[1] Building on the ideas of J. C. R. Licklider, Bob Taylor initiated the ARPANET project in 1966 to enable resource sharing between remote computers.

[3] He incorporated Donald Davies' concepts and designs for packet switching,[4][5] and sought input from Paul Baran on dynamic routing.

[6] 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 and others.

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.

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.

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).

[30] Taylor hired Larry Roberts as a program manager in the ARPA Information Processing Techniques Office in January 1967 to work on the ARPANET.

[32][33] Roberts asked Frank Westervelt to explore the questions of message size and contents for the network, and to write a position paper on the intercomputer communication protocol including “conventions for character and block transmission, error checking and re-transmission, and computer and user identification.

[38] Donald Davies' work on packet switching and the NPL network, presented by a colleague (Roger Scantlebury), and that of Paul Baran, came to the attention of the ARPA investigators at this conference.

[39][23] Roberts applied Davies' concept of packet switching for the ARPANET,[40][41] and sought input from Paul Baran on dynamic routing.

[26] The initial, seven-person BBN team were much aided by the technical specificity of their response to the ARPA RFQ, and thus quickly produced the first working system.

[26][37][50] The BBN team continued to interact with the NPL team with meetings between them taking place in the U.S. and the U.K.[51][52][53] As with the NPL network, the first-generation IMPs were built by BBN using a rugged computer version of the Honeywell DDP-516 computer, configured with 24KB of expandable magnetic-core memory, and a 16-channel Direct Multiplex Control (DMC) direct memory access unit.

According to Charles Herzfeld, ARPA Director (1965–1967):The ARPANET was not started to create a Command and Control System that would survive a nuclear attack, as many now claim.

The later work on internetworking did emphasize robustness and survivability, including the capability to withstand losses of large portions of the underlying networks.

[60] Minutes taken by Elmer Shapiro of Stanford Research Institute at the ARPANET design meeting of 9–10 October 1967 indicate that a version of Baran's routing method ("hot potato") may be used,[61] consistent with the NPL team's proposal at the Symposium on Operating System Principles in Gatlinburg.

[66][67][68] The locations were selected not only to reduce leased line costs but also because each had specific expertise beneficial for this initial implementation phase:[1] The first successful host-to-host connection on the ARPANET was made between Stanford Research Institute (SRI) and UCLA, by SRI programmer Bill Duvall and UCLA student programmer Charley Kline, at 10:30 pm PST on 29 October 1969 (6:30 UTC on 30 October 1969).

[78] By March 1970, the ARPANET reached the East Coast of the United States, when an IMP at BBN in Cambridge, Massachusetts was connected to the network.

Peter Kirstein's research group at University College London (UCL) was subsequently chosen in 1971 in place of NPL for the UK connection.

In June 1973, a transatlantic satellite link connected ARPANET to the Norwegian Seismic Array (NORSAR),[79] via the Tanum Earth Station in Sweden, and onward via a terrestrial circuit to a TIP at UCL.

[88][89] Both networks carried unclassified information and were connected at a small number of controlled gateways which would allow total separation in the event of an emergency.

-Vinton Cerf The technological advancements and practical applications achieved through the ARPANET were instrumental in shaping modern computer networking including the Internet.

However, the IMPs did nonetheless communicate amongst themselves to perform link-state routing, to do reliable forwarding of messages, and to provide remote monitoring and management functions to ARPANET's Network Control Center.

[citation needed] In addition to primary routing and forwarding responsibilities, the IMP ran several background programs, titled TTY, DEBUG, PARAMETER-CHANGE, DISCARD, TRACE, and STATISTICS.

This problem was addressed with the Network Control Protocol (NCP), which provided a standard method to establish reliable, flow-controlled, bidirectional communications links among different processes in different host computers.

Crocker created and led the Network Working Group (NWG) which was made up of a collection of graduate students at universities and research laboratories, including Jon Postel and Vint Cerf at UCLA.

[citation needed] The original specification for the File Transfer Protocol was written by Abhay Bhushan and published as RFC 114 on 16 April 1971.

Research led by Kahn and Cerf resulted in the formulation of the Transmission Control Program,[13] which incorporated concepts from the French CYCLADES project directed by Louis Pouzin.

[15] The Purdy Polynomial hash algorithm was developed for the ARPANET to protect passwords in 1971 at the request of Larry Roberts, head of ARPA at that time.

Leonard Kleinrock claims to have committed the first illegal act on the Internet, having sent a request for return of his electric razor after a meeting in England in 1973.

[108][109] In 1978, against the rules of the network, Gary Thuerk of Digital Equipment Corporation (DEC) sent out the first mass email to approximately 400 potential clients via the ARPANET.