1xx Informational SIP Responses

• · 100 Trying – Extended search is being perform 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 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 dialog 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• · 301 Moved Permanently – The original Request URI is no longer valid, the new address is given in the Contact header.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 fulfill 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).
• · 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 Uknown 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 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 de-referenced.
• · 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 “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 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 dialog.
• · 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.
• · 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.