Internet Cache Protocol

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ICP in the TCP / IP protocol stack :
application ICP
transport UDP
Internet IP ( IPv4 , IPv6 )
Network access Ethernet Token
bus 		Token
ring 		FDDI ...

The Internet Cache Protocol (ICP) is an in RFC described 2186 protocol to Web - caches to coordinate. The core of the protocol is to interconnect proxy or cache servers to form a network using small messages, with the aim of managing the cache as efficiently as possible and minimizing the number of times the server is accessed.

Properties and use

The protocol is the best known and most widespread cache protocol and emerged from the development of a hierarchical cache system network in the course of the Harvest Research Project . Alternatives to ICP are the Hyper Text Caching Protocol (HTCP) and the Cache Array Routing Protocol (CARP).

ICP allows communication using the UDP protocol within different cache instances of a network, in order to search for objects and improve the cache data. One advantage of UDP is that each cache only has to manage one UDP socket. A disadvantage of ICP messages can manifest itself in the form of traffic congestion, which can occur precisely when caching is needed most. The planned delay, which corresponds to the maximum round trip time (RTT) to the neighboring nodes (due to UDP), does not make ICP optimal for all purposes.

Within a hierarchy, a distinction is made between "parents", "children" and "siblings". Parents are usually closer to the Internet connection (on the backbone ) than children. If a cache could not achieve a hit, ICP tries to find it with neighboring siblings and / or parents instead of fetching the object from the remote server. Parents can load the object themselves from the remote server, save it and pass it on to the child, while siblings only return objects that were actually already cached with them. Each cache instance can decide independently and independently of its position in the hierarchy whether missing objects are to be fetched from the target page, the parents or the siblings.

Web proxies that support ICP:

The file-sharing program BitTorrent has supported the Cache Discovery Protocol , an implementation of the ICP , since version 4.20.0 (June 2006) . The aim is to conserve the bandwidth of the provider.

Web links