Locate the response family
- 1xx ProvisionalRequest is progressing
- 2xx SuccessRequest succeeded
- 3xx RedirectionAnother destination
- 4xx Request failureInterpret this request
- 5xx Server failureServer could not fulfil500 belongs here
- 6xx Global failureFailure across destinations
Read the status with its request method and call leg. For example, 200 after REGISTER confirms a binding; it does not prove an INVITE succeeded.
What this response means
The server encountered an unexpected condition that prevented it from completing the request. The response is a starting point for server-side evidence.
Read it in context
Application faults, resource problems or transient internal state can be relevant, but the code does not prove CPU exhaustion or a particular module defect. The sender may be your PBX or an upstream service.
Administrator checks
Record the rejecting method, timestamp and call identifier. Check server logs, recent changes and resource alerts at that time. Inspect Retry-After if supplied and follow documented retry behavior rather than generating an aggressive loop.
Next action and common mistake
Do not restart every network device because a server reported an internal condition. Localize the emitting component, preserve useful evidence and test recovery after the justified repair. Escalate upstream errors with a concise reproducible example.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.