atch the news." Just as a session description in the TV context should contain information about how to receive the broadcast session The Internet Multimedia Conferencing Architecture (channel 5), when the session is broadcast (from nine o'clock to approxi- mately eleven o'clock), and information about the contents of the session (soccer). We can get information about our favorite TV programs in many ways. We can read about a program in the newspaper or in the TV guide. We can consult the teletext or we can even receive a telephone call from a friend telling us about a program. However, no matter how we find out about our favorite program, we always need the same information: which channel, when, and what program. The information needed in the Internet context to receive a multimedia session is slightly different, but the concept is the same. SDP can be used to describe sessions no matter how session descriptions are distributed. They can be distributed using SAP, or they can be sent inside an e-mail. They can also be found on a Web page and retrieved using a normal Internet browser. We will shortly discover that SIP also carries session descriptions in its messages. SDP Syntax It is worthwhile to spend some time studying what SDP session descrip- tions look like because they appear in many SIP messages. SDP session descriptions are text-based, as opposed to a binary encoding such as ASN.1 1. An SDP session description consists of a set of lines of text of the form: Type = value The type field is always one character long and the format of the value field depends on which type it applies. An SDP description contains session- level information and media-level information. The session-level informa- tion applies to the whole session. It can be, for instance, the originator of the session or the session name. The media-level information applies to a par- ticular media stream. It can be, for instance, the codec used for encoding the audio stream or the port number where the video stream is headed. An SDP session desc