Ribbon Communications (RBBN) 10-Q 30 Apr 21 2021 Q1 Quarterly report Financial data

Cover

Cover - shares	3 Months Ended
	Mar. 31, 2021	Apr. 23, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-38267
Entity Registrant Name	RIBBON COMMUNICATIONS INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	82-1669692
Entity Address, Address Line One	6500 Chase Oaks Boulevard, Suite 100,
Entity Address, City or Town	Plano
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	75023
City Area Code	978
Local Phone Number	614-8100
Title of 12(b) Security	Common Stock, par value $0.0001
Trading Symbol	RBBN
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		147,367,469
Entity Central Index Key	0001708055
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 106,228	$ 128,428
Restricted cash		7,269
Accounts receivable, net	209,163	237,738
Inventory	44,854	45,750
Other current assets	34,018	28,461
Total current assets	396,922	447,646
Property and equipment, net	49,237	48,888
Intangible assets, net	401,533	417,356
Goodwill	416,892	416,892
Investments	92,742	115,183
Deferred income taxes	10,832	10,651
Operating lease right-of-use assets	62,579	69,757
Other assets	22,047	20,892
Total assets	1,452,784	1,547,265
Current liabilities:
Current portion of term debt	20,058	15,531
Accounts payable	58,549	63,387
Accrued expenses and other	98,185	134,865
Operating lease liabilities	17,627	17,023
Deferred revenue	102,103	96,824
Total current liabilities	296,522	327,630
Long-term debt, net of current	363,888	369,035
Operating lease liabilities, net of current	68,100	72,614
Deferred revenue, net of current	23,054	26,010
Deferred income taxes	17,303	16,842
Other long-term liabilities	41,184	48,281
Total liabilities	810,051	860,412
Commitments and contingencies
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; 147,358,590 shares issued and outstanding at March 31, 2021; 145,425,248 shares issued and outstanding at December 31, 2020	15	15
Additional paid-in capital	1,864,107	1,870,256
Accumulated deficit	(1,223,163)	(1,178,476)
Accumulated other comprehensive income (loss)	1,774	(4,942)
Total stockholders' equity	642,733	686,853
Total liabilities and stockholders' equity	$ 1,452,784	$ 1,547,265

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
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)	147,358,590	145,425,248
Common stock, shares outstanding (in shares)	147,358,590	145,425,248
Investments	$ 92,742	$ 115,183

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue:
Total revenue	$ 192,772	$ 157,982
Cost of revenue:
Total cost of revenue	82,225	67,458
Gross profit	110,547	90,524
Operating expenses:
Research and development	47,410	42,295
Sales and marketing	37,218	30,971
General and administrative	15,553	17,205
Amortization of acquired intangible assets	15,823	14,334
Acquisition-, disposal- and integration-related	1,197	12,384
Restructuring and related	5,950	2,075
Total operating expenses	123,151	119,264
Loss from operations	(12,604)	(28,740)
Interest expense, net	(5,819)	(3,395)
Other expense, net	(25,448)	(844)
Loss before income taxes	(43,871)	(32,979)
Income tax provision	(816)	(191)
Net loss	$ (44,687)	$ (33,170)
Loss per share:
Basic (in dollars per share)	$ (0.31)	$ (0.27)
Diluted (in dollars per share)	$ (0.31)	$ (0.27)
Weighted average shares used to compute loss per share:
Basic (in shares)	145,936	120,992
Diluted (in shares)	145,936	120,992
Product
Revenue:
Total revenue	$ 97,889	$ 75,899
Cost of revenue:
Total cost of revenue	44,445	35,979
Service
Revenue:
Total revenue	94,883	82,083
Cost of revenue:
Total cost of revenue	$ 37,780	$ 31,479

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net loss	$ (44,687)	$ (33,170)
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on interest rate swap	6,669	(9,527)
Foreign currency translation adjustments	47	777
Other comprehensive income (loss), net of tax	6,716	(8,750)
Comprehensive loss, net of tax	$ (37,971)	$ (41,920)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	ECI Telecom Group Ltd.	Anova Data, Inc.	Common stock	Common stockECI Telecom Group Ltd.	Common stockAnova Data, Inc.	Additional paid-in capital	Additional paid-in capitalECI Telecom Group Ltd.	Additional paid-in capitalAnova Data, Inc.	Accumulated deficit	Accumulated other comprehensive income (loss)
Beginning balance (in shares) at Dec. 31, 2019				110,471,995
Beginning balance at Dec. 31, 2019	$ 483,255			$ 11			$ 1,747,784			$ (1,267,067)	$ 2,527
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)				3,014
Exercise of stock options	5						5
Vesting of restricted stock awards and units (in shares)				1,016,982
Vesting of performance-based stock awards (in shares)				315,866
Shares of restricted stock returned to the Company under net share settlements to satisfy tax withholding obligations (in shares)				(273,104)
Shares of restricted stock returned to the Company under net share settlements to satisfy tax withholding obligations	(792)						(792)
Shares issued as consideration in connection with acquisition (in shares)					32,500,000	316,551
Shares issued as consideration in connection with acquisition		$ 108,550	$ 1,630		$ 3			$ 108,547	$ 1,630
Stock-based compensation expense	2,976						2,976
Other comprehensive loss	(8,750)										(8,750)
Net loss	(33,170)									(33,170)
Ending balance (in shares) at Mar. 31, 2020				144,351,304
Ending balance at Mar. 31, 2020	$ 553,704			$ 14			1,860,150			(1,300,237)	(6,223)
Beginning balance (in shares) at Dec. 31, 2020	145,425,248			145,425,248
Beginning balance at Dec. 31, 2020	$ 686,853			$ 15			1,870,256			(1,178,476)	(4,942)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)	13,389			13,389
Exercise of stock options	$ 24						24
Vesting of restricted stock awards and units (in shares)				1,662,628
Vesting of performance-based stock awards (in shares)				1,525,681
Shares of restricted stock returned to the Company under net share settlements to satisfy tax withholding obligations (in shares)				(1,268,356)
Shares of restricted stock returned to the Company under net share settlements to satisfy tax withholding obligations	(11,233)						(11,233)
Stock-based compensation expense	5,060						5,060
Other comprehensive loss	6,716										6,716
Net loss	$ (44,687)									(44,687)
Ending balance (in shares) at Mar. 31, 2021	147,358,590			147,358,590
Ending balance at Mar. 31, 2021	$ 642,733			$ 15			$ 1,864,107			$ (1,223,163)	$ 1,774

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Cash flows from operating activities:
Net loss	$ (44,687)	$ (33,170)
Adjustments to reconcile net loss to cash flows (used in) provided by operating activities:
Depreciation and amortization of property and equipment	4,226	3,474
Amortization of intangible assets	15,823	14,334
Amortization of debt issuance costs	3,141	1,854
Stock-based compensation	5,060	2,976
Deferred income taxes	293	(99)
Decrease in fair value of investments	22,441	0
Reduction in deferred purchase consideration	0	(69)
Foreign currency exchange losses	1,716	854
Changes in operating assets and liabilities:
Accounts receivable	28,083	46,156
Inventory	(330)	4,468
Other operating assets	979	(478)
Accounts payable	(3,800)	(27,029)
Accrued expenses and other long-term liabilities	(41,480)	22,310
Deferred revenue	2,323	4,351
Net cash (used in) provided by operating activities	(6,212)	39,932
Cash flows from investing activities:
Purchases of property and equipment	(5,357)	(6,017)
Business acquisitions, net of cash acquired	0	(346,852)
Proceeds from the sale of fixed assets	0	43,500
Net cash used in investing activities	(5,357)	(309,369)
Cash flows from financing activities:
Principal payments on revolving line of credit	0	(8,000)
Proceeds from issuance of term debt	74,625	403,500
Principal payments of term debt	(77,132)	(48,750)
Principal payments of finance leases	(272)	(338)
Payment of debt issuance costs	(789)	(10,573)
Proceeds from the exercise of stock options	24	5
Payment of tax withholding obligations related to net share settlements of restricted stock awards	(11,233)	(792)
Net cash (used in) provided by financing activities	(14,777)	335,052
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(464)	(190)
Net (decrease) increase in cash, cash equivalents and restricted cash	(26,810)	65,425
Cash and cash equivalents, beginning of year	135,697	44,643	$ 44,643
Cash, cash equivalents and restricted cash, end of period	108,887	110,068	$ 135,697
Supplemental disclosure of cash flow information:
Interest paid	4,317	688
Income taxes paid	7,656	1,259
Income tax refunds received	766	0
Supplemental disclosure of non-cash investing activities:
Capital expenditures incurred, but not yet paid	3,059	6,300
Acquisition purchase consideration - assumed equity awards	0	110,180
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	$ 28,182	$ 3,182

BASIS OF PRESENTATION

BASIS OF PRESENTATION	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
BASIS OF PRESENTATION	BASIS OF PRESENTATION Business Ribbon Communications Inc. ("Ribbon" or the "Company") is a leading global provider of communications technology to service providers and enterprises. The Company provides a broad range of software and high-performance hardware products, solutions and services that enable the secure delivery of data and voice communications for residential consumers and for small, medium, and large enterprises and industry verticals such as finance, education, government, utilities and transportation. Ribbon's mission is to create a recognized global technology leader providing cloud-centric solutions that enable the secure exchange of information, with unparalleled scale, performance and elasticity. The Company is headquartered in Plano, Texas, and has a global presence with research and development, or sales and support locations in over thirty-five countries around the world. 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 December 1, 2020 (the "Kandy Sale Date"), American Virtual Cloud Technologies, Inc. ("AVCT") completed the purchase of the Company's cloud-based enterprise service business (the "Kandy Communications Business") and accordingly, the revenue and expenses of the Kandy Communications Business are excluded from the Company's condensed consolidated financial statements for the three months ended March 31, 2021. On March 3, 2020 (the "ECI Acquisition Date"), a subsidiary of the Company merged with ECI Telecom Group Ltd ("ECI") (the "ECI Acquisition"). The financial results of ECI are included in the Company's condensed consolidated financial statements for the period subsequent to the ECI 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, 2020 (the "Annual Report"), which was filed with the SEC on February 26, 2021. Operating Segments The Company's chief operating decision maker (the "CODM") is its President and Chief Executive Officer. Effective in the fourth quarter of 2020 and in connection with the ECI Acquisition, the CODM began to assess the Company's performance based on the performance of two separate organizations within Ribbon: the Cloud and Edge segment ("Cloud and Edge") and the IP Optical Networks segment ("IP Optical Networks"). Financial information for the IP Optical Networks segment included in the Company's financial results for the three months ended March 31, 2020 is for the period subsequent to the ECI Acquisition Date through March 31, 2020. Reclassifications In the fourth quarter of 2020, the Company reclassified amounts recorded for amortization of acquired intangible assets in prior presentations from Cost of revenue - product and Sales and marketing to a separate line included in operating expenses in the condensed consolidated statements of operations, as management believes this presentation enhances the comparability of the Company's financial statements with industry peers. These reclassifications also did not impact the condensed consolidated balance sheets or statements of cash flows for any historical periods. The Company did not reclassify depreciation of property and equipment related to production activities from cost of revenue to other accounts. These reclassifications for the three months ended March 31, 2020 were as follows (in thousands): Three months ended March 31, 2020 Prior presentation Amounts reclassified Revised presentation Product revenue $ 75,899 $ — $ 75,899 Service revenue 82,083 — 82,083 Total revenue 157,982 — 157,982 Cost of revenue - product 44,933 (8,954) 35,979 Cost of revenue - service 31,479 — 31,479 Total cost of revenue 76,412 (8,954) 67,458 Total gross profit 81,570 8,954 90,524 Research and development 42,295 — 42,295 Sales and marketing 36,351 (5,380) 30,971 General and administrative 17,205 — 17,205 Amortization of acquired intangible assets — 14,334 14,334 Acquisition-, disposal- and integration-related 12,384 — 12,384 Restructuring and related 2,075 — 2,075 Total operating expenses 110,310 8,954 119,264 Operating loss $ (28,740) $ — $ (28,740) Certain reclassifications, not affecting previously reported net loss, have been made to the previously issued financial statements to conform to the current period presentation. Significant Accounting Policies The Company's significant accounting policies are disclosed in Note 2 to the Consolidated Financial Statements included in the Annual Report. There were no material changes to the significant accounting policies during the three months ended March 31, 2021. 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 Ribbon 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 revenue and expenses during the reporting periods. Significant estimates and judgments relied upon in preparing these condensed consolidated financial statements include accounting for business combinations, revenue recognition for multiple element arrangements, inventory valuations, assumptions used to determine the fair value of stock-based compensation, intangible asset 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. Restricted Cash The Company classifies as restricted cash all cash pledged as collateral to secure long-term obligations and all cash whose use is otherwise limited by contractual provisions. At March 31, 2021, the Company had $2.7 million of restricted cash, representing restricted short-term bank deposits pledged to secure certain performance and financial bonds as security for the Company's obligations under tenders, contracts and to one of its main subcontractors. At December 31, 2020, the Company had $7.3 million of restricted cash, comprised of $4.6 million restricted in connection with a tax payment on certain fixed assets formerly held by ECI that were sold in connection with the ECI Acquisition, and $2.7 million of restricted short-term bank deposits pledged to secure certain performance and financial bonds as security for the Company's obligations under tenders, contracts and to one of its main subcontractors. Transfers of Financial Assets The Company maintains customer receivables factoring agreements with a number of financial institutions primarily for IP Optical Networks sales outside of the United States. Under the terms of these agreements, the Company may transfer receivables to the financial institutions, on a non-recourse basis, provided that the financial institutions approve the receivables in advance. The Company maintains credit insurance policies from major insurance providers or obtains letters of credit from the customers for a majority of its factored trade receivables. The Company accounts for the factoring of its financial assets as a sale of the assets and records the factoring fees, when incurred, as a component of interest expense in the condensed consolidated statements of operations, and the proceeds from the sales of receivables are included in cash from operating activities in the condensed consolidated statements of cash flows. During the three months ended March 31, 2021, the Company received $31.1 million of cash from the sale of certain accounts receivable and recorded $0.2 million of interest expense in connection with these transactions. During the three months ended March 31, 2020, the Company received $15.1 million of cash from the sale of certain accounts receivable and recorded $0.1 million of interest expense in connection with these transactions. Fair Value of Financial Instruments and Fair Value Hierarchy The carrying amounts of the Company's financial instruments approximate their fair values and include cash equivalents, accounts receivable, borrowings under a revolving credit facility, accounts payable and long-term debt. 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. Recent Accounting Pronouncements The Financial Accounting Standards Board ("FASB") issued the following accounting pronouncement which became effective for the Company in 2021, and which did not have a material impact on its condensed consolidated financial statements: In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes ("ASU 2019-12"), which modifies ASC 740 to simplify the accounting for income taxes. ASU 2019-12 addresses the accounting for hybrid tax regimes, tax basis step-up in goodwill obtained in a transaction that is not a business combination, separate financial statements of legal entities not subject to tax, intraperiod tax allocation exception to incremental approach, ownership changes in investments - changes from a subsidiary to an equity method investment, ownership changes in investments - changes from an equity method investment to a subsidiary, interim period accounting for enacted changes in tax law and year-to-date loss limitation in interim period tax accounting. The FASB issued the following accounting pronouncement, which the Company does not believe will have a material impact on its condensed consolidated financial statements upon adoption: In January 2021, the FASB issued ASU 2021-01, Reference Rate Reform (Topic 848): Scope ("ASU 2021-01"), which refines the scope of Accounting Standards Codification 848, Reference Rate Reform ("ASC 848") and clarifies some of its guidance as part of the FASB's monitoring of global reference rate reform activities. ASU 2021-01 permits entities to elect certain optional expedients and exceptions when accounting for derivative contracts and certain hedging relationships affected by changes in the interest rates used for discounting cash flows, for computing variation margin settlements, and for calculating price alignment interest in connection with reference rate reform activities under way in global financial markets (the "discounting transition"). ASU 2021-01 is effective for the Company prospectively in any period through December 31, 2022 that a modification is made to the terms of the derivatives affected by the discounting transition.

ACQUISITION OF ECI

ACQUISITION OF ECI	3 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
ACQUISITION OF ECI	ACQUISITION OF ECI On the ECI Acquisition Date, Ribbon completed its previously announced merger transaction with ECI in accordance with the terms of the Agreement and Plan of Merger, dated as of November 14, 2019, by and among Ribbon, ECI, an indirect wholly-owned subsidiary of Ribbon ("Merger Sub"), Ribbon Communications Israel Ltd. and ECI Holding (Hungary) kft, pursuant to which Merger Sub merged with and into ECI, with ECI surviving such merger as a wholly-owned subsidiary of Ribbon. Prior to the ECI Acquisition Date, ECI was a privately-held global provider of end-to-end packet-optical transport and software-defined networking ("SDN") and network function virtualization ("NFV") solutions for service providers, enterprises and data center operators. As consideration for the ECI Acquisition, Ribbon issued the ECI shareholders and certain others 32.5 million shares of Ribbon common stock with a fair value of $108.6 million (the "Stock Consideration") and paid $322.5 million of cash (the "Cash Consideration"), comprised of $183.3 million to repay ECI's outstanding debt, including both principal and interest, and $139.2 million paid to ECI's selling shareholders. In addition, ECI shareholders received $33.4 million from the sale of certain of ECI's real estate assets. Cash Consideration was financed through cash on hand and committed debt financing consisting of a new $400 million term loan facility and new $100 million revolving credit facility, which was undrawn at the ECI Acquisition Date. The ECI Acquisition has been accounted for as a business combination and the financial results of ECI have been included in the Company's condensed consolidated financial statements for the periods subsequent to the ECI Acquisition. The Company's financial results for the three months ended March 31, 2020 include $30.0 million of revenue and $3.3 million of net loss attributable to ECI. The Company finalized the valuation of acquired assets, identifiable intangible assets and certain assumed liabilities in the fourth quarter of 2020. A summary of the allocation of the purchase consideration for ECI is as follows (in thousands): Fair value of consideration transferred: Cash consideration: Repayment of ECI outstanding debt obligations $ 183,266 Cash paid to selling shareholders 139,244 Payment to selling shareholders from sale of ECI real estate assets 33,400 Less cash and restricted cash acquired (9,058) Net cash consideration 346,852 Fair value of Ribbon stock issued 108,550 Fair value of total consideration $ 455,402 Fair value of assets acquired and liabilities assumed: Current assets, net of cash and restricted cash acquired $ 120,203 Property and equipment 54,913 Intangible assets: In-process research and development 34,000 Developed technology 111,900 Customer relationships 116,000 Trade names 3,000 Goodwill 191,996 Other noncurrent assets 37,528 Deferred revenue (4,369) Other current liabilities (146,618) Deferred revenue, net of current (3,726) Deferred tax liability (13,308) Other long-term liabilities (46,117) $ 455,402 The valuation of the acquired intangible assets is inherently subjective and relies on significant unobservable inputs. The Company used an income approach to value the acquired in-process research and development, 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 arising from the ECI Acquisition in relation to the expected cash flows from the individual intangible assets over their respective useful lives, which have a weighted average life of 12.38 years (see Note 6). Goodwill results from assets that are not separately identifiable as part of the transaction and is not deductible for tax purposes. Pro Forma Results The following unaudited pro forma information presents the condensed combined results of operations of Ribbon and ECI for the three months ended March 31, 2020 as if the ECI Acquisition had been completed on January 1, 2019, with adjustments to give effect to pro forma events that are directly attributable to the ECI Acquisition. These pro forma adjustments include an increase in research and development expense related to the conformance of ECI's cost capitalization policy to Ribbon's, additional amortization expense for the acquired identifiable intangible assets, a decrease in historical ECI interest expense reflecting the extinguishment of certain of ECI's debt as a result of the ECI Acquisition, and an increase in interest expense reflecting the new debt entered into by the Company in connection with the ECI Acquisition. Pro forma adjustments also include the elimination of acquisition-, disposal- and integration-related expenses directly attributable to the acquisition from the three months ended March 31, 2020 and inclusion of such costs in the same prior year period. 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 Ribbon and ECI. 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 ECI Acquisition occurred at January 1, 2019, nor are they intended to represent or be indicative of future results of operations (in thousands, except per share amounts): Revenue $ 183,189 Net loss $ (39,129) Loss per share $ (0.25) Acquisition-, Disposal- and Integration-Related Expenses Acquisition-related expenses include those expenses related to acquisitions that would otherwise not have been incurred by the Company, including professional and services fees, such as legal, audit, consulting, paying agent and other fees. Disposal-related expenses are professional and services fees related to disposals of subsidiaries or portions of the business. Integration-related expenses represent incremental costs related to combining the Company and its business acquisitions, such as third-party consulting and other third-party services related to merging the previously separate companies' systems and processes. The disposal-related expenses in the three months ended March 31, 2021 relate to the Kandy Sale (as defined below). The acquisition-related expenses in the three months ended March 31, 2020 primarily relate to the ECI Acquisition. The Company's acquisition-, disposal- and integration-related expenses for the three months ended March 31, 2021 and 2020 were as follows (in thousands): Three months ended March 31, March 31, Professional and services fees (acquisition-related) $ — $ 12,374 Professional and services fees (disposal-related) 241 — Integration-related expenses 956 10 $ 1,197 $ 12,384

SALE OF KANDY COMMUNICATIONS BU

SALE OF KANDY COMMUNICATIONS BUSINESS	3 Months Ended
	Mar. 31, 2021
Discontinued Operations and Disposal Groups [Abstract]
SALE OF KANDY COMMUNICATIONS BUSINESS	SALE OF KANDY COMMUNICATIONS BUSINESS On August 5, 2020, the Company announced that it had entered into a definitive agreement (as amended, the "Kandy Purchase Agreement") with AVCT to sell the Kandy Communications Business. Under the Kandy Purchase Agreement, AVCT agreed to purchase the assets and assume certain liabilities associated with the Kandy Communications Business, as well as all of the outstanding interests in Kandy Communications LLC, a subsidiary of the Company (the "Kandy Sale"). On December 1, 2020, the Company completed the Kandy Sale. The assets acquired and liabilities assumed by AVCT in connection with the Kandy Sale were primarily comprised of accounts receivable, property and equipment, trade accounts payable and employee-related accruals. As sale consideration, AVCT paid Ribbon $45.0 million, subject to certain adjustments, in the form of units of AVCT's securities (the "AVCT Units"), with each AVCT Unit consisting of: $1,000 in principal amount of AVCT’s Series A-1 convertible debentures (the “Debentures”); and (ii) one warrant to purchase 100 shares of AVCT common stock, $0.0001 par value (the “Warrants”), as consideration for the Kandy Sale. The Company received 43,778 AVCT Units as sale consideration on the Kandy Sale Date. The Debentures bear interest at a rate of 10% per annum, which will be added to the principal amount of the Debentures, except upon maturity, in which case accrued and unpaid interest is payable in cash. The entire principal of each Debenture, together with accrued and unpaid interest thereon, is due and payable on the earlier of the May 1, 2023 maturity date or the occurrence of a Change in Control as defined in the Kandy Purchase Agreement. Each Debenture is convertible, in whole or in part, at any time at the Company's option into that number of shares of AVCT common stock, calculated by dividing the principal amount being converted, together with all accrued and unpaid interest thereon, by the applicable conversion price, initially $3.45. The Debentures are subject to mandatory redemption if the AVCT stock price is at or above $6.00 per share for 40 trading days in any 60 consecutive trading day period, subject to the satisfaction of certain other conditions. The conversion price is subject to customary adjustments including, but not limited to, stock dividends, stock splits and reclassifications. At the Company's option, up to $5.0 million of the Debentures may be redeemed by AVCT at par in the event AVCT raises at least $50.0 million in its offering of AVCT Units. As of February 19, 2021, the stock price had traded above $6.00 for 40 days within a 60 consecutive trading day period, and accordingly, the Debentures will be converted to shares of AVCT common stock upon the completion of customary regulatory filings by AVCT. The Warrants are independent of the Debentures and entitle the Company to purchase 4,377,800 shares of AVCT common stock at an exercise price of $0.01 per share. The Warrants expire on December 1, 2025, and were immediately exercisable on the Kandy Sale Date. The Company had not redeemed any of the Debentures or exercised any of the Warrants as of March 31, 2021. The Company is also subject to a lock-up provision which limits the Company's ability to sell any shares of AVCT common stock underlying the Debentures and the Warrants prior to June 1, 2021, except in certain transactions. The Company determined that the AVCT Units had a fair value of $84.9 million at the Kandy Sale Date, comprised of the Debentures with a fair value of $66.3 million and the Warrants with a fair value of $18.6 million. The value of the net assets sold to AVCT totaled $1.3 million, resulting in a gain on the sale of $83.6 million. The Company calculated the fair value of the Debentures using a Lattice-based valuation approach, which utilizes a binomial tree to model the different paths the price of AVCT's common stock might take over the Debentures' life by using assumptions regarding the stock price volatility and risk-free interest rate. These results are then used to calculate the fair value of the Debentures at each measurement date. The Company uses the Black-Scholes valuation model for estimating the fair value of the Warrants at each measurement date. The fair value of the Warrants is affected by AVCT's stock price as well as valuation assumptions, including the volatility of AVCT's stock price, expected term of the option, risk-free interest rate and expected dividends. Both the Lattice and Black-Scholes valuation models are based on available market data, giving consideration to all of the rights and obligations of each instrument and precluding the use of "blockage" discounts or premiums in determining the fair value of a large block of financial instruments. The Company is calculating the fair value of the Debentures and Warrants at each quarter-end and recording any adjustments to the fair values in Other expense, net. At March 31, 2021 and December 31, 2020, the aggregate fair value of the Debentures and Warrants was $92.7 million and $115.2 million, respectively. The Company recorded the loss of $23.9 million arising from the decrease in the fair value of the Debentures and Warrants from January 1, 2021 to March 31, 2021 in Other expense, net, in its condensed consolidated statement of operations for the three months ended March 31, 2021. The loss was partially offset by $1.5 million of interest which was added to the principal of the Debentures. The interest is included in Interest (expense) income, net, in the condensed consolidated statement of operations for the three months ended March 31, 2021. The fair values of the Debentures and Warrants are reported as Investments in the Company's condensed consolidated balance sheets at March 31, 2021 and December 31, 2020 and are classified as Level 2 fair value measurements within the fair value hierarchy (see Note 1).

EARNINGS (LOSS) PER SHARE

EARNINGS (LOSS) PER SHARE	3 Months Ended
	Mar. 31, 2021
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 earnings (loss) per share were as follows (in thousands): Three months ended March 31, March 31, Weighted average shares outstanding - basic 145,936 120,992 Potential dilutive common shares — — Weighted average shares outstanding - diluted 145,936 120,992 Options to purchase the Company's common stock and unvested shares of restricted and performance-based stock and stock units aggregating 12.8 million shares and 11.7 million shares have not been included in the computation of diluted loss per share for the three months ended March 31, 2021 and 2020, respectively, because their effect would have been antidilutive.

INVENTORY

INVENTORY	3 Months Ended
	Mar. 31, 2021
Inventory Disclosure [Abstract]
INVENTORY	INVENTORY Inventory at March 31, 2021 and December 31, 2020 consisted of the following (in thousands): March 31, December 31, On-hand final assemblies and finished goods inventories $ 48,529 $ 46,921 Deferred cost of goods sold 1,609 1,165 50,138 48,086 Less noncurrent portion (included in other assets) (5,284) (2,336) Current portion $ 44,854 $ 45,750

INTANGIBLE ASSETS AND GOODWILL

INTANGIBLE ASSETS AND GOODWILL	3 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
INTANGIBLE ASSETS AND GOODWILL	INTANGIBLE ASSETS AND GOODWILL The Company's intangible assets at March 31, 2021 and December 31, 2020 consisted of the following (in thousands): March 31, 2021 Weighted average amortization period Cost Accumulated Net In-process research and development * $ 34,000 $ — $ 34,000 Developed technology 7.93 306,380 153,111 153,269 Customer relationships 11.86 268,140 56,049 212,091 Trade names 3.88 5,000 2,827 2,173 Internal use software 3.00 730 730 — 9.17 $ 614,250 $ 212,717 $ 401,533 December 31, 2020 Weighted average amortization period Cost Accumulated Net In-process research and development * $ 34,000 $ — $ 34,000 Developed technology 7.93 306,380 143,050 163,330 Customer relationships 11.86 268,140 50,627 217,513 Trade names 3.88 5,000 2,487 2,513 Internal use software 3.00 730 730 — 9.17 $ 614,250 $ 196,894 $ 417,356 * 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. Estimated future amortization expense for the Company's intangible assets at March 31, 2021 was as follows (in thousands): Years ending December 31, Remainder of 2021 $ 50,803 2022 60,104 2023 52,256 2024 44,048 2025 37,027 2026 33,200 Thereafter 124,095 $ 401,533 There were no changes to the carrying value of the Company's goodwill in the three months ended March 31, 2021. The changes in the carrying value of the Company's goodwill in the three months ended March 31, 2020 were as follows (in thousands): Cloud and Edge IP Optical Networks Total Balance at January 1, 2020* $ 224,896 $ — $ 224,896 Acquisition of ECI — 189,493 189,493 Balance at March 31, 2020 $ 224,896 $ 189,493 $ 414,389 (1) Balance is presented net of accumulated impairment losses of $167.4 million for the Cloud and Edge segment. The components of goodwill at March 31, 2021 and 2020 were as follows (in thousands): Cloud and Edge IP Optical Networks Total Balance at March 31, 2021 Goodwill $ 392,302 $ 191,996 $ 584,298 Accumulated impairment losses (167,406) — (167,406) $ 224,896 $ 191,996 $ 416,892 Balance at March 31, 2020 Goodwill $ 392,302 $ 189,493 $ 581,795 Accumulated impairment losses (167,406) — (167,406) $ 224,896 $ 189,493 $ 414,389

ACCRUED EXPENSES AND OTHER

ACCRUED EXPENSES AND OTHER	3 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
ACCRUED EXPENSES AND OTHER	ACCRUED EXPENSES AND OTHER Accrued expenses at March 31, 2021 and December 31, 2020 consisted of the following (in thousands): March 31, December 31, Employee compensation and related costs $ 41,128 $ 66,039 Other 57,057 68,826 $ 98,185 $ 134,865

WARRANTY ACCRUALS

WARRANTY ACCRUALS	3 Months Ended
	Mar. 31, 2021
Guarantees and Product Warranties [Abstract]
WARRANTY ACCRUALS	WARRANTY ACCRUALS The changes in the Company's accrual balance in the three months ended March 31, 2021 were as follows (in thousands): Balance at January 1, 2021 $ 14,855 Current period provisions 478 Settlements (1,456) Balance at March 31, 2021 $ 13,877 Of the amounts recorded at March 31, 2021 and December 31, 2020, $5.7 million and $6.5 million, respectively, were current and included as components of Accrued expenses and other, and $8.2 million and $8.4 million, respectively, were long-term and included as components of Other long-term liabilities in the Company's condensed consolidated balance sheets.

RESTRUCTURING AND FACILITIES CO

RESTRUCTURING AND FACILITIES CONSOLIDATION INITIATIVES	3 Months Ended
	Mar. 31, 2021
Restructuring and Related Activities [Abstract]
RESTRUCTURING AND FACILITIES CONSOLIDATION INITIATIVES	RESTRUCTURING AND FACILITIES CONSOLIDATION INITIATIVES The Company recorded restructuring and related expense aggregating $6.0 million and $2.1 million in the three months ended March 31, 2021 and 2020, respectively. Restructuring and related expense includes both restructuring expense for severance and related costs and facilities-related costs, primarily comprised estimated future variable lease costs for vacated properties with no intent or ability of sublease, and accelerated rent amortization expense. For restructuring events that involve lease assets and liabilities, the Company applies lease reassessment and modification guidance and evaluates the right-of-use assets for potential impairment. If the Company plans to exit all or distinct portions of a facility and does not have the ability or intent to sublease, the Company will accelerate the amortization of each of those lease components through the vacate date. The accelerated amortization is recorded as a component of Restructuring and related expense in the Company's condensed consolidated statements of operations. Related variable lease expenses will continue to be expensed as incurred through the vacate date, at which time the Company will reassess the liability balance to ensure it appropriately reflects the remaining liability associated with the premises and record a liability for the estimated future variable lease costs. The components of Restructuring and related expense for the three months ended March 31, 2021 and 2020 were as follows (in thousands): Three months ended March 31, March 31, Severance and related costs $ 669 $ 1,771 Variable and other facilities-related costs 1,913 234 Accelerated amortization of lease assets due to cease-use 3,368 70 $ 5,950 $ 2,075 Accelerated Rent Amortization Accelerated rent amortization is recognized from the date that the Company commences the plan to fully or partially vacate a facility, for which there is no intent or ability to enter into a sublease, through the final vacate date. The accelerated rent amortization recorded in connection with the Facilities Initiative reduced the value of the Company's Operating lease right-of-use assets recorded in the Company's condensed consolidated balance sheets at March 31, 2021 and December 31, 2020, respectively. The liability for the total lease payments for each respective facility is included as a component of Operating lease liabilities in the Company's condensed consolidated balance sheets, both current and noncurrent (see Note 17). The Company may incur additional future expense if it is unable to sublease other locations included in its restructuring initiatives. 2020 Restructuring Initiative In 2020, the Company implemented a restructuring plan to eliminate certain positions and redundant facilities, primarily in connection with the ECI Acquisition, to further streamline the Company's global footprint and improve its operations (the "2020 Restructuring Initiative"). In connection with this initiative, the Company expects to eliminate duplicate functions arising from the ECI Acquisition and support its efforts to integrate the two companies. The Company recorded restructuring and related expense of $0.4 million and $1.1 million in connection with the 2020 Restructuring Initiative in the three months ended March 31, 2021 and 2020, respectively. The amount recorded in the three months ended March 31, 2021 was comprised of $0.7 million for severance and related costs for approximately 10 employees and $0.4 million of expense for variable costs related to restructured facilities, offset by a credit of $0.7 million for changes in estimate related to amounts previously recorded. The amount recorded in the three months ended March 31, 2020 was for severance for three former executives of ECI. The Company expects the amounts related to severance will be paid in 2021. The Company expects that it will record additional restructuring and related expense approximating $4 million under the 2020 Restructuring Initiative in the aggregate for severance and planned facility consolidations. A summary of the 2020 Restructuring Initiative accrual activity for severance and related costs for the three months ended March 31, 2021 is as follows (in thousands): Balance at Initiatives Adjustments for changes in estimate Cash Balance at Severance $ 5,237 $ 669 $ — $ (2,116) $ 3,790 Facilities 1,256 367 (670) (916) 37 $ 6,493 $ 1,036 $ (670) $ (3,032) $ 3,827 2019 Restructuring and Facilities Consolidation Initiative In June 2019, the Company implemented a restructuring plan to further streamline the Company's global footprint, improve its operations and enhance its customer delivery (the "2019 Restructuring Initiative"). The 2019 Restructuring Initiative includes facility consolidations, refinement of the Company's research and development activities, and a reduction in workforce. The facility consolidations under the 2019 Restructuring Initiative (the "Facilities Initiative") include a consolidation of the Company's North Texas sites into a single campus, housing engineering, customer training and support, and administrative functions, as well as a reduction or elimination of certain excess and duplicative facilities worldwide. In addition, the Company is substantially consolidating its global software laboratories and server farms into two lower cost North American sites. The Company continues to evaluate its properties included in the Facilities Initiative for accelerated amortization and/or right-of-use asset impairment. The Company expects that the actions under the Facilities Initiative will be completed in 2021. In connection with the 2019 Restructuring Initiative, the Company recorded restructuring and related expense of $5.6 million and $1.0 million in the three months ended March 31, 2021 and 2020, respectively. The amount recorded in the three months ended March 31, 2021 related to facilities, including $3.4 million of accelerated amortization of lease assets. The amount recorded in the three months ended March 31, 2020 was comprised of $0.7 million for severance and related costs for five employees and $0.3 million related to facilities. The Company expects that the entire amount accrued for severance and related costs will be paid in 2021. The Company estimates that it will record nominal, if any, additional restructuring and related expense related to severance and related costs under the 2019 Restructuring Initiative. A summary of the 2019 Restructuring Initiative accrual activity for the three months ended March 31, 2021 is as follows (in thousands): Balance at Initiatives Reclassify accelerated amortization to operating lease liabilities Cash Balance at Severance $ 173 $ — $ — $ (173) $ — Facilities 766 5,584 (3,368) (914) 2,068 $ 939 $ 5,584 $ (3,368) $ (1,087) $ 2,068 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 long-term portions of accrued restructuring relate to facilities and totaled $2.1 million at March 31, 2021 and $0.8 million at December 31, 2020.

DEBT

DEBT	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
DEBT	DEBT 2020 Credit Facility On March 3, 2020, the Company entered into a Senior Secured Credit Facilities Credit Agreement (as amended, the "2020 Credit Facility"), by and among the Company, as a guarantor, Ribbon Communications Operating Company, Inc., as the borrower ("Borrower"), Citizens Bank, N.A. ("Citizens"), as administrative agent, a lender, issuing lender, swingline lender, joint lead arranger and bookrunner, Santander Bank, N.A., as a lender, joint lead arranger and bookrunner, and the other lenders party thereto (each, together with Citizens Bank, N.A. and Santander Bank, N.A., referred to individually as a "Lender", and collectively, the "Lenders"). The proceeds of the 2020 Credit Facility were used, in part, to pay off in full all obligations of the Company under its prior credit facility (the "2019 Credit Facility"). The 2020 Credit Facility provides for $500 million of commitments from the lenders to the Borrower, comprised of $400 million in term loans (the "2020 Term Loan Facility") and a $100 million facility available for revolving loans (the "2020 Revolving Credit Facility"). Under the 2020 Revolving Credit Facility, a $30 million sublimit is available for letters of credit and a $20 million sublimit is available for swingline loans. Under the 2020 Credit Facility, the Company was originally required to make quarterly principal payments aggregating approximately $10 million in the first year, $20 million per year for the following three years, and $30 million in the last year, with the remaining balance due on the maturity date. The 2020 Credit Facility also requires periodic interest payments until maturity. The indebtedness and other obligations under the 2020 Credit Facility are unconditionally guaranteed on a senior secured basis by the Company, Edgewater Networks, Inc., a wholly-owned subsidiary of the Company, and GENBAND Inc., a wholly-owned subsidiary of the Company (together, the "Guarantors"). The facilities under the 2020 Credit Facility are secured by first-priority liens on substantially all of the assets of the Borrower and the Guarantors, including substantially all of the assets of the Company. The 2020 Credit Facility requires compliance with certain financial covenants, including a minimum Consolidated Fixed Charge Coverage Ratio and a maximum Consolidated Net Leverage Ratio (each as defined in the 2020 Credit Facility, and each tested on a quarterly basis). In addition, the 2020 Credit Facility contains various covenants that, among other restrictions, limit the Company’s and its subsidiaries’ ability to incur or assume indebtedness; grant or assume liens; make acquisitions or engage in mergers; sell, transfer, assign or convey assets; repurchase equity and make dividend and certain other restricted payments; make investments; engage in transactions with affiliates; enter into sale and leaseback transactions; enter into burdensome agreements; change the nature of its business; modify their organizational documents; and amend or make prepayments on certain junior debt. The 2020 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 the Company or any of its subsidiaries occurs, all obligations under the 2020 Credit Facility will immediately become due and payable. If any other event of default occurs under the 2020 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 2020 Credit Facility, the lenders can commence foreclosure or other actions against the collateral. On August 18, 2020 (the "First Amendment Effective Date"), the Borrower entered into a First Amendment to the 2020 Credit Facility (the "First Amendment"). Pursuant to an assignment and assumption agreement entered into by Citizens and certain affiliates of Whitehorse Capital on the First Amendment Effective Date (collectively, "HIG Whitehorse"), and consented to by Citizens and the Borrower, $75 million of the 2020 Term Loan Facility, designated as the Term B Loan (the "Term B Loan"), was assigned from Citizens to HIG Whitehorse. The remaining $325 million of the 2020 Term Loan Facility that was not assigned to HIG Whitehorse was deemed the Term A Loan (the "Term A Loan" and, together with the Term B Loan, the "Amended 2020 Term Loan Facility"). The Term A Loan and the 2020 Revolving Credit Facility mature in March 2025. The Term A Loan and 2020 Revolving Credit Facility bear interest at the Borrower's option at either the LIBOR rate plus a margin ranging from 1.50% to 3.50% per year, or the base rate (the highest of the Federal Funds Effective Rate (as defined in the 2020 Credit Facility) plus 0.50%, or the prime rate announced from time to time in The Wall Street Journal) plus a margin ranging from 0.50% to 2.50% per year (the "Applicable Margin"). The Applicable Margin varies depending on the Company's Consolidated Net Leverage Ratio (as defined in the 2020 Credit Agreement). The base rate and the LIBOR rate are each subject to a zero percent floor. The Company was required to make quarterly principal payments on the Term A Loan aggregating approximately $10 million in the first year, $16 million per year in each of the next two years, $20 million in the fourth year and $16 million in the last year, with the final payment approximating $244 million due on the maturity date. The Borrower could prepay all amounts under the Term A Loan and the 2020 Revolving Credit Facility at any time without premium or penalty (other than customary LIBOR breakage costs), subject to certain notice requirements. The Term B Loan was scheduled to mature in March 2026 and bore interest, at the Borrower's option, at either the LIBOR rate plus a margin of 7.50% per year, or the base rate (the highest of the Federal Funds Effective Rate (as defined in the First Amendment) plus 0.50%, or the prime rate announced from time to time in The Wall Street Journal, plus a margin of 6.50% per year. The Term B Loan had a lower rate of amortization than the Term A Loan and was subject to a 1.0% premium if voluntarily repaid in connection with a repricing transaction (as defined in the 2020 Credit Facility) occurring prior to the six month anniversary of the First Amendment Effective Date. The Company was required to make quarterly principal payments totaling approximately $1 million in the first year and $8 million in the aggregate over the next four and a half years, with the final payment approximating $66 million. The First Amendment reduced the Borrower's ability to incur new tranches of term loans, or increases in commitments under the Amended 2020 Term Loan Facility or the 2020 Revolving Credit Facility. Specifically, such indebtedness could be incurred up to an aggregate dollar amount equal to 75% of the Company's Consolidated Adjusted EBITDA (as defined in the 2020 Credit Facility), reduced from 100% prior to the First Amendment, as of the most recently ended fiscal quarter for which financial statements had been delivered to the lenders, plus additional amounts, so long as the Borrower's Consolidated Net Leverage Ratio (as defined in the 2020 Credit Agreement) did not exceed 2.25:1.00, reduced from 2.75:1.00 under the 2020 Credit Agreement. The First Amendment also reduced the amount of Unrestricted Cash (as defined in the 2020 Credit Agreement) used in calculating the Borrower's Consolidated Net Leverage Ratio from $25 million to $10 million. On December 1, 2020, the Borrower entered into a Second Amendment to the 2020 Credit Facility to obtain consent for an equity exchange with AVCT in connection with the Kandy Sale, as well as to amend certain other provisions of the 2020 Credit Facility. At December 31, 2020, the Company had an outstanding Term A Loan balance of $318.5 million at an average interest rate of 3.4%, and an outstanding Term B Loan balance of $74.6 million at an average interest rate of 8.4%. The 2020 Revolving Credit Facility did not have an outstanding balance but had $5.6 million of letters of credit outstanding with an interest rate of 2.5%. On March 3, 2021 (the "Third Amendment Effective Date"), the Company, the Borrower and certain of its subsidiaries entered into a Third Amendment to Credit Agreement (the "Third Amendment"), which further amends the 2020 Credit Facility. The Third Amendment provided for an incremental term loan facility to the Borrower in the original principal amount of $74.6 million, the proceeds of which were used on the Third Amendment Effective Date to consummate an open market purchase of all outstanding amounts under the Term B Loan. Upon the consummation of the open market purchase, the Term B Loans were assigned to the Borrower and immediately cancelled, such that the outstanding amount under the Term A Loan and incremental term loan facility were combined and held by the Lenders (the "2020 Term Loan") with the same terms as the Term A Loan. The Company wrote off $2.5 million of capitalized debt issuance costs in connection with the Third Amendment, which is included in Interest expense, net, in the Company's condensed consolidated statement of operations for the three months ended March 31, 2021. The Company is required to make quarterly principal payments on the 2020 Term Loan aggregating approximately $20 million per year in the first three years and $30 million in the fourth year, with the final payment approximating $300 million due on the maturity date. The Third Amendment increased the Borrower's ability to incur new incremental revolving commitments or term loans. Such indebtedness can be incurred up to an aggregate dollar limit equal to 100% of the Company's Consolidated Adjusted EBITDA (as defined in the 2020 Credit Facility) as of the most recently ended fiscal quarter for which financial statements have been delivered to the Lenders, plus additional amounts, so long as the Borrower's Consolidated Net Leverage Ratio (as defined in the Credit Agreement) does not exceed 2.75:1.00, increased from 2.25:1.00 under the First Amendment. The Third Amendment also increased the amount of Unrestricted Cash (as defined in the 2020 Credit Facility) used in calculating the Borrower's Consolidated Net Leverage Ratio from $10.0 million to $25.0 million. At March 31, 2021, the Company had an outstanding 2020 Term Loan balance of $390.6 million at an average interest rate of 3.40% and $6.4 million of letters of credit outstanding with an interest rate of 2.50%. The Company was in compliance with all covenants of the 2020 Credit Facility at both March 31, 2021 and December 31, 2020. Short-Term Loan From time to time, the Company enters into uncommitted and unsecured short-term loans to finance exports in China. The Company did not have any such short-term loans outstanding at March 31, 2021 and December 31, 2020. Letters of Credit and Performance and Bid Bonds The Company uses letters of credit, performance and bid bonds in the course of its business. At March 31, 2021, the Company had bank guarantees, performance and bid bonds under various uncommitted facilities (collectively, the "Guarantees") aggregating $26.9 million and $6.4 million of letters of credit under the 2020 Credit Facility (the "Letters of Credit"). At December 31, 2020, the Company had Guarantees aggregating $27.0 million and $5.6 million of Letters of Credit. At both March 31, 2021 and December 31, 2020, the Company had cash collateral of $2.7 million supporting the Guarantees, which are included in Restricted cash in the condensed consolidated balance sheets.

DERIVATIVE INSTRUMENTS AND HEDG

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES	3 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES	DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES The Company is exposed to financial market risk related to foreign currency fluctuations and changes in interest rates. These exposures are actively monitored by management. To manage the volatility related to the exposure to changes in interest rates, the Company has entered into a derivative financial instrument. Management's objective is to reduce, where it is deemed appropriate to do so, fluctuations in earnings and cash flows associated with changes in interest rates. Ribbon's policies and practices are to use derivative financial instruments only to the extent necessary to manage exposures. Ribbon does not hold or issue derivative financial instruments for trading or speculative purposes. The Company records derivatives on the balance sheet at fair value. The accounting for changes in the fair value of derivatives depends on the intended use of the derivative, whether the Company has elected to designate a derivative in a hedging relationship and apply hedge accounting and whether the hedging relationship has satisfied the criteria necessary to apply hedge accounting. Derivatives designated and qualifying as a hedge of the exposure to changes in the fair value of an asset, liability, or firm commitment attributable to a specific risk, such as interest rate risk, are considered fair value hedges. Derivatives designated and qualifying as a hedge of the exposure to variability in expected future cash flows, or other types of forecasted transactions, are considered cash flow hedges. Derivatives may also be designated as hedges of the foreign currency exposure of a net investment in a foreign operation. Hedge accounting generally provides for the matching of the timing of gain or loss recognition on the hedging instrument with the recognition of the changes in the fair value of the hedged asset or liability that are attributable to the hedged risk in a fair value hedge, or the earnings effect of the hedged forecasted transactions in a cash flow hedge. The Company may enter into derivative contracts that are intended to economically hedge certain of its risk even though hedge accounting does not apply or the Company elects not to apply hedge accounting. Cash Flow Hedge of Interest Rate Risk The 2020 Term Loan Facility had outstanding balances of $390.6 million and $393.1 million at March 31, 2021 and December 31, 2020, respectively. The 2020 Revolving Credit Facility was undrawn at both March 31, 2021 and December 31, 2020. Borrowings under the 2020 Credit Facility have variable interest rates based on LIBOR (see Note 10). As a result of exposure to interest rate movements, during March 2020, the Company entered into an interest rate swap arrangement, which effectively converted its $400 million term loan with its variable interest rate based upon one-month LIBOR to an aggregate fixed rate of 0.904%, plus a leverage-based margin as defined in the 2020 Credit Facility. The notional amount of this swap at March 31, 2021 was $400 million, and the swap matures on March 3, 2025, the same date the 2020 Credit Facility matures. The Company’s objectives in using interest rate derivatives are to add stability to interest expense and to manage its exposure to interest rate movements. To accomplish this objective, the Company is using an interest rate swap as part of its interest rate risk management strategy. Interest rate swaps designated as cash flow hedges involve the receipt of variable amounts from a counterparty in exchange for the Company making fixed-rate payments over the life of the agreements without exchange of the underlying notional amount. The effective portion of changes in the fair value of designated derivatives that qualify as cash flow hedges is recorded in accumulated other comprehensive income (loss) in the condensed consolidated balance sheet and is subsequently reclassified into earnings in the period that the hedged forecasted transactions affect earnings. During the three months ended March 31, 2021 and 2020, such a derivative was used to hedge the variable cash flows associated with the outstanding borrowings under the 2020 Credit Facility and the Company has accounted for this derivative as an effective hedge. Any ineffective portion of the change in the fair value of the derivative would be recognized directly in earnings. Amounts reported in accumulated other comprehensive income (loss) related to the Company's derivative are reclassified to interest expense as interest is accrued on the Company’s variable-rate debt. Based upon projected forward rates, the Company estimates as of March 31, 2021 that $3.1 million may be reclassified as an increase to interest expense over the next twelve months. The impact of the Company’s derivative financial instrument on its condensed consolidated statement of comprehensive income (loss) for the three months ended March 31, 2021 and 2020 was as follows (in thousands): Three months ended March 31, March 31, Gain (loss) recognized in other comprehensive loss on derivative (effective portion) $ 5,889 $ (9,337) Amount reclassified to (from) accumulated other comprehensive income (loss) to interest expense (effective portion) 780 (190) $ 6,669 (9,527) The fair values and locations in the condensed consolidated balance sheets at March 31, 2021 and December 31, 2020 of the Company's derivative liability designated as a hedging instrument were as follows (in thousands): Balance sheet location March 31, December 31, Interest rate derivative - liability derivative Accrued expenses and other $ 3,119 $ 3,157 Interest rate derivative - liability derivative Other long-term liabilities $ 1,160 $ 7,791 The Company has classified the interest rate derivative aggregating $4.3 million and $10.9 million at March 31, 2021 and December 31, 2020, respectively, as Level 2 fair value measurements within the fair value hierarchy (see Note 1).

REVENUE RECOGNITION

REVENUE RECOGNITION	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
REVENUE RECOGNITION	REVENUE RECOGNITION The Company derives revenue 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 allocate the transaction price to each performance obligation on a relative standalone selling price basis. The Company utilizes the observable price of goods and services when they are sold separately to similar customers in order to estimate standalone selling price. 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. Product revenue is typically recognized upon transfer of control or when the software is made available for download, as this is the point 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 begins to recognize software revenue related to the renewal of subscription software licenses at the start of the subscription period. The Company offers warranties on its products. Certain of the Company's warranties are considered to be assurance-type in nature, ensuring the product is functioning as intended. 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. Services revenue includes revenue from customer support and other professional services. 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. 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. However, in some instances, the Company uses the output method because it best depicts the transfer of asset to the customer. 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 versus the total estimated labor time required to complete the performance obligation. Revenue is recorded proportionally as costs are incurred or as 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. 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) Generally, 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) Generally, within 30 days of invoicing Hardware When control of the hardware 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) Generally, within 30 days of invoicing Professional Services Other professional services (excluding training services) As work is performed (over time) Generally, within 30 days of invoicing (upon completion of services) Training When the class is taught (point in time) Generally, within 30 days of services being performed Significant Judgments The Company's contracts with customers often include promises to transfer multiple products and services to the customer. Determining whether products and services are considered distinct performance obligations that should be accounted for separately versus together may require significant judgment. Judgment is required to determine the standalone selling price ("SSP") for each distinct performance obligation. 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 is a contract liability representing 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 recognition of revenue. Disaggregation of Revenue The Company disaggregates its revenue from contracts with customers based on the nature of the products and services and the geographic regions in which each customer is domiciled. The Company's revenue for the three months ended March 31, 2021 and 2020 was disaggregated as follows: Three months ended March 31, 2021 Product revenue Service revenue (maintenance) Service revenue (professional services) Total revenue United States $ 36,812 $ 31,606 $ 11,162 $ 79,580 Europe, Middle East and Africa 28,208 19,655 6,910 54,773 Asia Pacific 25,582 9,748 5,803 41,133 Other 7,287 7,696 2,303 17,286 $ 97,889 $ 68,705 $ 26,178 $ 192,772 Three months ended March 31, 2020 Product revenue Service revenue (maintenance) Service revenue (professional services) Total revenue United States $ 36,365 $ 31,466 $ 10,566 $ 78,397 Europe, Middle East and Africa 20,365 14,810 4,015 39,190 Asia Pacific 14,943 7,511 4,878 27,332 Other 4,226 7,281 1,556 13,063 $ 75,899 $ 61,068 $ 21,015 $ 157,982 The Company's product revenue from indirect sales through its channel partner program and from its direct sales program for the three months ended March 31, 2021 and 2020 was as follows (in thousands): Three months ended March 31, March 31, Indirect sales through channel partner program $ 20,163 $ 28,604 Direct sales 77,726 47,295 $ 97,889 $ 75,899 The Company's product revenue from sales to enterprise customers and from sales to service provider customers for the three months ended March 31, 2021 and 2020 was as follows (in thousands): Three months ended March 31, March 31, Sales to enterprise customers $ 22,668 $ 27,281 Sales to service provider customers 75,221 48,618 $ 97,889 $ 75,899 The Company's product revenue and service revenue components by segment for the three months ended March 31, 2021 and 2020 was as follows (in thousands): Three months ended March 31, March 31, Product revenue Cloud and Edge $ 50,152 $ 54,210 IP Optical Networks 47,737 21,689 Total product revenue $ 97,889 $ 75,899 Service revenue Maintenance Cloud and Edge $ 54,673 $ 55,556 IP Optical Networks 14,032 5,512 Total maintenance revenue 68,705 61,068 Professional services Cloud and Edge 20,597 18,265 IP Optical Networks 5,581 2,750 Total professional services revenue 26,178 21,015 Total service revenue $ 94,883 $ 82,083 Revenue Contract Balances The timing of revenue recognition, billings and cash collections results in billed accounts receivable; unbilled receivables, which are contract assets; and customer advances and deposits, which are 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. Completion of services and 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 that 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. Changes in the contract asset and liability balances during the three months ended March 31, 2021 were not materially impacted by any factors other than billing and revenue recognition. Nearly all of the Company's deferred revenue balance is related to services revenue, primarily customer support contracts. Unbilled receivables stem primarily from engagements where services have been performed; however, billing cannot occur until services are completed. In some arrangements, the Company allows customers to pay for term-based software licenses and products over the term of the software license. The Company also sells SaaS-based software under subscription arrangements, with payment terms over the term of the SaaS agreement. Amounts recognized as revenue in excess of amounts billed are recorded as unbilled receivables. Unbilled receivables that are anticipated to be invoiced in the next twelve months are included in Accounts receivable on the Company's condensed consolidated balance sheets. The changes in the Company's accounts receivable, unbilled receivables and deferred revenue balances for the three months ended March 31, 2021 were as follows (in thousands): Accounts receivable Unbilled accounts receivable Deferred revenue (current) Deferred revenue (long-term) Balance at January 1, 2021 $ 179,331 $ 58,407 $ 96,824 $ 26,010 Increase (decrease), net (27,719) (856) 5,279 (2,956) Balance at March 31, 2021 $ 151,612 57,551 $ 102,103 $ 23,054 The Company recognized approximately $42 million of revenue in the months ended March 31, 2021 that was recorded as deferred revenue at December 31, 2020 and approximately $41 million of revenue in the three months ended March 31, 2020 that was recorded as deferred revenue at December 31, 2019. Of the Company's deferred revenue reported as long-term in its condensed consolidated balance sheet at March 31, 2021, the Company expects that approximately $11 million will be recognized as revenue in 2022, approximately $8 million will be recognized as revenue in 2023 and approximately $4 million will be recognized as revenue in 2024 and beyond. All freight-related customer invoicing is recorded as revenue, while the shipping and handling costs that occur after control of the promised goods or services transfer to the customer are reported as fulfillment costs, a component of Cost of revenue - product in the Company's condensed consolidated statements of operations. Deferred Commissions Cost Sales commissions earned by the Company's employees are considered incremental and recoverable costs of obtaining a contract with a customer. Expense related to commission payments has been deferred on our condensed consolidated balance sheet and is being amortized over the expected life of the customer contract, which averages five years. The current and long-term portions of deferred commission expense are included as components of Other current assets and Other assets, respectively. At both March 31, 2021 and December 31, 2020, the Company had $4.1 million of deferred sales commissions capitalized.

OPERATING SEGMENT INFORMATION

OPERATING SEGMENT INFORMATION	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
OPERATING SEGMENT INFORMATION	OPERATING SEGMENT INFORMATION The Company has two reportable segments, which are intended to align with the manner in which the business is managed: Cloud and Edge, and IP Optical Networks. The Cloud and Edge segment provides secure and reliable software and hardware products, solutions and services for enabling Voice over Internet Protocol ("VoIP") communications, Voice over Long-Term Evolution ("VoLTE") and Voice Over 5G ("VoNR") communications and Unified Communications and Collaboration ("UC&C") within service provider and enterprise networks and from the cloud. The Cloud and Edge products are increasingly software-centric and cloud-native for deployment on private, public or hybrid cloud infrastructures, in data centers, on enterprise premises and within service provider networks. Ribbon's Cloud and Edge product portfolio consists of our Session Border Controller ("SBC") products and our Network Transformation ("NTR") products. The IP Optical Networks segment provides high-performance, secure and reliable hardware and software products solutions for IP networking, switching, routing and optical transport designed to support and enable technologies like 5G, distributed cloud computing and corresponding applications by delivering ultra-low cost-per-bit transport and multi-service flexibility. The IP Optical Networks portfolio offers multiple solutions, including 5G-native solutions for mobile backhaul, metro and edge aggregation, core networking, data center interconnect, legacy NTR and transport solutions for wholesale carriers. This portfolio is offered to service provider, enterprise and industry verticals with critical transport network infrastructures including utilities, government, defense, transportation, and education and research Information for the IP Optical Networks segment for the three months ended March 31, 2020 includes the financial results of this segment for the period subsequent to the ECI Acquisition Date. The Company has not provided segment asset information as such information is not provided to the CODM and accordingly, asset information is not used in assessing segment performance. Please see Note 6 for information regarding the allocation of goodwill between segments. Segment revenue and expenses included in the tables below represent direct revenue and expenses attributable to each segment for revenue, adjusted gross profit, and the research and development expense component of adjusted EBITDA. The Company's sales, marketing, and general and administrative functions support both segments and accordingly, these costs are allocated to both segments. The CODM utilizes revenue, adjusted gross profit and adjusted EBITDA (earnings before interest, taxes, depreciation and amortization) to measure and assess each segment's performance. The Company calculates adjusted EBITDA by excluding from income (loss) from operations: depreciation; amortization of acquired intangible assets; stock-based compensation; certain litigation costs; acquisition-, disposal- and integration-related expense; and restructuring and related expense. These adjusted measures may also exclude other items in future periods that the Company believes are not part of the Company's core business. Adjusted gross profit and adjusted EBITDA are not financial measures determined in accordance with U.S. GAAP and may not be comparable to similarly titled measures used by other companies and should not be considered a substitute for income (loss) from operations or gross profit or other results reported in accordance with U.S. GAAP. See below for a reconciliation of adjusted gross profit to gross profit and adjusted EBITDA to income (loss) from operations, as those are the most directly comparable U.S. GAAP measures. The tables below provide net sales, adjusted gross profit, adjusted EBITDA and depreciation expense by reportable segment for the three months ended March 31, 2021 and 2020 (in thousands): Three months ended March 31, March 31, Segment revenue: Cloud and Edge $ 125,422 $ 128,031 IP Optical Networks 67,350 29,951 Revenue $ 192,772 $ 157,982 Three months ended March 31, March 31, Segment adjusted gross profit: Cloud and Edge $ 84,335 $ 78,935 IP Optical Networks 26,474 11,746 Total segment adjusted gross profit 110,809 90,681 Stock-based compensation expense (262) (157) Gross profit $ 110,547 $ 90,524 Three months ended March 31, March 31, Segment adjusted EBITDA: Cloud and Edge $ 28,330 $ 9,739 IP Optical Networks (8,678) (198) Total segment adjusted EBITDA 19,652 9,541 Depreciation (4,226) (3,474) Amortization of intangible assets (15,823) (14,334) Stock-based compensation (5,060) (2,976) Litigation costs — (3,038) Acquisition-, disposal- and integration-related expense (1,197) (12,384) Restructuring and related expense (5,950) (2,075) Loss from operations $ (12,604) $ (28,740) Segment depreciation expense: Cloud and Edge $ 3,137 $ 2,993 IP Optical Networks 1,089 481 Depreciation expense $ 4,226 $ 3,474

MAJOR CUSTOMERS

MAJOR CUSTOMERS	3 Months Ended
	Mar. 31, 2021
Risks and Uncertainties [Abstract]
MAJOR CUSTOMERS	MAJOR CUSTOMERS The following customers contributed 10% or more of the Company's revenue in the three months ended March 31, 2021 and 2020: Three months ended March 31, March 31, Verizon Communications Inc. 16% 13% AT&T Inc. * 10% * Represents less than 10% of total revenue. At March 31, 2021, one customer accounted for 10% or more of the Company's accounts receivable balance, representing approximately 16% of total accounts receivable. At December 31, 2020, one customer accounted for 10% or more of the Company's accounts receivable balance, representing approximately 12% of total accounts receivable. The Company performs ongoing credit evaluations of its customers and generally does not require collateral on accounts receivable, although in some instances the Company may require letters of credit to support customer outstanding accounts receivable balances. The Company maintains an allowance for doubtful accounts and such losses have been within management's expectations.

COMMON STOCK REPURCHASES

COMMON STOCK REPURCHASES	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
COMMON STOCK REPURCHASES	COMMON STOCK REPURCHASESIn the second quarter of 2019, the Company's Board of Directors (the "Board") approved a stock repurchase program (the "Repurchase Program") pursuant to which the Company could repurchase up to $75 million of its common stock prior to April 18, 2021. The Company did not repurchase any common stock during the three months ended March 31, 2021 or 2020. At both March 31, 2020 and December 31, 2020, the Company had $70.5 million remaining under the Repurchase Program for future repurchases. The Repurchase Program expired on April 18, 2021.

STOCK-BASED COMPENSATION PLANS

STOCK-BASED COMPENSATION PLANS	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
STOCK-BASED COMPENSATION PLANS	STOCK-BASED COMPENSATION PLANS 2019 Stock Incentive Plan The Company's Amended and Restated 2019 Incentive Award Plan (the "2019 Plan") provides for the award of options to purchase the Company's common stock ("stock options"), stock appreciation rights ("SARs"), restricted stock awards ("RSAs"), performance-based stock awards ("PSAs"), restricted stock units ("RSUs"), performance-based stock units ("PSUs") and other stock- or cash-based awards. Awards can be granted under the 2019 Plan to the Company's employees, officers and non-employee directors, as well as consultants and advisors of the Company and its subsidiaries. 2007 Plan The Company's 2007 Plan provided for the award of stock options, SARs, RSAs, PSAs, RSUs, PSUs and other stock-based awards to employees, officers, non-employee directors, consultants and advisors of the Company and its subsidiaries. On and following June 5, 2019, with the exception of shares underlying awards outstanding as of that date, no additional shares may be granted under the 2007 Plan. Assumed Stock Plans In connection with the acquisition of Edgewater Networks, Inc. in August 2018, 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 Ribbon stock options (the "Ribbon Replacement Options") which are vesting under the same schedules as the respective Edgewater Options. In connection with the Company's acquisitions of Performance Technologies Inc. ("PT") in 2014, and Network Equipment Technologies, Inc. ("NET") in 2012, the Company assumed their stock plans (collectively, the "Assumed Plans"). Any outstanding awards under the Assumed Plans that in the future expire, terminate, are cancelled or surrendered, or are repurchased by the Company will be returned to the 2019 Plan. Accordingly, no additional shares may be granted under the Assumed Plans. Executive Equity Arrangements Inducement Awards In connection with his appointment as President and Chief Executive Office of Ribbon, and as an inducement for Bruce McClelland's ("Mr. McClelland") commencement of employment, the Company awarded Mr. McClelland sign-on equity grants, comprised of 462,963 RSUs and a PSU grant with both market and service conditions (the "Inducement PSUs") on March 16, 2020. The RSUs vested and were released to Mr. McClelland on March 16, 2021. Subject to Mr. McClelland's continued employment, the Inducement PSUs are eligible to vest and be settled in up to 4,750,000 shares of Ribbon common stock upon the achievement of specified share price thresholds on or prior to September 1, 2024. The first share price threshold for Mr. McClelland’s Inducement PSUs was achieved on February 26, 2021, and accordingly 1,333,333 shares were released to him. These releases are included in the applicable tables below. Performance-Based Stock Grants In addition to granting RSUs to its executives and certain of its employees, the Company also grants PSUs to certain of its executives, including the Inducement PSUs granted to Mr. McClelland as described above. In 2021, 2020 and 2019, the Company granted certain of its executives (the "2021 PSUs", "2020 PSUs" and "2019 PSUs", respectively), of which 60% of each executive's PSU grant had both performance and service conditions (the "Performance PSUs") and 40% had both market and service conditions (the "Market PSUs"). Each executive's Performance PSU grant is comprised of three consecutive fiscal year performance periods beginning in the year of grant (each, a "Fiscal Year Performance Period"), with one-third of the Performance PSUs attributable to each Fiscal Year Performance Period. The number of shares that will be vest for each Fiscal Year Performance Period, if any, will be based on the achievement of certain metrics related to the Company's financial performance for the applicable year on a standalone basis (each, a "Fiscal Year Performance Condition"). The Company's achievement of the goals for each Fiscal Year Performance Condition (and the number of shares of Company common stock to vest as a result thereof) are being measured on a linear sliding scale in relation to specific threshold, target and stretch performance conditions, with any shares earned vesting in the first quarter of the fiscal year following the third Performance Period of the grant, pending each executive's continued employment with the Company through that date. The number of shares of common stock underlying the Performance PSUs that can be earned will in no event exceed 200% of the Performance PSUs. Shares subject to the Performance PSUs that fail to be earned will be forfeited. The Market PSUs have one three-year performance period, beginning January 1 in the year of grant and ending on December 31, three years thereafter (the "Market Performance Period"). The number of shares subject to the Market PSUs that will vest, if any, will be dependent upon the Company's total shareholder return ("TSR") compared with the TSR of the companies included in a custom index for the applicable Market Performance Period, measured by the Compensation Committee after the Market Performance Period ends, with any shares earned vesting in the first quarter of the fiscal year following the respective Market Performance Period, pending each executive's continued employment with the Company through that date. The number of shares of common stock underlying the Market PSUs that can be earned will in no event exceed 200% of the Market PSUs. Shares subject to the Market PSUs that fail to be earned will be forfeited. In addition, in connection with his appointment as Executive Vice President and General Manager, Packet Optical Networking, the Company granted Sam Bucci 133,333 PSUs (the "Bucci Stock Price PSUs") with both market and service conditions. Subject to Mr. Bucci's continued employment, the Bucci Stock Price PSUs were eligible to vest and be settled in shares of Ribbon's common stock upon the achievement of a specific share price threshold on or prior to January 31, 2022. The share price threshold for Mr. Bucci’s Stock Price PSUs was achieved on February 12, 2021, and the shares were released to him. This release is included in the applicable table below. Accounting for Performance PSUs. Once the grant date criteria have been met for a Fiscal Year Performance Period, the Company records stock-based compensation expense for the respective underlying Performance PSUs based on its assessment of the probability that each performance condition will be achieved and the level, if any, of such achievement. The Compensation Committee determines the number of shares earned, if any, after the Company's financial results for each Fiscal Year Performance Period are finalized. Upon the determination by the Compensation Committee of the number of shares that will be received upon vesting of the Performance PSUs, such number of shares becomes fixed and the unamortized expense is recorded through the remainder of the service period, generally three years from the date of grant, at which time the total Performance PSUs earned, if any, will vest, pending each executive's continued employment with the Company through that date. Accounting for Market PSUs . PSUs that include a market condition require 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 are 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. At March 31, 2021, the calculation of the grant date fair value of the Market PSUs granted on March 15, 2021 had not been completed. The Company used a grant date fair value of $8.65, the closing stock price on the date of grant, to calculate expense attributable to the three months ended March 31, 2021 for these Market PSUs. The Company expects to complete the Monte Carlo valuation of these Market PSUs and will record a cumulative adjustment to expense to account for the change in grant date fair value, if any, in the second quarter of 2021. The Company does not expect any such adjustment to have a material impact on its consolidated financial statements. Employee Bonus Program Effective in 2021, the Company added an equity component to its cash bonus program for eligible employees, under which RSUs with a grant date fair value equal to 50% of each employee's target cash bonus were granted to each such employee (the "Bonus RSUs"). Correspondingly, cash target bonuses for eligible employees were reduced by 50%. The Company implemented this program to expand the opportunities for stock ownership more broadly throughout the Company. The Bonus RSU grants are included in the applicable table below. Stock Options The activity related to the Company's outstanding stock options for the three months ended March 31, 2021 was as follows: Number of Weighted Weighted Aggregate Outstanding at January 1, 2021 207,710 $ 12.69 Exercised (13,389) $ 1.76 Outstanding at March 31, 2021 194,321 $ 13.44 3.31 $ 267 Vested or expected to vest at March 31, 2021 194,253 $ 13.45 3.31 $ 266 Exercisable at March 31, 2021 191,930 $ 13.59 3.27 $ 252 The total intrinsic value of options exercised was $0.1 million for the three months ended March 31, 2021. The Company received cash from option exercises of $24,000 in the three months ended March 31, 2021. Restricted Stock Awards and Units The activity related to the Company's RSAs for the three months ended March 31, 2021 was as follows: Shares Weighted Unvested balance at January 1, 2021 86,983 $ 7.04 Vested (86,983) $ 7.04 Unvested balance at March 31, 2021 — $ — The activity related to the Company's RSUs for the three months ended March 31, 2021 was as follows: Shares Weighted Unvested balance at January 1, 2021 6,531,110 $ 3.32 Granted 2,885,002 $ 8.59 Vested (1,575,645) $ 2.60 Forfeited (372,984) $ 3.68 Unvested balance at March 31, 2021 7,467,483 $ 5.49 The total grant date fair value of shares of restricted stock granted under RSAs and RSUs that vested during the three months ended March 31, 2021 was $4.7 million. Performance-Based Stock Units The activity related to the Company's PSUs for the three months ended March 31, 2021 was as follows: Shares Weighted Unvested balance at January 1, 2021 6,035,931 $ 1.56 Granted 642,121 $ 5.83 Vested (1,525,681) $ 0.98 Forfeited (57,480) $ 5.12 Unvested balance at March 31, 2021 5,094,891 $ 2.40 The total grant date fair value of shares of restricted stock granted under PSUs that vested during the three months ended March 31, 2021 was $1.5 million. Stock-Based Compensation The condensed consolidated statements of operations include stock-based compensation for the three months ended March 31, 2021 and 2020 as follows (in thousands): Three months ended March 31, March 31, Product cost of revenue $ 27 $ 27 Service cost of revenue 235 130 Research and development 627 558 Sales and marketing 1,874 752 General and administrative 2,297 1,509 $ 5,060 $ 2,976 There was a nominal income tax benefit for stock-based compensation in the three months ended March 31, 2021; however, there was no income tax benefit in the three months ended March 31, 2020 due to the valuation allowance recorded. At March 31, 2021, there was $36.4 million, net of expected forfeitures, of unrecognized stock-based compensation expense related to unvested stock options, stock awards and stock units. This expense is expected to be recognized over a weighted average period of approximately two years.

LEASES

LEASES	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
LEASES	LEASES The Company has operating and finance leases for corporate offices, research and development facilities, and certain equipment. Operating leases are reported separately in the Company's condensed consolidated balance sheets. Assets acquired under finance leases are included in Property and equipment, net, in the condensed consolidated balance sheets. The Company determines if an arrangement is a lease at inception. A contract is determined to contain a lease component if the arrangement provides the Company with a right to control the use of an identified asset. Lease agreements may include lease and non-lease components. In such instances for all classes of underlying assets, the Company does not separate lease and non-lease components but rather, accounts for the entire arrangement under leasing guidance. Leases with an initial term of 12 months or less are not recorded on the balance sheet and lease expense for these leases is recognized on a straight-line basis over the lease term. Right-of-use assets and lease liabilities are initially measured based on the present value of the future minimum fixed lease payments (i.e., fixed payments in the lease contract) over the lease term at the commencement date. As the Company's existing leases do not have a readily determinable implicit rate, the Company uses its incremental borrowing rate based on the information available at the commencement date in determining the present value of future minimum fixed lease payments. The Company calculates its incremental borrowing rate to reflect the interest rate that it would have to pay to borrow on a collateralized basis an amount equal to the lease payments in a similar economic environment over a similar term and considers its historical borrowing activities and market data from entities with comparable credit ratings in this determination. The measurement of the right-of-use asset also includes any lease payments made prior to the commencement date (excluding any lease incentives) and initial direct costs incurred. The Company assessed its right-of-use assets for impairment as of March 31, 2021 and December 31, 2020 and determined no impairment has occurred. Lease terms may include options to extend or terminate the lease and the Company incorporates such options in the lease term when it has the unilateral right to make such an election and it is reasonably certain that the Company will exercise that option. In making this determination, the Company considers its prior renewal and termination history and planned usage of the assets under lease, incorporating expected market conditions. For operating leases, lease expense for minimum fixed lease payments is recognized on a straight-line basis over the lease term. The expense for finance leases includes both interest and amortization expense components, with the interest component calculated based on the effective interest method and the amortization component calculated based on straight-line amortization of the right-of-use asset over the lease term. Lease contracts may contain variable lease costs, such as common area maintenance, utilities and tax reimbursements that vary over the term of the contract. Variable lease costs are not included in minimum fixed lease payments and as a result, are excluded from the measurement of the right-of-use assets and lease liabilities. The Company expenses all variable lease costs as incurred. In connection with the 2019 Restructuring Initiative, certain lease assets related to facilities are being partially or fully vacated as the Company consolidates its facilities. The Company has no plans to enter into sublease agreements for certain facilities. The Company ceased use of these facilities in the first quarter of 2021, the first and fourth quarters of 2020 and the third quarter of 2019. Accordingly, the Company accelerated the amortization of the associated lease assets through the planned cease-use date of each facility, resulting in additional amortization expense of $3.4 million and $0.1 million in the three months ended March 31, 2021 and 2020, respectively. The Company also recorded expense of $1.4 million in the aggregate in the three months ended March 31, 2021 for all estimated future variable lease costs related to these facilities. The Company recorded nominal expense for all estimated future variable lease costs in the three months ended March 31, 2020. All accelerated amortization and accrual of future variable costs were recorded as Restructuring and related expense in the Company's condensed consolidated statements of operations. At March 31, 2021 and December 31, 2020, the Company had accruals of $2.1 million and $0.8 million, respectively, for all future anticipated variable lease costs related to these facilities. The Company may incur additional future expense if it is unable to sublease other locations included in the Facilities Initiative. The Company leases its corporate offices and other facilities under operating leases, which expire at various times through 2032. In December 2020, the Company began relocating from its former leased Plano, Texas facility to its recently completed leased facility, also located in Plano, Texas, which became the Company's corporate headquarters. The Company's relocation to the new corporate headquarters was completed in the first quarter of 2021. The Company's right-of-use lease assets and lease liabilities at March 31, 2021 and December 31, 2020 were as follows (in thousands): Classification March 31, December 31, Assets Operating lease assets Operating lease right-of-use assets $ 62,579 $ 69,757 Finance lease assets* Property and equipment, net 754 983 Total leased assets $ 63,333 $ 70,740 Liabilities Current Operating Operating lease liabilities $ 17,627 $ 17,023 Finance Accrued expenses and other 820 902 Noncurrent Operating Operating lease liabilities, net of current 68,100 72,614 Finance Other long-term liabilities 398 568 Total lease liabilities $ 86,945 $ 91,107 * Finance lease assets were recorded net of accumulated depreciation of $2.2 million and $1.9 million at March 31, 2021 and December 31, 2020, respectively. The components of lease expense for the three months ended March 31, 2021 and 2020 were as follows (in thousands): Three months ended March 31, March 31, Operating lease cost* $ 8,837 $ 3,344 Finance lease cost Amortization of leased assets 229 319 Interest on lease liabilities 26 55 Short-term lease cost 3,292 5,523 Variable lease costs (costs excluded from minimum fixed lease payments)** 2,158 637 Sublease income (276) — Net lease cost $ 14,266 $ 9,878 * Operating lease cost for the three months ended March 31, 2021 included $3.4 million of accelerated amortization for certain assets partially or fully vacated in 2021 with no intent or ability to sublease. Operating lease cost for the three months ended March 31, 2020 included $0.1 million of accelerated amortization for certain assets partially or fully vacated in 2020 with no ability to sublease. ** Variable lease costs for the three months ended March 31, 2021 included an accrual of $1.4 million for all future estimated variable expenses related to certain assets partially or fully vacated in 2021 with no intent or ability to sublease. No such variable costs were accrued in the three months ended March 31, 2020. Cash flow information related to the Company's leases for the three months ended March 31, 2021 and 2020 was as follows (in thousands): Three months ended March 31, March 31, Cash paid for amounts included in the measurement of lease liabilities Operating cash flows for operating leases $ 5,561 $ 3,113 Operating cash flows for finance leases $ 26 $ 55 Financing cash flows for finance leases $ 272 $ 338 Other information related to the Company's leases as of March 31, 2021 and December 31, 2020 was as follows: March 31, December 31, Weighted average remaining lease term (years) Operating leases 6.52 6.59 Finance leases 1.51 1.70 Weighted average discount rate Operating leases 5.72 % 5.67 % Finance leases 5.74 % 6.15 % Future minimum fixed lease payments under noncancelable leases at March 31, 2021 were as follows (in thousands): March 31, 2021 Operating Finance leases leases Remainder of 2021 $ 16,397 $ 701 2022 20,026 509 2023 17,267 62 2024 10,392 — 2025 8,540 — 2026 and beyond 32,592 — Total lease payments 105,214 1,272 Less: interest (19,487) (54) Present value of lease liabilities $ 85,727 $ 1,218
LEASES	LEASES The Company has operating and finance leases for corporate offices, research and development facilities, and certain equipment. Operating leases are reported separately in the Company's condensed consolidated balance sheets. Assets acquired under finance leases are included in Property and equipment, net, in the condensed consolidated balance sheets. The Company determines if an arrangement is a lease at inception. A contract is determined to contain a lease component if the arrangement provides the Company with a right to control the use of an identified asset. Lease agreements may include lease and non-lease components. In such instances for all classes of underlying assets, the Company does not separate lease and non-lease components but rather, accounts for the entire arrangement under leasing guidance. Leases with an initial term of 12 months or less are not recorded on the balance sheet and lease expense for these leases is recognized on a straight-line basis over the lease term. Right-of-use assets and lease liabilities are initially measured based on the present value of the future minimum fixed lease payments (i.e., fixed payments in the lease contract) over the lease term at the commencement date. As the Company's existing leases do not have a readily determinable implicit rate, the Company uses its incremental borrowing rate based on the information available at the commencement date in determining the present value of future minimum fixed lease payments. The Company calculates its incremental borrowing rate to reflect the interest rate that it would have to pay to borrow on a collateralized basis an amount equal to the lease payments in a similar economic environment over a similar term and considers its historical borrowing activities and market data from entities with comparable credit ratings in this determination. The measurement of the right-of-use asset also includes any lease payments made prior to the commencement date (excluding any lease incentives) and initial direct costs incurred. The Company assessed its right-of-use assets for impairment as of March 31, 2021 and December 31, 2020 and determined no impairment has occurred. Lease terms may include options to extend or terminate the lease and the Company incorporates such options in the lease term when it has the unilateral right to make such an election and it is reasonably certain that the Company will exercise that option. In making this determination, the Company considers its prior renewal and termination history and planned usage of the assets under lease, incorporating expected market conditions. For operating leases, lease expense for minimum fixed lease payments is recognized on a straight-line basis over the lease term. The expense for finance leases includes both interest and amortization expense components, with the interest component calculated based on the effective interest method and the amortization component calculated based on straight-line amortization of the right-of-use asset over the lease term. Lease contracts may contain variable lease costs, such as common area maintenance, utilities and tax reimbursements that vary over the term of the contract. Variable lease costs are not included in minimum fixed lease payments and as a result, are excluded from the measurement of the right-of-use assets and lease liabilities. The Company expenses all variable lease costs as incurred. In connection with the 2019 Restructuring Initiative, certain lease assets related to facilities are being partially or fully vacated as the Company consolidates its facilities. The Company has no plans to enter into sublease agreements for certain facilities. The Company ceased use of these facilities in the first quarter of 2021, the first and fourth quarters of 2020 and the third quarter of 2019. Accordingly, the Company accelerated the amortization of the associated lease assets through the planned cease-use date of each facility, resulting in additional amortization expense of $3.4 million and $0.1 million in the three months ended March 31, 2021 and 2020, respectively. The Company also recorded expense of $1.4 million in the aggregate in the three months ended March 31, 2021 for all estimated future variable lease costs related to these facilities. The Company recorded nominal expense for all estimated future variable lease costs in the three months ended March 31, 2020. All accelerated amortization and accrual of future variable costs were recorded as Restructuring and related expense in the Company's condensed consolidated statements of operations. At March 31, 2021 and December 31, 2020, the Company had accruals of $2.1 million and $0.8 million, respectively, for all future anticipated variable lease costs related to these facilities. The Company may incur additional future expense if it is unable to sublease other locations included in the Facilities Initiative. The Company leases its corporate offices and other facilities under operating leases, which expire at various times through 2032. In December 2020, the Company began relocating from its former leased Plano, Texas facility to its recently completed leased facility, also located in Plano, Texas, which became the Company's corporate headquarters. The Company's relocation to the new corporate headquarters was completed in the first quarter of 2021. The Company's right-of-use lease assets and lease liabilities at March 31, 2021 and December 31, 2020 were as follows (in thousands): Classification March 31, December 31, Assets Operating lease assets Operating lease right-of-use assets $ 62,579 $ 69,757 Finance lease assets* Property and equipment, net 754 983 Total leased assets $ 63,333 $ 70,740 Liabilities Current Operating Operating lease liabilities $ 17,627 $ 17,023 Finance Accrued expenses and other 820 902 Noncurrent Operating Operating lease liabilities, net of current 68,100 72,614 Finance Other long-term liabilities 398 568 Total lease liabilities $ 86,945 $ 91,107 * Finance lease assets were recorded net of accumulated depreciation of $2.2 million and $1.9 million at March 31, 2021 and December 31, 2020, respectively. The components of lease expense for the three months ended March 31, 2021 and 2020 were as follows (in thousands): Three months ended March 31, March 31, Operating lease cost* $ 8,837 $ 3,344 Finance lease cost Amortization of leased assets 229 319 Interest on lease liabilities 26 55 Short-term lease cost 3,292 5,523 Variable lease costs (costs excluded from minimum fixed lease payments)** 2,158 637 Sublease income (276) — Net lease cost $ 14,266 $ 9,878 * Operating lease cost for the three months ended March 31, 2021 included $3.4 million of accelerated amortization for certain assets partially or fully vacated in 2021 with no intent or ability to sublease. Operating lease cost for the three months ended March 31, 2020 included $0.1 million of accelerated amortization for certain assets partially or fully vacated in 2020 with no ability to sublease. ** Variable lease costs for the three months ended March 31, 2021 included an accrual of $1.4 million for all future estimated variable expenses related to certain assets partially or fully vacated in 2021 with no intent or ability to sublease. No such variable costs were accrued in the three months ended March 31, 2020. Cash flow information related to the Company's leases for the three months ended March 31, 2021 and 2020 was as follows (in thousands): Three months ended March 31, March 31, Cash paid for amounts included in the measurement of lease liabilities Operating cash flows for operating leases $ 5,561 $ 3,113 Operating cash flows for finance leases $ 26 $ 55 Financing cash flows for finance leases $ 272 $ 338 Other information related to the Company's leases as of March 31, 2021 and December 31, 2020 was as follows: March 31, December 31, Weighted average remaining lease term (years) Operating leases 6.52 6.59 Finance leases 1.51 1.70 Weighted average discount rate Operating leases 5.72 % 5.67 % Finance leases 5.74 % 6.15 % Future minimum fixed lease payments under noncancelable leases at March 31, 2021 were as follows (in thousands): March 31, 2021 Operating Finance leases leases Remainder of 2021 $ 16,397 $ 701 2022 20,026 509 2023 17,267 62 2024 10,392 — 2025 8,540 — 2026 and beyond 32,592 — Total lease payments 105,214 1,272 Less: interest (19,487) (54) Present value of lease liabilities $ 85,727 $ 1,218

INCOME TAXES

INCOME TAXES	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXESThe Company's income tax provisions for the three months ended March 31, 2021 and 2020 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 tax rate includes the impact of valuation allowances in various jurisdictions.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Liabilities for Royalty Payments to the IIA . Prior to the ECI Acquisition, ECI had received research and development grants from the Office of the Innovation Authority of the Israeli Ministry of Economics (the "IIA"). The Company assumed ECI's contract with the IIA, which requires the Company to pay royalties to the IIA on proceeds from the sale of products which the Israeli government has supported by way of research and development grants. The royalties for grants prior to 2017 were calculated at the rates of 1.3% to 5.0% of the aggregated proceeds from the sale of such products developed at certain of the Company's R&D centers, up to an amount not exceeding 100% of such grants plus interest at LIBOR. Effective for grants approved in 2017 and subsequently, interest was calculated at the higher of LIBOR plus 1.5% to 2.75%. At March 31, 2021, the Company's maximum possible future royalties commitment, including $5.2 million of unpaid royalties accrued, was $42.0 million, including interest of $2.0 million, based on estimates of future product sales, grants received from the IIA not yet repaid, and management's estimation of products still to be sold. Research and Development Grants . The Company records grants received from the IIA as a reduction to research and development expense. Royalties payable to the IIA are recognized pursuant to sales of related products and are classified as Cost of revenue. Litigation . On November 8, 2018, Ron Miller, a purported stockholder of the Company, filed a Class Action Complaint (the "Miller Complaint") in the United States District Court for the District of Massachusetts (the "Massachusetts District Court") against the Company and three of its former officers (collectively, the "Defendants"), claiming to represent a class of purchasers of Sonus common stock during the period from January 8, 2015 through March 24, 2015 and alleging violations of the federal securities laws. Similar to a previous complaint entitled Sousa et al. vs. Sonus Networks, Inc. et al., which was dismissed with prejudice by an order dated June 6, 2017, the Miller Complaint claims that the Defendants made misleading forward-looking statements concerning Sonus' expected fiscal first quarter of 2015 financial performance, which statements were also the subject of an August 7, 2018 Securities and Exchange Commission Cease and Desist Order, whose findings the Company neither admitted nor denied. The Miller plaintiffs are seeking monetary damages. After the Miller Complaint was filed, several parties filed and briefed motions seeking to be selected by the Massachusetts District Court to serve as a Lead Plaintiff in the action. On June 21, 2019, the Massachusetts District Court appointed a group as Lead Plaintiffs and the Lead Plaintiffs filed an amended complaint on July 19, 2019. On August 30, 2019, the Defendants filed a motion to dismiss the Miller Complaint and, on October 4, 2019, the Lead Plaintiffs filed an opposition to the motion to dismiss. There was an oral argument on the motion to dismiss on February 12, 2020. 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 condensed consolidated financial statements.

BASIS OF PRESENTATION (Policies

BASIS OF PRESENTATION (Policies)	3 Months Ended
	Mar. 31, 2021
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 December 1, 2020 (the "Kandy Sale Date"), American Virtual Cloud Technologies, Inc. ("AVCT") completed the purchase of the Company's cloud-based enterprise service business (the "Kandy Communications Business") and accordingly, the revenue and expenses of the Kandy Communications Business are excluded from the Company's condensed consolidated financial statements for the three months ended March 31, 2021. On March 3, 2020 (the "ECI Acquisition Date"), a subsidiary of the Company merged with ECI Telecom Group Ltd ("ECI") (the "ECI Acquisition"). The financial results of ECI are included in the Company's condensed consolidated financial statements for the period subsequent to the ECI 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, 2020 (the "Annual Report"), which was filed with the SEC on February 26, 2021.
Operating Segments	Operating Segments The Company's chief operating decision maker (the "CODM") is its President and Chief Executive Officer. Effective in the fourth quarter of 2020 and in connection with the ECI Acquisition, the CODM began to assess the Company's performance based on the performance of two separate organizations within Ribbon: the Cloud and Edge segment ("Cloud and Edge") and the IP Optical Networks segment ("IP Optical Networks"). Financial information for the IP Optical Networks segment included in the Company's financial results for the three months ended March 31, 2020 is for the period subsequent to the ECI Acquisition Date through March 31, 2020.
Reclassifications	Reclassifications In the fourth quarter of 2020, the Company reclassified amounts recorded for amortization of acquired intangible assets in prior presentations from Cost of revenue - product and Sales and marketing to a separate line included in operating expenses in the condensed consolidated statements of operations, as management believes this presentation enhances the comparability of the Company's financial statements with industry peers. These reclassifications also did not impact the condensed consolidated balance sheets or statements of cash flows for any historical periods. The Company did not reclassify depreciation of property and equipment related to production activities from cost of revenue to other accounts.
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 Ribbon 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 revenue and expenses during the reporting periods. Significant estimates and judgments relied upon in preparing these condensed consolidated financial statements include accounting for business combinations, revenue recognition for multiple element arrangements, inventory valuations, assumptions used to determine the fair value of stock-based compensation, intangible asset 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.
Restricted Cash	Restricted Cash The Company classifies as restricted cash all cash pledged as collateral to secure long-term obligations and all cash whose use is otherwise limited by contractual provisions. At March 31, 2021, the Company had $2.7 million of restricted cash, representing restricted short-term bank deposits pledged to secure certain performance and financial bonds as security for the Company's obligations under tenders, contracts and to one of its main subcontractors. At December 31, 2020, the Company had $7.3 million of restricted cash, comprised of $4.6 million restricted in connection with a tax payment on certain fixed assets formerly held by ECI that were sold in connection with the ECI Acquisition, and $2.7 million of restricted short-term bank deposits pledged to secure certain performance and financial bonds as security for the Company's obligations under tenders, contracts and to one of its main subcontractors.
Transfers of Financial Assets	Transfers of Financial AssetsThe Company maintains customer receivables factoring agreements with a number of financial institutions primarily for IP Optical Networks sales outside of the United States. Under the terms of these agreements, the Company may transfer receivables to the financial institutions, on a non-recourse basis, provided that the financial institutions approve the receivables in advance. The Company maintains credit insurance policies from major insurance providers or obtains letters of credit from the customers for a majority of its factored trade receivables. The Company accounts for the factoring of its financial assets as a sale of the assets and records the factoring fees, when incurred, as a component of interest expense in the condensed consolidated statements of operations, and the proceeds from the sales of receivables are included in cash from operating activities in the condensed consolidated statements of cash flows.
Fair Value of Financial Instruments and Fair Value Hierarchy	Fair Value of Financial Instruments and Fair Value Hierarchy The carrying amounts of the Company's financial instruments approximate their fair values and include cash equivalents, accounts receivable, borrowings under a revolving credit facility, accounts payable and long-term debt. 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.
Recent Accounting Pronouncements	Recent Accounting Pronouncements The Financial Accounting Standards Board ("FASB") issued the following accounting pronouncement which became effective for the Company in 2021, and which did not have a material impact on its condensed consolidated financial statements: In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes ("ASU 2019-12"), which modifies ASC 740 to simplify the accounting for income taxes. ASU 2019-12 addresses the accounting for hybrid tax regimes, tax basis step-up in goodwill obtained in a transaction that is not a business combination, separate financial statements of legal entities not subject to tax, intraperiod tax allocation exception to incremental approach, ownership changes in investments - changes from a subsidiary to an equity method investment, ownership changes in investments - changes from an equity method investment to a subsidiary, interim period accounting for enacted changes in tax law and year-to-date loss limitation in interim period tax accounting. The FASB issued the following accounting pronouncement, which the Company does not believe will have a material impact on its condensed consolidated financial statements upon adoption: In January 2021, the FASB issued ASU 2021-01, Reference Rate Reform (Topic 848): Scope ("ASU 2021-01"), which refines the scope of Accounting Standards Codification 848, Reference Rate Reform ("ASC 848") and clarifies some of its guidance as part of the FASB's monitoring of global reference rate reform activities. ASU 2021-01 permits entities to elect certain optional expedients and exceptions when accounting for derivative contracts and certain hedging relationships affected by changes in the interest rates used for discounting cash flows, for computing variation margin settlements, and for calculating price alignment interest in connection with reference rate reform activities under way in global financial markets (the "discounting transition"). ASU 2021-01 is effective for the Company prospectively in any period through December 31, 2022 that a modification is made to the terms of the derivatives affected by the discounting transition.

BASIS OF PRESENTATION (Tables)

BASIS OF PRESENTATION (Tables)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Schedule of Error Corrections and Prior Period Adjustments	These reclassifications for the three months ended March 31, 2020 were as follows (in thousands): Three months ended March 31, 2020 Prior presentation Amounts reclassified Revised presentation Product revenue $ 75,899 $ — $ 75,899 Service revenue 82,083 — 82,083 Total revenue 157,982 — 157,982 Cost of revenue - product 44,933 (8,954) 35,979 Cost of revenue - service 31,479 — 31,479 Total cost of revenue 76,412 (8,954) 67,458 Total gross profit 81,570 8,954 90,524 Research and development 42,295 — 42,295 Sales and marketing 36,351 (5,380) 30,971 General and administrative 17,205 — 17,205 Amortization of acquired intangible assets — 14,334 14,334 Acquisition-, disposal- and integration-related 12,384 — 12,384 Restructuring and related 2,075 — 2,075 Total operating expenses 110,310 8,954 119,264 Operating loss $ (28,740) $ — $ (28,740)

ACQUISITION OF ECI (Tables)

ACQUISITION OF ECI (Tables)	3 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
Summary of Allocation of Purchase Consideration	A summary of the allocation of the purchase consideration for ECI is as follows (in thousands): Fair value of consideration transferred: Cash consideration: Repayment of ECI outstanding debt obligations $ 183,266 Cash paid to selling shareholders 139,244 Payment to selling shareholders from sale of ECI real estate assets 33,400 Less cash and restricted cash acquired (9,058) Net cash consideration 346,852 Fair value of Ribbon stock issued 108,550 Fair value of total consideration $ 455,402 Fair value of assets acquired and liabilities assumed: Current assets, net of cash and restricted cash acquired $ 120,203 Property and equipment 54,913 Intangible assets: In-process research and development 34,000 Developed technology 111,900 Customer relationships 116,000 Trade names 3,000 Goodwill 191,996 Other noncurrent assets 37,528 Deferred revenue (4,369) Other current liabilities (146,618) Deferred revenue, net of current (3,726) Deferred tax liability (13,308) Other long-term liabilities (46,117) $ 455,402
Unaudited Pro Forma Results	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 Ribbon and ECI. 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 ECI Acquisition occurred at January 1, 2019, nor are they intended to represent or be indicative of future results of operations (in thousands, except per share amounts): Revenue $ 183,189 Net loss $ (39,129) Loss per share $ (0.25)
Schedule of Components of Acquisition Related Costs	The Company's acquisition-, disposal- and integration-related expenses for the three months ended March 31, 2021 and 2020 were as follows (in thousands): Three months ended March 31, March 31, Professional and services fees (acquisition-related) $ — $ 12,374 Professional and services fees (disposal-related) 241 — Integration-related expenses 956 10 $ 1,197 $ 12,384

EARNINGS (LOSS) PER SHARE (Tabl

EARNINGS (LOSS) PER SHARE (Tables)	3 Months Ended
	Mar. 31, 2021
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 earnings (loss) per share were as follows (in thousands): Three months ended March 31, March 31, Weighted average shares outstanding - basic 145,936 120,992 Potential dilutive common shares — — Weighted average shares outstanding - diluted 145,936 120,992

INVENTORY (Tables)

INVENTORY (Tables)	3 Months Ended
	Mar. 31, 2021
Inventory Disclosure [Abstract]
Schedule of Inventory	Inventory at March 31, 2021 and December 31, 2020 consisted of the following (in thousands): March 31, December 31, On-hand final assemblies and finished goods inventories $ 48,529 $ 46,921 Deferred cost of goods sold 1,609 1,165 50,138 48,086 Less noncurrent portion (included in other assets) (5,284) (2,336) Current portion $ 44,854 $ 45,750

INTANGIBLE ASSETS AND GOODWILL

INTANGIBLE ASSETS AND GOODWILL (Tables)	3 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets	The Company's intangible assets at March 31, 2021 and December 31, 2020 consisted of the following (in thousands): March 31, 2021 Weighted average amortization period Cost Accumulated Net In-process research and development * $ 34,000 $ — $ 34,000 Developed technology 7.93 306,380 153,111 153,269 Customer relationships 11.86 268,140 56,049 212,091 Trade names 3.88 5,000 2,827 2,173 Internal use software 3.00 730 730 — 9.17 $ 614,250 $ 212,717 $ 401,533 December 31, 2020 Weighted average amortization period Cost Accumulated Net In-process research and development * $ 34,000 $ — $ 34,000 Developed technology 7.93 306,380 143,050 163,330 Customer relationships 11.86 268,140 50,627 217,513 Trade names 3.88 5,000 2,487 2,513 Internal use software 3.00 730 730 — 9.17 $ 614,250 $ 196,894 $ 417,356 * 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.
Schedule of Estimated Future Amortization Expense for Intangible Assets	Estimated future amortization expense for the Company's intangible assets at March 31, 2021 was as follows (in thousands): Years ending December 31, Remainder of 2021 $ 50,803 2022 60,104 2023 52,256 2024 44,048 2025 37,027 2026 33,200 Thereafter 124,095 $ 401,533
Schedule of Goodwill	The changes in the carrying value of the Company's goodwill in the three months ended March 31, 2020 were as follows (in thousands): Cloud and Edge IP Optical Networks Total Balance at January 1, 2020* $ 224,896 $ — $ 224,896 Acquisition of ECI — 189,493 189,493 Balance at March 31, 2020 $ 224,896 $ 189,493 $ 414,389 (1) Balance is presented net of accumulated impairment losses of $167.4 million for the Cloud and Edge segment. The components of goodwill at March 31, 2021 and 2020 were as follows (in thousands): Cloud and Edge IP Optical Networks Total Balance at March 31, 2021 Goodwill $ 392,302 $ 191,996 $ 584,298 Accumulated impairment losses (167,406) — (167,406) $ 224,896 $ 191,996 $ 416,892 Balance at March 31, 2020 Goodwill $ 392,302 $ 189,493 $ 581,795 Accumulated impairment losses (167,406) — (167,406) $ 224,896 $ 189,493 $ 414,389

ACCRUED EXPENSES AND OTHER (Tab

ACCRUED EXPENSES AND OTHER (Tables)	3 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses at March 31, 2021 and December 31, 2020 consisted of the following (in thousands): March 31, December 31, Employee compensation and related costs $ 41,128 $ 66,039 Other 57,057 68,826 $ 98,185 $ 134,865

WARRANTY ACCRUALS (Tables)

WARRANTY ACCRUALS (Tables)	3 Months Ended
	Mar. 31, 2021
Guarantees and Product Warranties [Abstract]
Changes in Accrual Balance	The changes in the Company's accrual balance in the three months ended March 31, 2021 were as follows (in thousands): Balance at January 1, 2021 $ 14,855 Current period provisions 478 Settlements (1,456) Balance at March 31, 2021 $ 13,877

RESTRUCTURING AND FACILITIES _2

RESTRUCTURING AND FACILITIES CONSOLIDATION INITIATIVES (Tables)	3 Months Ended
	Mar. 31, 2021
Restructuring and Related Activities [Abstract]
Summary of Restructuring Accrual Activity	The components of Restructuring and related expense for the three months ended March 31, 2021 and 2020 were as follows (in thousands): Three months ended March 31, March 31, Severance and related costs $ 669 $ 1,771 Variable and other facilities-related costs 1,913 234 Accelerated amortization of lease assets due to cease-use 3,368 70 $ 5,950 $ 2,075 Balance at Initiatives Adjustments for changes in estimate Cash Balance at Severance $ 5,237 $ 669 $ — $ (2,116) $ 3,790 Facilities 1,256 367 (670) (916) 37 $ 6,493 $ 1,036 $ (670) $ (3,032) $ 3,827 Balance at Initiatives Reclassify accelerated amortization to operating lease liabilities Cash Balance at Severance $ 173 $ — $ — $ (173) $ — Facilities 766 5,584 (3,368) (914) 2,068 $ 939 $ 5,584 $ (3,368) $ (1,087) $ 2,068

DERIVATIVE INSTRUMENTS AND HE_2

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Tables)	3 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Impact of Derivative Financial Instrument on Condensed Consolidated Statement of Operations	The impact of the Company’s derivative financial instrument on its condensed consolidated statement of comprehensive income (loss) for the three months ended March 31, 2021 and 2020 was as follows (in thousands): Three months ended March 31, March 31, Gain (loss) recognized in other comprehensive loss on derivative (effective portion) $ 5,889 $ (9,337) Amount reclassified to (from) accumulated other comprehensive income (loss) to interest expense (effective portion) 780 (190) $ 6,669 (9,527)
Derivative Liability Designed as a Hedging Instrument	The fair values and locations in the condensed consolidated balance sheets at March 31, 2021 and December 31, 2020 of the Company's derivative liability designated as a hedging instrument were as follows (in thousands): Balance sheet location March 31, December 31, Interest rate derivative - liability derivative Accrued expenses and other $ 3,119 $ 3,157 Interest rate derivative - liability derivative Other long-term liabilities $ 1,160 $ 7,791

REVENUE RECOGNITION (Tables)

REVENUE RECOGNITION (Tables)	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
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) Generally, 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) Generally, within 30 days of invoicing Hardware When control of the hardware 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) Generally, within 30 days of invoicing Professional Services Other professional services (excluding training services) As work is performed (over time) Generally, within 30 days of invoicing (upon completion of services) Training When the class is taught (point in time) Generally, within 30 days of services being performed
Disaggregation of Revenue	The Company's revenue for the three months ended March 31, 2021 and 2020 was disaggregated as follows: Three months ended March 31, 2021 Product revenue Service revenue (maintenance) Service revenue (professional services) Total revenue United States $ 36,812 $ 31,606 $ 11,162 $ 79,580 Europe, Middle East and Africa 28,208 19,655 6,910 54,773 Asia Pacific 25,582 9,748 5,803 41,133 Other 7,287 7,696 2,303 17,286 $ 97,889 $ 68,705 $ 26,178 $ 192,772 Three months ended March 31, 2020 Product revenue Service revenue (maintenance) Service revenue (professional services) Total revenue United States $ 36,365 $ 31,466 $ 10,566 $ 78,397 Europe, Middle East and Africa 20,365 14,810 4,015 39,190 Asia Pacific 14,943 7,511 4,878 27,332 Other 4,226 7,281 1,556 13,063 $ 75,899 $ 61,068 $ 21,015 $ 157,982 The Company's product revenue from indirect sales through its channel partner program and from its direct sales program for the three months ended March 31, 2021 and 2020 was as follows (in thousands): Three months ended March 31, March 31, Indirect sales through channel partner program $ 20,163 $ 28,604 Direct sales 77,726 47,295 $ 97,889 $ 75,899 The Company's product revenue from sales to enterprise customers and from sales to service provider customers for the three months ended March 31, 2021 and 2020 was as follows (in thousands): Three months ended March 31, March 31, Sales to enterprise customers $ 22,668 $ 27,281 Sales to service provider customers 75,221 48,618 $ 97,889 $ 75,899 The Company's product revenue and service revenue components by segment for the three months ended March 31, 2021 and 2020 was as follows (in thousands): Three months ended March 31, March 31, Product revenue Cloud and Edge $ 50,152 $ 54,210 IP Optical Networks 47,737 21,689 Total product revenue $ 97,889 $ 75,899 Service revenue Maintenance Cloud and Edge $ 54,673 $ 55,556 IP Optical Networks 14,032 5,512 Total maintenance revenue 68,705 61,068 Professional services Cloud and Edge 20,597 18,265 IP Optical Networks 5,581 2,750 Total professional services revenue 26,178 21,015 Total service revenue $ 94,883 $ 82,083
Schedule of Customer Assets and Liabilities	The changes in the Company's accounts receivable, unbilled receivables and deferred revenue balances for the three months ended March 31, 2021 were as follows (in thousands): Accounts receivable Unbilled accounts receivable Deferred revenue (current) Deferred revenue (long-term) Balance at January 1, 2021 $ 179,331 $ 58,407 $ 96,824 $ 26,010 Increase (decrease), net (27,719) (856) 5,279 (2,956) Balance at March 31, 2021 $ 151,612 57,551 $ 102,103 $ 23,054

OPERATING SEGMENT INFORMATION (

OPERATING SEGMENT INFORMATION (Tables)	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Schedule of Segment Reporting Information	The tables below provide net sales, adjusted gross profit, adjusted EBITDA and depreciation expense by reportable segment for the three months ended March 31, 2021 and 2020 (in thousands): Three months ended March 31, March 31, Segment revenue: Cloud and Edge $ 125,422 $ 128,031 IP Optical Networks 67,350 29,951 Revenue $ 192,772 $ 157,982 Three months ended March 31, March 31, Segment adjusted gross profit: Cloud and Edge $ 84,335 $ 78,935 IP Optical Networks 26,474 11,746 Total segment adjusted gross profit 110,809 90,681 Stock-based compensation expense (262) (157) Gross profit $ 110,547 $ 90,524 Three months ended March 31, March 31, Segment adjusted EBITDA: Cloud and Edge $ 28,330 $ 9,739 IP Optical Networks (8,678) (198) Total segment adjusted EBITDA 19,652 9,541 Depreciation (4,226) (3,474) Amortization of intangible assets (15,823) (14,334) Stock-based compensation (5,060) (2,976) Litigation costs — (3,038) Acquisition-, disposal- and integration-related expense (1,197) (12,384) Restructuring and related expense (5,950) (2,075) Loss from operations $ (12,604) $ (28,740) Segment depreciation expense: Cloud and Edge $ 3,137 $ 2,993 IP Optical Networks 1,089 481 Depreciation expense $ 4,226 $ 3,474

MAJOR CUSTOMERS (Tables)

MAJOR CUSTOMERS (Tables)	3 Months Ended
	Mar. 31, 2021
Risks and Uncertainties [Abstract]
Schedule of Customer Contributing 10% or More of the Revenue	The following customers contributed 10% or more of the Company's revenue in the three months ended March 31, 2021 and 2020: Three months ended March 31, March 31, Verizon Communications Inc. 16% 13% AT&T Inc. * 10% * Represents less than 10% of total revenue.

STOCK-BASED COMPENSATION PLANS

STOCK-BASED COMPENSATION PLANS (Tables)	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Schedule of Activity Related to Outstanding Stock Options	The activity related to the Company's outstanding stock options for the three months ended March 31, 2021 was as follows: Number of Weighted Weighted Aggregate Outstanding at January 1, 2021 207,710 $ 12.69 Exercised (13,389) $ 1.76 Outstanding at March 31, 2021 194,321 $ 13.44 3.31 $ 267 Vested or expected to vest at March 31, 2021 194,253 $ 13.45 3.31 $ 266 Exercisable at March 31, 2021 191,930 $ 13.59 3.27 $ 252
Schedule of Activity Related to Unvested Restricted Stock Grants	The activity related to the Company's RSAs for the three months ended March 31, 2021 was as follows: Shares Weighted Unvested balance at January 1, 2021 86,983 $ 7.04 Vested (86,983) $ 7.04 Unvested balance at March 31, 2021 — $ — The activity related to the Company's RSUs for the three months ended March 31, 2021 was as follows: Shares Weighted Unvested balance at January 1, 2021 6,531,110 $ 3.32 Granted 2,885,002 $ 8.59 Vested (1,575,645) $ 2.60 Forfeited (372,984) $ 3.68 Unvested balance at March 31, 2021 7,467,483 $ 5.49
Schedule of Activity Related to Performance Stock Awards	The activity related to the Company's PSUs for the three months ended March 31, 2021 was as follows: Shares Weighted Unvested balance at January 1, 2021 6,035,931 $ 1.56 Granted 642,121 $ 5.83 Vested (1,525,681) $ 0.98 Forfeited (57,480) $ 5.12 Unvested balance at March 31, 2021 5,094,891 $ 2.40
Schedule of Stock-based Compensation Expenses Which Are Included in Condensed Consolidated Statement of Operations	The condensed consolidated statements of operations include stock-based compensation for the three months ended March 31, 2021 and 2020 as follows (in thousands): Three months ended March 31, March 31, Product cost of revenue $ 27 $ 27 Service cost of revenue 235 130 Research and development 627 558 Sales and marketing 1,874 752 General and administrative 2,297 1,509 $ 5,060 $ 2,976

LEASES (Tables)

LEASES (Tables)	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Schedule of Right-of-use lease assets and lease liabilities	The Company's right-of-use lease assets and lease liabilities at March 31, 2021 and December 31, 2020 were as follows (in thousands): Classification March 31, December 31, Assets Operating lease assets Operating lease right-of-use assets $ 62,579 $ 69,757 Finance lease assets* Property and equipment, net 754 983 Total leased assets $ 63,333 $ 70,740 Liabilities Current Operating Operating lease liabilities $ 17,627 $ 17,023 Finance Accrued expenses and other 820 902 Noncurrent Operating Operating lease liabilities, net of current 68,100 72,614 Finance Other long-term liabilities 398 568 Total lease liabilities $ 86,945 $ 91,107 * Finance lease assets were recorded net of accumulated depreciation of $2.2 million and $1.9 million at March 31, 2021 and December 31, 2020, respectively.
Schedule of Components of lease expense	The components of lease expense for the three months ended March 31, 2021 and 2020 were as follows (in thousands): Three months ended March 31, March 31, Operating lease cost* $ 8,837 $ 3,344 Finance lease cost Amortization of leased assets 229 319 Interest on lease liabilities 26 55 Short-term lease cost 3,292 5,523 Variable lease costs (costs excluded from minimum fixed lease payments)** 2,158 637 Sublease income (276) — Net lease cost $ 14,266 $ 9,878 * Operating lease cost for the three months ended March 31, 2021 included $3.4 million of accelerated amortization for certain assets partially or fully vacated in 2021 with no intent or ability to sublease. Operating lease cost for the three months ended March 31, 2020 included $0.1 million of accelerated amortization for certain assets partially or fully vacated in 2020 with no ability to sublease. ** Variable lease costs for the three months ended March 31, 2021 included an accrual of $1.4 million for all future estimated variable expenses related to certain assets partially or fully vacated in 2021 with no intent or ability to sublease. No such variable costs were accrued in the three months ended March 31, 2020. Cash flow information related to the Company's leases for the three months ended March 31, 2021 and 2020 was as follows (in thousands): Three months ended March 31, March 31, Cash paid for amounts included in the measurement of lease liabilities Operating cash flows for operating leases $ 5,561 $ 3,113 Operating cash flows for finance leases $ 26 $ 55 Financing cash flows for finance leases $ 272 $ 338 Other information related to the Company's leases as of March 31, 2021 and December 31, 2020 was as follows: March 31, December 31, Weighted average remaining lease term (years) Operating leases 6.52 6.59 Finance leases 1.51 1.70 Weighted average discount rate Operating leases 5.72 % 5.67 % Finance leases 5.74 % 6.15 %
Schedule of Future minimum fixed lease payments under noncancelable operating leases	Future minimum fixed lease payments under noncancelable leases at March 31, 2021 were as follows (in thousands): March 31, 2021 Operating Finance leases leases Remainder of 2021 $ 16,397 $ 701 2022 20,026 509 2023 17,267 62 2024 10,392 — 2025 8,540 — 2026 and beyond 32,592 — Total lease payments 105,214 1,272 Less: interest (19,487) (54) Present value of lease liabilities $ 85,727 $ 1,218
Schedule of Future minimum fixed lease payments under noncancelable finance leases	Future minimum fixed lease payments under noncancelable leases at March 31, 2021 were as follows (in thousands): March 31, 2021 Operating Finance leases leases Remainder of 2021 $ 16,397 $ 701 2022 20,026 509 2023 17,267 62 2024 10,392 — 2025 8,540 — 2026 and beyond 32,592 — Total lease payments 105,214 1,272 Less: interest (19,487) (54) Present value of lease liabilities $ 85,727 $ 1,218

BASIS OF PRESENTATION - Narrati

BASIS OF PRESENTATION - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)country	Dec. 31, 2020USD ($)segment	Mar. 31, 2020USD ($)
Product Warranty Liability [Line Items]
Number of countries | country	35
Restricted cash, current		$ 7,269
Cash received from the sale of certain accounts receivable	$ 31,100		$ 15,100
Interest expense	200		$ 100
Tax payment on certain fixed assets
Product Warranty Liability [Line Items]
Restricted cash		4,600
Restricted short-term bank deposits
Product Warranty Liability [Line Items]
Restricted cash, current	$ 2,659
Restricted cash		$ 2,700
Operating Segments
Product Warranty Liability [Line Items]
Number of operating segments | segment		2

BASIS OF PRESENTATION - Reclass

BASIS OF PRESENTATION - Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue	$ 192,772	$ 157,982
Total cost of revenue	82,225	67,458
Total gross profit	110,547	90,524
Research and development	47,410	42,295
Sales and marketing	37,218	30,971
General and administrative	15,553	17,205
Amortization of acquired intangible assets		14,334
Acquisition-, disposal- and integration-related	1,197	12,384
Restructuring and related	5,950	2,075
Total operating expenses	123,151	119,264
Operating loss	(12,604)	(28,740)
Prior presentation
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue		157,982
Total cost of revenue		76,412
Total gross profit		81,570
Research and development		42,295
Sales and marketing		36,351
General and administrative		17,205
Amortization of acquired intangible assets		0
Acquisition-, disposal- and integration-related		12,384
Restructuring and related		2,075
Total operating expenses		110,310
Operating loss		(28,740)
Amounts reclassified
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue		0
Total cost of revenue		(8,954)
Total gross profit		8,954
Research and development		0
Sales and marketing		(5,380)
General and administrative		0
Amortization of acquired intangible assets		14,334
Acquisition-, disposal- and integration-related		0
Restructuring and related		0
Total operating expenses		8,954
Operating loss		0
Product
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue	97,889	75,899
Total cost of revenue	44,445	35,979
Product | Prior presentation
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue		75,899
Total cost of revenue		44,933
Product | Amounts reclassified
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue		0
Total cost of revenue		(8,954)
Service
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue	94,883	82,083
Total cost of revenue	$ 37,780	31,479
Service | Prior presentation
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue		82,083
Total cost of revenue		31,479
Service | Amounts reclassified
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total revenue		0
Total cost of revenue		$ 0

ACQUISITION OF ECI - Narrative

ACQUISITION OF ECI - Narrative (Details) - USD ($) shares in Millions	Nov. 14, 2019	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Business Acquisition [Line Items]
Net cash consideration		$ 0	$ 346,852,000
Term Loan Facility
Business Acquisition [Line Items]
Commitments from lender	$ 400,000,000
Revolving Credit Facility
Business Acquisition [Line Items]
Commitments from lender	100,000,000
ECI
Business Acquisition [Line Items]
Proceeds from sale of real estate assets	$ 33,400,000
Revenue			30,000,000
Net loss			$ 3,300,000
ECI
Business Acquisition [Line Items]
Common stock to be issued (in shares)	32.5
Fair value of stock issued	$ 108,600,000			$ 108,550,000
Net cash consideration	322,500,000			346,852,000
Repayment of ECI outstanding debt obligations	183,300,000			183,266,000
Payment to selling shareholders	$ 139,200,000			$ 139,244,000
Weighted average useful life of intangible assets (in years)		12 years 4 months 17 days

ACQUISITION OF ECI - Summary of

ACQUISITION OF ECI - Summary of Preliminary Allocation of Purchase Consideration (Details) - USD ($) $ in Thousands	Nov. 14, 2019	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Cash consideration:
Net cash consideration		$ 0	$ 346,852
Fair value of assets acquired and liabilities assumed:
Goodwill		$ 416,892	$ 414,389	$ 416,892	$ 224,896
ECI
Cash consideration:
Repayment of ECI outstanding debt obligations	$ 183,300			183,266
Cash paid to selling shareholders	139,200			139,244
Payment to selling shareholders from sale of ECI real estate assets				33,400
Less cash and restricted cash acquired				(9,058)
Net cash consideration	322,500			346,852
Fair value of Ribbon stock issued	$ 108,600			108,550
Fair value of total consideration				455,402
Fair value of assets acquired and liabilities assumed:
Current assets, net of cash and restricted cash acquired				120,203
Property and equipment				54,913
Goodwill				191,996
Other noncurrent assets				37,528
Deferred revenue				(4,369)
Other current liabilities				(146,618)
Deferred revenue, net of current				(3,726)
Deferred tax liability				(13,308)
Other long-term liabilities				(46,117)
Fair value of assets acquired and liabilities assumed				455,402
ECI | In-process research and development
Fair value of assets acquired and liabilities assumed:
Intangible assets				34,000
ECI | Developed technology
Fair value of assets acquired and liabilities assumed:
Intangible assets				111,900
ECI | Customer relationships
Fair value of assets acquired and liabilities assumed:
Intangible assets				116,000
ECI | Trade names
Fair value of assets acquired and liabilities assumed:
Intangible assets				$ 3,000

ACQUISITION OF ECI - Unaudited

ACQUISITION OF ECI - Unaudited Pro Forma Results (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020USD ($)$ / shares
Business Combinations [Abstract]
Revenue	$ 183,189
Net loss	$ (39,129)
Loss per share (in dollars per share) | $ / shares	$ (0.25)

ACQUISITION OF ECI - Summary _2

ACQUISITION OF ECI - Summary of Acquisition Related Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Business Combinations [Abstract]
Professional and services fees (acquisition-related)	$ 0	$ 12,374
Professional and services fees (disposal-related)	241	0
Integration-related expenses	956	10
Total	$ 1,197	$ 12,384

SALE OF KANDY COMMUNICATIONS _2

SALE OF KANDY COMMUNICATIONS BUSINESS (Details) $ / shares in Units, $ in Thousands	Feb. 19, 2021day$ / shares	Dec. 01, 2020USD ($)day$ / sharesshares	Mar. 31, 2021USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Increase in fair value of investments			$ (22,441)	$ 0
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Kandy Communications Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration from sale		$ 45,000
Principal amount of debentures		$ 1
Number of warrants acquired (in shares) | shares		1
Number of shares entitled from warrant (in shares) | shares		100
Par value of common stock (in dollars per share) | $ / shares		$ 0.0001
Number of AVCT Units acquired (in shares) | shares		43,778
Interest rate		10.00%
Debenture, conversion price (in dollars per share) | $ / shares		$ 3.45
Debenture, stock price trigger (in dollars per share) | $ / shares	$ 6	$ 6
Debenture, number of trading days | day	40	40
Debenture, number of consecutive trading days | day	60	60
Amount from option to redeem debentures		$ 5,000
Threshold amount raised in offering		$ 50,000
Number of shares of common stock entitled from warrants (in shares) | shares		4,377,800
Exercise price of warrants (in dollars per share) | $ / shares		$ 0.01
Fair value of AVCT units		$ 84,900	92,700		$ 115,200
Fair value of debentures		66,300
Fair value of warrants		18,600
Net assets sold		$ 1,300
Gain on sale			83,600
Increase in fair value of investments			23,900
Loss partially offset principal of the debentures			$ 1,500

EARNINGS (LOSS) PER SHARE (Deta

EARNINGS (LOSS) PER SHARE (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Reconciliation of weighted average shares outstanding from basic to diluted
Weighted average shares outstanding—basic (in shares)	145,936	120,992
Potential dilutive common shares (in shares)	0	0
Weighted average shares outstanding—diluted (in shares)	145,936	120,992
Options, restricted and performance-based stock and stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities not included in computation of diluted loss per share (in shares)	12,800	11,700

INVENTORY (Details)

INVENTORY (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Inventory Disclosure [Abstract]
On-hand final assemblies and finished goods inventories	$ 48,529	$ 46,921
Deferred cost of goods sold	1,609	1,165
Gross inventory	50,138	48,086
Less noncurrent portion (included in other assets)	(5,284)	(2,336)
Current portion	$ 44,854	$ 45,750

INTANGIBLE ASSETS AND GOODWIL_2

INTANGIBLE ASSETS AND GOODWILL - Schedule of Intangible Assets and Amortization (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Intangible Assets And Goodwill
Weighted average amortization period (years)	9 years 2 months 1 day	9 years 2 months 1 day
Cost	$ 614,250	$ 614,250
Accumulated amortization	212,717	196,894
Net carrying value	401,533	417,356
Estimated future amortization expense for intangible assets
Remainder of 2021	50,803
2022	60,104
2023	52,256
2024	44,048
2025	37,027
2026	33,200
Thereafter	124,095
Total	401,533
In-process research and development
Intangible Assets And Goodwill
Cost	34,000	34,000
Accumulated amortization	0	0
Net carrying value	$ 34,000	$ 34,000
Developed technology
Intangible Assets And Goodwill
Weighted average amortization period (years)	7 years 11 months 4 days	7 years 11 months 4 days
Cost	$ 306,380	$ 306,380
Accumulated amortization	153,111	143,050
Net carrying value	$ 153,269	$ 163,330
Customer relationships
Intangible Assets And Goodwill
Weighted average amortization period (years)	11 years 10 months 9 days	11 years 10 months 9 days
Cost	$ 268,140	$ 268,140
Accumulated amortization	56,049	50,627
Net carrying value	$ 212,091	$ 217,513
Trade names
Intangible Assets And Goodwill
Weighted average amortization period (years)	3 years 10 months 17 days	3 years 10 months 17 days
Cost	$ 5,000	$ 5,000
Accumulated amortization	2,827	2,487
Net carrying value	$ 2,173	$ 2,513
Internal use software
Intangible Assets And Goodwill
Weighted average amortization period (years)	3 years	3 years
Cost	$ 730	$ 730
Accumulated amortization	730	730
Net carrying value	$ 0	$ 0

INTANGIBLE ASSETS AND GOODWIL_3

INTANGIBLE ASSETS AND GOODWILL - Schedule of Changes in Carrying Value of Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2021
Goodwill [Roll Forward]
Goodwill. beginning of period	$ 224,896
Goodwill, end of period	414,389
Accumulated impairment losses	167,406	$ 167,406
ECI
Goodwill [Roll Forward]
Acquisition	189,493
Cloud and Edge
Goodwill [Roll Forward]
Goodwill. beginning of period	224,896
Goodwill, end of period	224,896
Accumulated impairment losses	167,406	167,406
Cloud and Edge | ECI
Goodwill [Roll Forward]
Acquisition	0
IP Optical Networks
Goodwill [Roll Forward]
Goodwill. beginning of period	0
Goodwill, end of period	189,493
Accumulated impairment losses	0	$ 0
IP Optical Networks | ECI
Goodwill [Roll Forward]
Acquisition	$ 189,493

INTANGIBLE ASSETS AND GOODWIL_4

INTANGIBLE ASSETS AND GOODWILL - Schedule of Components of Goodwill (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Goodwill, gross	$ 584,298		$ 581,795
Accumulated impairment losses	(167,406)		(167,406)
Goodwill	416,892	$ 416,892	414,389	$ 224,896
Cloud and Edge
Goodwill [Line Items]
Goodwill, gross	392,302		392,302
Accumulated impairment losses	(167,406)		(167,406)
Goodwill	224,896		224,896	224,896
IP Optical Networks
Goodwill [Line Items]
Goodwill, gross	191,996		189,493
Accumulated impairment losses	0		0
Goodwill	$ 191,996		$ 189,493	$ 0

ACCRUED EXPENSES AND OTHER (Det

ACCRUED EXPENSES AND OTHER (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Employee compensation and related costs	$ 41,128	$ 66,039
Other	57,057	68,826
Total accrued expenses	$ 98,185	$ 134,865

WARRANTY ACCRUALS - Changes in

WARRANTY ACCRUALS - Changes in Accrual Balance (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)
Movement in Standard Product Warranty Accrual [Roll Forward]
Balance at January 1, 2021	$ 14,855
Current period provisions	478
Settlements	(1,456)
Balance at March 31, 2021	$ 13,877

WARRANTY ACCRUALS - Narrative (

WARRANTY ACCRUALS - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Guarantees and Product Warranties [Abstract]
Accrued expenses and other	$ 5.7	$ 6.5
Other long-term liabilities	$ 8.2	$ 8.4

RESTRUCTURING AND FACILITIES _3

RESTRUCTURING AND FACILITIES CONSOLIDATION INITIATIVES - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)executive	Mar. 31, 2020USD ($)segmentemployee	Dec. 31, 2020USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and related	$ 5,950	$ 2,075
Accelerated amortization of lease assets due to cease-use	3,368	70
Long-term portion of accrued restructuring	2,100		$ 800
2020 Restructuring Initiative
Restructuring Cost and Reserve [Line Items]
Restructuring and related	1,036
Restructuring charges, net of adjustments	400	$ 1,100
Number of positions eliminated | employee		10
Credit offset	670
Restructuring and related cost, expected cost	4,000
2020 Restructuring Initiative | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and related	669
Restructuring charges, net of adjustments		$ 700
Credit offset	$ 0
2020 Restructuring Initiative | Severance | Executives
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated | executive	3
2020 Restructuring Initiative | Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring and related	$ 367
Restructuring charges, net of adjustments	400
Credit offset	670
2019 Restructuring Initiative
Restructuring Cost and Reserve [Line Items]
Restructuring and related	5,584
Restructuring charges, net of adjustments	5,600	$ 1,000
Number of positions eliminated | segment		5
Accelerated amortization of lease assets due to cease-use	3,400
2019 Restructuring Initiative | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and related	0
Restructuring charges, net of adjustments		$ 700
2019 Restructuring Initiative | Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring and related	5,584
Restructuring charges, net of adjustments		300
Accelerated amortization of lease assets due to cease-use	$ 3,400	$ 100

RESTRUCTURING AND FACILITIES _4

RESTRUCTURING AND FACILITIES CONSOLIDATION INITIATIVES - Components of Restructuring Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Restructuring and Related Activities [Abstract]
Severance and related costs	$ 669	$ 1,771
Variable and other facilities-related costs	1,913	234
Accelerated amortization of lease assets due to cease-use	3,368	70
Restructuring and related expense	$ 5,950	$ 2,075

RESTRUCTURING AND FACILITIES _5

RESTRUCTURING AND FACILITIES CONSOLIDATION INITIATIVES - Accrual Activity for Severance and Related Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Restructuring Reserve [Roll Forward]
Initiatives charged to expense	$ 5,950	$ 2,075
Facilities
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	800
Balance at the end of the period	2,100
2020 Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	6,493
Initiatives charged to expense	1,036
Adjustments for changes in estimate	(670)
Cash payments	(3,032)
Balance at the end of the period	3,827
2020 Restructuring Initiative | Severance
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	5,237
Initiatives charged to expense	669
Adjustments for changes in estimate	0
Cash payments	(2,116)
Balance at the end of the period	3,790
2020 Restructuring Initiative | Facilities
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	1,256
Initiatives charged to expense	367
Adjustments for changes in estimate	(670)
Cash payments	(916)
Balance at the end of the period	$ 37

RESTRUCTURING AND FACILITIES _6

RESTRUCTURING AND FACILITIES CONSOLIDATION INITIATIVES - Assumed Restructuring Initiative Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Restructuring Reserve [Roll Forward]
Initiatives charged to expense	$ 5,950	$ 2,075
2019 Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	939
Initiatives charged to expense	5,584
Reclassify accelerated amortization to operating lease liabilities	(3,368)
Cash payments	(1,087)
Balance at the end of the period	2,068
Severance | 2019 Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	173
Initiatives charged to expense	0
Reclassify accelerated amortization to operating lease liabilities	0
Cash payments	(173)
Balance at the end of the period	0
Facilities
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	800
Balance at the end of the period	2,100
Facilities | 2019 Restructuring Initiative
Restructuring Reserve [Roll Forward]
Balance at the beginning of the period	766
Initiatives charged to expense	5,584
Reclassify accelerated amortization to operating lease liabilities	(3,368)
Cash payments	(914)
Balance at the end of the period	$ 2,068

DEBT - Credit Facilities (Detai

DEBT - Credit Facilities (Details)	Mar. 03, 2021USD ($)	Aug. 18, 2020USD ($)	Mar. 03, 2020USD ($)	Mar. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Nov. 14, 2019USD ($)
2020 Credit Facility
Debt Instrument [Line Items]
Commitments from lender			$ 500,000,000
Repayments of principal in first year				$ 10,000,000
Repayments of principal in year two				20,000,000
Repayments of principal in year three				20,000,000
Repayments of principal in year four				20,000,000
Repayments of principal in last year				30,000,000
Default rate percentage			2.00%
Percentage of consolidated adjusted EBITDA	100.00%	75.00%	100.00%
2020 Credit Facility | Minimum
Debt Instrument [Line Items]
Consolidated net leverage ratio	2.75	2.25
Borrower's consolidated net leverage ratio	$ 10,000,000	$ 25,000,000
2020 Credit Facility | Maximum
Debt Instrument [Line Items]
Consolidated net leverage ratio	2.25	2.75
Borrower's consolidated net leverage ratio	$ 25,000,000	$ 10,000,000
Term Loan Facility
Debt Instrument [Line Items]
Commitments from lender						$ 400,000,000
Term Loan Facility | 2020 Credit Facility
Debt Instrument [Line Items]
Commitments from lender			$ 400,000,000
Outstanding balance				$ 390,600,000	$ 393,100,000
Revolving Credit Facility
Debt Instrument [Line Items]
Commitments from lender						$ 100,000,000
Revolving Credit Facility | 2020 Credit Facility
Debt Instrument [Line Items]
Commitments from lender			100,000,000
Revolving Credit Facility | 2020 Credit Facility | Line of Credit | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate		0.00%
Letter of Credit
Debt Instrument [Line Items]
Letters of credit outstanding					$ 5,600,000
Letter of Credit | 2020 Credit Facility
Debt Instrument [Line Items]
Commitments from lender			30,000,000
Debt interest rate				2.50%	2.50%
Letters of credit outstanding				$ 6,400,000	$ 5,600,000
Swingline Loan | 2020 Credit Facility
Debt Instrument [Line Items]
Commitments from lender			$ 20,000,000
Term Loan Facility, Term A Loan | 2020 Credit Facility
Debt Instrument [Line Items]
Commitments from lender		$ 325,000,000
Repayments of principal in first year		10,000,000
Repayments of principal in year two		16,000,000
Repayments of principal in year three		16,000,000
Repayments of principal in year four		20,000,000
Repayments of principal in last year		16,000,000
Repayments of principal on the maturity date		$ 244,000,000
Outstanding balance				$ 390,600,000	$ 318,500,000
Debt interest rate				3.40%	3.40%
Term Loan Facility, Term A Loan | 2020 Credit Facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate		1.50%
Term Loan Facility, Term A Loan | 2020 Credit Facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate		3.50%
Term Loan Facility, Term A Loan | 2020 Credit Facility | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate		0.50%
Term Loan Facility, Term A Loan | 2020 Credit Facility | Additional Applicable Margin | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate		0.50%
Term Loan Facility, Term A Loan | 2020 Credit Facility | Additional Applicable Margin | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate		2.50%
Term Loan Facility, Term B Loan | Additional Applicable Margin
Debt Instrument [Line Items]
Basis spread on variable rate		6.50%
Term Loan Facility, Term B Loan | 2020 Credit Facility
Debt Instrument [Line Items]
Commitments from lender		$ 75,000,000
Repayments of principal in first year		1,000,000
Repayments of principal in year two		8,000,000
Repayments of principal in year three		8,000,000
Repayments of principal in year four		8,000,000
Repayments of principal in last year		8,000,000
Repayments of principal on the maturity date		$ 66,000,000
Premium percentage from voluntary repayment		1.00%
Outstanding balance					$ 74,600,000
Debt interest rate					8.40%
Term Loan Facility, Term B Loan | 2020 Credit Facility | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate		7.50%
Term Loan Facility, Term B Loan | 2020 Credit Facility | Prime Rate | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate		0.50%
2020 Term Loan
Debt Instrument [Line Items]
Repayments of principal in first year	20,000,000
Repayments of principal in year two	20,000,000
Repayments of principal in year three	20,000,000
Repayments of principal in year four	30,000,000
Repayments of principal in last year	300,000,000
Quarterly principal payment amount	$ 74,600,000
Write off of capitalized debt issuance costs				$ 2,500,000

DEBT - Letters of Credit and Pe

DEBT - Letters of Credit and Performance and Bid Bonds (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Line of Credit Facility [Line Items]
Cash collateral	$ 2.7	$ 2.7
Various Uncommitted Facilities
Line of Credit Facility [Line Items]
Letters of credit outstanding	26.9	27
Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding		5.6
2020 Credit Facility | Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding	$ 6.4	$ 5.6

DERIVATIVE INSTRUMENTS AND HE_3

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Narrative (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Derivative [Line Items]
Reclassified as an increase to interest expense over the next twelve months	$ 3,100,000
Interest Rate Swap
Derivative [Line Items]
Notional amount	400,000,000
Interest Rate Swap | Level Two
Derivative [Line Items]
Interest rate derivative - liability derivative	4,300,000	$ 10,900,000
2020 Credit Facility | Term Loan Facility
Derivative [Line Items]
Outstanding balance	$ 390,600,000	$ 393,100,000
Principal amount			$ 400,000,000
Fixed rate	0.904%

DERIVATIVE INSTRUMENTS AND HE_4

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Impact of Derivative Financial Instrument on Condensed Consolidated Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Gain (loss) recognized in other comprehensive loss on derivative (effective portion)	$ 5,889	$ (9,337)
Amount reclassified to (from) accumulated other comprehensive income (loss) to interest expense (effective portion)	780	(190)
Other comprehensive income (loss), cash flow hedge, gain (loss), after reclassification, before tax, parent	$ 6,669	$ (9,527)

DERIVATIVE INSTRUMENTS AND HE_5

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Fair Values and Locations in the Condensed Consolidated Balance Sheet (Details) - Interest Rate Swap - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Accrued expenses and other
Derivative [Line Items]
Interest rate derivative - liability derivative	$ 3,119	$ 3,157
Other long-term liabilities
Derivative [Line Items]
Interest rate derivative - liability derivative	$ 1,160	$ 7,791

REVENUE RECOGNITION - Narrative

REVENUE RECOGNITION - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue agreement term	1 year
Revenue recognized	$ 42	$ 41
Customer contract expected life (in years)	5 years
Deferred sales commissions capitalized	$ 4.1		$ 4.1
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Disaggregation of Revenue [Line Items]
Revenue to be recognized	$ 11
Revenue, remaining performance obligation, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Disaggregation of Revenue [Line Items]
Revenue to be recognized	$ 8
Revenue, remaining performance obligation, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Disaggregation of Revenue [Line Items]
Revenue to be recognized	$ 4
Revenue, remaining performance obligation, period

REVENUE RECOGNITION - Schedule

REVENUE RECOGNITION - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Total revenue	$ 192,772	$ 157,982
Cloud and Edge
Disaggregation of Revenue [Line Items]
Total revenue	125,422	128,031
IP Optical Networks
Disaggregation of Revenue [Line Items]
Total revenue	67,350	29,951
Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	97,889	75,899
Product revenue | Cloud and Edge
Disaggregation of Revenue [Line Items]
Total revenue	50,152	54,210
Product revenue | IP Optical Networks
Disaggregation of Revenue [Line Items]
Total revenue	47,737	21,689
Product revenue | Sales to enterprise customers
Disaggregation of Revenue [Line Items]
Total revenue	22,668	27,281
Product revenue | Sales to service provider customers
Disaggregation of Revenue [Line Items]
Total revenue	75,221	48,618
Product revenue | Indirect sales through channel partner program
Disaggregation of Revenue [Line Items]
Total revenue	20,163	28,604
Product revenue | Direct sales
Disaggregation of Revenue [Line Items]
Total revenue	77,726	47,295
Service
Disaggregation of Revenue [Line Items]
Total revenue	94,883	82,083
Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	68,705	61,068
Service revenue (maintenance) | Cloud and Edge
Disaggregation of Revenue [Line Items]
Total revenue	54,673	55,556
Service revenue (maintenance) | IP Optical Networks
Disaggregation of Revenue [Line Items]
Total revenue	14,032	5,512
Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	26,178	21,015
Service revenue (professional services) | Cloud and Edge
Disaggregation of Revenue [Line Items]
Total revenue	20,597	18,265
Service revenue (professional services) | IP Optical Networks
Disaggregation of Revenue [Line Items]
Total revenue	5,581	2,750
United States
Disaggregation of Revenue [Line Items]
Total revenue	79,580	78,397
United States | Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	36,812	36,365
United States | Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	31,606	31,466
United States | Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	11,162	10,566
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenue	54,773	39,190
Europe, Middle East and Africa | Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	28,208	20,365
Europe, Middle East and Africa | Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	19,655	14,810
Europe, Middle East and Africa | Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	6,910	4,015
Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	41,133	27,332
Asia Pacific | Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	25,582	14,943
Asia Pacific | Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	9,748	7,511
Asia Pacific | Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	5,803	4,878
Other
Disaggregation of Revenue [Line Items]
Total revenue	17,286	13,063
Other | Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	7,287	4,226
Other | Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	7,696	7,281
Other | Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	$ 2,303	$ 1,556

REVENUE RECOGNITION - Schedul_2

REVENUE RECOGNITION - Schedule of Customer Assets & Liabilities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)
Accounts receivable
Beginning balance	$ 179,331
Increase (decrease), net	(27,719)
Ending balance	151,612
Unbilled accounts receivable
Beginning balance	58,407
Increase (decrease), net	(856)
Ending balance	57,551
Deferred revenue (current)
Beginning balance	96,824
Increase (decrease), net	5,279
Ending balance	102,103
Deferred revenue (long-term)
Beginning balance	26,010
Increase (decrease), net	(2,956)
Ending balance	$ 23,054

OPERATING SEGMENT INFORMATION_2

OPERATING SEGMENT INFORMATION (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)segment	Mar. 31, 2020USD ($)
Segment Reporting [Abstract]
Number of reportable operating segments | segment	2
Segment Reporting Information [Line Items]
Total revenue	$ 192,772	$ 157,982
Total segment adjusted gross profit	110,809	90,681
Stock-based compensation expense	(262)	(157)
Gross profit	110,547	90,524
Adjusted EBITDA	19,652	9,541
Depreciation	(4,226)	(3,474)
Amortization of intangible assets	(15,823)	(14,334)
Stock-based compensation	(5,060)	(2,976)
Litigation costs	0	(3,038)
Acquisition-, disposal- and integration-related expense	(1,197)	(12,384)
Restructuring and related expense	(5,950)	(2,075)
Loss from operations	(12,604)	(28,740)
Segment depreciation expense:
Depreciation expense	4,226	3,474
Cloud and Edge
Segment Reporting Information [Line Items]
Total revenue	125,422	128,031
Total segment adjusted gross profit	84,335	78,935
Adjusted EBITDA	28,330	9,739
Depreciation	(3,137)	(2,993)
Segment depreciation expense:
Depreciation expense	3,137	2,993
IP Optical Networks
Segment Reporting Information [Line Items]
Total revenue	67,350	29,951
Total segment adjusted gross profit	26,474	11,746
Adjusted EBITDA	(8,678)	(198)
Depreciation	(1,089)	(481)
Segment depreciation expense:
Depreciation expense	$ 1,089	$ 481

MAJOR CUSTOMERS (Details)

MAJOR CUSTOMERS (Details) - Customer	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Revenue | Verizon Communications Inc.
MAJOR CUSTOMERS
Concentration risk, percentage	16.00%	13.00%
Revenue | AT&T Inc.
MAJOR CUSTOMERS
Concentration risk, percentage		10.00%
Accounts receivable balance
MAJOR CUSTOMERS
Concentration risk, percentage	16.00%		12.00%

COMMON STOCK REPURCHASES (Detai

COMMON STOCK REPURCHASES (Details) - Repurchase Program - USD ($)	Dec. 31, 2020	Mar. 31, 2020	Jun. 30, 2019
Class of Stock [Line Items]
Repurchase amount authorized (up to)			$ 75,000,000
Remaining authorized repurchase amount	$ 70,500,000	$ 70,500,000

STOCK-BASED COMPENSATION PLAN_2

STOCK-BASED COMPENSATION PLANS - Narrative (Details)	Feb. 26, 2021shares	Mar. 16, 2020shares	Mar. 31, 2021USD ($)performance_period$ / sharesshares	Mar. 31, 2020USD ($)	Dec. 31, 2020$ / sharesshares	Dec. 31, 2019
Stock-based compensation
Total intrinsic values of stock options exercised (in dollars per share) | $			$ 100,000
Cash received from the exercise of stock options (in dollars per share) | $			24,000
Total fair value of restricted stock awards, restricted stock units and performance-based stock units on date vested | $			28,182,000	$ 3,182,000
Tax benefit from stock based compensation expense | $			0	$ 0
Fair value of the assumed awards attributable to future stock-based compensation expense | $			$ 36,400,000
Expected period for unrecognized expense			2 years
RSUs
Stock-based compensation
Eligible to vest (in shares)			7,467,483		6,531,110
Granted (in shares)			2,885,002
Grant date fair value (in dollars per share) | $ / shares			$ 5.49		$ 3.32
RSUs | Employee Bonus Program
Stock-based compensation
Percent of target cash bonus of employee			50.00%
Percent reduction of cash target bonus			50.00%
PSUs
Stock-based compensation
Eligible to vest (in shares)			5,094,891		6,035,931
Granted (in shares)			642,121
Grant date fair value (in dollars per share) | $ / shares			$ 2.40		$ 1.56
Total fair value of restricted stock awards, restricted stock units and performance-based stock units on date vested | $			$ 1,500,000
PSUs | Bucci Stock Price PSUs
Stock-based compensation
Granted (in shares)					133,333
Performance Shares, Performance Based
Stock-based compensation
Granted percentage			60.00%		60.00%	60.00%
Number of performance periods | performance_period			3
Vesting percentage			33.33%
Percent of performance metrics achieved			200.00%
Service period			3 years
Performance Shares, Market Based
Stock-based compensation
Granted percentage			40.00%		40.00%	40.00%
Number of performance periods | performance_period			1
Percent of performance metrics achieved			200.00%
Performance period (in years)			3 years
Grant date fair value (in dollars per share) | $ / shares			$ 8.65
RSAs and RSUs
Stock-based compensation
Total fair value of restricted stock awards, restricted stock units and performance-based stock units on date vested | $			$ 4,700,000
Chief Executive Officer | RSUs
Stock-based compensation
Eligible to vest (in shares)		462,963
Chief Executive Officer | PSUs
Stock-based compensation
Maximum number of shares to be settled (in shares)		4,750,000
Granted (in shares)	1,333,333

STOCK-BASED COMPENSATION PLAN_3

STOCK-BASED COMPENSATION PLANS - Stock Options (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)$ / sharesshares
Number of Shares
Outstanding at the beginning of the period (in shares) | shares	207,710
Exercised (in shares) | shares	(13,389)
Outstanding at the end of the period (in shares) | shares	194,321
Vested or expected to vest (in shares) | shares	194,253
Exercisable (in shares) | shares	191,930
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 12.69
Exercised (in dollars per share) | $ / shares	1.76
Outstanding at the end of the period (in dollars per share) | $ / shares	13.44
Vested or expected to vest (in dollars per share) | $ / shares	13.45
Exercisable (in dollars per share) | $ / shares	$ 13.59
Weighted Average Remaining Contractual Term (years)
Outstanding	3 years 3 months 21 days
Vested or expected to vest	3 years 3 months 21 days
Exercisable	3 years 3 months 7 days
Aggregate Intrinsic Value (in thousands)
Outstanding (in dollars per share) | $	$ 267
Vested or expected to vest (in dollars per share) | $	266
Exercisable (in dollars per share) | $	$ 252

STOCK-BASED COMPENSATION PLAN_4

STOCK-BASED COMPENSATION PLANS - Restricted Stock Awards and Units and Performance-Based Stock Units (Details)	3 Months Ended
	Mar. 31, 2021$ / sharesshares
RSAs
Shares
Unvested balance at the beginning of the period (in shares) | shares	86,983
Vested (in shares) | shares	(86,983)
Unvested balance at the end of the period (in shares) | shares	0
Weighted Average Grant Date Fair Value
Unvested balance at the end of the period (in dollars per share) | $ / shares	$ 7.04
Vested (in dollars per share) | $ / shares	7.04
Unvested balance at end of the period (in dollars per share) | $ / shares	$ 0
RSUs
Shares
Unvested balance at the beginning of the period (in shares) | shares	6,531,110
Granted (in shares) | shares	2,885,002
Vested (in shares) | shares	(1,575,645)
Forfeited (in shares) | shares	(372,984)
Unvested balance at the end of the period (in shares) | shares	7,467,483
Weighted Average Grant Date Fair Value
Unvested balance at the end of the period (in dollars per share) | $ / shares	$ 3.32
Granted (in dollars per share) | $ / shares	8.59
Vested (in dollars per share) | $ / shares	2.60
Forfeited (in dollars per share) | $ / shares	3.68
Unvested balance at end of the period (in dollars per share) | $ / shares	$ 5.49
PSUs
Shares
Unvested balance at the beginning of the period (in shares) | shares	6,035,931
Granted (in shares) | shares	642,121
Vested (in shares) | shares	(1,525,681)
Forfeited (in shares) | shares	(57,480)
Unvested balance at the end of the period (in shares) | shares	5,094,891
Weighted Average Grant Date Fair Value
Unvested balance at the end of the period (in dollars per share) | $ / shares	$ 1.56
Granted (in dollars per share) | $ / shares	5.83
Vested (in dollars per share) | $ / shares	0.98
Forfeited (in dollars per share) | $ / shares	5.12
Unvested balance at end of the period (in dollars per share) | $ / shares	$ 2.40

STOCK-BASED COMPENSATION PLAN_5

STOCK-BASED COMPENSATION PLANS - Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Stock-based compensation
Stock-based compensation	$ 5,060	$ 2,976
Product cost of revenue
Stock-based compensation
Stock-based compensation	27	27
Service cost of revenue
Stock-based compensation
Stock-based compensation	235	130
Research and development
Stock-based compensation
Stock-based compensation	627	558
Sales and marketing
Stock-based compensation
Stock-based compensation	1,874	752
General and administrative
Stock-based compensation
Stock-based compensation	$ 2,297	$ 1,509

LEASES - Narrative (Details)

LEASES - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Lessee, Lease, Description [Line Items]
Additional amortization expense	$ 3,368	$ 70
Facilities
Lessee, Lease, Description [Line Items]
Accrual for future anticipated variable lease costs	2,100		$ 800
2019 Restructuring Initiative
Lessee, Lease, Description [Line Items]
Additional amortization expense	3,400
Accrual for future anticipated variable lease costs	2,068		939
2019 Restructuring Initiative | Facilities
Lessee, Lease, Description [Line Items]
Additional amortization expense	3,400	$ 100
Expense recorded for estimated future variable lease costs	1,400
Accrual for future anticipated variable lease costs	$ 2,068		$ 766

LEASES - Assets and Liabilities

LEASES - Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets
Operating lease assets	$ 62,579	$ 69,757
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Property and equipment, net	Property and equipment, net
Finance lease assets	$ 754	$ 983
Total leased assets	63,333	70,740
Current
Operating	$ 17,627	$ 17,023
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Accrued expenses and other	Accrued expenses and other
Finance	$ 820	$ 902
Noncurrent
Operating	$ 68,100	$ 72,614
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other long-term liabilities	Other long-term liabilities
Finance	$ 398	$ 568
Total lease liabilities	86,945	91,107
Finance lease, accumulated deprecation	$ 2,200	$ 1,900

LEASES - Components of Lease Ex

LEASES - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Leases [Abstract]
Operating lease, cost	$ 8,837	$ 3,344
Finance lease cost
Amortization of leased assets	229	319
Interest on lease liabilities	26	55
Short-term lease cost	3,292	5,523
Variable lease costs (costs excluded from minimum fixed lease payments)	2,158	637
Sublease income	(276)	0
Net lease cost	14,266	9,878
Accelerated amortization	3,400	100
Variable lease cost accrued	$ 1,400	$ 0

LEASES - Other Information (Det

LEASES - Other Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows for operating leases	$ 5,561	$ 3,113
Operating cash flows for finance leases	26	55
Financing cash flows for finance leases	$ 272	$ 338
Weighted average remaining lease term (years)
Operating leases	6 years 6 months 7 days		6 years 7 months 2 days
Finance leases	1 year 6 months 3 days		1 year 8 months 12 days
Weighted average discount rate
Operating leases	5.72%		5.67%
Finance leases	5.74%		6.15%

LEASES - Future Minimum Lease P

LEASES - Future Minimum Lease Payments (Details) $ in Thousands	Mar. 31, 2021USD ($)
Operating leases
Remainder of 2021	$ 16,397
2022	20,026
2023	17,267
2024	10,392
2025	8,540
2026 and beyond	32,592
Total lease payments	105,214
Less: interest	(19,487)
Present value of lease liabilities	85,727
Finance leases
Remainder of 2021	701
2022	509
2023	62
2024	0
2025	0
2026 and beyond	0
Total lease payments	1,272
Less: interest	(54)
Present value of lease liabilities	$ 1,218

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)	Nov. 08, 2018executive	Dec. 31, 2016
Loss Contingencies [Line Items]
Sale of stock grant interest (as a percentage)			100.00%
Maximum future royalty commitment	$ 5.2
Maximum future royalty commitment	42
Maximum future royalty commitment, interest	$ 2
Number of former officers | executive		3
Minimum
Loss Contingencies [Line Items]
Royalties rates (as a percentage)			1.30%
Minimum | LIBOR
Loss Contingencies [Line Items]
Basis spread on variable rate	1.50%
Maximum
Loss Contingencies [Line Items]
Royalties rates (as a percentage)			5.00%
Maximum | LIBOR
Loss Contingencies [Line Items]
Basis spread on variable rate	2.75%