SIP Trunk 408 Timeouts During JMeter Ramp-up

Can anyone clarify why our SIP trunk registrations are failing with 408 Request Timeout when we push concurrent SIP UA instances above 800 in JMeter? We are running a load test to determine the maximum capacity of our Genesys Cloud SIP trunk configuration.

The setup involves a simple JMeter script that initiates SIP REGISTER requests to the Genesys Cloud SIP endpoint. Everything works fine up to 750 concurrent threads. Once we cross that threshold, about 40% of the registrations start timing out.

Here are the environment details:

  • Genesys Cloud Version: Latest (SaaS)
  • JMeter Version: 5.6.2
  • SIP Library: JsSIP 3.7.0
  • Concurrent Threads: 1000
  • Ramp-up Time: 60 seconds

The error log shows:

SIP 408 Request Timeout
Request URI: sip:sip.provider.genesis.com:5060
From: <sip:[email protected]>
To: <sip:[email protected]>
Call-ID: abc123-def456
CSeq: 1 REGISTER

We have verified that our network can handle the bandwidth. Is there a known limit on concurrent SIP registrations per trunk in Genesys Cloud? Or is this a JsSIP configuration issue? We need to scale up to 5000 concurrent registrations for our project.