Locate the response family
- 1xx ProvisionalRequest is progressing
- 2xx SuccessRequest succeeded
- 3xx RedirectionAnother destination
- 4xx Request failureInterpret this request401 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 server requests authentication or rejects an unauthenticated attempt. An initial 401 challenge can be a normal part of SIP registration or calling.
Read it in context
The useful question is whether the client answers the challenge and then succeeds. Repeated challenges can involve username, secret, realm, algorithm compatibility or account policy. The reason phrase alone does not distinguish these causes.
Administrator checks
Inspect the challenge and subsequent request, preserving method and realm while protecting secrets. Compare the configured authentication identity with the provider’s requirements. Check current digest-algorithm support on both sides, including the RFC 8760 update.
Next action and common mistake
Do not disable authentication to eliminate 401 messages. Accept a successful challenge sequence as normal, then test registration renewal or calling separately. Proxy challenges use 407 and should not be conflated with this server challenge.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.