A research network with a practical purpose
ARPANET was funded by the Advanced Research Projects Agency of the US Department of Defense, whose Information Processing Techniques Office supported computer science at universities. The aim was to let researchers at different sites use each other’s computers and share results without moving tapes or traveling. Bob Taylor, who ran the office in the late 1960s, and Larry Roberts, who managed the network project, are the people most often named as its leaders.
The first sites
Four sites formed the original network in 1969. UCLA was first, where Leonard Kleinrock’s group handled measurement of the network. The Stanford Research Institute followed, then the University of California, Santa Barbara, and the University of Utah. Each had a computer that specialized in some area, such as graphics or mathematical modeling. A link between UCLA and SRI carried the first message in October 1969, and the four-node network was working by December.
Growth in the 1970s
The network expanded quickly. By 1971, there were about 15 sites, including government labs and companies such as BBN itself. In October 1972, ARPANET was demonstrated at the International Computer Communication Conference in Washington, D.C., where dozens of terminals and programs were shown to engineers who had doubted that packet networks would work. The demonstration is generally seen as an important step in convincing the wider community.
Applications changed what the network was used for. File transfer and remote login were the intended functions, but electronic mail, begun in 1971, became popular in a short time, and mailing lists let groups share news and discussion. According to some accounts, mail made up a large part of the traffic by the mid-1970s, though exact figures are uncertain.
The network also reached beyond the continental United States. A satellite link reached Hawaii in the early 1970s, and in 1973, University College London in Britain and the NORSAR seismic array in Norway joined. By the late 1970s, ARPANET had around a hundred hosts, a number that sounds small but was significant at that stage.
Changing the rules
In its first years, ARPANET used the Network Control Protocol to manage connections between hosts. It worked only within a single network. As radio and satellite networks were built, the need for a protocol that could cross network boundaries led to TCP/IP. On January 1, 1983, ARPANET switched all of its hosts to the new protocols. In the same year, the military sites were moved into a separate network named MILNET, leaving ARPANET for research.
Other networks join in
Not every computer science department had an ARPANET connection, since access was limited to projects with defense funding. This led to other networks. CSNET, supported by the National Science Foundation, connected computer science departments from the early 1980s. BITNET linked university computers, and Usenet, started in 1979 and 1980, spread discussion groups over telephone lines. Gateways connected many of these to the ARPANET. The network of networks grew, even as ARPANET itself was only one part of it.
In 1986, the National Science Foundation started NSFNET, a backbone linking supercomputing centers, with regional networks attached. Its capacity was raised in 1988. As traffic grew, it became clear that NSFNET, not ARPANET, was the main academic route.
The end of ARPANET
By 1989, most of ARPANET’s work could be done by newer networks, and its aging equipment was costly to maintain. It was formally decommissioned in 1990. Connections were moved to NSFNET and regional networks, so users saw little disruption. The research that had started it, however, left a lasting legacy in protocols, routers and experience in running networks.
From research to the public
The final step from a research network to a public one took place in the early 1990s. NSFNET’s acceptable-use policy had barred most commercial traffic, which led businesses to create their own long-distance links. Commercial providers formed exchange points for sharing traffic, and the policy was eased; the NSFNET backbone ended in April 1995, with traffic handled by private networks. Meanwhile, the web, launched in 1991, and the Mosaic browser in 1993 brought in millions of ordinary users.
What ARPANET contributed
ARPANET did not invent every idea it used. Packet switching came from several researchers, and email grew from earlier time-sharing mail systems. Its importance was in bringing them together, running a real network for years, and publishing results. People trained there went on to build later systems, and the habits of open documentation set a model for later work. Early security incidents, such as the Creeper program that moved between machines on the network in the early 1970s, also hinted at problems that would continue.