SIP (Session Initiation Protocol)

An IETF defined protocol (RFC3261) that defines a method for establishing multimedia sessions over the Internet. Used as the call signaling protocol in VoIP, i2 and i3

SIP Transactions
A SIP transaction occurs between a UAC and a UAS. The SIP transaction comprises all messages from the first request sent from the UAC to the UAS up to a final response (non-1xx) sent from the UAS to the UAC. If the request is INVITE, and the final response is a non-2xx, the SIP transaction also includes an ACK to the response. The ACK for a 2xx response to an INVITE request is a separate SIP transaction.

BYE

A SIP transaction used to terminate a session.

CANCEL

A SIP transaction which is used to cancel an INVITE transaction which has not yet completed.

INFO

A SIP transaction used to pass information from the caller to the called party.

INVITE

A SIP transaction used to initiate a session.

reINVITE

A SIP INVITE transaction within an established session used to change the parameters of a call or refresh a session.

SIP Methods
The primary function that an SIP request is meant to call on a server. This method is carried in the request message itself.

MESSAGE

A SIP method which passes information, often an Instant Message, between endpoints in the body of the SIP message.

NOTIFY

A SIP method used to send a notification to a subscriber of the occurrence of an asynchronous event.

OPTIONS

A SIP method used to request the SIP protocol options supported by an endpoint.

REFER

A SIP method that is used as part of a transfer operation to refer a call to another endpoint.

REGISTER

A SIP method that is used to communicate the availability and address of an endpoint to the proxy server that directs incoming calls.

UPDATE

A SIP method used to update parameters in a call not yet established.

Related Terms:
REFER/Replaces

Use of the SIP REFER method together with a Replaces header as part of a transfer operation to indicate that a new leg is to be created that replaces an existing call leg.

SUBSCRIBE / NOTIFY

The two actions in an asynchronous event notification system. The subscription is the request to receive notifications of the events. The Notify is the notification of the event itself. Also refers to the SIP methods used for this purpose.

NENA-STA-010, Detailed Functional and Interface Standards for the NENA i3 Solution