Locate the response family
- 1xx ProvisionalRequest is progressing
- 2xx SuccessRequest succeeded
- 3xx RedirectionAnother destination
- 4xx Request failureInterpret this request408 belongs here
- 5xx Server failureServer could not fulfil
- 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 request did not receive a timely result under the processing path that produced the response. It does not identify a single universal network cause.
Read it in context
The response can be generated by an intermediary after waiting for another participant, while a user-agent client can also treat its own transaction timeout as though 408 arrived. RFC 4320 changes the non-INVITE branch: a transaction-stateful SIP element must not generate 408 for an expired non-INVITE transaction, so a REGISTER or OPTIONS timeout may present as no final response instead.
Administrator checks
Identify who generated 408 and what it was waiting for. Compare request transmission, responses and routing on both sides of the relevant boundary. Check current contacts and transport reachability before changing account secrets.
Next action and common mistake
Do not treat every timeout as proof that a firewall is responsible. Preserve the method, timing, branch identifier, selected destination and response direction, then test the same flow after one justified repair. Distinguish an observed 408 response from a client's local transaction timeout. For Asterisk PJSIP, use the focused 408 investigation.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.