Real Time Streaming Protocol

Real Time Streaming Protocol. It is a network control protocol designed for establishing and managing media sessions between endpoints in streaming media systems. Primarily used for entertainment and communications, it enables clients to issue commands like play, pause, and record to media servers. The protocol works in conjunction with core transport protocols and other standards to deliver audio and video content.

Overview

Developed by a consortium including RealNetworks, Netscape, and researchers at Columbia University, it was first standardized in April 1998 as RFC 2326. The protocol is an application-level framework for controlled, on-demand delivery of real-time data, such as audio and video. It is intentionally similar in syntax and operation to other internet protocols like Hypertext Transfer Protocol and is designed to be compatible with existing IP network infrastructure. A significant revision was published in 2016 as RFC 7826, which clarified and updated the original specification while maintaining backward compatibility.

Technical details

Operating at the application layer of the Internet protocol suite, it typically uses TCP or UDP on well-known port 554. The protocol itself does not typically transport the continuous media streams; instead, it establishes and controls the session, while the actual audio and video data is delivered via separate protocols like the Real-time Transport Protocol. It uses Session Description Protocol messages to describe the multimedia session parameters. Communication is conducted via textual requests and responses, with methods including DESCRIBE, SETUP, PLAY, PAUSE, and TEARDOWN, providing direct VCR-like control over the media playback.

Protocol operation

A typical session begins with the client establishing a TCP connection to the server and sending a DESCRIBE request to obtain a media description via Session Description Protocol. The client then issues a SETUP request to determine the transport mechanism, prompting the server to allocate resources and establish a data channel, often using RTP Control Protocol for stream synchronization. Subsequent PLAY requests initiate the media delivery via Real-time Transport Protocol, with PAUSE and TEARDOWN commands providing session control. The stateful nature of the protocol allows for precise navigation within a media timeline, supporting features like absolute time seeks.

Applications and use cases

It is widely implemented in IPTV systems, video surveillance setups, and internet-based media services for delivering live broadcasts and video on demand. Many legacy streaming media servers and players, including those from Apple (QuickTime), RealNetworks (RealPlayer), and various closed-circuit television vendors, have historically supported it. The protocol is also commonly used in embedded systems, such as network cameras and digital video recorders, enabling remote viewing and management. Its control capabilities make it suitable for applications requiring interactive media playback, from distance learning platforms to corporate communications.

Security considerations

The original specification lacked mandatory security features, making basic implementations vulnerable to attacks like session hijacking, unauthorized access, and denial-of-service. Common security enhancements include using the protocol over Transport Layer Security to encrypt the control channel, often referred to as RTSP over HTTPS. Authentication mechanisms, such as Basic access authentication and Digest access authentication, are defined but were initially optional. Implementers must also secure the accompanying Real-time Transport Protocol data streams, often through Secure Real-time Transport Protocol, to prevent eavesdropping or media manipulation.

Alternatives and competing protocols

For adaptive bitrate streaming over HTTP, modern protocols like MPEG-DASH and HTTP Live Streaming have become dominant, as they leverage standard web server infrastructure and CDN caching. The WebRTC framework provides direct, low-latency peer-to-peer streaming for real-time communication without requiring a separate control protocol. Microsoft developed the Microsoft Media Server protocol for its streaming services, while proprietary systems often use custom protocols. For simpler, non-interactive streaming, direct use of Real-time Transport Protocol without session control remains an alternative in specialized applications like voice over IP. Category:Internet protocols Category:Streaming media Category:Application layer protocols Category:RealNetworks