Locate the response family
- 1xx ProvisionalRequest is progressing
- 2xx SuccessRequest succeeded
- 3xx RedirectionAnother destination
- 4xx Request failureInterpret this request481 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 recipient cannot associate the request with the expected existing call or transaction. This often matters for in-dialog operations and cancellation.
Read it in context
A request can reach a different server instance, contain mismatched dialog identifiers or refer to state that expired or was lost. A restart or routing change during a call can therefore be relevant.
Administrator checks
Identify the method receiving 481 and compare its Call-ID, tags and routing with the original exchange. Check whether an intermediary or failover moved the request to a system without the required state. Preserve the sequence before the error.
Next action and common mistake
Do not create new extension records to repair lost dialog state. Correct the routing or lifecycle issue and test hold, transfer and hangup as appropriate. Treat a late request after normal teardown differently from a reproducible mid-call failure.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.