What are SIP Methods / Requests and Responses?

SIP Methods / Requests and Responses

SIP uses Methods / Requests and corresponding Responses to communicate and establish a call session.

SIP Methods

SIP Requests:

There are fourteen SIP Request methods of which the first six are the most basic request / method types:

  • INVITE = Establishes a session.
  • ACK = Confirms an INVITE request.
  • BYE = Ends a session.
  • CANCEL = Cancels establishing of a session.
  • REGISTER = Communicates user location (host name, IP).
  • OPTIONS = Communicates information about the capabilities of the calling and receiving SIP phones.
  • PRACK = Provisional Acknowledgement.
  • SUBSCRIBE = Subscribes for Notification from the notifier.
  • NOTIFY = Notifies the subscriber of a new event.
  • PUBLISH = Publishes an event to the Server.
  • INFO = Sends mid session information.
  • REFER = Asks the recipient to issue call transfer.
  • MESSAGE = Transports Instant Messages.
  • UPDATE = Modifies the state of a session.

SIP Responses:

SIP Requests are answered with SIP responses, of which there are six classes:

1xx = Informational responses, such as 180 (ringing).
2xx = Success responses.
3xx = Redirection responses.
4XX = Request failures.
5xx = Server errors.
6xx = Global failures.