====== Internet ======

In networking terms, an //internet// is simply the interconnection of two or more networks (it is a contraction of the words //inter// and //network// meaning literally a **network of networks**). 

Literally a interconnection of networks, **the Internet** (capital I) is the global network of networks that provides the infrastructure for, among many other things, the [[www|World-Wide Web]], [[email]], and [[video on demand]] systems like BBC's iPlayer. In physical terms, the //Internet// is the collection of [[hosts]], [[router|routers]] and [[link|links]] that allow heterogeneous networks to connect to each other and participate in the transfer of information from [[end-system]] (host) to [[end-system]]. In protocol terms [[IP]] is the network protocol that defines the encapsulation, addressing and routing scheme that is needed to transmit packets of data from host to router and router to router. For many applications, [[rdt|reliable data transfer]] over IP is provided by [[TCP]] and so the Internet is often said to be a TCP/IP network. However, strictly speaking, IP defines the Internet and is the protocol that all hosts and routers must implement to participate in the Internet. 

The Internet is a [[packet_switching|Packet Switched Network]] in which long messages are broken up into small packets of data (called [[datagrams]]) that are addressed, transmitted and [[ip_routing|routed]] independently of each other (rather like letters in envelopes are moved by the Royal Mail) by the Packet Switches (routers) that act as sorting offices for the network. The networks themselves are interconnected by [[router|routers]], and the [[ip_address|Internet addressing]] scheme is based on a hierarchy of [[isp|Internet Service Providers]] (ISPs). //See also//: [[IP]], [[IP address]] and [[IP routing]].

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