Caching service described

Basic caching objective

A proxy-cache server (a NetCache appliance or third-party device) is deployed between clients and origin servers on the network and intercepts requests for content being sent from clients to origin servers. The basic objective of caching is to store content close to users. Benefits of caching include the following:

You can provide content more quickly to your users than you can without caching service.
You can save money because your Internet connection is used efficiently.
- The physical distance that information must travel to reach end users is reduced.
- Duplicate requests for the same content are satisfied from the proxy-cache server instead of being sent over the WAN, which decreases bandwidth costs and reduces the amount of traffic on your network.
You can improve the quality of content delivered.
- For streaming media, the more congested the network, the poorer the quality of the presentation. Caching streaming media content reduces the possibility of network congestion affecting streaming media quality.

How a cache is populated

A cache, the area on the disk of a proxy-cache server that is used to store objects, can be populated in the following ways:

As a result of user requests. This is the traditional caching service model.
By prefilling caches, for example, with training videos, videos of corporate meetings, and Web pages.

The following illustration shows content retrieved from origin servers as a result of cache misses and content being pushed to a cache from a central management console.

The request flow, as shown in the previous illustration, is listed in the following table.

Stage	Description
1	A user enters a URL or requests streaming media through a media player.
2	NetCache checks its cache for the requested content.
3	If the requested content is not in the cache, NetCache Attempts to fetch the requested content from the origin server. Caches the content (if the object is cacheable) while returning it to the client. This content is then available for the next client that requests it.
4	If the requested content is in the cache (because NetCache fetched it as a result of a previous request or the content was pushed to the cache), NetCache returns the content to the client immediately.

Organizations that prefill caches might also populate the cache as a result of user requests.

About prefilling content in the cache

Providers of content are becoming increasingly interested in controlling content so they can provide the best possible experience for their end users. They want to push content from the center of the network to remote offices, closer to end users.

Pushing content to NetCache appliances in remote offices has quite a few advantages. For example:

You can proactively distribute content at off-peak hours, which enables you to optimize bandwidth use and ensure that users enjoy fast response times.
Multimedia, in particular, requires great amounts of network bandwidth, and network congestion greatly affects the quality of the content that is delivered. By pushing streaming media content close to end users, that content is less susceptible to quality degradation due to network congestion.

See Appendix D, Considerations When Pushing Content, for more information about pushing content.