NetCache support for on-demand streams

Transport

Transmission for on-demand streams is over unicast. Multicast transmission applies only to live streams.

Caching on-demand streams

A streaming media cache caches on-demand streaming media. When streaming media caches are deployed near clients, the number of connections to the streaming media server is significantly reduced because NetCache can deliver on-demand streams directly to clients.

Types of on-demand content that NetCache caches

A streaming media cache caches on-demand streams from the following vendors:

Microsoft (Windows Media)
RealNetworks (RealMedia)
Apple (QuickTime)

Overview of on-demand streaming media request flow

When an on-demand stream is requested by a client, NetCache checks to see if the stream is already in the cache. If the stream is in the cache, NetCache serves it directly to the client from the cache. If the stream is not in the cache, NetCache fetches the on-demand stream from the streaming server and delivers the stream to the client while caching it for future clients.

Path taken by a request for on-demand streaming media

NetCache handles the first request for an on-demand stream differently than it handles subsequent requests for the same on-demand stream.

Path of the first request for an on-demand stream

Typically, the first request for an on-demand stream will be proxied to the streaming server because the stream is not yet in the cache. The following illustration shows what happens when a client makes a request for an on-demand stream that has not been cached.

The streaming media cache intercepts the streaming request sent by the client. Because the stream has not yet been cached, the cache asks the streaming server to deliver the requested stream. As it receives the requested stream, NetCache caches the stream and delivers it to the client.

Path of subsequent requests for the same stream

The following illustration shows the path for additional requests for the same unique stream that Client 1 requested.

The flow of requests and streams in the preceding illustration is as follows:

Assume that Client 1 already requested an on-demand stream and that NetCache cached the stream after fetching it from the streaming server. Client 2 and Client 3 now request the same unique stream that Client 1 requested.
Because the streaming media cache previously delivered the requested stream to Client 1, the stream is already in the cache and NetCache can satisfy the requests from Client 2 and Client 3 directly from the cache.
If Client 2 or 3 had requested the same streaming media content that Client 1 requested but at a bit rate encoding that had not been cached, the streaming media cache would have fetched that stream from the streaming server, as it did for Client 1. (Each bit rate encoding represents a different unique stream).

Caching streaming media content and delivering it directly to clients from a local source results in superior playback because it is more likely that packets will be delivered smoothly and on time. Additionally, considerable bandwidth is saved because streams can be served from the cache instead of traveling the entire distance from the streaming server.