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1.7 Meshes, Clusters, and Hierarchies

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1.7 Meshes, Clusters, and Hierarchies

There are a number of situations where it's beneficial for caching proxies to talk to each other. There are different names for some different configurations. A cluster is a tightly coupled collection of caches, usually designed to appear as a single service. That is, even if there are seven systems in a cluster, to the outside world it looks like just one system. The members of a cluster are normally located together, both physically and topologically. As I explain in Chapter 9, many people like cache clusters because they provide scalability and reliability.

A loosely coupled collection of caches is called a hierarchy or mesh . If the arrangement is tree-like, with a clear distinction between upper- and lower-layer nodes, it is called a hierarchy. If the topology is flat or ill-defined, it is called a mesh. A hierarchy of caches make sense because the Internet itself is hierarchical. However, when a mesh or hierarchy spans multiple organizations, a number of issues arise. We'll talk more about hierarchies in Chapter 7. Then, in Chapter 8, we'll explore the various protocols and techniques that caches use to communicate with each other.

only for RuBoard - do not distribute or recompile
only for RuBoard - do not distribute or recompile

1.8 Products

By now you should have a pretty good view of the web caching landscape. In the rest of this book, we'll explore many of the topics of this chapter in much greater detail, so you can fully comprehend all the issues involved. When you finish this book, you'll be able to design and operate a web cache for your environment. You might even think about writing your own software. But since I'm sure most of you have other responsibilities, you'll probably want to use an existing product. Following is a list of caching products that are currently available, many of which are mentioned throughout this book:

Squid
http://www.squid-cache.org

Squid is an open source software package that runs on a wide range of Unix platforms. There has also been some recent success in porting Squid to Windows NT. As with most free software, users receive technical support from a public mailing list. Squid was originally derived from the Harvest project in 1996.

Netscape Proxy Server
http://home.netscape.com/proxy/v3.5/index.html

The Netscape Proxy Server was the first caching proxy product available. The lead developer, Ari Luotonen, also worked extensively on the CERN HTTP server during the Web's formative years in 1993 and 1994. Netscape's Proxy runs on a handful of Unix systems, as well as Windows NT.

Microsoft Internet Security and Acceleration Server
http://www.microsoft.com/isaserver/

Microsoft currently has two caching proxy products available. The older Proxy Server runs on Windows NT, while the newer ISA product requires Windows 2000.

Volera
http://www.volera.com

Volera is a recent spin-off of Novell. The product formerly known as Internet Caching System (ICS) is now called Excelerator. Volera does not sell this product directly. Rather, it is bundled on hardware appliances available from a number of OEM partners .

Network Appliance Netcache
http://www.netapp.com/products/netcache/

Network Appliance was the second company to sell a caching proxy, and the first to sell an appliance. The Netcache products also have roots in the Harvest project.

Inktomi Traffic Server
http://www.inktomi.com/products/network/traffic/

Inktomi boasts some of the largest customer installations, such as America Online and Exodus. Their Traffic Server product has been available since 1997.

CacheFlow
http://www.cacheflow.com

Intelligent prefetching and refreshing features distinguish CacheFlow from their competitors .

InfoLibria
http://www.infolibria.com

InfoLibria's products are designed for high reliability and fault tolerance.

Cisco Cache Engine
http://www.cisco.com/go/cache/

The Cisco 500 series Cache Engine is a small, low-profile system designed to work with their Web Cache Control Protocol (WCCP). As your demand for capacity increases , you can easily add more units.

Lucent imminet WebCache
http://www.lucent.com/serviceprovider/imminet/

Lucent's products offer carrier-grade reliability and active refresh features.

iMimic DataReactor
http://www.imimic.com

iMimic is a relative newcomer to this market. However, their DataReactor product is already licensed to a number of OEM partners. iMimic also sells their product directly.

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