Specifications

Appendix
371
SIP uses six request methods:
 INVITE—Indicates a user is being invited to participate in a call session.
 ACK—Confirms that the client has received a final response to an INVITE request.
 BYE—Terminates a call and can be sent by either the caller or the callee.
 CANCEL—Cancels any pending searches but does not terminate a call that has
already been accepted.
 OPTIONS—Queries the capabilities of servers.
 REGISTER—Registers the address listed in the To header field with a SIP server.
The following types of responses are used by SIP and generated by the IP phone or the
SIP server:
 SIP 1xx—Informational Responses
 SIP 2xx—Successful Responses
 SIP 3xx—Redirection Responses
 SIP 4xx—Client Failure Responses
 SIP 5xx—Server Failure Responses
 SIP 6xx—Global Failure Responses