(RTSP) An application layer protocol for controlling delivery of a stream of real-time multimedia content. RTSP allows users to start playing from a certain position. It does not actually deliver the data, but works alongside existing delivery channels such as UDP, TCP, or IP multicast. RTSP was developed by RealNetworks, Netscape Communications, and Columbia University, and is described in RFC 2326, April 1998. RTSP is an IETF proposed standard.