SIP Trunk 503 Service Unavailable during JMeter SIP load test on Genesys Cloud US1

Running a JMeter 5.6 load test to validate SIP trunk capacity on Genesys Cloud US1. The objective is to simulate 50 concurrent inbound SIP calls via a custom SIP endpoint configured in Genesys Cloud. After 2 minutes of steady traffic, the SIP proxy starts returning “503 Service Unavailable” responses for new INVITE requests. Existing calls remain stable, but new call setup fails.

The JMeter thread group uses 50 threads with a ramp-up period of 60 seconds and a loop count of 10. Each thread sends an SIP INVITE request to the Genesys Cloud SIP URI. The SIP trunk is configured with a maximum concurrent call limit of 100. No rate limiting errors are observed in the Genesys Cloud admin dashboard during the test.

Has anyone seen this behavior during SIP load testing? Is there a default connection limit or timeout setting that needs to be adjusted? Any insights into tuning SIP trunk settings for high-concurrency scenarios would be helpful. The test environment is Genesys Cloud US1, and the JMeter test plan includes standard SIP headers with a 10-second timeout for each request.

This sounds like a concurrency bottleneck, but check your WFM schedule first. If 50 agents aren’t logged in and available, Genesys returns 503. Ensure your shift coverage matches the test volume. Also, verify trunk capacity limits in the admin console.

The 503 likely stems from SIP registration state mismatches rather than WFM coverage. Verify the US1 proxy isn’t dropping the REGISTER due to stale credentials during the ramp-up. Check Genesys logs for 401 Unauthorized or 403 Forbidden preceding the 503. Carrier failover settings might also be triggering prematurely under this synthetic load.