Nortel Networks WEB OS 212777 - Manual (Page 155)

Web OS 10.0 Application Guide
Chapter 6: Server Load Balancing n 155
212777-A, February 2002
Real Time Streaming Protocol SLB
Real Time Streaming Protocol (RTSP) is an application-level protocol for control over the
delivery of data with real-time properties as documented in RFC 2326.
RTSP is used as a “network remote control” for multimedia servers. Typically, a multimedia
presentation consists of several streams of data (for example, video stream, audio stream, and
text) that must be presented in a synchronized fashion. A multimedia client like Real Player or
Quick Time Player downloads these multiple streams of data from the multimedia servers and
presents them on the player screen.
RTSP is used to control the flow of these multimedia streams. Each presentation uses one
RTSP control connection and several other connections to carry the audio/video/text
multimedia streams. In this document, the term RTSP server refers to any multimedia server
that implements the RTSP protocol for multimedia presentation.
How RTSP Server Load Balancing Works
The objective of RTSP server load balancing is to intelligently switch an RTSP request, and the
other media streams associated with a presentation, to a suitable RTSP server based on the
configured load-balancing metric. Web OS supports one Layer 7 metric (URL hashing and
URL pattern matching) and all Layer 4 load-balancing metrics.
RTSP load balancing with the URL hash metric can be used to load balance cache servers
that cache multimedia presentations. Since multimedia presentations consume a large amount
of Internet bandwidth, and their correct presentation depends upon the real time delivery of the
data over the Internet, several caching servers cache the multimedia data. As a result, the data
is available quickly from the cache, when required. The Layer 7 metric of URL hashing directs
all requests with the same URL to the same cache server, ensuring that no data is duplicated
across the cache servers.
Typically, an RTSP client establishes a control connection to an RTSP server over TCP port
554 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 HTTP
protocol to tunnel RTSP traffic. To ensure that RTSP server load balancing works, make sure
the 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 two
prominent RTSP server and client implementations: Real Server marketed by Real Networks