The abstract of the RTSP Internet draft, issued in February 1997, gives pretty good idea what RTSP should be:

The RTSP, is an application-level protocol for control over the delivery of data with real-time properties. RTSP provides a framework to enable controlled, on-demand delivery of real-time data, such as audio and video. Sources of data can include both live data feeds and stored clips. This protocol is intended to control multiple data delivery sessions, provide a means for choosing delivery channels such as UDP, multicast UDP and TCP, and delivery mechanisms based upon RTP (RFC 1889).

To control the delivery of one or more streams of data, RTSP uses the Session Control Protocol (SCP). The SCP uses one TCP connection between the client and server. For delivery of data, unicast and multicast UDP, as well as TCP in some cases are used.

The RTSP should provide techniques to:

• request delivery of real-time data
• request a specific transport type and destination for the delivery of the data
• request information about the data in a format-specific fashion
• start, stop, and pause the delivery of the data
• provide random access to various portions of the data