1xx SIP Response Codes, Klasse 1: Provisional Messages

100 Trying
180 Ringing
181 Call Is Being Forwarded
182 Queued
183 Session Progress

2xx SIP Response Codes: Klasse 2: Success

200 OK
202 accepted: Used for referrals

3xx SIP Response Codes, Klasse 3: Redirection

300 Multiple Choices
301 Moved Permanently
302 Moved Temporarily
305 Use Proxy
380 Alternative Service

4xx SIP Response Codes, Klasse 4: Request Failures

400 Bad Request
401 Unauthorized: Used only by registrars. Proxys should use proxy authorization 407
402 Payment Required (Reserved for future use)
403 Forbidden
404 Not Found: User not found
405 Method Not Allowed
406 Not Acceptable
407 Proxy Authentication Required
408 Request Timeout: Couldn't find the user in time
410 Gone: The user existed once, but is not available here any more.
413 Request Entity Too Large
414 Request-URI Too Long
415 Unsupported Media Type
416 Unsupported URI Scheme
420 Bad Extension: Bad SIP Protocol Extension used, not understood by the server
421 Extension Required
423 Interval Too Brief
480 Temporarily Unavailable
481 Call/Transaction Does Not Exist
482 Loop Detected
483 Too Many Hops
484 Address Incomplete
485 Ambiguous
486 Busy Here
487 Request Terminated
488 Not Acceptable Here
491 Request Pending
493 Undecipherable: Could not decrypt S/MIME body part

5xx SIP Response Codes, Klasse 5: Server Failures

500 Server Internal Error
501 Not Implemented: The SIP request method is not implemented here
502 Bad Gateway
503 Service Unavailable
504 Server Time-out
505 Version Not Supported: The server does not support this version of the SIP protocol
513 Message Too Large

6xx SIP Response Codes, Klasse 6: Global Failures

600 Busy Everywhere
603 Decline
604 Does Not Exist Anywhere
606 Not Acceptable