REVENUE RECOGNITION - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2023	Mar. 31, 2022
Disaggregation of Revenue [Line Items]
Total revenue	$ 186,159	$ 173,198
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-04-01
Disaggregation of Revenue [Line Items]
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, remaining performance obligation, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Disaggregation of Revenue [Line Items]
Revenue, remaining performance obligation, period	1 year
Cloud and Edge
Disaggregation of Revenue [Line Items]
Total revenue	$ 114,480	109,806
IP Optical Networks
Disaggregation of Revenue [Line Items]
Total revenue	71,679	63,392
United States
Disaggregation of Revenue [Line Items]
Total revenue	81,993	75,649
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenue	54,137	48,963
Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	38,131	36,262
Other
Disaggregation of Revenue [Line Items]
Total revenue	11,898	12,324
Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	93,318	81,990
Product revenue \| Cloud and Edge
Disaggregation of Revenue [Line Items]
Total revenue	42,839	37,635
Product revenue \| IP Optical Networks
Disaggregation of Revenue [Line Items]
Total revenue	50,479	44,355
Product revenue \| Sales to enterprise customers
Disaggregation of Revenue [Line Items]
Total revenue	27,412	22,083
Product revenue \| Sales to service provider customers
Disaggregation of Revenue [Line Items]
Total revenue	65,906	59,907
Product revenue \| Indirect sales through channel partner program
Disaggregation of Revenue [Line Items]
Total revenue	35,914	23,500
Product revenue \| Direct sales
Disaggregation of Revenue [Line Items]
Total revenue	57,404	58,490
Product revenue \| United States
Disaggregation of Revenue [Line Items]
Total revenue	38,067	31,940
Product revenue \| Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenue	27,435	24,410
Product revenue \| Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	25,615	22,390
Product revenue \| Other
Disaggregation of Revenue [Line Items]
Total revenue	2,201	3,250
Service
Disaggregation of Revenue [Line Items]
Total revenue	92,841	91,208
Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	70,588	68,605
Service revenue (maintenance) \| Cloud and Edge
Disaggregation of Revenue [Line Items]
Total revenue	54,810	55,030
Service revenue (maintenance) \| IP Optical Networks
Disaggregation of Revenue [Line Items]
Total revenue	15,778	13,575
Service revenue (maintenance) \| United States
Disaggregation of Revenue [Line Items]
Total revenue	33,073	33,064
Service revenue (maintenance) \| Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenue	20,127	17,742
Service revenue (maintenance) \| Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	9,372	10,425
Service revenue (maintenance) \| Other
Disaggregation of Revenue [Line Items]
Total revenue	8,016	7,374
Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	22,253	22,603
Service revenue (professional services) \| Cloud and Edge
Disaggregation of Revenue [Line Items]
Total revenue	16,831	17,141
Service revenue (professional services) \| IP Optical Networks
Disaggregation of Revenue [Line Items]
Total revenue	5,422	5,462
Service revenue (professional services) \| United States
Disaggregation of Revenue [Line Items]
Total revenue	10,853	10,645
Service revenue (professional services) \| Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenue	6,575	6,811
Service revenue (professional services) \| Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	3,144	3,447
Service revenue (professional services) \| Other
Disaggregation of Revenue [Line Items]
Total revenue	$ 1,681	$ 1,700