ARPANET

— The panel of the very first Interface Message Processor (IMP). This one was used at the UCLA Boelter 3420 lab to transmit the first message on the Internet

The Advanced Research Projects Agency Network (ARPANET) was an early packet-switching network and the first network to implement the TCP/IP protocol suite. Both technologies became the technical foundation of the Internet. The ARPANET was initially funded by the Advanced Research Projects Agency (ARPA) of the United States Department of Defense to ensure military communications in the event of a nuclear attack. By using packet-switching to disassemble data into addressed parcels, blip them over high-speed lines, and reassemble them just before they reach their destination, ARPANET rendered itself invulnerable to conventional attack; if a portion of the network went down, traffic would automatically be rerouted.

In 1983, ARPANET was divided into military and civilian networks (MILNET and Arpa Internet), respectively); shortly thereafter, the U.S. National Science Foundation (NSF) took charge of the administration and maintenance of the lines and equipment that made up the Arpa Internet "backbone". Whereas the Defense Department restricted system access to institutions receiving Pentagon or NSF funding, the NFS made the network available to all faculty and students at member institutions. As universities, research and development companies, and government agencies connected their computers to the NFS's system, what had once been the Arpa Internet mutated into an anarchic global network of networks known, increasingly, as the Internet (from "internetworking").

— ARPANET logical map (1977)

The packet-switching methodology employed in the ARPANET was based on concepts and designs by Leonard Kleinrock, Paul Baran, Donald Davies, and Lawrence Roberts. The TCP/IP communications protocols were developed for the ARPANET by computer scientists Robert Kahn and Vint Cerf, and incorporated concepts from the French CYCLADES project directed by Louis Pouzin.

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. Such stations might be telephones or computers. The temporarily dedicated line typically comprises many intermediary lines which are assembled into a chain that reaches from the originating station to the destination station. With packet switching, a network could share a single communication link for communication between multiple pairs of receivers and transmitters.

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.

Bob Taylor convinced ARPA's Director Charles M. Herzfeld to fund a network project in February 1966, and Herzfeld transferred a million dollars from a ballistic missile defense program to Taylor's budget. Taylor hired Larry Roberts as a program manager in the ARPA Information Processing Techniques Office in January 1967 to work on the ARPANET. In April 1967, Roberts held a design session on technical standards. The initial standards for identification and authentication of users, transmission of characters, and error checking and retransmission procedures were discussed. At the meeting, Wesley Clark proposed minicomputers called Interface Message Processors (IMPs) should be used to interface to the network rather than the large mainframes that would be the nodes of the ARPANET.

— Larry Roberts opens the talk detailing the early history of packet switching networks and his first work with ARPA

— https://en.wikipedia.org/wiki/ARPANET