Compare SDP offers, codecs, and media settings when a trunk or endpoint rejects a call.
Before you start
Work on a copy or a controlled test when the change can affect production. Keep timestamps, screenshots and the previous configuration so the result can be compared.
Step by step
- Capture SIP signaling around the INVITE and 488 response.
- Compare offered codecs with those allowed on the trunk or endpoint.
- Check SRTP, RTP, DTMF, and required SDP attributes.
- Review any SDP transformations performed by an SBC or NAT device.
- Retest with a minimal offer and document the actual incompatible parameter.
Validation
Repeat the original test after the change and confirm that the expected service works without creating a new regression. Document the final state.