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A router is a device that analyzes the contents of data packets transmitted within a network or to another network. Routers determine whether the source and destination are on the same network or whether data must be transferred from one network type to another, which requires encapsulating the data packet with routing protocol header information for the new network type.
Based on designs developed in the 1960s, the Advanced Research Projects Agency Network (ARPANET) was created in 1969 by the U.S. Department of Defense. This early network design was based on circuit switching. The first device to function as a router was the Interface Message Processors that made up ARPANET to form the first data packet network.
The initial idea for a router, which was then called a gateway, came from a group of computer networking researchers who formed an organization called the International Network Working Group, which became a subcommittee of the International Federation for Information Processing in 1972.
In 1974, the first true router was developed and by 1976, three PDP-11-based routers were used to form a prototype experimental version of the Internet. From the mid-1970s to the 1980s, mini-computers were used as routers. Today, high-speed modern routers are actually very specialized computers with extra hardware for rapid data packet forwarding and specialized security functions such as encryption.
When several routers are used in a collection of interconnected networks, they exchange and analyze information, and then build a table of the preferred routes and the rules for determining routes and destinations for that data. As a network interface, routers convert computer signals from one standard protocol to another that's more appropriate for the destination network.
Large routers determine interconnectivity within an enterprise, between enterprises and the Internet, and between different internet service providers (ISPs); small routers determine interconnectivity for office or home networks. ISPs and major enterprises exchange routing information using border gateway protocol (BGP).