Real Time Streaming Protocol (RTSP) is an application-level network communication system that transfers real-time data from multimedia to an endpoint device by communicating directly with the server streaming the data.

The protocol establishes and controls the media stream between client devices and servers by serving as a network remote control for continuous media, such as audio and video. It does not stream the multimedia itself but communicates with the server that streams the multimedia data. When a user pauses a video he is streaming, for example, RTSP conveys the user's request to pause the video to the video streaming server.

RTSP allows users to play audio and video straight from the internet, rather than having to download media files to their devices.

RTSP is a stateful protocol.

A stateless protocol does not require the server to retain session information or status about each communicating partner for the duration of multiple requests. In contrast, a protocol that requires keeping of the internal state on the server is known as a stateful protocol.

In stateful protocol there is tight dependency between client and server. If client sends a request to the server then it expects some kind of response, if it does not get any response then resend request. A stateful server keeps state of connections.

RTSP Commands/Operations

• DESCRIBE: A DESCRIBE request includes an RTSP URL and the type of reply data that can be handled. This reply includes the presentation description. The client retrieves the description of a presentation or media object identified by the request URL from the server

• SETUP: A SETUP request specifies how a single media stream must be transported. This must be done before a PLAY request is sent. The request contains the media stream URL and a transport specifier. This specifier typically includes a local port for receiving RTP data (audio or video), and another for RTCP data (meta information). The server reply usually confirms the chosen parameters, and fills in the missing parts, such as the server's chosen ports. Each media stream must be configured using SETUP before an aggregate play request may be sent.

• PLAY: A PLAY request will cause one or all media streams to be played. Play requests can be stacked by sending multiple PLAY requests. The URL may be the aggregate URL (to play all media streams), or a single media stream URL (to play only that stream). A range can be specified. If no range is specified, the stream is played from the beginning and plays to the end, or, if the stream is paused, it is resumed at the point it was paused.

• PAUSE: A PAUSE request temporarily halts one or all media streams, so it can later be resumed with a PLAY request. The request contains an aggregate or media stream URL. A range parameter on a PAUSE request specifies when to pause. When the range parameter is omitted, the pause occurs immediately and indefinitely.

• Pause: The pause request freezes the specified media until the user presses play.

• Teardown: A TEARDOWN request is used to terminate the session. It stops all media streams and frees all session-related data on the server.