 use of the remote control with a VCR. The user can tell the multimedia server, for instance, to initiate a certain audio/video stream using the play button, to freeze the stream at a particular moment using the pause button, or to begin replay at a certain position using the forward and rewind buttons. The user can also command the server to record certain media using the record button. RTSP can be used, for example, to implement a distributed answering machine, or to record an event that is being multicast on the Internet. Usage Example of the Internet Multimedia Conferencing Toolkit Let us see how some of the protocols analyzed in this chapter can be com- bined in order to multicast a film on the Internet. The end user controlling the multicast of the film elaborates a session description using SDP, Chapter 3 Multimedia server Figure 3-24 RTSP is used to control remote multimedia servers. RTSP: Stop playing the movie! The Internet RTSP: Stop playing the movie! indicating when the film is going to be multicast, what the film is about, and the parameters needed to receive the media. These parameters will include multicast addresses, port numbers, and media formats at a mini- mum. This SDP session description is then distributed via SAP to potential receivers, making use of multicast routing. Interested end users will examine the SDP they've received and config- ure their media tools properly to be able to watch the film at the appointed time. When the film is programmed, the session controller will use RSTP to alert the multimedia server where the film resides to begin multicast using the SDP session description that was previously distributed. The media server will multicast RTP packets containing the audio and the video of the film. It will use RTCP to store statistics about the reception quality that the receivers are experiencing. RSVP might also be used grant a certain QoS between media server and receivers. CHAPTER The Session Initiation Protocol: SIP Chapter 4 This chapter focuses squarely on the Session 