I’m curious as to why the SIP trunk returns 503 Service Unavailable when JMeter initiates 200 concurrent INVITE requests? The test environment uses Genesys Cloud v2.14.3 with a dedicated SIP trunk configured for 500 concurrent channels. The goal is to validate the telephony capacity limits before a major deployment. The JMeter script uses the SIP Sampler plugin with a ramp-up time of 10 seconds to simulate burst traffic. Initial calls connect successfully, but after approximately 150 active sessions, the system starts rejecting new INVITEs with 503 errors. The response headers indicate the server is temporarily unable to handle the request. I have verified that the trunk registration is stable and the firewall allows the required UDP ports. The issue persists even when reducing the concurrent thread count to 100. The error logs in Genesys Cloud show no specific SIP dialog failures, only the generic service unavailable status. Is there a hidden rate limit on INVITE processing per second that is not documented? The current configuration sets the max concurrent calls to 500, but the failure occurs well below this threshold. Please advise on how to tune the SIP settings or JMeter parameters to avoid this bottleneck.
Ah, yeah, this is a known issue…
Coming from Zendesk, where CTI integration was largely abstracted, seeing raw SIP errors feels like stepping into the deep end. In Genesys Cloud, the 503 during high concurrency usually stems from the SIP trunk’s maximum concurrent calls setting being hit or the underlying BYOC provider rejecting the burst. Even if configured for 500 channels, the initial handshake rate matters.
Check the SIP trunk configuration in Admin > Telephony. Ensure the ‘Maximum Concurrent Calls’ matches your intent, but more importantly, verify the ‘SIP Options Keep Alive’ interval. A rapid burst of INVITEs without proper keep-alive can cause the provider to drop connections. Also, review the JMeter ramp-up. Ten seconds for 200 calls is extremely aggressive.
Try increasing the ramp-up time to 60 seconds in JMeter. This mimics real-world traffic patterns better and prevents the provider from flagging the traffic as malicious. If the 503 persists, check the Genesys Cloud logs for ‘SIP 503’ specifically related to the trunk ID. This often points to a licensing or capacity issue on the provider side rather than Genesys itself.