Session Description Protocol

With the Session Description Protocol (SDP, RFC 4566 ) the properties of the multimedia data streams are described below. It is used to manage communication sessions, and is for example used in conjunction with SIP and H.323 in IP telephony in the negotiation of codecs, transport protocols and addresses and for transmission of metadata. SDP itself does not have its own negotiation mechanism, but only a description of the data streams. Records in the SDP format can be transferred with different transport protocols, for example, with such a " transport protocols " such as your e -mail.


V = 0 o = Alice 1234 1234 IN IP4 s = Video of 987654 c = IN IP4 t = 0 0 m = audio 20000 RTP / AVP 97 a = rtpmap: 97 iLBC/16000 m = video 20001 RTP / AVP 31 a = rtpmap: 31 H261/90000 Alice offers to the recipient of starting the Meeting No. 1234, including two message streams (m =), both of which are sent with the transport protocol RTP. The first is an audio stream in the format iLBC (97 ) on port 20000, the other a video stream in the format H.261 (31 ) on port 20,001th The attributes (a = ) of the respective data streams describe format parameter which has the number 97 the name iLBC and a sample rate of 16 kHz.

RFC 4317 provides detailed examples of how a negotiation protocol using SDP could look.


  • V = protocol version
  • O = creator of the session and session identification
  • S = name of the session
  • I = additional session information (optional)
  • U = URI with the further leading (optional)
  • E = e- mail address ( optional)
  • P = Phone number ( optional)
  • C = connection information (not required if indicated on all media, optional)
  • B = Information about the bandwidth (optional)
  • One or more time descriptions (see below)
  • Z = time zone adjustments ( optional)
  • K = encryption key (encryption key) (optional)
  • A = zero or more session attributes (optional )
  • Zero or more media descriptions ( S.U. )

Time Descriptions:

  • T = time during which the session is active
  • R = zero or more repetitions ( optional)

Description of the media:

  • M = media type, port, and protocol for media transport and media formats
  • I = Title of the medium ( optional)
  • C = connection information, optional if they are not defined in the session ( see above, optional)
  • B = zero or more bandwidth information (optional)
  • K = encryption key ( "encryption key", optional)
  • A = zero or more media attributes (optional )

Source: IETF RFC 4566: SDP: Session Description Protocol (M. Handley, V. Jacobson, C. Perkins, July 2006)

  • Internet application protocol