RTP is similar to the more familiar HTTP and FTP file transfer protocols, but it is tailored for the special needs of real-time streaming. Unlike HTTP and FTP, RTP does not download an entire movie to the client computer. A streamed one-minute movie plays in exactly one minute. As long as the connection has enough bandwidth to handle the data stream, the movie will play. After the data is displayed, it's discarded.
Viewers can see the broadcast again only by requesting it from the streaming server.
RTSP is used when viewers communicate with a unicast server. QuickTime automatically translates the viewer interaction with the on-screen movie controller into the proper RTSP requests. By contrast, RTP is a one-way protocol used to send live or stored streams from the server to the client. An SDP file is a text file that contains information about what will be streamed and tells how to tune in. QuickTime Player and the QuickTime Plug-in can open SDP files as if they were movies.