Read a SIP failure in message order
Preserve the INVITE, provisional responses, final response and ACK or CANCEL, plus the Call-ID and timestamps. The same numeric code can have different operational meaning depending on which system sent it.
A SIP failure in message order
- Compare a failed and successful attempt at the same trace point. Check the called number, authentication challenge, route and destination before changing a rule.
- If the call completed but audio failed, inspect SDP and media flow separately; the final SIP code cannot diagnose one-way audio.
Redact customer numbers in shared traces while retaining enough context for the provider to find the call.
Keep the comparison precise
Check whether a proxy forwarded the response or generated it locally. The Via path, related request and responding address help locate that distinction. If a carrier is involved, retain its call reference and the local Call-ID so the two traces can be matched.
Use the SIP response codes: a practical troubleshooting guide to interpret the recorded messages and settings.