Having some config trouble here… The predictive dialer is routing calls to a specific BYOC trunk in the Singapore region, but 60% of attempts fail immediately with SIP 480 Temporarily Unavailable, despite the trunk showing as registered and healthy in the telephony dashboard. This happens specifically when the outbound campaign triggers high concurrency bursts.
{
"trunk_id": "byoc_trunk_sg_04",
"dialer_mode": "predictive",
"concurrency_level": 50,
"destination_number": "+6591234567",
"error_code": "SIP_480"
}
It depends, but generally…
SIP 480 during predictive bursts on BYOC is almost exclusively a media path or resource contention issue at the edge, not an API problem. Check if your trunk’s associated SIP profile has allow-transfer and allow-sub disabled, and ensure the downstream carrier isn’t dropping early media packets by verifying the 100rel extension is negotiated correctly in the INVITE. If the trunk is healthy but calls fail under load, the carrier is likely rejecting the SDP due to missing or incompatible codecs; force PCMU and PCMA only in the outbound trunk codec list to eliminate negotiation latency.
check your outbound flow settings instead of just sip headers. in zendesk we had simple click-to-call, but here the predictive dialer needs explicit trunk selection logic. if the flow defaults to a different region or trunk under load, you get 480s. ensure the ‘connect to’ step explicitly targets that sg trunk.
It depends, but generally… the 480 errors during predictive bursts on BYOC trunks often stem from API rate limiting on the dialer configuration endpoints rather than pure SIP media path issues. When the dialer attempts to scale concurrency rapidly, it triggers a high volume of configuration updates and status checks. If the service account running the dialer lacks sufficient API throughput allowance, Genesys Cloud may temporarily throttle these requests, causing the dialer engine to fail to reserve trunk resources correctly. This manifests as SIP 480 because the trunk appears healthy in the dashboard, but the dialer cannot secure a channel due to backend throttling. To verify this, monitor the API rate limit headers in the response when the dialer starts. If you see Retry-After headers or 429 status codes preceding the 480s, adjust the dialer’s ramp-up period. In JMeter, simulate this by staggering the campaign start requests. Instead of hitting the dialer API with 100 concurrent threads, use a step ramp-up of 10 threads per second. This reduces the initial spike in API calls. Additionally, check the trunk’s concurrent call limit in the admin console. If it is set too low relative to the dialer’s predicted answer rate, the trunk will reject calls even if it is registered. Increase the trunk capacity or reduce the dialer’s speed factor. For a quick fix, add a delay between dialer start and ramp-up in your test script. This allows the backend to process the initial configuration load before the high-volume call attempts begin. This approach usually resolves the intermittent 480s by aligning the API load with the system’s throughput capabilities.