Sip request types

RFC 3261 (SIP) uses six types (methods) of requests:

  • INVITE — Indicates a client 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.

RFC 3262 Reliability of Provisional Responses in SIP

  • PRACK - Provisional acknowledgement.

RFC 3265 extends the basic requests, to support notification:

  • SUBSCRIBE — Subscribes for an Event of Notification from the Notifier.
  • NOTIFY — Notify the subscriber of a new Event.

RFC 3903 extends the basic requests, to publish event changes to the server:

  • PUBLISH - publishes an event to the Server.

Other requests introduced in SIP are:

  • INFO - Sends mid-session information that does not modify the session state. (RFC 2976)
  • REFER - Ask recipient to issue SIP request (call transfer.) (RFC 3515)
  • MESSAGE - The MESSAGE is used to transport instant messages using SIP. (RFC 3428)
  • UPDATE - The UPDATE method is used to modify the state of a session without changing the state of the dialog. (RFC 3311)