15 did not have a material impact on the Company's condensed consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) Section A - Leases: Amendments to the FASB Accounting Standards Codification ("ASU 2016-02"), its new standard on accounting for leases. ASU 2016-02 introduces a lessee model that brings most leases onto the balance sheet. ASU 2016-02 eliminates the current GAAP requirement for an entity to use bright-line tests in determining lease classification. ASU 2016-02 is effective for the Company for both interim and annual periods beginning January 1, 2019. Upon adoption of ASU 2016-02, the Company will recognize lease obligations for the right to use these assets in connection with its existing lease agreements. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements ("ASU 2018-11") and ASU 2018-10, Codification Improvements to Topic 842, Leases , both of which provided improvements to certain aspects of the guidance in ASC 842, Lease s. In January 2018, the FASB issued ASU 2018-01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842 , which provided additional clarification and implementation guidance. The Company has elected to use the alternative transition method as described in ASU 2018-11, which allows entities to initially apply ASU 2016-02 at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings, with no subsequent adjustments to prior period lease costs for comparability. The Company has essentially completed the lease assessment phase of implementation and is currently reviewing the contracts within its lease portfolio in order to quantify the impact of adoption on its consolidated balance sheet as of January 1, 2019. The Company expects to quantify such amounts to be recognized on the balance sheet by the end of the fourth quarter of 2018. In addition, the FASB has issued the following accounting pronouncements, none of which the Company believes will have a material impact on its consolidated financial statements: In August 2018, the FASB issued ASU 2018-14, Compensation - Retirement Benefits - Defined Benefit Plans - General (Subtopic 715-20): Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans (“ASU 2018-14”), which amends ASC 715, Compensation - Retirement Benefits (“ASC 715”) to add, remove and clarify disclosure requirements related to defined benefit pension and other postretirement plans. ASU 2018-14 is effective for the Company beginning January 1, 2020. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”), which changes the fair value measurement requirements of ASC 820, Fair Value Measurement (“ASC 820”). ASU 2018-13 is effective for the Company beginning January 1, 2020 for both interim and annual reporting. In July 2018, the FASB issued ASU 2018-09, Codification Improvements (“ASU 2018-09”), which contains amendments to clarify, correct errors in or make minor improvements to the Codification. ASU 2018-09 makes improvements to multiple topics, including but not limited to comprehensive income, debt, income taxes related to both stock-based compensation and business combinations, fair value measurement and defined contribution benefit plans. ASU 2018-09 is effective for the Company beginning January 1, 2019. In June 2018, the FASB issued ASU 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting ("ASU 2018-07"), which expands the scope of ASC 718, Compensation - Stock Compensation ("ASC 718"), to include all share-based payment arrangements related to the acquisition of goods and services from both nonemployees and employees. As a result, most of the guidance in ASC 718 associated with employee share-based payments, including most of its requirements related to classification and measurement, applies to nonemployee share-based payment arrangements. ASU 2018-07 is effective for the Company beginning January 1, 2019, although early adoption is permitted. In October 2016, the FASB issued ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory ("ASU 2016-16"), which removes the prohibition in ASC 740, Income Taxes, against the immediate recognition of the current and deferred income tax effects of intra-entity transfers of assets other than inventory. ASU 2016-16 is effective for the Company beginning January 1, 2019 for both interim and annual reporting periods. 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.

BUSINESS ACQUISITIONS (Tables)

BUSINESS ACQUISITIONS (Tables)	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Schedule of Business Acquisitions, by Acquisition	A summary of the preliminary allocation of the purchase consideration for Edgewater is as follows (in thousands): Fair value of consideration transferred: Cash consideration: Cash paid to Edgewater Selling Stakeholders $ 51,162 Less cash acquired (4,773 ) Net cash consideration 46,389 Unpaid cash consideration 30,000 Fair value of Ribbon stock issued 30,000 Fair value of equity awards assumed (see Note 11) 747 Fair value of total consideration $ 107,136 Fair value of assets acquired and liabilities assumed: Current assets, net of cash acquired $ 16,837 Property and equipment 380 Intangible assets: Developed technology 29,500 Customer relationships 26,100 Trade names 1,100 Goodwill 46,777 Other noncurrent assets 103 Deferred revenue (2,749 ) Other current liabilities (9,402 ) Deferred revenue, net of current (669 ) Other long-term liabilities (841 ) $ 107,136
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	A summary of the final allocation of the purchase consideration for GENBAND is as follows (in thousands): Fair value of consideration transferred: Cash consideration: Repayment of GENBAND long-term debt and accrued interest, related party $ 47,973 Payment of GENBAND management fees due to majority shareholder 10,302 Less cash acquired (15,324 ) Net cash consideration 42,951 Fair value of Sonus stock issued 413,982 Promissory note issued to GENBAND equity holders 22,500 Fair value of total consideration $ 479,433 Fair value of assets acquired and liabilities assumed: Current assets, net of cash acquired $ 99,126 Property and equipment 16,770 Intangible assets: In-process research and development 5,600 Developed technology 129,000 Customer relationships 101,300 Trade names 900 Goodwill 285,825 Other noncurrent assets 6,732 Revolving credit facility (17,930 ) Deferred revenue (32,390 ) Other current liabilities (80,023 ) Deferred revenue, net of current (6,804 ) Other long-term liabilities (28,673 ) $ 479,433
Pro Forma Information	Accordingly, these unaudited pro forma results are presented for illustrative purposes and are not intended to represent or be indicative of the actual results of operations of the combined company that would have been achieved had the Merger occurred at the beginning of the period presented, nor are they intended to represent or be indicative of future results of operations (in thousands, except per share amounts): Three months ended September 30, 2017 Nine months ended September 30, 2017 Revenue $ 147,608 $ 419,749 Net loss $ (22,148 ) $ (105,666 ) Loss per share $ (0.22 ) $ (1.04 )
Schedule of Components of Acquisition Related Costs	The Company's acquisition- and integration-related expenses for the three and nine months ended September 30, 2018 and 2017 were as follows (in thousands): Three months ended Nine months ended September 30, September 30, September 30, September 30, Professional and services fees (acquisition-related) $ 2,905 $ 1,543 $ 5,314 $ 6,278 Management bonuses (acquisition-related) — — 1,972 — Integration-related expenses 2,665 — 6,976 — $ 5,570 $ 1,543 $ 14,262 $ 6,278

EARNINGS (LOSS) PER SHARE (Tabl

EARNINGS (LOSS) PER SHARE (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Schedule of calculations of shares used to compute basic and diluted earnings (loss) per share	The calculations of shares used to compute loss per share were as follows (in thousands): Three months ended Nine months ended September 30, September 30, September 30, September 30, Weighted average shares outstanding—basic 104,918 49,753 103,009 49,472 Potential dilutive common shares — 378 — — Weighted average shares outstanding—diluted 104,918 50,131 103,009 49,472

CASH EQUIVALENTS, MARKETABLE _2

CASH EQUIVALENTS, MARKETABLE SECURITIES AND INVESTMENTS (Tables)	9 Months Ended
	Sep. 30, 2018
Investments, All Other Investments [Abstract]
Schedule of amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments	The amortized cost, gross unrealized gains and losses and fair value of the Company's marketable debt securities and investments at September 30, 2018 and December 31, 2017 were comprised of the following (in thousands): September 30, 2018 Amortized cost Unrealized gains Unrealized losses Fair value Cash equivalents $ 427 $ — $ — $ 427 Marketable securities U.S. government agency notes $ 3,997 $ — $ (17 ) $ 3,980 Corporate debt securities 3,317 — (13 ) 3,304 $ 7,314 $ — $ (30 ) $ 7,284 December 31, 2017 Amortized cost Unrealized gains Unrealized losses Fair value Cash equivalents $ 1,254 $ — $ — $ 1,254 Marketable securities U.S. government agency notes $ 4,091 $ — $ (19 ) $ 4,072 Corporate debt securities 8,048 — (31 ) 8,017 Certificates of deposit 5,135 — — 5,135 $ 17,274 $ — $ (50 ) $ 17,224 Investments U.S. government agency notes $ 3,992 $ — $ (28 ) $ 3,964 Corporate debt securities 3,908 — (24 ) 3,884 Certificates of deposit 1,183 — — 1,183 $ 9,083 $ — $ (52 ) $ 9,031
Schedule of fair value of financial assets	The following table shows the fair value of the Company's financial assets at September 30, 2018 and December 31, 2017 . These financial assets are comprised of the Company's available-for-sale debt securities and reported under the captions Cash and cash equivalents, Marketable securities and Investments in the condensed consolidated balance sheets (in thousands): Fair value measurements at Total carrying Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) Cash equivalents $ 427 $ 427 $ — $ — Marketable securities U.S. government agency notes $ 3,980 $ — $ 3,980 $ — Corporate debt securities 3,304 — 3,304 — $ 7,284 $ — $ 7,284 $ — 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 $ 1,254 $ 1,254 $ — $ — Marketable securities U.S. government agency notes $ 4,072 $ — $ 4,072 $ — Corporate debt securities 8,017 — 8,017 — Certificates of deposit 5,135 — 5,135 — $ 17,224 $ — $ 17,224 $ — Investments U.S. government agency notes $ 3,964 $ — $ 3,964 $ — Corporate debt securities 3,884 — 3,884 — Certificates of deposit 1,183 — 1,183 — $ 9,031 $ — $ 9,031 $ —

INVENTORY (Tables)

INVENTORY (Tables)	9 Months Ended
	Sep. 30, 2018
Inventory Disclosure [Abstract]
Schedule of inventory	Inventory at September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, December 31, On-hand final assemblies and finished goods inventories $ 19,371 $ 18,374 Deferred cost of goods sold 3,707 4,569 23,078 22,943 Less noncurrent portion (included in other assets) (1,354 ) (1,640 ) Current portion $ 21,724 $ 21,303

INTANGIBLE ASSETS AND GOODWILL

INTANGIBLE ASSETS AND GOODWILL (Tables)	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of intangible assets	The Company's intangible assets at September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, 2018 Weighted average amortization period (years) Cost Accumulated amortization Net carrying value In-process research and development * $ 5,600 $ — $ 5,600 Developed technology 6.91 182,880 53,666 129,214 Customer relationships 9.44 146,940 19,896 127,044 Trade names 3.00 2,000 465 1,535 Internal use software 3.00 730 730 — 7.86 $ 338,150 $ 74,757 $ 263,393 December 31, 2017 Weighted average amortization period (years) Cost Accumulated amortization Net carrying value In-process research and development * $ 5,600 $ — $ 5,600 Developed technology 6.90 153,380 24,211 129,169 Customer relationships 9.32 120,840 12,015 108,825 Trade names 3.00 900 80 820 Internal use software 3.00 730 730 — 7.77 $ 281,450 $ 37,036 $ 244,414
Schedule of amortization expense related to intangible assets	Amortization expense for intangible assets for the three and nine months ended September 30, 2018 and 2017 was as follows (in thousands): Three months ended Nine months ended Statement of operations classification September 30, September 30, September 30, September 30, Developed technology $ 10,593 $ 1,602 $ 29,455 $ 4,769 Cost of revenue - product Customer relationships 2,695 691 7,881 2,076 Sales and marketing Trade names 160 — 385 — Sales and marketing $ 13,448 $ 2,293 $ 37,721 $ 6,845
Schedule of estimated future amortization expense for intangible assets	Estimated future amortization expense for the Company's intangible assets at September 30, 2018 was as follows (in thousands): Years ending December 31, Remainder of 2018 $ 12,003 2019 47,411 2020 46,552 2021 40,571 2022 34,156 Thereafter 82,700 $ 263,393
Schedule of goodwill	The changes in the carrying value of the Company's goodwill in the nine months ended September 30, 2018 and 2017 were as follows (in thousands): Balance at January 1 2018 2017 Goodwill $ 338,822 $ 52,499 Accumulated impairment losses (3,106 ) (3,106 ) 335,716 49,393 Acquisition of Edgewater 46,777 — Purchase accounting adjustments - acquisition of Taqua, LLC — 498 Balance at September 30 $ 382,493 $ 49,891 Balance at September 30 Goodwill $ 385,599 $ 52,997 Accumulated impairment losses (3,106 ) (3,106 ) $ 382,493 $ 49,891

ACCRUED EXPENSES (Tables)

ACCRUED EXPENSES (Tables)	9 Months Ended
	Sep. 30, 2018
Payables and Accruals [Abstract]
Schedule of accrued expenses	Accrued expenses at September 30, 2018 and December 31, 2017 consisted of the following (in thousands): September 30, December 31, Employee compensation and related costs $ 33,174 $ 37,782 Professional fees 8,997 13,743 Deferred purchase consideration - Edgewater 15,000 — Other 17,439 24,855 $ 74,610 $ 76,380

RESTRUCTURING ACCRUALS (Tables)

RESTRUCTURING ACCRUALS (Tables)	9 Months Ended
	Sep. 30, 2018
Restructuring and Related Activities [Abstract]
Summary of restructuring accrual activity	A summary of the Taqua Restructuring Initiative accrual activity for the nine months ended September 30, 2018 is as follows (in thousands): Balance at Initiatives Adjustments for changes in estimate Cash Balance at Facilities $ 365 $ — $ — $ (255 ) $ 110 A summary of the Merger Restructuring Initiative accrual activity for the nine months ended September 30, 2018 is as follows (in thousands): Balance at Initiatives Adjustments for changes in estimate Cash Balance at Severance $ 7,595 $ 14,121 $ (5 ) $ (18,928 ) $ 2,783 Facilities — 193 — (70 ) 123 $ 7,595 $ 14,314 $ (5 ) $ (18,998 ) $ 2,906 A summary of the 2016 Restructuring Initiative accrual activity for the nine months ended September 30, 2018 is as follows (in thousands): Balance at Initiatives Adjustments for changes in estimate Cash Balance at Facilities $ 95 $ — $ — $ (25 ) $ 70 A summary of the GENBAND Restructuring Initiative accrual activity for the nine months ended September 30, 2018 is as follows (in thousands): Balance at Initiatives Adjustments for changes in estimate Cash Balance at Severance $ 1,916 $ — $ 487 $ (2,358 ) $ 45 Facilities 205 — 366 (401 ) 170 $ 2,121 $ — $ 853 $ (2,759 ) $ 215

REVENUE RECOGNITION (Tables)

REVENUE RECOGNITION (Tables)	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The Company's product revenue from its direct sales program and from indirect sales through its channel partner program for the three and nine months ended September 30, 2018 and 2017 was as follows (in thousands): Three months ended Nine months ended September 30, September 30, September 30, September 30, Indirect sales through channel program $ 26,309 $ 10,704 $ 42,151 $ 28,063 Direct sales 50,974 33,416 149,786 70,242 $ 77,283 $ 44,120 $ 191,937 $ 98,305 The Company's revenue for the three and nine months ended September 30, 2018 and 2017 was disaggregated as follows: Three months ended September 30, 2018 Product revenue Service revenue (maintenance) Service revenue (professional services) Total revenue United States $ 49,699 $ 34,065 $ 9,040 $ 92,804 Europe, Middle East and Africa 10,380 11,504 2,169 24,053 Japan 3,588 2,882 503 6,973 Other Asia Pacific 6,959 3,551 906 11,416 Other 6,657 8,154 2,411 17,222 $ 77,283 $ 60,156 $ 15,029 $ 152,468 Three months ended September 30, 2017 Product revenue Service revenue (maintenance) Service revenue (professional services) Total revenue United States $ 35,126 $ 16,745 $ 4,263 $ 56,134 Europe, Middle East and Africa 3,072 2,960 272 6,304 Japan 3,376 2,489 1,552 7,417 Other Asia Pacific 1,771 992 47 2,810 Other 775 1,070 119 1,964 $ 44,120 $ 24,256 $ 6,253 $ 74,629 Nine months ended September 30, 2018 Product revenue Service revenue (maintenance) Service revenue (professional services) Total revenue United States $ 109,977 $ 98,354 $ 25,535 $ 233,866 Europe, Middle East and Africa 29,807 35,550 8,157 73,514 Japan 16,128 8,431 2,296 26,855 Other Asia Pacific 21,970 8,905 3,185 34,060 Other 14,055 23,049 5,610 42,714 $ 191,937 $ 174,289 $ 44,783 $ 411,009 Nine months ended September 30, 2017 Product revenue Service revenue (maintenance) Service revenue (professional services) Total revenue United States $ 72,123 $ 48,502 $ 10,116 $ 130,741 Europe, Middle East and Africa 10,295 8,006 1,456 19,757 Japan 8,569 7,536 3,768 19,873 Other Asia Pacific 4,180 2,920 383 7,483 Other 3,138 2,234 504 5,876 $ 98,305 $ 69,198 $ 16,227 $ 183,730 The Company's product revenue from sales to enterprise customers and from sales to service provider customers for the three and nine months ended September 30, 2018 and 2017 was as follows (in thousands): Three months ended Nine months ended September 30, September 30, September 30, September 30, Sales to enterprise customers $ 23,581 $ 9,602 $ 37,534 $ 23,903 Sales to service provider customers 53,702 34,518 154,403 74,402 $ 77,283 $ 44,120 $ 191,937 $ 98,305
Schedule of Customer Assets and Liabilities	The changes in the Company's accounts receivable, unbilled receivables and deferred revenue balances for the nine months ended September 30, 2018 were as follows (in thousands): Accounts receivable Unbilled accounts receivable Deferred revenue (current) Deferred revenue (long-term) Balance at January 1, 2018 $ 149,122 $ 16,034 $ 100,571 $ 14,184 Increase (decrease), net (13,317 ) (1,162 ) (18,082 ) 1,801 Balance at September 30, 2018 $ 135,805 $ 14,872 $ 82,489 $ 15,985
Schedule of Timing of Performance Obligation	The Company's typical performance obligations include the following: Performance Obligation When Performance Obligation is Typically Satisfied When Payment is Typically Due Software and Product Revenue Software licenses (perpetual or term) Upon transfer of control; typically, when made available for download (point in time) Within 30 days of invoicing except for term licenses which may be paid for over time Software licenses (subscription) Upon activation of hosted site (over time) Within 30 days of invoicing Hardware When control of the appliances passes to the customer; typically, upon delivery (point in time) Generally, within 30 days of invoicing Software upgrades Upon transfer of control; typically, when made available for download (point in time) Generally, within 30 days of invoicing Customer Support Revenue Customer support Ratably over the course of the support contract (over time) At the beginning of the contract period Professional Services Other professional services (excluding education services) As work is performed (over time) Within 30 days of invoicing (upon completion of services) Training When the class is taught (point in time) Within 30 days of services being performed

STOCK-BASED COMPENSATION PLANS

STOCK-BASED COMPENSATION PLANS (Tables)	9 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of activity related to outstanding stock options	The activity related to the Company's outstanding stock options for the nine months ended September 30, 2018 was as follows: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (years) Aggregate Intrinsic Value (in thousands) Outstanding at January 1, 2018 435,187 $ 14.71 Granted — $ — Edgewater outstanding options converted to Ribbon options 312,452 $ 1.97 Exercised (8,653 ) $ 4.97 Forfeited — $ — Expired (109,486 ) $ 14.40 Outstanding at September 30, 2018 629,500 $ 8.57 6.12 $ 1,538 Vested or expected to vest at September 30, 2018 589,719 $ 9.01 5.96 $ 1,352 Exercisable at September 30, 2018 344,653 $ 14.01 4.41 $ 161
Schedule of stock options, additional information	Additional information regarding the Company's stock options for the three and nine months ended September 30, 2018 was as follows: Three months ended Nine months ended September 30, September 30, Total intrinsic value of stock options exercised (in thousands) $ 13 $ 21 Cash received from the exercise of stock options (in thousands) $ 33 $ 43
Schedule of activity related to unvested restricted stock grants	The activity related to the Company's RSAs for the nine months ended September 30, 2018 was as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2018 1,696,582 $ 7.68 Granted 1,123,956 $ 6.90 Vested (752,085 ) $ 8.46 Forfeited (270,075 ) $ 7.36 Unvested balance at September 30, 2018 1,798,378 $ 6.91 The activity related to the Company's RSUs for the nine months ended September 30, 2018 was as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2018 17,932 $ 6.99 Granted 899,500 $ 6.27 Vested (17,110 ) $ 7.00 Forfeited (41,822 ) $ 6.72 Unvested balance at September 30, 2018 858,500 $ 6.25
Schedule of activity related to performance stock awards	The activity related to the Company's PSUs for the nine months ended September 30, 2018 was as follows: Shares Weighted Average Grant Date Fair Value Unvested balance at January 1, 2018 60,834 $ 9.65 Granted 207,350 $ 5.78 Vested (57,768 ) $ 9.90 Forfeited — $ — Unvested at September 30, 2018 210,416 $ 5.77
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 and nine months ended September 30, 2018 and 2017 as follows (in thousands): Three months ended Nine months ended September 30, September 30, September 30, September 30, Product cost of revenue $ 21 $ 75 $ 91 $ 261 Service cost of revenue 65 199 264 777 Research and development 313 1,095 1,364 3,650 Sales and marketing 585 871 1,944 1,690 General and administrative 1,532 1,647 3,758 5,009 $ 2,516 $ 3,887 $ 7,421 $ 11,387

MAJOR CUSTOMERS (Tables)

MAJOR CUSTOMERS (Tables)	9 Months Ended
	Sep. 30, 2018
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 the three and nine months ended September 30, 2018 and 2017 : Three months ended Nine months ended September 30, September 30, September 30, September 30, Verizon Communications Inc. 13% 16% 15% 15% AT&T Inc. 12% 11% 10% 10%

BASIS OF PRESENTATION - Narrati

BASIS OF PRESENTATION - Narrative (Details) customer in Thousands, $ in Millions	9 Months Ended
	Sep. 30, 2018segmentcustomer	Dec. 31, 2017USD ($)
Number of customers | customer	1
Number of reportable operating segments | segment	1
Accounting Standards Update 2014-09 | Retained earnings
Adjustment to accumulated deficit in connection with adoption of ASC 606 | $		$ 12

BUSINESS ACQUISITIONS - Edgewat

BUSINESS ACQUISITIONS - Edgewater Narrative (Details) - USD ($) $ in Thousands, shares in Millions	Jun. 24, 2018	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Payment to selling shareholders			$ 46,389	$ 0
Acquisition purchase consideration - deferred payments			30,000	$ 0
Edgewater Networks, Inc.
Business Acquisition [Line Items]
Payment to selling shareholders	$ 46,400		$ 46,389
Common stock to be issued (in shares)	4.2
Acquisition purchase consideration - deferred payments	$ 30,000
Deferred cash payments, within 6 months from closing date	15,000
Deferred cash payments, within 9 to 18 months from closing date	$ 15,000
Weighted average useful life of intangible assets (in years)			8 years 3 months 18 days
Revenue attributable to Edgewater since the acquisition date		$ 10,000	$ 10,000

BUSINESS ACQUISITIONS - Schedul

BUSINESS ACQUISITIONS - Schedule of Edgewater Acquisition (Details) - USD ($) $ in Thousands	Jun. 24, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Cash consideration:
Net cash consideration		$ 46,389	$ 0
Intangible assets:
Goodwill		382,493	$ 49,891	$ 335,716	$ 49,393
Edgewater Networks, Inc.
Cash consideration:
Cash paid to Edgewater Selling Stakeholders		51,162
Less cash acquired		(4,773)
Net cash consideration	$ 46,400	46,389
Unpaid cash consideration		30,000
Fair value of Ribbon stock issued		30,000
Fair value of equity awards assumed (see Note 11)	$ 700	747
Fair value of total consideration		107,136
Fair value of assets acquired and liabilities assumed:
Current assets, net of cash acquired		16,837
Property and equipment		380
Intangible assets:
Goodwill		46,777
Other noncurrent assets		103
Deferred revenue		(2,749)
Other current liabilities		(9,402)
Deferred revenue, net of current		(669)
Other long-term liabilities		(841)
Total		(107,136)
Developed technology | Edgewater Networks, Inc.
Intangible assets:
Finite-lived intangibles		29,500
Customer relationships | Edgewater Networks, Inc.
Intangible assets:
Finite-lived intangibles		26,100
Trade names | Edgewater Networks, Inc.
Intangible assets:
Finite-lived intangibles		$ 1,100

BUSINESS ACQUISITIONS - GENBAND

BUSINESS ACQUISITIONS - GENBAND Merger (Narrative) (Details) - USD ($)	Oct. 27, 2017	Sep. 30, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Average interest rate		5.26%	4.51%
Former Sonus Networks Inc. Shareholders
Business Acquisition [Line Items]
Percentage of ownership after transaction		50.00%
Former GENBAND Holdings Company Shareholders
Business Acquisition [Line Items]
Sale of stock, percentage of ownership after transaction	50.00%
GENBAND
Business Acquisition [Line Items]
Shares issued as consideration in connection with acquisition of GENBAND (in shares)	50,900,000
Repayment of GENBAND long-term debt and accrued interest, related party	$ 47,973,000
Payment of GENBAND management fees due to majority shareholder	10,302,000
Promissory note issued to GENBAND equity holders	$ 22,500,000
Average interest rate	4.67%
Weighted average useful life of intangible assets (in years)		8 years 3 months 18 days
GENBAND | Outstanding Borrowings
Business Acquisition [Line Items]
Debt assumed as part of GENBAND merger	$ 17,900,000
Average interest rate	4.67%
GENBAND | Letters of Credit
Business Acquisition [Line Items]
Debt assumed as part of GENBAND merger	$ 2,900,000

BUSINESS ACQUISITIONS - Sched_2

BUSINESS ACQUISITIONS - Schedule of GENBAND Business Acquisition (Details) - USD ($)	Oct. 27, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Cash consideration:
Net cash consideration		$ 46,389,000	$ 0
Intangible assets:
Goodwill		$ 382,493,000	$ 49,891,000	$ 335,716,000	$ 49,393,000
GENBAND
Cash consideration:
Repayment of GENBAND long-term debt and accrued interest, related party	$ 47,973,000
Payment of GENBAND management fees due to majority shareholder	10,302,000
Less cash acquired	(15,324,000)
Net cash consideration	42,951,000
Fair value of Sonus stock issued	413,982,000
Promissory note issued to GENBAND equity holders	22,500,000
Fair value of total consideration	479,433,000
Fair value of assets acquired and liabilities assumed:
Current assets, net of cash acquired	99,126,000
Property and equipment	16,770,000
Intangible assets:
Goodwill	285,825,000
Other noncurrent assets	6,732,000
Revolving credit facility	(17,930,000)
Deferred revenue	(32,390,000)
Other current liabilities	(80,023,000)
Deferred revenue, net of current	(6,804,000)
Other long-term liabilities	(28,673,000)
Total	479,433,000
In-process research and development | GENBAND
Intangible assets:
Finite-lived intangibles	5,600,000
Developed technology | GENBAND
Intangible assets:
Finite-lived intangibles	129,000,000
Customer relationships | GENBAND
Intangible assets:
Finite-lived intangibles	101,300,000
Trade names | GENBAND
Intangible assets:
Finite-lived intangibles	$ 900,000

BUSINESS ACQUISITIONS - Sched_3

BUSINESS ACQUISITIONS - Schedule of GENBAND Pro Forma Results (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017
Business Combinations [Abstract]
Revenue	$ 147,608	$ 419,749
Net loss	$ (22,148)	$ (105,666)
Loss (in dollars per share)	$ (0.22)	$ (1.04)

BUSINESS ACQUISITIONS - Summary

BUSINESS ACQUISITIONS - Summary of Acquisition Related Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Total	$ 5,570	$ 1,543	$ 14,262	$ 6,278
Taqua, LLC
Business Acquisition [Line Items]
Professional and services fees (acquisition-related)	2,905	1,543	5,314	6,278
Management bonuses (acquisition-related)	0	0	1,972	0
Integration-related expenses	2,665	0	6,976	0
Total	$ 5,570	$ 1,543	$ 14,262	$ 6,278

EARNINGS (LOSS) PER SHARE - (De

EARNINGS (LOSS) PER SHARE - (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reconciliation of weighted average shares outstanding from basic to diluted
Weighted average shares outstanding—basic	104,918	49,753	103,009	49,472
Potential dilutive common shares	0	378	0	0
Weighted average shares outstanding—diluted	104,918	50,131	103,009	49,472
Options not included in computation of diluted loss per share	3,500	5,200		7,400

CASH EQUIVALENTS, MARKETABLE _3

CASH EQUIVALENTS, MARKETABLE SECURITIES AND INVESTMENTS - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Sale of available-for-sale securities	$ 12,500	$ 12,500
Gross losses from sale of securities	$ 20	$ 20
Period considered to classify available-for-sale securities as investments		1 year
Minimum
Debt Securities, Available-for-sale [Line Items]
Period considered to classify available-for-sale securities as investments		1 year	1 year
Maximum
Debt Securities, Available-for-sale [Line Items]
Period considered to classify available-for-sale securities as investments		2 years	2 years

CASH EQUIVALENTS, MARKETABLE _4

CASH EQUIVALENTS, MARKETABLE SECURITIES AND INVESTMENTS - Schedule of Activity for Short-Term Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Cash equivalents, amortized cost	$ 427	$ 1,254
Cash equivalents, fair value	427	1,254
Marketable securities, amortized cost	7,314	17,274
Marketable securities, unrealized gains	0	0
Marketable securities, unrealized losses	(30)	(50)
Marketable securities, fair value	7,284	17,224
Investments, amortized cost		9,083
Investments, unrealized gains		0
Investments, unrealized losses		52
Investments, fair value	0	9,031
U.S. government agency notes
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Investments, amortized cost		3,992
Investments, unrealized gains		0
Investments, unrealized losses		28
Investments, fair value		3,964
Corporate debt securities
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Investments, amortized cost		3,908
Investments, unrealized gains		0
Investments, unrealized losses		24
Investments, fair value		3,884
Certificates of deposit
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Investments, amortized cost		1,183
Investments, unrealized gains		0
Investments, unrealized losses		0
Investments, fair value		1,183
U.S. government agency notes
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Marketable securities, amortized cost	3,997	4,091
Marketable securities, unrealized gains	0	0
Marketable securities, unrealized losses	(17)	(19)
Marketable securities, fair value	3,980	4,072
Investments, fair value		3,964
Corporate debt securities
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Marketable securities, amortized cost	3,317	8,048
Marketable securities, unrealized gains	0	0
Marketable securities, unrealized losses	(13)	(31)
Marketable securities, fair value	$ 3,304	8,017
Investments, fair value		3,884
Certificates of deposit
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Marketable securities, amortized cost		5,135
Marketable securities, unrealized gains		0
Marketable securities, unrealized losses		0
Marketable securities, fair value		5,135
Investments, fair value		$ 1,183

CASH EQUIVALENTS, MARKETABLE _5

CASH EQUIVALENTS, MARKETABLE SECURITIES AND INVESTMENTS - Schedule of Short-Term Investments by Measurement (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	$ 427	$ 1,254
Marketable securities, fair value	7,284	17,224
Investments, fair value	0	9,031
Quoted prices in active markets (Level 1)
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	427	1,254
Marketable securities, fair value	0	0
Investments, fair value		0
Significant other observable inputs (Level 2)
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	0	0
Marketable securities, fair value	7,284	17,224
Investments, fair value		9,031
Significant unobservable inputs (Level 3)
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	0	0
Marketable securities, fair value	0	0
Investments, fair value		0
U.S. government agency notes
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	3,980	4,072
Investments, fair value		3,964
U.S. government agency notes | Quoted prices in active markets (Level 1)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value		0
U.S. government agency notes | Significant other observable inputs (Level 2)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	3,980	4,072
Investments, fair value		3,964
U.S. government agency notes | Significant unobservable inputs (Level 3)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value		0
Corporate debt securities
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	3,304	8,017
Investments, fair value		3,884
Corporate debt securities | Quoted prices in active markets (Level 1)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value		0
Corporate debt securities | Significant other observable inputs (Level 2)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	3,304	8,017
Investments, fair value		3,884
Corporate debt securities | Significant unobservable inputs (Level 3)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	$ 0	0
Investments, fair value		0
Certificates of deposit
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value		5,135
Investments, fair value		1,183
Certificates of deposit | Quoted prices in active markets (Level 1)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value		0
Investments, fair value		0
Certificates of deposit | Significant other observable inputs (Level 2)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value		5,135
Investments, fair value		1,183
Certificates of deposit | Significant unobservable inputs (Level 3)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value		0
Investments, fair value		$ 0

INVENTORY - (Details)

INVENTORY - (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
On-hand final assemblies and finished goods inventories	$ 19,371	$ 18,374
Deferred cost of goods sold	3,707	4,569
Gross inventory	23,078	22,943
Less noncurrent portion (included in other assets)	(1,354)	(1,640)
Current portion	$ 21,724	$ 21,303

INTANGIBLE ASSETS AND GOODWIL_2

INTANGIBLE ASSETS AND GOODWILL - (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Intangible Assets And Goodwill
Weighted average amortization period (years)			7 years 10 months 8 days		7 years 9 months 8 days
Cost	$ 338,150		$ 338,150		$ 281,450
Accumulated amortization	74,757		74,757		37,036
Net carrying value	263,393		263,393		244,414
Amortization expense	13,448	$ 2,293	37,721	$ 6,845
Estimated future amortization expense for intangible assets
Remainder of 2018	12,003		12,003
2,019	47,411		47,411
2,020	46,552		46,552
2,021	40,571		40,571
2,022	34,156		34,156
Thereafter	82,700		82,700
Total	263,393		263,393
In-process research and development
Intangible Assets And Goodwill
Cost	5,600		5,600		5,600
Accumulated amortization	0		0		0
Net carrying value	5,600		$ 5,600		$ 5,600
Developed technology
Intangible Assets And Goodwill
Weighted average amortization period (years)			6 years 10 months 28 days		6 years 10 months 25 days
Cost	182,880		$ 182,880		$ 153,380
Accumulated amortization	53,666		53,666		24,211
Net carrying value	129,214		129,214		$ 129,169
Amortization expense	10,593	1,602	$ 29,455	4,769
Customer relationships
Intangible Assets And Goodwill
Weighted average amortization period (years)			9 years 5 months 8 days		9 years 3 months 25 days
Cost	146,940		$ 146,940		$ 120,840
Accumulated amortization	19,896		19,896		12,015
Net carrying value	127,044		127,044		$ 108,825
Amortization expense	2,695	691	$ 7,881	2,076
Trade names
Intangible Assets And Goodwill
Weighted average amortization period (years)			3 years		3 years
Cost	2,000		$ 2,000		$ 900
Accumulated amortization	465		465		80
Net carrying value	1,535		1,535		$ 820
Amortization expense	160	$ 0	$ 385	$ 0
Internal use software
Intangible Assets And Goodwill
Weighted average amortization period (years)			3 years		3 years
Cost	730		$ 730		$ 730
Accumulated amortization	730		730		730
Net carrying value	$ 0		$ 0		$ 0

INTANGIBLE ASSETS AND GOODWIL_3

INTANGIBLE ASSETS AND GOODWILL - Schedule of Changes in Carrying Value of Goodwill (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill	$ 385,599	$ 52,997	$ 338,822	$ 52,499
Accumulated impairment losses	(3,106)	(3,106)	$ (3,106)	$ (3,106)
Goodwill	335,716	49,393
Goodwill, end of period	382,493	49,891
Edgewater Networks, Inc.
Goodwill [Roll Forward]
Purchase accounting adjustments	46,777	0
Goodwill, end of period	46,777
Taqua, LLC
Goodwill [Roll Forward]
Purchase accounting adjustments	$ 0	$ 498

ACCRUED EXPENSES - Schedule of

ACCRUED EXPENSES - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Employee compensation and related costs	$ 33,174	$ 37,782
Professional fees	8,997	13,743
Deferred purchase consideration - Edgewater	15,000	0
Other	17,439	24,855
Total	$ 74,610	$ 76,380

RESTRUCTURING ACCRUALS - Narrat

RESTRUCTURING ACCRUALS - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Restructuring and Related Activities [Abstract]
Restructuring	$ 2,397	$ 0	$ 15,162	$ 1,071

RESTRUCTURING ACCRUALS - Merger

RESTRUCTURING ACCRUALS - Merger Restructuring Activities (Details) $ in Thousands	3 Months Ended					9 Months Ended
	Sep. 30, 2018USD ($)employee	Jun. 30, 2018USD ($)employee	Mar. 31, 2018USD ($)employee	Dec. 31, 2017USD ($)employee	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	$ 2,397				$ 0	$ 15,162	$ 1,071
Merger Restructuring Initiative
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	2,500	$ 5,300	$ 6,500			14,314
Number of positions eliminated | employee			115	120
Expected restructuring and related costs	$ 1,000					1,000
Severance | Merger Restructuring Initiative
Restructuring Cost and Reserve [Line Items]
Restructuring expenses		$ 5,100		$ 8,500		$ 14,121
UNITED KINGDOM | Merger Restructuring Initiative
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated | employee	30	140
UNITED KINGDOM | Severance | Merger Restructuring Initiative
Restructuring Cost and Reserve [Line Items]
Restructuring expenses		$ 200

RESTRUCTURING ACCRUALS - Rollfo

RESTRUCTURING ACCRUALS - Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended					6 Months Ended	8 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2017
Restructuring Reserve [Roll Forward]
Initiatives charged to expense	$ 2,397				$ 0			$ 15,162	$ 1,071
Merger Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period			$ 7,595					7,595
Initiatives charged to expense	2,500	$ 5,300	6,500					14,314
Adjustments for changes in estimate								(5)
Cash payments								(18,998)
Balance at the end of the period	2,906			$ 7,595				2,906
GENBAND Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period			2,121					2,121
Initiatives charged to expense								0
Adjustments for changes in estimate								853
Cash payments								(2,759)
Balance at the end of the period	215			2,121				215
2016 Restructuring Initiative
Restructuring Reserve [Roll Forward]
Initiatives charged to expense									500	$ 2,000
Taqua Restructuring Incentive
Restructuring Reserve [Roll Forward]
Initiatives charged to expense						$ 600	$ 1,800
Severance | Merger Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period			7,595					7,595
Initiatives charged to expense		$ 5,100		8,500				14,121
Adjustments for changes in estimate								(5)
Cash payments								(18,928)
Balance at the end of the period	2,783			7,595				2,783
Severance | GENBAND Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period			1,916					1,916
Initiatives charged to expense								0
Adjustments for changes in estimate								487
Cash payments								(2,358)
Balance at the end of the period	45			1,916				45
Severance | 2016 Restructuring Initiative
Restructuring Reserve [Roll Forward]
Initiatives charged to expense									400	1,900
Severance | Taqua Restructuring Incentive
Restructuring Reserve [Roll Forward]
Initiatives charged to expense						200	1,200
Facilities | Merger Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period			0					0
Initiatives charged to expense								193
Adjustments for changes in estimate								0
Cash payments								(70)
Balance at the end of the period	123			0				123
Facilities | GENBAND Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period			205					205
Initiatives charged to expense								0
Adjustments for changes in estimate								366
Cash payments								(401)
Balance at the end of the period	170			205				170
Facilities | 2016 Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period			95					95
Initiatives charged to expense								0	$ 100	$ 100
Adjustments for changes in estimate								0
Cash payments								(25)
Balance at the end of the period	70			95				70
Facilities | Taqua Restructuring Incentive
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period			$ 365					365
Initiatives charged to expense						$ 400	$ 600	0
Adjustments for changes in estimate								0
Cash payments								(255)
Balance at the end of the period	$ 110			$ 365				$ 110

RESTRUCTURING ACCRUALS - Assume

RESTRUCTURING ACCRUALS - Assumed Restructuring Initiative (Details) - GENBAND - USD ($) $ in Millions	Sep. 30, 2018	Oct. 27, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring liabilities		$ 4.1
Expected restructuring and related costs	$ 0.9
Severance
Restructuring Cost and Reserve [Line Items]
Restructuring liabilities		3.7
Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring liabilities		$ 0.4
Scenario, Adjustment | Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring liabilities	$ (0.1)

RESTRUCTURING ACCRUALS - Balanc

RESTRUCTURING ACCRUALS - Balance Sheet Classification (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Current portion of accrued restructuring reserve	$ 3.2	$ 10
Long-term portion of accrued restructuring	$ 0.1	$ 0.2

DEBT - Assumed Senior Secured C

DEBT - Assumed Senior Secured Credit Agreement (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017	Dec. 21, 2017	Oct. 27, 2017
Debt Instrument [Line Items]
Average interest rate	5.26%	4.51%
Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Line of credit potential increases			$ 100,000,000
Silicon Valley Bank | Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Current borrowing capacity for line of credit	$ 50,000,000
Potential further increases	75,000,000
Line of credit potential increases	$ 125,000,000
GENBAND
Debt Instrument [Line Items]
Average interest rate				4.67%
Line of Credit | GENBAND
Debt Instrument [Line Items]
Debt assumed as part of GENBAND merger				$ 17,900,000
Average interest rate				4.67%
Letter of Credit | GENBAND
Debt Instrument [Line Items]
Debt assumed as part of GENBAND merger				$ 2,900,000

DEBT - Senior Secured Credit Fa

DEBT - Senior Secured Credit Facility (Details) - USD ($)	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Dec. 21, 2017
Debt Instrument [Line Items]
Outstanding debt	$ 58,000,000	$ 20,000,000
Debt interest rate	5.26%	4.51%
Line of Credit
Debt Instrument [Line Items]
Commitment potential aggregate increase amount			$ 50,000,000
Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Commitments from lender			100,000,000
Fronting fee percentage	0.125%
Default rate percentage	2.00%
Revolving Credit Facility | Line of Credit | Minimum
Debt Instrument [Line Items]
Commitment fee percentage	0.25%
Letter of credit, fee multiplier	1.50%
Revolving Credit Facility | Line of Credit | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	2.00%
Commitment fee percentage	0.40%
Letter of credit, fee multiplier	2.00%
Revolving Credit Facility | Line of Credit | London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	2.50%
Revolving Credit Facility | Line of Credit | London Interbank Offered Rate (LIBOR) | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	3.00%
Revolving Credit Facility | Line of Credit | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate	0.50%
Revolving Credit Facility | Line of Credit | Additional Applicable Margin | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	1.50%
Letter of Credit | Line of Credit
Debt Instrument [Line Items]
Commitments from lender			15,000,000
Outstanding debt	$ 2,600,000	$ 2,900,000
Debt interest rate	1.75%	2.00%
Swingline loan | Line of Credit
Debt Instrument [Line Items]
Commitments from lender			$ 15,000,000

DEBT - Promissory Note (Details

DEBT - Promissory Note (Details) - USD ($)	Sep. 30, 2018	Oct. 27, 2017
GENBAND
Debt Instrument [Line Items]
Promissory Note		$ 22,500,000
GENBAND | Minimum
Debt Instrument [Line Items]
Promissory note interest rate	7.50%
GENBAND | Maximum
Debt Instrument [Line Items]
Promissory note interest rate	10.00%
Promissory Note
Debt Instrument [Line Items]
Promissory Note	$ 23,500,000
Principal amount	22,500,000
Interest converted to principal	$ 1,000,000

REVENUE RECOGNITION (Details)

REVENUE RECOGNITION (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue recognized that was previously recorded as deferred revenue	$ 18.4	$ 79.1
Revenue recognized in 2019		3
Revenue recognized in 2020		9
Revenue recognized in 2021 and beyond		4
Retained earnings | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Adjustment to accumulated deficit in connection with adoption of ASC 606			$ 12
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Revenues	$ 8	$ 9

REVENUE RECOGNITION - Schedule

REVENUE RECOGNITION - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Total revenue	$ 152,468	$ 74,629	$ 411,009	$ 183,730
United States
Disaggregation of Revenue [Line Items]
Total revenue	92,804	56,134	233,866	130,741
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenue	24,053	6,304	73,514	19,757
Japan
Disaggregation of Revenue [Line Items]
Total revenue	6,973	7,417	26,855	19,873
Other Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	11,416	2,810	34,060	7,483
Other
Disaggregation of Revenue [Line Items]
Total revenue	17,222	1,964	42,714	5,876
Product
Disaggregation of Revenue [Line Items]
Total revenue	77,283	44,120	191,937	98,305
Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	77,283	44,120	191,937	98,305
Product revenue | United States
Disaggregation of Revenue [Line Items]
Total revenue	49,699	35,126	109,977	72,123
Product revenue | Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenue	10,380	3,072	29,807	10,295
Product revenue | Japan
Disaggregation of Revenue [Line Items]
Total revenue	3,588	3,376	16,128	8,569
Product revenue | Other Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	6,959	1,771	21,970	4,180
Product revenue | Other
Disaggregation of Revenue [Line Items]
Total revenue	6,657	775	14,055	3,138
Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	60,156	24,256	174,289	69,198
Service revenue (maintenance) | United States
Disaggregation of Revenue [Line Items]
Total revenue	34,065	16,745	98,354	48,502
Service revenue (maintenance) | Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenue	11,504	2,960	35,550	8,006
Service revenue (maintenance) | Japan
Disaggregation of Revenue [Line Items]
Total revenue	2,882	2,489	8,431	7,536
Service revenue (maintenance) | Other Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	3,551	992	8,905	2,920
Service revenue (maintenance) | Other
Disaggregation of Revenue [Line Items]
Total revenue	8,154	1,070	23,049	2,234
Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	15,029	6,253	44,783	16,227
Service revenue (professional services) | United States
Disaggregation of Revenue [Line Items]
Total revenue	9,040	4,263	25,535	10,116
Service revenue (professional services) | Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenue	2,169	272	8,157	1,456
Service revenue (professional services) | Japan
Disaggregation of Revenue [Line Items]
Total revenue	503	1,552	2,296	3,768
Service revenue (professional services) | Other Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	906	47	3,185	383
Service revenue (professional services) | Other
Disaggregation of Revenue [Line Items]
Total revenue	2,411	119	5,610	504
Indirect sales through channel program | Product
Disaggregation of Revenue [Line Items]
Total revenue	26,309	10,704	42,151	28,063
Direct sales | Product
Disaggregation of Revenue [Line Items]
Total revenue	50,974	33,416	149,786	70,242
Sales to enterprise customers | Product
Disaggregation of Revenue [Line Items]
Total revenue	23,581	9,602	37,534	23,903
Sales to service provider customers | Product
Disaggregation of Revenue [Line Items]
Total revenue	$ 53,702	$ 34,518	$ 154,403	$ 74,402

REVENUE RECOGNITION - Schedul_2

REVENUE RECOGNITION - Schedule of Customer Assets & Liabilities (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)
Accounts receivable
Beginning balance	$ 149,122
Increase (decrease), net	(13,317)
Ending balance	135,805
Unbilled accounts receivable
Beginning balance	16,034
Increase (decrease), net	(1,162)
Ending balance	14,872
Deferred revenue (current)
Beginning balance	100,571
Increase (decrease), net	(18,082)
Ending balance	82,489
Deferred revenue (long-term)
Beginning balance	14,184
Increase (decrease), net	1,801
Ending balance	$ 15,985

STOCK-BASED COMPENSATION PLAN_2

STOCK-BASED COMPENSATION PLANS - 2002 Stock Option Plan (Details) - Edgewater Networks, Inc. - USD ($) $ / shares in Units, $ in Thousands	Jun. 24, 2018	Sep. 30, 2018
Stock-based compensation
Conversion factor	17.00%
Acquisition consideration (in dollars per share)	$ 1.20
Additional purchase consideration	$ 700	$ 747
Fair value of Ribbon Replacement Options	$ 1,000
Fair value of Ribbon Replacement Options, weighted average period (in years)	2 years

STOCK-BASED COMPENSATION PLAN_3

STOCK-BASED COMPENSATION PLANS - Executive Equity Arrangements (Details) $ in Thousands	Apr. 01, 2018shares	Mar. 16, 2018shares	Mar. 31, 2017executiveshares	Apr. 01, 2016executiveshares	Mar. 16, 2015executiveshares	May 31, 2018shares	Mar. 31, 2018executiveshares	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)shares	Sep. 30, 2017USD ($)
Stock-based compensation
Stock-based compensation expense | $								$ 2,516	$ 3,887	$ 7,421	$ 11,387
PSUs
Stock-based compensation
Granted (in shares)						195,000				207,350
Stock-based compensation expense | $								$ 154		$ 194
Percent of performance metrics achieved						150.00%
Vested (in shares)										57,768
2017 Performance Share Units | PSUs
Stock-based compensation
Granted (in shares)			165,000
Number of executives granted shares | executive			5
Percent of performance metrics achieved							130.00%
Vested (in shares)							33,584
Number of executives shares were released to | executive							3
2017 Performance Share Units | March 31, 2017 | PSUs
Stock-based compensation
Percent of performance metrics achieved							100.00%
Vested (in shares)							25,834
2017 Performance Share Units | March 31, 2018 | PSUs
Stock-based compensation
Vested (in shares)							7,750
Percent of achievement over target							30.00%
2016 Performance Share Units | PSUs
Stock-based compensation
Granted (in shares)				131,250
Number of executives granted shares | executive				6
Percent of performance metrics achieved							130.00%
Vested (in shares)							16,250
Number of executives shares were released to | executive							2
2016 Performance Share Units | April 1, 2016 | PSUs
Stock-based compensation
Percent of performance metrics achieved							100.00%
Vested (in shares)							12,500
2016 Performance Share Units | April 1, 2018 | PSUs
Stock-based compensation
Vested (in shares)	3,750
Percent of achievement over target	30.00%
2015 Performance Share Units | PSUs
Stock-based compensation
Granted (in shares)					131,250
Number of executives granted shares | executive					8
Percent of performance metrics achieved							112.00%
Vested (in shares)							7,934
Number of executives shares were released to | executive							2
2015 Performance Share Units | March 16, 2015 | PSUs
Stock-based compensation
Percent of performance metrics achieved							100.00%
Vested (in shares)							7,084
2015 Performance Share Units | March 16, 2018 | PSUs
Stock-based compensation
Vested (in shares)		850
Percent of achievement over target		12.00%

STOCK-BASED COMPENSATION PLAN_4

STOCK-BASED COMPENSATION PLANS - Schedules (Details) - USD ($)	Mar. 31, 2017	Apr. 01, 2016	Mar. 16, 2015	May 31, 2018	Mar. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Weighted average grant-date fair value
Total fair value of restricted stock awards, restricted stock units and performance-based stock units on date vested								$ 5,462,000	$ 6,225,000
Stock-based compensation expense (reversal)						$ 2,516,000	$ 3,887,000	7,421,000	11,387,000
Tax benefit from stock based compensation expense								0	0
Fair value of the assumed awards attributable to future stock-based compensation expense						12,600,000		$ 12,600,000
Expected period for unrecognized expense								2 years
Product cost of revenue
Weighted average grant-date fair value
Stock-based compensation expense (reversal)						21,000	75,000	$ 91,000	261,000
Service cost of revenue
Weighted average grant-date fair value
Stock-based compensation expense (reversal)						65,000	199,000	264,000	777,000
Research and development
Weighted average grant-date fair value
Stock-based compensation expense (reversal)						313,000	1,095,000	1,364,000	3,650,000
Sales and marketing
Weighted average grant-date fair value
Stock-based compensation expense (reversal)						585,000	871,000	1,944,000	1,690,000
General and administrative
Weighted average grant-date fair value
Stock-based compensation expense (reversal)						$ 1,532,000	$ 1,647,000	$ 3,758,000	$ 5,009,000
PSUs
Change in unvested restricted stock awards
Unvested balance at the beginning of the period (in shares)								60,834
Granted (in shares)				195,000				207,350
Vested (in shares)								(57,768)
Forfeited (in shares)								0
Unvested balance at the end of the period (in shares)						210,416		210,416
Weighted average grant-date fair value
Unvested balance at the end of the period (in dollars per share)								$ 9.65
Granted (in dollars per share)								5.78
Vested (in dollars per share)								9.90
Forfeited (in dollars per share)								0
Unvested balance at end of the period (in dollars per share)						$ 5.77		$ 5.77
Total fair value of restricted stock awards, restricted stock units and performance-based stock units on date vested								$ 600,000
Stock-based compensation expense (reversal)						$ 154,000		$ 194,000
Stock Options
Number of shares
Outstanding at the beginning of the period (in shares)								435,187
Granted (in shares)								0
Edgewater outstanding options converted to Ribbon options (in shares)								312,452
Exercised (in shares)								(8,653)
Forfeited (in shares)								0
Expired (in shares)								(109,486)
Outstanding at the end of the period (in shares)						629,500		629,500
Vested or expected to vest at the end of the period (in shares)						589,719		589,719
Exercisable at the end of the period (in shares)						344,653		344,653
Weighted average exercise price
Outstanding at the beginning of the period (in dollars per share)								$ 14.71
Granted (in dollars per share)								0
Edgewater outstanding options converted to Ribbon options (in dollars per share)								1.97
Exercised (in dollars per share)								4.97
Forfeited (in dollars per share)								0
Expired (in dollars per share)								14.40
Outstanding at the end of the period (in dollars per share)						$ 8.57		8.57
Vested or expected to vest at the end of the period (in dollars per share)						9.01		9.01
Exercisable at the end of the period (in dollars per share)						$ 14.01		$ 14.01
Weighted average remaining contractual life (in years)
Outstanding at the end of the period								6 years 1 month 12 days
Vested or expected to vest at the end of the period								5 years 11 months 17 days
Exercisable at the end of the period								4 years 4 months 28 days
Aggregate intrinsic value (in dollars)
Outstanding at the end of the period (in dollars)						$ 1,538,000		$ 1,538,000
Vested or expected to vest at the end of the period (in dollars)						1,352,000		1,352,000
Exercisable at the end of the period (in dollars)						161,000		161,000
Total intrinsic values of stock options exercised (in dollars)						13,000		21,000
Cash received from the exercise of stock options (in dollars)						$ 33,000		$ 43,000
RSAs
Change in unvested restricted stock awards
Unvested balance at the beginning of the period (in shares)								1,696,582
Granted (in shares)								1,123,956
Vested (in shares)								(752,085)
Forfeited (in shares)								(270,075)
Unvested balance at the end of the period (in shares)						1,798,378		1,798,378
Weighted average grant-date fair value
Unvested balance at the end of the period (in dollars per share)								$ 7.68
Granted (in dollars per share)								6.90
Vested (in dollars per share)								8.46
Forfeited (in dollars per share)								7.36
Unvested balance at end of the period (in dollars per share)						$ 6.91		$ 6.91
Total fair value of restricted stock awards, restricted stock units and performance-based stock units on date vested								$ 6,500,000
RSUs
Change in unvested restricted stock awards
Unvested balance at the beginning of the period (in shares)								17,932
Granted (in shares)								899,500
Vested (in shares)								(17,110)
Forfeited (in shares)								(41,822)
Unvested balance at the end of the period (in shares)						858,500		858,500
Weighted average grant-date fair value
Unvested balance at the end of the period (in dollars per share)								$ 6.99
Granted (in dollars per share)								6.27
Vested (in dollars per share)								7
Forfeited (in dollars per share)								6.72
Unvested balance at end of the period (in dollars per share)						$ 6.25		$ 6.25
Employee Stock
Weighted average grant-date fair value
Offering period (in months)								6 months
Purchase price of common stock (percentage)								85.00%
Maximum number of shares purchasable per employee								500
2017 Performance Share Units | PSUs
Change in unvested restricted stock awards
Granted (in shares)	165,000
Vested (in shares)					(33,584)
2016 Performance Share Units | PSUs
Change in unvested restricted stock awards
Granted (in shares)		131,250
Vested (in shares)					(16,250)
2015 Performance Share Units | PSUs
Change in unvested restricted stock awards
Granted (in shares)			131,250
Vested (in shares)					(7,934)

MAJOR CUSTOMERS - (Details)

MAJOR CUSTOMERS - (Details) - Customer	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Revenue | Verizon Communications Inc.
MAJOR CUSTOMERS
Concentration risk, percentage	13.00%	16.00%	15.00%	15.00%
Revenue | AT&T Inc.
MAJOR CUSTOMERS
Concentration risk, percentage	12.00%	11.00%	10.00%	10.00%
Accounts receivable balance
MAJOR CUSTOMERS
Concentration risk, percentage			25.00%		31.00%

RELATED PARTY TRANSACTIONS (Det

RELATED PARTY TRANSACTIONS (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017	Oct. 27, 2017
Related Party Transaction [Line Items]
Long-term debt, related party	$ 23,500,000	$ 22,500,000
Accrued expenses and other	74,610,000	$ 76,380,000
GENBAND
Related Party Transaction [Line Items]
Promissory note issued to GENBAND equity holders			$ 22,500,000
Long-term debt, related party	1,000,000
Accrued expenses and other	$ 400,000
Minimum | GENBAND
Related Party Transaction [Line Items]
Promissory note interest rate	7.50%
Maximum | GENBAND
Related Party Transaction [Line Items]
Promissory note interest rate	10.00%

INCOME TAXES - (Details)

INCOME TAXES - (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Tax Act impact on tax benefit		$ 4.8
Decrease in net deferred tax asset as a result of Tax Act	$ 0.2

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) $ in Millions	Apr. 10, 2018USD ($)	Mar. 22, 2018USD ($)	Mar. 08, 2018case	Jan. 15, 2016USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2018case
Loss Contingencies [Line Items]
Ongoing lawsuits | case						5
Royalty damages awarded				$ 8.2
Damages awarded from other party		$ 8.9
Awarded judgment interests and costs	$ 0.4
Number of lawsuits | case			2
Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Civil penalty					$ 1.9