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Caching and streaming on-demand content

This topic discusses a type of behavior that a cache/proxy plug-in could provide when used with Windows Media Services. The cache/proxy plug-in you obtain or create may behave differently.

After a cache/proxy plug-in is installed on a Windows Media server it can provide support for caching on-demand content from another Windows Media server. When a client requests on-demand content, the cache/proxy plug-in verifies that the content is cached locally and is current. To do this, the plug-in first checks the cache expiration property of the content. If the content is set to expire after a certain time that has already passed, the plug-in then requests that the cache/proxy server open a connection to the origin server and verifies that the content in the cache matches the content on the origin server. A cache hit occurs if the content matches; a cache miss occurs if the content does not match. If the origin server is unavailable or cannot provide the requested content, the server returns an error message to the client stating that the content cannot be found.

If a cache hit occurs, the plug-in requests that the cache/proxy server stream the content from its cache to the client.

Cache hit

If a cache miss occurs, the content is purged from the cache, and the cache/proxy server downloads the updated content from the origin server. The cache/proxy server initiates another connection to the origin server to act as a proxy server to deliver the content to the client.

Cache miss

If a cache miss occurs when the cache/proxy server attempts to stream multiple-bit-rate (MBR) content, the cache/proxy server will attempt to download all of the different bit rate streams from the origin server at once. If you have set a bandwidth limit for outgoing distribution streams on the origin server or a limit on the incoming bandwidth for the cache/proxy server, the aggregate bandwidth of the multiple-bit-rate stream may exceed these limits. If so, the cache/proxy server will not be able to download the content to its cache and will only stream the content at the bandwidth requested by the client.

If content was moved to a different location on the origin server, the cache/proxy plug-in can transfer client requests to the new location. For example, if the cache/proxy plug-in receives an HTTP code 301 or 302 when checking whether content is current, the plug-in updates its internal database to recognize requests for the new location.

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