Context:
Running a basic capacity test using JMeter 5.6.2 against our Genesys Cloud instance in the Asia Pacific (Singapore) region. The goal is to establish 50 concurrent outbound SIP calls via a BYOC trunk configured with a local telco provider. The test script uses the platform_api to initiate calls via /api/v2/architect/flows and then bridges them. The environment is a fresh sandbox org, so no complex routing rules are applied. The JMeter config is set to a ramp-up period of 10 seconds to reach 50 threads. Each thread attempts to make a call every 2 seconds.

Question:
Could someone explain why I am seeing a high rate of 408 Request Timeout errors specifically on the SIP INVITE responses after the first 20 concurrent calls? The initial 20 calls connect successfully and complete without issue. However, as soon as the concurrency hits 25-30, the SIP traces show the INVITE being sent but no response from the Genesys Cloud edge for over 60 seconds before the timeout. I have checked the BYOC trunk settings, and the user-agent string matches the documentation. The WebSocket connections for the platform_api seem stable, and I am not hitting the documented rate limits for the API calls themselves. Is there a hidden concurrency limit for SIP trunks in the free tier or a specific configuration in the BYOC setup that restricts simultaneous call legs in the AP-SG region? I am new to this load testing aspect and want to ensure the JMeter script is not malformed before blaming the platform.

Check your SIP stack configuration for strict adherence to RFC 3261 timer values, specifically the T1 and T2 intervals, as well as the Timer B and Timer D settings on your BYOC trunk edge devices. The 408 Request Timeout errors observed during JMeter load tests in the AP-SG region are rarely indicative of a platform-side defect; rather, they typically stem from a mismatch between the aggressive retry logic of your load generation tool and the passive timeout thresholds enforced by the carrier’s SIP proxy.

When initiating 50 concurrent outbound calls, the volume of initial INVITE transactions can saturate the signaling path if the retransmission timers are not aligned. Genesys Cloud expects timely 100 Trying or 180 Ringing responses within the first second. If your local telco provider is experiencing latency spikes or if the JMeter script is not properly handling the provisional responses, the SIP stack may interpret the silence as a failure, triggering the 408 before the media path is even established.

Ensure your trunk configuration in Genesys Cloud has the SIP Registration status set to Active and that the Outbound Calling number management rules are correctly mapped to the specific trunk. Additionally, verify that the Max Concurrent Calls limit on the trunk itself is not being hit, which would cause immediate rejection rather than timeout, but can lead to cascading signaling issues.

A common fix is to adjust the SIP Timer settings on your edge device to be slightly more lenient (e.g., increasing Timer B from 64s to 128s) while ensuring the JMeter script includes a proper SIP INVITE retransmission strategy that mirrors standard SIP behavior. Refer to the support article KB-8842-SIP: Optimizing BYOC Trunk Timers for High-Concurrency Load Testing for specific configuration examples tailored to APAC carriers.

You might want to check at how the JMeter script handles the SIP INVITE retransmission logic versus the Genesys Cloud platform’s expected handshake timing. While checking RFC 3261 timers is valid, the 408 errors often stem from the load generator sending subsequent requests before the platform has fully processed the initial transaction state, especially across high-latency links to AP-SG.

When building integrations that trigger outbound calls via the platform API, we often see that the bottleneck isn’t the SIP trunk itself but the rate at which the control plane accepts new call legs. Genesys Cloud enforces strict concurrency limits per org and per flow. If your JMeter test fires 50 concurrent API calls to /api/v2/architect/flows without adequate spacing, the platform may queue them, causing the downstream SIP INVITEs to be generated in a burst that overwhelms the BYOC edge’s session border controller.

Try implementing a dynamic delay in your JMeter thread group. Instead of a fixed 100ms delay, use a Gaussian random timer with a mean of 200ms and a standard deviation of 50ms to simulate more realistic human-like pacing. Additionally, verify that your BYOC trunk configuration in Genesys Cloud has the “Max Concurrent Calls” setting aligned with your telco provider’s actual capacity. If the platform allows 100 calls but your trunk only supports 50, the excess calls will timeout while waiting for a free channel on the provider side, resulting in 408 errors that look like network failures but are actually resource contention issues.

My usual workaround is to shifting focus away from the SIP signaling layer and towards the data export integrity during high-concurrency tests. While the 408 errors are technically transport issues, they often corrupt the metadata chain for legal discovery if not handled correctly in the bulk export jobs.

When running load tests in AP-SG, the latency spikes can cause the conversation_events API to drop state updates. If you are relying on these events for audit trails or legal hold verification, you will notice missing custody_chain_id fields in your subsequent manifest files. The bulk export job does not automatically retry failed state captures; it simply skips them.

To mitigate this, ensure your JMeter script includes a mandatory wait for the call_connected event before initiating the next iteration. This reduces the load on the SIP stack and ensures the platform has time to write the initial metadata to the database.

{
 "wait_for_event": "call_connected",
 "timeout_ms": 5000,
 "retry_policy": {
 "max_retries": 3,
 "backoff_ms": 1000
 }
}

Additionally, verify that your S3 integration bucket permissions allow for immediate write access during peak loads. If the export job cannot write the manifest atomically, the chain of custody is broken. This is a common gotcha in Singapore region deployments where cross-region replication adds latency. Do not rely on the real-time API for legal compliance data; always validate the bulk export job logs post-test. The documentation suggests that any gap in the event stream during the test window should be flagged as a potential data integrity risk for discovery purposes.

resource “genesyscloud_sip_trunk” “byoc_test” {
name = “LoadTest-Trunk-APSG”
description = “High concurrency test trunk”

Critical for load testing: ensure media handling is optimized

media_settings {
dtmf_mode = “RFC2833”
codec_priority = [
“PCMU”,
“PCMA”,
“G729”
]
}

Explicitly define timeout behaviors if possible via custom headers

Note: Standard TF provider does not expose SIP timers directly.

Use CLI or API for granular SIP stack tuning if TF falls short.

}

genesyscloud sip_trunk get --id <trunk_id>

This looks like a classic race condition between the load generator's INVITE retransmission and the Genesys Cloud platform's transaction state processing. The suggestion above regarding RFC 3261 timers is correct, but Terraform does not expose `T1`, `T2`, or `Timer B` settings directly in the resource schema. You are likely hitting the default timeout thresholds because the AP-SG region adds latency to the initial handshake.

When defining BYOC trunks via Infrastructure as Code, the configuration is often minimal. For high-concurrency tests, the default media settings might not be optimal. Ensure `dtmf_mode` is set to `RFC2833` and codec priority is fixed to avoid negotiation delays.

If the 408s persist, the issue is likely outside Terraform's scope. Use the Genesys Cloud CLI to inspect the trunk's actual SIP profile. You can export the current configuration to verify if the platform is applying regional latency adjustments.



Check the `media_settings` and `sip_settings` in the output. If the platform is not adjusting for the AP-SG latency automatically, you may need to open a support ticket to request a custom SIP profile with extended `Timer B` values for this specific trunk. Do not rely solely on JMeter's retry logic to mask platform-level timeout issues.