Web OS 10.0 Application GuideChapter 6: Server Load Balancing n 155212777-A, February 2002Real Time Streaming Protocol SLBReal Time Streaming Protocol (RTSP) is an application-level protocol for control over thedelivery of data with real-time properties as documented in RFC 2326.RTSP is used as a “network remote control” for multimedia servers. Typically, a multimediapresentation consists of several streams of data (for example, video stream, audio stream, andtext) that must be presented in a synchronized fashion. A multimedia client like Real Player orQuick Time Player downloads these multiple streams of data from the multimedia servers andpresents them on the player screen.RTSP is used to control the flow of these multimedia streams. Each presentation uses oneRTSP control connection and several other connections to carry the audio/video/textmultimedia streams. In this document, the term RTSP server refers to any multimedia serverthat implements the RTSP protocol for multimedia presentation.How RTSP Server Load Balancing WorksThe objective of RTSP server load balancing is to intelligently switch an RTSP request, and theother media streams associated with a presentation, to a suitable RTSP server based on theconfigured load-balancing metric. Web OS supports one Layer 7 metric (URL hashing andURL pattern matching) and all Layer 4 load-balancing metrics.RTSP load balancing with the URL hash metric can be used to load balance cache serversthat cache multimedia presentations. Since multimedia presentations consume a large amountof Internet bandwidth, and their correct presentation depends upon the real time delivery of thedata over the Internet, several caching servers cache the multimedia data. As a result, the datais available quickly from the cache, when required. The Layer 7 metric of URL hashing directsall requests with the same URL to the same cache server, ensuring that no data is duplicatedacross the cache servers.Typically, an RTSP client establishes a control connection to an RTSP server over TCP port554 and the data flows over UDP or TCP. For information on using RTSP with Web cache redi-rection, see “RTSP Web Cache Redirection” on page 211.N OTE – This feature is not applicable if the streaming media (multimedia) servers use HTTPprotocol to tunnel RTSP traffic. To ensure that RTSP server load balancing works, make surethe streaming media server is configured for RTSP protocol.In a typical scenario, the RTSP client issues several sequences of commands to establish con-nections for each component stream of a presentation. There are several variations to this pro-cedure, depending upon the RTSP client and the server involved. For example, there are twoprominent RTSP server and client implementations: Real Server marketed by Real Networks
