Trace a VoIP protocol failure across signalling and media

When a call fails, first locate the stage that failed. A SIP rejection, an unanswered INVITE and a connected call with one-way audio point to different parts of the voice path.

Record one call attempt

Note the local time and time zone, call direction, anonymised source and destination, affected endpoint, and the call identifier if available. Preserve the original SIP trace or provider export. Keep response codes and the order of INVITE, provisional responses, final response and ACK together.

Compare the media path

For a call that connects, check the negotiated addresses, ports and codecs in SDP against the actual RTP or SRTP flow at the same network boundary. Compare with a known-good call from the same capture point. One-way audio after a 200 OK is not explained by a SIP response code alone.

Redact customer numbers before sharing traces, but retain timing and message order. Escalate across the provider boundary with the call identifier and the smallest useful capture.

Use the VoIP protocols guide to identify which protocol owns the failing step.