Appendix A. SIP Methods and Responses

Table A-1 shows SIP methods.

INVITE	A SIP device is being invited to participate in a call.
ACK	Confirms that the client has received a final response to an INVITE request.
BYE	Terminates a SIP call. Can be sent by any party involved.
CANCEL	Cancels any pending call but does not terminate a call that has already been connected.
OPTIONS	Queries the capabilities of servers without requesting to establish a call.
REGISTER	Registers an IP with a SIP registrar.
PRACK	Insures reliability of provisional 1xx responses if a UAS offers them.
UPDATE	Updates a previously made offer for a not-yet-established session.
REFER	Initiates a call transfer by telling the recipient (specified by URI) to contact a third party using the contact information provided in the request.
SUBSCRIBE	Subscribes to be notified of an event occurrence; for example a user presence update.
NOTIFY	Used to notify that an event has occurred.
MESSAGE	A method signifying the payload is an instant message.

Table A-2 shows SIP responses.

100		Trying
180		Ringing
181		Call Is Being Forwarded
182		Queued
183		Session Progress
200		OK
202		Accepted
300		Multiple Choices
301		Moved Permanently
302		Moved Temporarily
305		Use Proxy
380		Alternative Service
400		Bad Request
401		Unauthorized to Use This Registrar
402		Payment Required
403		Forbidden
404		User Not Found
405		Method Not Allowed
406		Not Acceptable
407		Proxy Authentication Required
408		Request Timeout
410		This User Is Gone From Here
413		Request Entity Too Large
414		Request URI Too Long
415		Unsupported Media Type
416		Unsupported URI Scheme
420		Bad Protocol Extension
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 s/MIME Part
500		Server Internal Error
501		Method Not Implemented on This Server
502		Bad Gateway
503		Service Unavailable
504		Server Timeout
505		Version Not Supported
513		Message Too Large
600		Busy Everywhere
603		Decline
604		Does Not Exist Anywhere
606		Not Acceptable