The Session Description Protocol (SDP) is a format for describing multimedia communication sessions for the purposes of announcement and invitation. Its predominant use is in support of streaming media applications, such as voice over IP (VoIP) and video conferencing. SDP does not deliver any media streams itself but is used between endpoints for negotiation of network metrics, media types, and other associated properties. The set of properties and parameters is called a session profile. SDP is extensible for the support of new media types and formats. SDP was originally a component of the Session Announcement Protocol (SAP), but found other uses in conjunction with the Real-time Transport Protocol (RTP), the Real-time Streaming Protocol (RTSP), Session Initiation Protocol (SIP), and as a standalone protocol for describing multicast sessions. The IETF published the original specification as a Proposed Standard in April 1998 (RFC 2327). Revised specifications were released in 2006 (RFC 4566), and in 2021 (RFC 8866).. Session description The Session Description Protocol describes a session as a group of fields in a text-based format, one field per line. The form of each field is as follows. <character>=<value><CR><LF> Where <character> is a single case-sensitive character and <value> is structured text in a format that depends on the character. Values are typically UTF-8 encoded. Whitespace is not allowed immediately to either side of the equal sign. Session descriptions consist of three sections: session, timing, and media descriptions. Each description may contain multiple timing and media descriptions. Names are only unique within the associated syntactic construct. Fields must appear in the order shown; optional fields are marked with an asterisk: Session description v= (protocol version number, currently only 0) o= (originator and session identifier : username, id, version number, network address) s= (session name : mandatory with at least one UTF-8-encoded character) i=* (session title or short information) u=* (URI of description) e=* (zero or more email address with optional name of contacts) p=* (zero or more phone number with optional name of contacts) c=* (connection information—not required if included in all media) b=* (zero or more bandwidth information lines) One or more time descriptions ("t=" and "r=" lines; see below) z=* (time zone adjustments) k=* (encryption key) a=* (zero or more session attribute lines) Zero or more Media descriptions (each one starting by an "m=" line; see below) (mandatory) t= (time the session is active) r=* (zero or more repeat times) (optional) m=