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SDP is a protocol that describes a format for conveying descriptive information about multimedia sessions. When a user wants to join a conference, he or she needs a way to know the multicast group address and the UDP port address for the conference.

SDP was designed as a session directory tool that could be used to advertise multimedia conferences, and communicate the conference addresses and conference tool-specific information necessary for participation. At the same time, SDP was designed for general-purpose use so that it could be used for a wide range of network applications.

This information includes session name and purpose, session time, type of media (voice or video), media format (MPEG, for example), transport protocol and port number, bandwidth requirements, and contact information. SDP is not a transport protocol, but relies instead on SIP (Session Initiation Protocol) or SAP (Session Announcement Protocol) to deliver the session information to destinations. For example, a caller can send SDP descriptive information in a SIP INVITE message. The callee then responds with acknowledgments regarding the descriptions that it can accept.

See "Multimedia" for more information about multimedia conferencing. Also see RFC 2327 (SDP: Session Description Protocol, April 1998).

Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.
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