A list of all known SIP responses


What does the acronym SIP mean?
SIP (Session Initiation Protocol) is a signalling protocol that is used for controlling communication sessions (e.g. VoIP phone calls). It is based on request/response transactions.

Let's see a list of all known SIP responses.

1xx - Provisional Responses

  • 100 Trying = Extended search being performed may take a significant time so a forking proxy must send a "100 Trying" response.
  • 180 Ringing = Destination user agent received INVITE, and is alerting user of call.
  • 181 Call is Being Forwarded = Servers can optionally send this response to indicate a call is being forwarded.
  • 182 Queued = Indicates that the destination was temporarily unavailable, so the server has queued the call until the destination is available. A server may send multiple 182 responses to update progress of the queue.
  • 183 Session in Progress = This response may be used to send extra information for a call which is still being set up.
  • 199 Early Dialog Terminated = Can be used by User Agent Server to indicate to upstream SIP entities that an early dialog has been terminated.
2xx - Successful Responses

  • 200 OK = Indicates that the request was successful.
  • 202 Accepted = Indicates that the request has been accepted for processing, but the processing has not been completed.
  • 204 No Notification = Indicates that the request was successful, but the corresponding response will not be received.
3xx - Redirection Responses

  • 300 Multiple Choices = The address resolved to one of the several options for the user or client to choose between, which are listed in the message body or the message's Contact fields.
  • 301 Moved Permanently = The original Request-URI is no longer valid, the new address is given in the Contact header field, and the client should update any records of the original Request-URI with the new value.
  • 302 Moved Temporarily = The client should try at the address in the Contact field. If an Expires field is present, the client may cache the result for that period of time.
  • 305 Use Proxy = The Contact field details a proxy that must be used to access the requested destination.
  • 380 Alternative Service = The call failed, but alternatives are detailed in the message body.
4xx - Client Failure Responses

  • 400 Bad Request = The request could not be understood due to malformed syntax.
  • 401 Unauthorized = The request requires user authentication. This response is issued by UASs and registrars.
  • 402 Payment Required = Reserved for future use.
  • 403 Forbidden = The server understood the request, but is refusing to fulfill 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.
  • 409 Conflict = User already registered.
  • 410 Gone = 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.
  • 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.
  • 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.
  • 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 incomplete.
  • 485 Ambiguous = 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 aspects of the session description of 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.
  • 493 Undecipherable = 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-
5xx - Server Failure Responses

  • 500 Server Internal Error = The server could not fulfill the request due to some unexpected condition.
  • 501 Not Implemented = The server does not have the ability to fulfill the request, such as because it does not recognize the request method.
  • 502 Bad Gateway = The server is acting as a gateway or proxy, and received an invalid response from a downstream server while attempting to fulfill the request.
  • 503 Service Unavailable = The server is undergoing maintenance or is temporarily overloaded and so cannot process the request. A "Retry-After" header field may specify when the client may reattempt its request.
  • 504 Server Time-out = The server attempted to access another server in attempting to process the request, and did not receive a prompt response.
  • 505 Version Not Supported = The SIP protocol version in the request is not supported by the server.
  • 513 Message Too Large = The request message length is longer than the server can process.
  • 580 Precondition Failure = The server is unable or unwilling to meet some constraints specified in the offer.
6xx - Global Failure Responses
  • 600 Busy Everywhere = All possible destinations are busy. Unlike the 486 response, this response indicates that the destination knows that there are no alternative destinations able to accept the call.
  • 603 Decline = The destination does not wish to participate in the call, or cannot do so, and additionally the client knows that there are no alternative destinations willing to accept the call.
  • 604 Does Not Exist Anywhere = The server has authoritative information that the requested user does not exist anywhere.
  • 606 Not Acceptable = The user's agent was contacted successfully but some aspects of the session description such as the requested media, bandwidth, or addressing style were not acceptable.

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