What are SIP Methods / Requests and Responses?

Question

Accepted Answer

SIP Methods/Requests and Responses are protocols used in Session Initiation Protocol for communication between devices.

SIP Methods/Requests are used to initiate and control communication sessions.
SIP Responses are used to provide feedback and status information during the session.
Examples of SIP Methods/Requests include INVITE, ACK, BYE, and CANCEL.
Examples of SIP Responses include 200 OK, 404 Not Found, and 503 Service Unavailable.

Accepted Answer

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.

What are SIP Methods / Requests and Responses?

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