(media name and transport address) i=* (media title or information field) c=* (connection information — optional if included at session level) b=* (zero or more bandwidth information lines) k=* (encryption key) a=* (zero or more media attribute lines — overriding the Session attribute lines) Below is a sample session description from RFC 4566. This session is originated by the user "jdoe", at IPv4 address 10.47.16.5. Its name is "SDP Seminar" and extended session information ("A Seminar on the session description protocol") is included along with a link for additional information and an email address to contact the responsible party, Jane Doe. This session is specified to last for two hours using NTP timestamps, with a connection address (which indicates the address clients must connect to or — when a multicast address is provided, as it is here — subscribe to) specified as IPv4 224.2.17.12 with a TTL of 127. Recipients of this session description are instructed to only receive media. Two media descriptions are provided, both using RTP Audio Video Profile. The first is an audio stream on port 49170 using RTP/AVP payload type 0 (defined by RFC 3551 as PCMU), and the second is a video stream on port 51372 using RTP/AVP payload type 99 (defined as "dynamic"). Finally, an attribute is included which maps RTP/AVP payload type 99 to format h263-1998 with a 90 kHz clock rate. RTCP ports for the audio and video streams of 49171 and 51373, respectively, are implied. v=0 o=jdoe 2890844526 2890842807 IN IP4 10.47.16.5 s=SDP Seminar i=A Seminar on the session description protocol u=http://www.example.com/seminars/sdp.pdf e=j.doe@example.com (Jane Doe) c=IN IP4 224.2.17.12/127 t=2873397496 2873404696 a=recvonly m=audio 49170 RTP/AVP 0 m=video 51372 RTP/AVP 99 a=rtpmap:99 h263-1998/90000 The SDP specification is purely a format for session description. It is intended to be distributed over different transport protocols as necessary, including SAP, SIP, and RTSP. SDP could even be transmitted by email or as an HTTP payload. Attributes SDP uses attributes to extend the core protocol. Attributes can appear within the Session or Media sections and are scoped accordingly as session-level or media-level. New attributes are added to the standard occasionally through registration with IANA. Attributes are either properties or values: Property: a=flag conveys a boolean property of the media or session. Value: a=attribute:value provides a named parameter. Two of these attributes are specially defined: a=charset:encoding is used in the session or media sections to specify a different