1.3 Overview

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The Real-Time Streaming Protocol (RTSP) [RFC2326] is used for transferring real-time multimedia data, including audio and video, between a server and a client. It is a streaming protocol, which means it attempts to facilitate scenarios in which the multimedia data is being simultaneously transferred and rendered; that is, video is displayed, and audio is played.

RTSP uses a Transmission Control Protocol (TCP) connection for control of the streaming media session, although it is also possible to use UDP for this purpose.

The entity that sends the RTSP request that initiates the session is referred as the client, and the entity that responds to that request is referred to as the server. Typically, the multimedia data flows from the server to the client. RTSP also allows multimedia data to flow in the opposite direction. However, the extensions defined in this specification were not designed for such scenarios.

Clients can send RTSP requests to the server requesting information on content before a session is established. The information that the server returns is formatted by using a syntax specified by the Session Description Protocol (SDP) [RFC4566].

Clients use RTSP requests to control the session and to request that the server perform actions, such as starting or stopping the flow of multimedia data. Each request has a corresponding RTSP response that is sent in the opposite direction. Servers can also send RTSP requests to clients, for example, to inform them that the session state has changed.

If TCP is used to exchange RTSP requests and responses, the multimedia data can also be transferred over the same TCP connection. Otherwise, the multimedia data is transferred over UDP.

The multimedia data is encapsulated in Real-Time Transport Protocol (RTP) packets [RFC3550]. For each RTP stream, the server and client can also exchange Real-Time Transport Control Protocol (RTCP) packets [RFC3556].

This specification defines extensions to RTSP, SDP, RTP, and RTCP that enable the delivery of multimedia data that is encapsulated in Advanced Systems Format (ASF) packets [ASF].