Streaming Media Supplement sa2150 and sa2250

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Chapter 4 Understanding Media-IXT and WMT
The example assumes that the user of a web browser equipped with Windows Media Player is viewing an
HTML page containing links to movies.
The story begins when the user clicks on a link to a movie.The URL invoked by the link is that of a WMT
metafile.
1. The web browser passes the URL to Windows Media Player and instructs Windows Media Player to open
the metafile.
2. Windows Media Player sends a request for the WMT metafile to the HTTP server.
3. The HTTP server serves the WMT metafile to Windows Media Player.
4. The web browser receives the metafile and sends it to Windows Media Player.
In the metafile script, Windows Media Player finds a pointer to the URL from which to obtain streaming
media content. Because Media-IXT rewrote the metafile, the URL directs Windows Media Player to obtain
streaming media content from Media-IXT.
5. Windows Media Player contacts Media-IXT on the MMS port, passing the rewritten URL.
6. Media-IXT checks the origin Windows Media server for metadata about the media content invoked by the
URL. If the origin Windows Media server has no metadata corresponding to the client request, Media-IXT
returns an error to Windows Media Player, because the content does not exist on the server.
7. If the origin Windows Media server does have metadata corresponding to the client request, Media-IXT
tries to find a match between the origin Windows Media server's metadata and metadata in Media-IXT's
cache.
8. Then one of two things happens:
o If an exact match exists, Media-IXT streams the content from cache.
o If no match exists, Media-IXT pulls the content from the origin Windows Media server, then
simultaneously streams it to the client and stores the updated content in the cache.
This use of metadata assures that Media-IXT serves only fresh content, and that if two origin servers serve the
same file, then only one copy is stored in cache. The figures below illustrate an instance of Media-IXT
performing proxy caching for WMT content.
Figure 4-4. WMT streaming with Media-IXT performing proxy caching (beginning)
Windows
Media Server
Media-IXT
Web Server
4
3
1
http
2
The web browser sends a request for a WMT metafile to Media-IXT.
Media-IXT obtainsthe WMT metafile from the HTTPserver.
Media-IXT rewritesthe contents of the metafile, then servesthe metafile to the browser. The
rewritten metafile directsWindowsMedia Player to obtain streaming media content from Media-IXT.
The web browser receivesthe metafile and sends it to WindowsMedia Player.
1
2
3
4
Me ia-IXTd
to Windows Media Player
from browser
WMT metafile
WMT metafile
Client browser
with Windows
Media Player