Type a code or a word. Each entry explains what the response means, what usually causes it, and links to the specification and to a fix guide where one exists.
52 of 52 codes shown. Search runs in your browser.
The next hop received the request and is working on it.
Typical causes
The far end is alerting the user.
Typical causes
The call is being forwarded to another destination.
Typical causes
The callee is temporarily unavailable and the call is queued.
Typical causes
Early media or progress information is available before answer.
Typical causes
Success. For INVITE, the call is answered; for REGISTER, the registration is accepted.
Typical causes
The request was accepted for processing, typically a REFER for transfer.
Typical causes
Several destinations are possible.
Typical causes
The user is permanently at another address.
Typical causes
Try the address in the Contact header for now.
Typical causes
The request must go through the named proxy.
Typical causes
The call failed but an alternative service is described.
Typical causes
The request was malformed.
Typical causes
Authentication is required. One 401 followed by a retry with credentials is normal; repeated 401s mean the credentials were rejected.
Typical causes
Reserved for future use; some providers use it for insufficient credit.
Typical causes
The server understood the request but refuses it, and retrying with credentials will not help.
Typical causes
The user or number does not exist at this domain.
Typical causes
The method (for example REFER) is not allowed for this address.
Typical causes
The resource cannot produce a response acceptable to the request's Accept headers.
Typical causes
Like 401, but issued by a proxy. One challenge is normal.
Typical causes
No response arrived in time. Often generated locally by the softphone when the server never answered.
Typical causes
The resource existed but is no longer available.
Typical causes
The message body is too big.
Typical causes
The body format is not supported.
Typical causes
The Request-URI scheme is not understood.
Typical causes
A required SIP extension is not supported.
Typical causes
The server needs an extension the client did not offer.
Typical causes
The registration expiry requested is too short.
Typical causes
The registration flow (connection) failed.
Typical causes
The callee is not reachable right now.
Typical causes
The server has no record of the dialog or transaction.
Typical causes
The request looped back to the same server.
Typical causes
Max-Forwards reached zero.
Typical causes
The dialed number is incomplete.
Typical causes
The address matches more than one user.
Typical causes
The callee is busy at this location.
Typical causes
The request was cancelled, usually by the caller hanging up before answer.
Typical causes
The offer (usually codecs or encryption) is not acceptable at this location.
Typical causes
The SUBSCRIBE event package is not understood.
Typical causes
A request in the same dialog is still being processed.
Typical causes
An encrypted body could not be decrypted.
Typical causes
The server hit an unexpected condition.
Typical causes
The server does not support the method.
Typical causes
A gateway or proxy received an invalid response downstream.
Typical causes
The server is temporarily unable to handle the request.
Typical causes
The server did not get a timely response from an upstream server.
Typical causes
The SIP version is not supported.
Typical causes
The message exceeds the server's limit.
Typical causes
The callee is busy and does not want the call anywhere.
Typical causes
The callee explicitly declined the call.
Typical causes
The server has authoritative information that the user does not exist anywhere.
Typical causes
The user agent was contacted but some aspect of the session is unacceptable.
Typical causes
Every SIP request receives one or more responses. The first digit is the class: 1xx provisional, 2xx success, 3xx redirection, 4xx client error, 5xx server error, 6xx global failure. Final responses (2xx to 6xx) end the transaction. The reason phrase after the number is informational; some servers customise it, and a Warning header or a Reason header may add detail.
They follow the same pattern (1xx to 6xx) and many numbers match, but the meanings are SIP-specific. 486 Busy Here and 487 Request Terminated, for example, have no HTTP equivalent.
No. A 401 or 407 challenge followed by a retry with credentials is how SIP digest authentication works. Only repeated 401s with the same credentials indicate a problem.
Turn on detailed logs in Settings, reproduce the problem, then open or share the logs. They contain the SIP messages, including the status line of each response.
408 is often generated locally when no response arrives at all: the request never reached the server because of a wrong address, a blocked port or a NAT device dropping packets.