400 Bad Request
The request could not be understood due to malformed syntax.
The request requires user authentication. This response is issued by UASs and registrars.
402 Payment Required
Reserved for future use.
The server understood the request, but is refusing to fulfil it
404 Not Found
The server has definitive information that the user does not exist at the domain specified in the Request-URI. This status is also returned if the domain in the Request-URI does not match any of the domains handled by the recipient of the request.
405 Method Not Allowed
The method specified in the Request-Line is understood, but not allowed for the address identified by the Request-URI
406 Not Acceptable
The resource identified by the request is only capable of generating response entities that have content characteristics but not acceptable according to the Accept header field sent in the request
407 Proxy Authentication Required
The request requires user authentication. This response is issued by proxys
408 Request Timeout
Couldn't find the user in time. The server could not produce a response within a suitable amount of time, for example, if it could not determine the location of the user in time. The client MAY repeat the request without modifications at any later time
User already registered.:§7.4.10 Deprecated by omission from later RFCs and by non-registration with the IANA.
The user existed once, but is not available here any more.
411 Length Required
The server will not accept the request without a valid Content-Length.:§7.4.12 Deprecated by omission from later RFC and by non-registration with the IANA
412 Conditional Request Failed
The given precondition has not been met
413 Request Entity Too Large
Request body too large
414 Request-URI Too Long
The server is refusing to service the request because the Request-URI is longer than the server is willing to interpret
415 Unsupported Media Type
Request body in a format not supported
416 Unsupported URI Scheme
Request-URI is unknown to the server.
417 Unknown Resource-Priority
There was a resource-priority option tag, but no Resource-Priority header
420 Bad Extension
Bad SIP Protocol Extension used, not understood by the server.
421 Extension Required
The server needs a specific extension not listed in the Supported header.
422 Session Interval Too Small
The received request contains a Session-Expires header field with a duration below the minimum timer.
423 Interval Too Brief
Expiration time of the resource is too short.
424 Bad Location Information
The request's location content was malformed or otherwise unsatisfactory.
428 Use Identity Header
The server policy requires an Identity header, and one has not been provided.
429 Provide Referrer Identity
The server did not receive a valid Referred-By token on the request.
430 Flow Failed
A specific flow to a user agent has failed, although other flows may succeed. This response is intended for use between proxy devices, and should not be seen by an endpoint (and if it is seen by one, should be treated as a 400 Bad Request response)
433 Anonymity Disallowed
The request has been rejected because it was anonymous.
436 Bad Identity-Info
The request has an Identity-Info header, and the URI scheme in that header cannot be dereferenced.
437 Unsupported Certificate
The server was unable to validate a certificate for the domain that signed the request.
438 Invalid Identity Header
The server obtained a valid certificate that the request claimed was used to sign the request, but was unable to verify that signature.
439 First Hop Lacks Outbound Support
The first outbound proxy the user is attempting to register through does not support the "outbound" feature of RFC 5626, although the registrar does.
470 Consent Needed
The source of the request did not have the permission of the recipient to make such a request.
480 Temporarily Unavailable
Callee currently unavailable.
481 Call/Transaction Does Not Exist
Server received a request that does not match any dialog or transaction.
482 Loop Detected.
Server has detected a loop.
483 Too Many Hops
Max-Forwards header has reached the value '0'.
484 Address Incomplete
Request-URI is ambiguous.
486 Busy Here
Callee is busy.
487 Request Terminated
Request has terminated by bye or cancel
488 Not Acceptable Here
Some aspect of the session description or the Request-URI is not acceptable
489 Bad Event
The server did not understand an event package specified in an Event header field.
491 Request Pending
Server has some pending request from the same dialog.
Request contains an encrypted MIME body, which recipient can not decrypt
494 Security Agreement Required
The server has received a request that requires a negotiated security mechanism, and the response contains a list of suitable security mechanisms for the requester to choose between or a digest authentication challenge