SIP Requests

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SIP requests are the codes used by Session Initiation Protocol for communication. To complement them there are SIP Responses, which generally indicate whether this request succeeded or failed, and in the latter case, why it failed.

[edit] Requests

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 a Event of Notification from the Notifier.
  • NOTIFY—Notify the subscriber of a new Event.

Other requests introduced in SIP are:

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