Streaming Media Supplement sa2150 and sa2250

2
Chapter 1 About Streaming Media
This manual is a companion to:
• The HP Cache Server Appliance sa2100/sa2150/sa2200/sa2250 Getting Started Guide
• The HP Cache Server Appliance Administrator Guide, which explains more fully many of the topics this
supplement only introduces. Keep the HP Cache Server Appliance Administrator Guide at hand while
reading this manual.
You should also consult:
• RealNetworks documentation, if you are using Media-IXT for proxy caching of RealNetworks content.
About streaming media
Audio and video are media. Audio and video that play over the Web without prior downloading of the complete
files that contain them are streaming media. The Web user hears sound and sees moving pictures as audio and
video data are streamed to a player. The player can operate as a standalone application, or be embedded in the
web browser. The player buffers incoming data, so there is some latency between the user's click demanding
particular content and the moment that content begins to play; but this latency is far smaller than the time
required to download an entire content file. The advent of streaming media on the Web has transformed the Web
user's experience, and marks one of the milestones in the development of the Internet.
What does streaming media mean for Media-IXT?
Streaming media data is hosted on an origin server. The streaming media player (together with the Web browser
if the player resides there) is called a client. Data flows upstream from client to origin server, and flows
downstream from origin server to client. Media-IXT is positioned in between the media streaming server and
the player, performing proxy caching of streaming media.
Media-IXT performs proxy caching of streaming content hosted on the three preeminent streaming media
servers found on the Web: RealNetworks, Windows Media Technologies, and QuickTime. We abbreviate
Windows Media Technologies as WMT throughout this manual.
RealNetworks, WMT, and QuickTime are streaming media formats. Each has its own media players, its own
origin servers, and its own chosen protocols and ways of handling streaming media data. Most streaming media
content on the Web is in one of these three streaming formats.
QuickTime is also a file format, and there are file formats that belong to RealNetworks and WMT as well.
Usually, context makes it clear whether a streaming media format or a file format is being discussed.
Media-IXT works with the RealProxy
™
software from RealNetworks, along with plugins to RealProxy, Traffic
Server, and the origin RealServer, to perform streaming media caching of RealNetworks content. RealProxy is
installed as a component of Media-IXT. RealProxy is only used if you configure Media-IXT to cache
RealNetworks content. No equivalent third-party software component is needed for proxy caching of WMT or
QuickTime content.
Media streaming servers and players
There are both commonalities and differences in the ways RealNetworks, Windows Media Technologies, and
QuickTime stream audio and video content.
All three formats, by default, employ:
• two channels between player and server: a control channel, and a data channel
• a control protocol for the control channel, and a data transfer protocol for the data channel, which vary from
one streaming format to another
• underlying transport protocols: TCP for the control channel, and UDP for the data channel