What are SIP responses?

1xx = Informational SIP responses

• 100 Trying - Extended search is being performed so a forking proxy must send a 100 Trying response.

• 180 Ringing - The Destination User Agent has received the INVITE message and is alerting the user of call.

• 181 Call Is Being Forwarded - Optional, send by Server to indicate a call is being forwarded.

• 182 Queued - Destination was temporarily unavailable, the server has queued the call until the destination is available.

• 183 Session Progress - This response may be used to send extra information for a call which is still being set up.

• 199 Early Dialog Terminated - Send by the User Agent Server to indicate that an early dialogue has been terminated.

2xx = Success responses

• 200 OK - Shows that the request was successful.

• 202 Accepted - Indicates that the request has been accepted for processing, mainly used for referrals.

• 204 No Notification - Indicates that the request was successful but no response will be received.

3xx = Redirection responses

• 300 Multiple Choices - The address resolved to one of several options for the user or client to choose between.

• 301 Moved Permanently - The original Request URI is no longer valid, the new address is given in the Contact header.

• 302 Moved Temporarily - The client should try at the address in the Contact field.

• 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 = Request failures

• 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 fulfil it.

• 404 Not Found - The server has definitive information that the user does not exist at the (User not found).

• 405 Method Not Allowed - The method specified in the Request-Line is understood, but not allowed.

• 406 Not Acceptable - The resource is only capable of generating responses with unacceptable content.

• 407 Proxy Authentication Required - The request requires user authentication.

• 408 Request Timeout - Couldn’t find the user in time.

• 409 Conflict - User already registered (deprecated).

• 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 (deprecated).

• 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 - Server refuses to service the request, the Req-URI is longer than the server can interpret.

• 415 Unsupported Media Type - Request body is in a non-supported format.

• 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 request contains a Session-Expires header field with a duration below the minimum.

• 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.

• 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 contained 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 - Server obtained a valid certificate used to sign a request, was unable to verify the signature.

• 439 First Hop Lacks Outbound Support - The first outbound proxy doesn’t support the “outbound” feature.

• 440 Max-Breadth Exceeded - If a SIP proxy determined a response context had insufficient Incoming Max-Breadth to carry out a desired parallel fork, and the proxy is unwilling/unable to compensate by forking serially or sending a redirect, that proxy MUST return a 440 response. A client receiving a 440 response can infer that its request did not reach all possible destinations.

• 469 Bad Info Package - If a SIP UA receives an INFO request associated with an Info Package that the UA has not indicated willingness to receive, the UA MUST send a 469 response, which contains a Recv-Info header field with Info Packages for which UA is willing to receive INFO requests.

• 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 dialogue 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 are 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 dialogue.

• 493 Undecipherable - UndecipherableRequest 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.

5xx = Server errors

• 500 Server Internal Error - The server could not fulfill the request due to some unexpected condition.

• 501 Not Implemented - The SIP request method is not implemented here.

• 502 Bad Gateway - The server, received an invalid response from a downstream server while trying to fulfill a request.

• 503 Service Unavailable - The server is in maintenance or is temporarily overloaded and cannot process the request.

• 504 Server Time-out - The server tried to access another server while trying to process a request, no timely 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.

• 555 Push Notification Service Not Supported - The server does not support the push notification service specified in the pn-provider SIP URI parameter.

• 580 Precondition Failure - The server is unable or unwilling to meet some constraints specified in the offer.

6xx = Global failures

• 600 Busy Everywhere - All possible destinations are busy.

• 603 Decline - Destination cannot/doesn’t wish to participate in the call, no alternative destinations.

• 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 were not acceptable.

• 607 Unwanted - The called party did not want his call from the calling party. Future attempts from the calling party are likely to be similarly rejected.