ARPANET

The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switched network with distributed control and one of the first computer networks to implement the TCP/IP protocol suite. Both technologies became the technical foundation of the Internet. The ARPANET was established by the Advanced Research Projects Agency (now DARPA) of the United States Department of Defense.

Building on the ideas of J. C. R. Licklider, Bob Taylor initiated the ARPANET project in 1966 to enable resource sharing between remote computers. Taylor appointed Larry Roberts as program manager. Roberts made the key decisions about the request for proposal to build the network. He incorporated Donald Davies' concepts and designs for packet switching, and sought input from Paul Baran on dynamic routing. In 1969, ARPA awarded the contract to build the Interface Message Processors (IMPs) for the network to Bolt Beranek & Newman (BBN). The design was led by Bob Kahn who developed the first protocol for the network. Roberts engaged Leonard Kleinrock at UCLA to develop mathematical methods for analyzing the packet network technology.

The first computers were connected in 1969 and the Network Control Protocol was implemented in 1970, development of which was led by Steve Crocker at UCLA and other graduate students, including Jon Postel. The network was declared operational in 1971. Further software development enabled remote login and file transfer, which was used to provide an early form of email. The network expanded rapidly and operational control passed to the Defense Communications Agency in 1975.

Bob Kahn moved to DARPA and, together with Vint Cerf at Stanford University, formulated the Transmission Control Program for internetworking. As this work progressed, a protocol was developed by which multiple separate networks could be joined into a network of networks; this incorporated concepts pioneered in the French CYCLADES project directed by Louis Pouzin. Version 4 of TCP/IP was installed in the ARPANET for production use in January 1983 after the Department of Defense made it standard for all military computer networking.

Access to the ARPANET was expanded in 1981 when the National Science Foundation (NSF) funded the Computer Science Network (CSNET). In the early 1980s, the NSF funded the establishment of national supercomputing centers at several universities and provided network access and network interconnectivity with the NSFNET project in 1986. The ARPANET was formally decommissioned in 1990, after partnerships with the telecommunication and computer industry had assured private sector expansion and commercialization of an expanded worldwide network, known as the Internet.

Historically, voice and data communications were based on methods of circuit switching, as exemplified in the traditional telephone network, wherein each telephone call is allocated a dedicated end-to-end electronic connection between the two communicating stations. The connection is established by switching systems that connected multiple intermediate call legs between these systems for the duration of the call.

The traditional model of the circuit-switched telecommunication network was challenged in the early 1960s by Paul Baran at the RAND Corporation, who had been researching systems that could sustain operation during partial destruction, such as by nuclear war. He developed the theoretical model of distributed adaptive message block switching. However, the telecommunication establishment rejected the development in favor of existing models. Donald Davies at the United Kingdom's National Physical Laboratory (NPL) independently arrived at a similar concept in 1965.

The earliest ideas for a computer network intended to allow general communications among computer users were formulated by computer scientist J. C. R. Licklider of Bolt Beranek and Newman (BBN), in April 1963, in memoranda discussing the concept of the "Intergalactic Computer Network". Those ideas encompassed many of the features of the contemporary Internet. In October 1963, Licklider was appointed head of the Behavioral Sciences and Command and Control programs at the Defense Department's Advanced Research Projects Agency (ARPA). He convinced Ivan Sutherland and Bob Taylor that this network concept was very important and merited development, although Licklider left ARPA before any contracts were assigned for development.