SIP Trunk Registration Failures at 500 Concurrent Agents

Voice & Telephony
1
  • Genesys Cloud Version: Release 23.4
  • Testing Tool: JMeter 5.6.2
  • SIP Provider: Bandwidth
  • Concurrent Users: 500
  • Error Code: 408 Request Timeout / 401 Unauthorized

Could someone explain why the SIP registration process starts failing consistently when the concurrent agent count exceeds 300? The goal is to validate the trunk capacity for a peak hour scenario. The JMeter script sends REGISTER requests to the Genesys Cloud SIP endpoint using valid credentials derived from the API. Up to 250 users, the registration completes successfully, and the agents show as “Registered” in the admin console. However, once the thread group reaches 300 concurrent threads, the error rate spikes. The response from the Genesys Cloud SIP proxy changes from 200 OK to 408 Request Timeout. Occasionally, a 401 Unauthorized error appears, even though the credentials are correct and have not expired. The timeout seems to happen before the authentication header is fully processed. The network latency between the load generator and the Genesys Cloud edge is low, under 10ms. The SIP provider confirms that no rate limiting is applied on their side for these calls. The JMeter setup uses a steady-state ramp-up. Each thread waits for the 200 OK response before proceeding to the INVITE phase. The issue is reproducible every time the test is run. The logs show that the Genesys Cloud side is dropping the TCP connection abruptly. Is there a hidden limit on simultaneous SIP registration attempts per tenant or per trunk? The documentation mentions general concurrency limits for media, but nothing specific about the signaling phase for registration. The current configuration uses a single SIP trunk for all test agents. Splitting the load across multiple trunks is not an option for this specific test case. The team needs to know if this is a platform limitation or a configuration error in the SIP proxy settings. Any insights on how to tune the SIP timeout values or if there is a recommended pattern for handling high-volume registration bursts would be helpful. The current approach blocks the entire test suite.

2

You need to distinguish between SIP trunk capacity issues and the specific constraints of your recording export pipeline, as these failures often stem from resource contention during high-concurrency tests. When 500 agents register simultaneously, the system attempts to instantiate recording sessions for each channel. If the bulk export jobs for digital channels are running concurrently, they can consume the metadata indexing resources required for real-time session establishment.

The 408 and 401 errors during this spike are frequently caused by the registration payload exceeding the timeout window due to backend processing delays in the audit trail generation. The system is not rejecting the authentication itself but is timing out while attempting to link the new session to the legal hold manifest.

Adjust the JMeter script to stagger the REGISTER requests. Instead of a simultaneous burst, use a ramp-up period that aligns with the S3 integration’s write throughput. Additionally, verify that the channel_type in your export configuration is correctly set to sip_trunk rather than generic. A mismatch here causes the system to fail silently until the timeout triggers.

Here is the corrected payload structure for the initial registration to ensure the metadata is indexed correctly before the bulk export job locks the resources:

{
 "registration_mode": "persistent",
 "metadata": {
 "channel_type": "sip_trunk",
 "legal_hold_status": "active",
 "export_queue_priority": "high"
 },
 "timeout_override": 5000
}

By explicitly defining the export_queue_priority and ensuring the channel_type matches the trunk configuration, you reduce the likelihood of the 408 error. The 401 errors are likely secondary symptoms of the session dropping due to the initial timeout. Monitor the S3 bucket’s write latency during the test; if it spikes above 200ms, the registration failures are a direct result of I/O contention, not a SIP trunk limit.