SIP/2.0:
CodeMeaning
1xx Informational -- request received, continuing to process the request
2xx Success -- the action was successfully received, understood, and accepted
3xx Redirection -- further action needs to be taken in order to complete the request
4xx Client Error -- the request contains bad syntax or cannot be fulfilled at this server
5xx Server Error -- the server failed to fulfill an apparently valid request
6xx Global Failure -- the request cannot be fulfilled at any server.
CodeMeaning
1xx Informational
100Trying
180Ringing
181Call Is Being Forwarded
182Queued
2xx Success
200OK
3xx Redirection
300Multiple Choices
301Moved Permanently
302Moved Temporarily
303See Other
305Use Proxy
380Alternative Service
4xx Client Error
400Bad Request
401Unauthorized
402Payment Required
403Forbidden
404Not Found
405Method Not Allowed
406Not Acceptable
407Proxy Authentication Required
408Request Timeout
409Conflict
410Gone
411Length Required
413Request Entity Too Large
414Request-URI Too Large
415Unsupported Media Type
420Bad Extension
480Temporarily not available
481Call Leg/Transaction Does Not Exist
482Loop Detected
483Too Many Hops
484Address Incomplete
485Ambiguous
486Busy Here
5xx Server Error
500Internal Server Error
501Not Implemented
502Bad Gateway
503Service Unavailable
504Gateway Time-out
505SIP Version not supported
6xx General Error
600Busy Everywhere
603Decline (9)
604Does not exist anywhere
606Does not exist anywhere

(9) La r-béponse Decline est retournée lorsque la machine de l'appelé a été contactée avec succès mais que l'utilisateur ne souhaite pas ou ne peut pas participer à la session SIP.

-A

Source