How do RTSP, RTP and H.323 relate to one another?
H.323 and RTSP are complementary in function. H.323 is useful for setting up audio/video conferences in moderately sized peer-to-peer groups, whereas RTSP is useful for large-scale broadcasts and audio/video-on-demand streaming. One could think of H.323 as offering services equivalent to a telephone with three-way calling, while RTSP offers services like a video store with delivery services, a VCR or cable television. RTSP provides “VCR-style” control functionality such as pause, fast forward, reverse, and absolute positioning, which is beyond the scope of H.323 and RTP. Both H.323 and RTSP use RTP as their standard means of actually delivering the multimedia data. This data-level compatibility makes efficient gateways between the protocols possible, since only control messages need to be translated.
