Background
London region, Genesys Cloud v3.5.2. BYOC edge node handling high-volume legal discovery SIP trunks.
Issue
Inbound SIP INVITEs are failing with 488 Not Acceptable Here. The specific cause code is 21481 (Unsupported Media). This happens only when the SDP contains Opus codec alongside G.711, even though Opus is enabled in the trunk configuration.
Troubleshooting
- Verified Opus is enabled on the Genesys trunk side.
- Checked BYOC edge logs; no handshake errors, just immediate rejection.
- Standard voice calls with G.711 only work fine.
- Digital channel exports are unaffected.
Have you tried forcing G.711 as the primary codec in the SDP negotiation? The 21481 error often triggers when the BYOC edge rejects Opus due to strict region-specific policy overrides, so stripping non-essential codecs from the trunk profile usually resolves the mismatch.
Check your SDP Offer construction in the load test script. The suggestion above about forcing G.711 is correct for immediate mitigation, but it does not address the root cause of the 21481 error during high-concurrency scenarios.
When running JMeter tests against BYOC edges, the SIP stack often encounters race conditions if the SDP payload is not strictly compliant with the Genesys Cloud codec negotiation rules. The error 21481 (Unsupported Media) frequently occurs when the a=rtpmap line for Opus is present, but the a=fmtp parameters are either missing or malformed in the rapid-fire INVITE stream.
In our recent load tests, we observed that the Genesys SIP stack rejects the INVITE if the Opus configuration lacks explicit ptime and maxaveragebitrate values, even if the trunk profile allows Opus. The edge node expects a complete codec definition.
Try updating your JMeter HTTP Request or SIP Sampler to ensure the SDP body looks exactly like this:
v=0
o=- 0 0 IN IP4 192.168.1.10
s=-
c=IN IP4 192.168.1.10
t=0 0
m=audio 5060 RTP/AVP 8 111
a=rtpmap:8 PCMU/8000
a=rtpmap:111 opus/48000/2
a=fmtp:111 maxaveragebitrate=30000; ptime=20
Notice the a=fmtp:111 line. Without the ptime=20 parameter, the BYOC edge may drop the packet as unsupported under load, interpreting the malformed SDP as a potential security risk or protocol violation.
We also recommend adding a small jitter buffer in the JMeter thread group (e.g., delay=50) to prevent the edge node from hitting its per-second INVITE rate limit, which can exacerbate codec negotiation failures. This simple config change resolved the 488 errors in our US-East load tests when scaling past 100 concurrent calls.
You need to evaluate whether the immediate technical mitigation aligns with your broader performance monitoring objectives. While forcing G.711 as the primary codec resolves the immediate 488 Not Acceptable Here error, it introduces significant variance in your Agent Performance and Queue Activity dashboards. The reduction in audio quality directly impacts Average Handle Time (AHT) metrics, particularly for complex legal discovery calls where clarity is paramount. This discrepancy often manifests as a sudden spike in call duration or an increase in transfer rates, which can skew the historical reporting data for the blended skill group.
When configuring the BYOC trunk profile, ensure that the codec priority list is explicitly defined to prevent the asynchronous replication process from defaulting to the unsupported Opus codec during high-concurrency scenarios. The configuration should prioritize G.711 (PCMU/PCMA) and exclude Opus from the active negotiation list if the region-specific policy overrides are strict. This approach stabilizes the SIP stack and prevents race conditions during SDP offer construction.
Monitor the real-time agent availability counts in the Queue Performance view to verify that the codec change does not inadvertently trigger agent status fluctuations. The dashboard should reflect a consistent trend in conversation detail views, with no sudden anomalies in call setup times. If the variance persists, review the edge logs for any remaining SDP negotiation failures that may not be immediately visible in the standard performance metrics.
Warning: Forcing G.711 may increase bandwidth consumption significantly, especially for high-volume legal discovery trunks. Ensure that your network infrastructure can handle the increased load without impacting other critical services. The documentation suggests reviewing the bandwidth allocation settings in the BYOC edge configuration to prevent potential congestion issues.