SIP response class1
SIP response codes, class 1: Provisional messages
These are sent within a SIP dialogue

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

SIP Response class2
SIP Response codes: 2xx class
The 2xx class of responses indicates a success

    * 200 OK
    * 202 accepted: Used for referrals


SIP Response class3
SIP response codes, class 3xx
The 3xx class of responses indicates a redirection of the call

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



SIP Response class4
SIP responses, class 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
    * 409 Conflict
    * 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
    * 422 Session Interval Too Small
    * 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


SIP Response class5
SIP responses, class 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


SIP Response class6
SIP response codes, class 6: Global failures

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