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Caching is about performance--anticipating the next content request and retrieving it before a command is issued, says Bob Zimmerman, director storage research, Giga Information Group, Cambridge, MA. "Think of the operating room nurse who has the right instrument in the surgeon's hand before he asks for it because she has been through the process before," says Zimmerman.

Caching is just one element of an eCDN. According to Gartner, the basic components of an eCDN include:

Caching. To store frequently used or prepositioned content to improve end-to-end performance. It can be local (proxy caching) or adjacent to the content server (server-side cache or reverse proxy caching).

Content management. It's essential to keep content up to date and synchronized between storage locations.

Content redirection (sometimes included in the cache): To route the request for the content to the most appropriate location--can be local or global or both.

Optional eCDN components include load balancing to balance the load among content origin servers, external content caches or external redirection devices.

An eCDN basically is a network storage product that lets enterprises combine local network storage with any kind of network bandwidth--especially WAN bandwidth--to deliver "the right content in the right format at the right place at the right time," says Jim O'Toole, chief technologist, content networking, Cisco.

ECDNs

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are an extension of--or a replacement for--existing proxy/caches in corporate networks, says Thomas Mendel, Giga analyst. "They enable the scheduled distribution of Web content and rich-media files to branch office caches during off-peak hours. Once content is in the remote caches, eCDNs enable the management of the content from a central location. Current eCDNs include some rudimentary bandwidth management, but are quickly evolving to include additional capabilities such as the ability to serve live and on-demand events," he adds.

Frank Russell Co., located in Tacoma, WA, wanted to simplify and expand its caching capabilities. The global investment services company used a Microsoft Proxy 2.0 for Windows NT 4.0 in conjunction with a Microsoft Internet Information Server 4.0 that could do some caching. But the company continuously ran into limitations from the layered environment that took multiple administrative workarounds such as entries in firewall or browser proxy exception lists.

With audio streaming, for example, if 10 people requested the same stream at the same time, each needed a separate WAN connection because the audio streaming wasn't buffered. And even though Russell has a big pipe to the Internet, the cost depends on usage.

With the company's migration to Windows 2000, the Frank Russell Co. went shopping for an alternative, settling on an eCDN solution from CacheFlow, Sunnyvale, CA. The CacheFlow 600 Series Client Accelerator--an integrated hardware/software solution--allows the company to store all filter, route and configuration scripts on a local Web server for easy maintenance and to automate the ability to centralize the collection of proxy logs for better forensics and analytics and allows the application of emergency filters to Web traffic in case of viruses or Trojans.

CacheFlow buffers streaming audio locally on the proxy server, allowing multiple people to pull the same archived stream faster. It also uses a splitting function for live streams, enabling objects to be written straight to disk, boosting performance.

This was first published in March 2003

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