The Session Description Protocol

The Session Description Protocol (SDP) is an ASCII text based protocol for describing multimedia sessions and their related scheduling information. It was originally based on the protocol used by the sd session directory from Lawrence Berkeley Labs, but has been extended and generalised significantly since then.

The purpose of SDP is to convey information about media streams in multimedia sessions to allow the recipients of a session description to participate in the session. SDP is primarily intended for use in a internetwork, although it is sufficiently general that it can describe conferences in other network environments.

A multimedia session, for these purposes, is defined as a set of media streams that exist for a duration of time. Media streams can be many-to-many. The times during which the session is active need not be continuous.

Multicast based sessions on the internet differ from many other forms of conferencing in that anyone receiving the traffic can join the session (unless the session traffic is encrypted). In such an environment, SDP serves two primary purposes - as a means to communicate the existence and timing of a session, and as a means to convey sufficient information to enable joining and participating in the session. In a unicast environment, only the latter purpose is likely to be relevant.

Thus the information SDP must convey includes: