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REVENUE RECOGNITION (Tables) | 3 Months Ended
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Mar. 31, 2026
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 revenue | ​ ​ ​ | ​ | ​
​ | Product | ​ | Service revenue | ​ | (professional | ​ | ​ | ​
Three months ended March 31, 2026 | revenue | ​ | (maintenance) | ​ | services) | ​ | Total revenue
United States | $ | 20,941 | ​ | $ | 33,733 | ​ | $ | 17,904 | ​ | $ | 72,578
Europe, Middle East and Africa | ​ | 16,962 | ​ | ​ | 14,683 | ​ | ​ | 7,425 | ​ | ​ | 39,070
Asia Pacific | ​ | 27,934 | ​ | ​ | 9,230 | ​ | ​ | 3,763 | ​ | ​ | 40,927
Other | ​ | 2,277 | ​ | ​ | 6,021 | ​ | ​ | 1,733 | ​ | ​ | 10,031
​ | $ | 68,114 | ​ | $ | 63,667 | ​ | $ | 30,825 | ​ | $ | 162,606
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ ​ ​ | ​ | ​ | ​ ​ ​ | Service revenue | ​ ​ ​ | ​ | ​
​ | Product | ​ | Service revenue | ​ | (professional | ​ | ​ | ​
Three months ended March 31, 2025 | revenue | ​ | (maintenance) | ​ | services) | ​ | Total revenue
United States | $ | 29,341 | ​ | $ | 33,324 | ​ | $ | 20,030 | ​ | $ | 82,695
Europe, Middle East and Africa |  | 19,460 | ​ |  | 17,383 | ​ |  | 8,656 | ​ |  | 45,499
Asia Pacific |  | 31,039 | ​ |  | 9,400 | ​ |  | 2,740 | ​ |  | 43,179
Other |  | 2,151 | ​ |  | 6,315 | ​ |  | 1,440 | ​ |  | 9,906
​ | $ | 81,991 | ​ | $ | 66,422 | ​ | $ | 32,866 | ​ | $ | 181,279
​ The Company’s product revenue from its direct sales program and from indirect sales through its channel partner program for the three months ended March 31, 2026 and 2025 was as follows (in thousands):
​ | ​ | ​ | ​ | ​ | ​
​ | Three months ended
​ | March 31, | ​ | March 31,
​ | 2026 | ​ ​ ​ | 2025
Indirect sales through channel partner program | $ | 19,329 | ​ | $ | 22,735
Direct sales |  | 48,785 | ​ |  | 59,256
​ | $ | 68,114 | ​ | $ | 81,991
​ The Company’s product revenue from sales to enterprise customers and from sales to service provider customers for the three months ended March 31, 2026 and 2025 was as follows (in thousands):
​ | ​ | ​ | ​ | ​ | ​
​ | Three months ended
​ | March 31, | ​ | March 31,
​ | 2026 | ​ ​ ​ | 2025
Sales to enterprise customers | $ | 21,516 | ​ | $ | 23,232
Sales to service provider customers |  | 46,598 | ​ |  | 58,759
​ | $ | 68,114 | ​ | $ | 81,991
​ The Company’s product revenue and service revenue components by segment for the three months ended March 31, 2026 and 2025 were as follows (in thousands):
​ | ​ | ​ | ​ | ​ | ​
​ | Three months ended
​ | March 31, | ​ | March 31,
​ | 2026 | ​ ​ ​ | 2025
Product revenue: | ​ | ​ | ​ | ​ | ​
Cloud and Edge | $ | 26,259 |  | $ | 31,861
IP Optical Networks | ​ | 41,855 |  | ​ | 50,130
Total product revenue | $ | 68,114 |  | $ | 81,991
​ | ​ | ​ | ​ | ​ | ​
Service revenue: | ​ | ​ |  | ​ | ​
Maintenance: | ​ | ​ |  | ​ | ​
Cloud and Edge | $ | 50,232 |  | $ | 50,768
IP Optical Networks | ​ | 13,435 |  | ​ | 15,654
Total maintenance revenue | ​ | 63,667 |  | ​ | 66,422
Professional services: | ​ | ​ |  | ​ | ​
Cloud and Edge | ​ | 23,021 |  | ​ | 24,962
IP Optical Networks | ​ | 7,804 |  | ​ | 7,904
Total professional services revenue | ​ | 30,825 |  | ​ | 32,866
Total service revenue | $ | 94,492 |  | $ | 99,288
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, 2026 were as follows (in thousands):
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | Unbilled | ​ | Deferred | ​ | Deferred
​ | Accounts | ​ | accounts | ​ | revenue | ​ | revenue
​ | receivable | ​ ​ ​ | receivable | ​ ​ ​ | (current) | ​ ​ ​ | (long-term)
Balance at January 1, 2026 | $ | 161,007 | ​ | $ | 70,878 | ​ | $ | 124,425 | ​ | $ | 31,654
Increase (decrease), net |  | (19,051) | ​ |  | (8,776) | ​ |  | (1,806) | ​ |  | 769
Balance at March 31, 2026 | $ | 141,956 | ​ | $ | 62,102 | ​ | $ | 122,619 | ​ | $ | 32,423

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