RTSP

Real Time Streaming Protocol (RTSP) is a network control protocol used to manage streaming media sessions between endpoints. It is designed to control streaming servers and clients, enabling operations such as initiating, pausing, resuming, or terminating a media stream. RTSP itself does not transport the media; it coordinates the delivery, which is typically done using the Real-time Transport Protocol (RTP).

RTSP operates with a text-based request/response model similar to HTTP. A client issues commands such as DESCRIBE to retrieve the session description (usually in SDP format), SETUP to negotiate transport parameters for individual media streams, PLAY to start delivery, PAUSE to temporarily suspend, and TEARDOWN to end the session. Additional methods include OPTIONS, ANNOUNCE, and RECORD. The server responds with status codes and, when appropriate, session identifiers that track the active stream.

RTSP can use either TCP or UDP for its control channel. The actual media data is usually transported over RTP, while RTCP provides control and quality feedback. A common usage pattern involves SETUP negotiating the transport for each media track, followed by PLAY to begin streaming. RTSP is often secured with RTSPS (RTSP over TLS) to protect control messages, and authentication (including digest) is commonly supported.

RTSP was defined in RFC 2326 in the late 1990s and has since been implemented in many streaming and surveillance products. It remains widely used in IP cameras, video-on-demand systems, and multimedia servers, where robust session control is essential.