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REVENUE RECOGNITION (Tables) | 12 Months Ended
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Dec. 31, 2025
REVENUE RECOGNITION |
Schedule of timing of performance obligation | ​
​ | ​ | ​ | ​ | ​
​ | ​ ​ ​ | When Performance Obligation is Typically | ​ ​ ​ | ​
Performance Obligation | ​ | Satisfied | ​ | When Payment is Typically Due
Software and Product Revenue | ​ | ​ | ​ | ​
Software licenses (perpetual or term) |  | For perpetual licenses, typically when made available for download (point in time); for term-based licenses, at the beginning of the specified term (point in time) |  | Generally, within 30-60 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 30-60 days of invoicing
Hardware |  | When control of the hardware passes to the customer; typically, upon delivery (point in time) |  | Generally, within 30-60 days of invoicing
Software upgrades |  | Upon transfer of control; typically, when made available for download (point in time) |  | Generally, within 30-60 days of invoicing
Customer Support Revenue |  | ​ |  | ​
Customer support |  | Ratably over the course of the support contract (over time) |  | Generally, within 30-60 days of invoicing
Professional Services |  | ​ |  | ​
Other professional services (excluding training services) |  | As work is performed (over time), typically on the input method based on hours incurred |  | Generally, within 30-60 days of invoicing (upon completion of services)
Training |  | As the training is delivered (over time), typically one to five days |  | Generally, within 30-60 days of services being performed
Schedule of disaggregation of revenue | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ ​ ​ | ​ | ​ | ​ | ​ | ​ | ​ | Service | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | Service | ​ | revenue | ​ | ​ | ​
​ | ​ | Product | ​ | revenue | ​ | (professional | ​ | ​ | ​
Year ended December 31, 2025 | ​ ​ ​ | revenue | ​ ​ ​ | (maintenance) | ​ ​ ​ | services) | ​ ​ ​ | Total revenue
United States | ​ | $ | 179,660 | ​ | $ | 136,452 | ​ | $ | 86,845 | ​ | $ | 402,957
Europe, Middle East and Africa | ​ |  | 111,235 | ​ |  | 69,594 | ​ |  | 33,322 | ​ |  | 214,151
Asia Pacific | ​ |  | 129,298 | ​ |  | 38,474 | ​ |  | 13,213 | ​ |  | 180,985
Other | ​ |  | 14,394 | ​ |  | 26,031 | ​ |  | 6,038 | ​ |  | 46,463
​ | ​ | $ | 434,587 | ​ | $ | 270,551 | ​ | $ | 139,418 | ​ | $ | 844,556
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ ​ ​ | ​ | ​ | ​ | ​ | ​ | ​ | Service | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | Service | ​ | revenue | ​ | ​ | ​
​ | ​ | Product | ​ | revenue | ​ | (professional | ​ | ​ | ​
Year ended December 31, 2024 | ​ ​ ​ | revenue | ​ ​ ​ | (maintenance) | ​ ​ ​ | services) | ​ ​ ​ | Total revenue
United States | ​ | $ | 201,340 | ​ | $ | 133,182 | ​ | $ | 61,462 | ​ | $ | 395,984
Europe, Middle East and Africa | ​ |  | 129,824 | ​ |  | 71,856 | ​ |  | 32,999 | ​ |  | 234,679
Asia Pacific | ​ |  | 100,766 | ​ |  | 39,863 | ​ |  | 10,941 | ​ |  | 151,570
Other | ​ |  | 15,299 | ​ |  | 29,681 | ​ |  | 6,668 | ​ |  | 51,648
​ | ​ | $ | 447,229 | ​ | $ | 274,582 | ​ | $ | 112,070 | ​ | $ | 833,881
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ ​ ​ | ​ | ​ | ​ | ​ | ​ | ​ | Service | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | Service | ​ | revenue | ​ | ​ | ​
​ | ​ | Product | ​ | revenue | ​ | (professional | ​ | ​ | ​
Year ended December 31, 2023 | ​ ​ ​ | revenue | ​ ​ ​ | (maintenance) | ​ ​ ​ | services) | ​ ​ ​ | Total revenue
United States | ​ | $ | 161,945 | ​ | $ | 133,737 | ​ | $ | 48,733 | ​ | $ | 344,415
Europe, Middle East and Africa | ​ |  | 151,938 | ​ |  | 75,478 | ​ |  | 34,485 | ​ |  | 261,901
Asia Pacific | ​ |  | 115,923 | ​ |  | 39,891 | ​ |  | 11,269 | ​ |  | 167,083
Other | ​ |  | 15,344 | ​ |  | 30,546 | ​ |  | 7,050 | ​ |  | 52,940
​ | ​ | $ | 445,150 | ​ | $ | 279,652 | ​ | $ | 101,537 | ​ | $ | 826,339
​ The Company’s product revenue from its direct sales program and from indirect sales through its channel partner program for the years ended December 31, 2025, 2024 and 2023 was as follows (in thousands):
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ ​ ​ | Year ended December 31,
​ | ​ ​ ​ | 2025 | ​ ​ ​ | 2024 | ​ ​ ​ | 2023
Indirect sales through channel partner program | ​ | $ | 134,154 | ​ | $ | 170,426 | ​ | $ | 157,495
Direct sales | ​ |  | 300,433 | ​ |  | 276,803 | ​ |  | 287,655
​ | ​ | $ | 434,587 | ​ | $ | 447,229 | ​ | $ | 445,150
​ ​ The Company’s product revenue from sales to enterprise customers and from sales to service provider customers for the years ended December 31, 2025, 2024 and 2023 was as follows (in thousands):
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ ​ ​ | Year ended December 31,
​ | ​ ​ ​ | 2025 | ​ ​ ​ | 2024 | ​ ​ ​ | 2023
Sales to enterprise customers | ​ | $ | 148,758 | ​ | $ | 176,064 | ​ | $ | 143,853
Sales to service provider customers | ​ |  | 285,829 | ​ |  | 271,165 | ​ |  | 301,297
​ | ​ | $ | 434,587 | ​ | $ | 447,229 | ​ | $ | 445,150
​ The Company’s product revenue and service revenue components by segment for the years ended December 31, 2025, 2024 and 2023 was as follows (in thousands):
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year ended December 31,
​ | ​ ​ ​ | 2025 | ​ ​ ​ | 2024 | ​ ​ ​ | 2023
Product revenue: | ​ | ​ | ​ | ​ | ​ | ​
Cloud and Edge |  | 198,163 |  | 211,001 |  | 184,730
IP Optical Networks |  | 236,424 |  | 236,228 |  | 260,420
Total product revenue |  | 434,587 |  | 447,229 |  | 445,150
​ | ​ | ​ | ​ | ​ | ​ | ​
Service revenue: |  | ​ |  | ​ |  | ​
Maintenance: |  | ​ |  | ​ |  | ​
Cloud and Edge |  | 206,604 |  | 212,988 |  | 219,939
IP Optical Networks |  | 63,947 |  | 61,594 |  | 59,713
Total maintenance revenue |  | 270,551 |  | 274,582 |  | 279,652
Professional services: |  | ​ |  | ​ |  | ​
Cloud and Edge |  | 106,663 |  | 81,168 |  | 72,979
IP Optical Networks |  | 32,755 |  | 30,902 |  | 28,558
Total professional services revenue |  | 139,418 |  | 112,070 |  | 101,537
Total service revenue |  | 409,969 |  | 386,652 |  | 381,189
Schedule of customer assets and liabilities | The changes in the Company’s accounts receivable, unbilled receivables and deferred revenue balances for the years ended December 31, 2025 and 2024 were as follows (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | Unbilled | ​ | Deferred | ​ | Deferred
​ | ​ | Accounts | ​ | accounts | ​ | revenue | ​ | revenue
​ | ​ ​ ​ | receivable | ​ ​ ​ | receivable | ​ ​ ​ | (current) | ​ ​ ​ | (long-term)
Balance at January 1, 2025 | ​ | $ | 176,575 | ​ | $ | 78,143 | ​ | $ | 119,295 | ​ | $ | 20,991
Increase (decrease), net | ​ |  | (15,568) | ​ |  | (7,265) | ​ |  | 5,130 | ​ |  | 10,663
Balance at December 31, 2025 | ​ | $ | 161,007 | ​ | $ | 70,878 | ​ | $ | 124,425 | ​ | $ | 31,654
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | Unbilled | ​ | Deferred | ​ | Deferred
​ | ​ | Accounts | ​ | accounts | ​ | revenue | ​ | revenue
​ | ​ ​ ​ | receivable | ​ ​ ​ | receivable | ​ ​ ​ | (current) | ​ ​ ​ | (long-term)
Balance at January 1, 2024 | ​ | $ | 186,938 | ​ | $ | 81,483 | ​ | $ | 113,381 | ​ | $ | 19,218
Increase (decrease), net | ​ |  | (10,363) | ​ |  | (3,340) | ​ |  | 5,914 | ​ |  | 1,773
Balance at December 31, 2024 | ​ | $ | 176,575 | ​ | $ | 78,143 | ​ | $ | 119,295 | ​ | $ | 20,991

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