Can anyone explain why the SIP trunk returns 503 Service Unavailable when concurrent call attempts exceed 20?
The environment is Genesys Cloud US1. We are using JMeter 5.6 with the SIP plugin to validate call capacity planning for a new client. The test sends INVITE requests to the Genesys Cloud SIP endpoint. At 10 concurrent threads, all calls connect successfully. When increasing to 25 threads, the majority of calls fail with 503 errors. The error message in the SIP response body indicates ‘Server busy’.
The SIP trunk configuration shows a maximum concurrent session limit of 100. The JMeter config uses a constant throughput timer to ramp up load gradually. The network latency is low. We have checked the SIP trunk status in the admin portal, and it shows as active. The issue seems related to connection handling or rate limiting at the SIP proxy level. We are not seeing this behavior with REST API calls. The goal is to determine the true concurrent call limit for this trunk type. Any insight into the SIP capacity limits or configuration settings that might cause this early drop would be helpful.