Chapter 1 Product Overview
What is Session Initiation Protocol?
SIP provides the capabilities to:
•Determine the location of the target end point—SIP supports address resolution, name mapping, and call redirection.
•Determine the media capabilities of the target end point—Via Session Description Protocol (SDP), SIP determines the “lowest level” of common services between the end points. Conferences are established using only the media capabilities that can be supported by all end points.
•Determine the availability of the target end point—If a call cannot be completed because the target end point is unavailable, SIP determines whether the called party is already on the phone or did not answer in the allotted number of rings. It then returns a message indicating why the target end point was unavailable.
•Establish a session between the originating and target end point—If the call can be completed, SIP establishes a session between the end points. SIP also supports mid-call changes, such as the addition of another end point to the conference or the changing of a media characteristic or codec.
•Handle the transfer and termination of calls—SIP supports the transfer of calls from one end point to another. During a call transfer, SIP simply establishes a session between the transferee and a new end point (specified by the transferring party) and terminates the session between the transferee and the transferring party. At the end of a call, SIP terminates the sessions between all parties.
Conferences can consist of two or more users and can be established using multicast or multiple unicast sessions.
Note The term conference means an established session (or call) between two or more end points. In this document, the terms conference and call are used interchangeably.
| Cisco SIP IP Phone 7960 Administrator Guide |
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