Internet Cache Protocol

The Internet Cache Protocol (ICP) is described in RFC 2186 protocol to coordinate Web caches. Core of the protocol is to interconnect these by small message to proxy or cache server to a network, with the aim of managing the cache as efficiently as possible and to minimize the number of accesses to servers.

Properties and Uses

The protocol is the best known and most widely used cache protocol and emerged from the development of a hierarchical cache system network as part of the Harvest Research Projects. Alternatives to ICP are the Hypertext Caching Protocol ( HTCP ) and the Cache Array Routing Protocol ( CARP ).

ICP allows communication using the UDP protocol within different cache instances of a composite, so as to search for wanted objects and thereby to improve the cache data. One advantage of UDP is that each cache must only manage a UDP socket. A disadvantage of ICP messages can show up in the form of a traffic overload that may occur if and only if caching is needed most. The scheduled delay corresponding to the maximum of the Round Trip Time (RTT ) to the neighboring nodes (due to UDP), ICP does not optimal for all applications.

Within a hierarchy, a distinction between "parent", " child" and " sibling ". Parents are usually located closer to the internet ( the backbone ) as children. If a cache has achieved no results, ICP tries to find bargains rather than to get the object from the remote server at adjacent siblings and / or parents. However, parents can load the object itself from the remote servers that store with you and pass it to the child while siblings return only objects that were actually already cached in them. Each cache instance can separate and independent from the position in the hierarchy to decide whether missing objects are fetched from the target page, the parents or the siblings.

Web proxies, the ICP support:

  • Squid cache
  • Microsoft Proxy
  • Cisco Content Engine
  • Proxy
  • Phion proxy

The BitTorrent file sharing program since version 4.20.0 (June 2006) supports cache discovery protocol, an implementation of the ICP. The aim is to conserve the bandwidth of the provider.

Cache (computing) BitTorrent (software)
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