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The Advanced Research Projects Agency Network (ARPANET) of the U.S. Department of Defense was the world's first operational packet switching network, and the progenitor of the global Internet.

Packet switching, now the dominant basis for both data and voice communication worldwide, was a new and important concept in data communications. Previously, data communications was based on the idea of circuit switching, as in the old typical telephone circuit, where a dedicated circuit is tied up for the duration of the call, and communication is only possible with the single party (machine) on the other end of the dedicated circuit.

With packet switching, a system could use one communication link to communicate with more than one machine by assembling data into packets. Not only could the link be shared (much as a single mailbox can be used to post letters to different destinations), but each packet could be routed independently of other packets. This was a big breakthrough.


Background of the ARPANET

The earliest ideas of a computer network intended to allow general communication between users of various computers was formulated by J.C.R. Licklider of MIT in August 1962, in a series of memos discussing his "Galactic Network" concept. These ideas contained almost everything that the Internet is today. In October 1962 Licklider was appointed head of the Behavioral Sciences and Command and Control programs at ARPA (as it was then called), the United States Department of Defense Advanced Research Projects Agency. He would then convince Ivan Sutherland and Bob Taylor that this was a very important concept, although he left ARPA before any actual work on his vision was performed.

Separately, Paul Baran had started work in 1959 at the RAND corporation on secure communications technologies that could enable a military communications network to withstand a nuclear attack. His results, published in a series of studies starting in 1960, described two key ideas: first, use of a decentralized network with multiple paths between any two points; and second, dividing complete user messages into what he called message blocks before sending them into the network. This first allowed the elimination of single points of failure, and enabled the network to automatically and efficiently work around any failures. A summary paper describing the entire scheme was presented in 1962, and published in 1964.

Leonard Kleinrock had performed tests on store and forward message systems in 1961, and wrote a very important book in 1964 covering queueing theory and routing in store and forward networks, although this work did not include the concept of breaking a user's message up into smaller units for transmission through the network.

Finally, Donald Davies of NPL had begun working with related concepts 1965, after a conference on in the United Kingdom on time-sharing brought up the inadequacies of existing circuit-switched networks. His work was originally carried out independently from Baran's work, although Davies learned of it after he gave a seminar on his ideas at NPL in 1966; incidentally, it was Davies who introduced the term packet.

Thus, the ideas that were to become the ARPANET came from three independent research centers: DARPA, NPL (in the UK) and the RAND corporation.

Origins of the ARPANET

While all this was happening, ARPA and Taylor continued to be interested in creating a computer communication network, in part to allow ARPA-sponsored researchers in various locations to use various computers which ARPA was providing, and in part to quickly make new software and other results widely available.

At the end of 1966, Taylor brought Lawrence G. Roberts to ARPA from MIT Lincoln Laboratory to head a project to create the network; Roberts had previously encountered Davies at the time-sharing conference.

Roberts' initial concept was to hook the various time-sharing machines directly to each other, through telephone lines. At an early meeting in 1967, many of the participants were unenthusiastic at having the load of managing this line put directly on their computer. One of the participants, Wesley Clark, came up with the idea of using separate smaller computers to manage the communication links; the small computers would then be connected to the large time-sharing main-frame computers. Initial planning for the ARPANET began on that basis.

Roberts then proceeded to author a "plan for the ARPANET", which was presented at a symposium in 1967; also presenting there was Roger Scantlebury , from Davies' group at NPL. He discussed packet switching with Roberts, and introduced Roberts to Baran's work. The exact impact is unclear, but Roberts' plans for the network were soon modified after his meeting with Scantlebury.

Creation of the ARPANET

By the summer of 1968, a complete plan had been prepared, and after approval at ARPA, a Request For Quotation (RFQ) was sent to 140 potential bidders. Most regarded the proposal as outlandish, and only 12 companies submitted bids, of which only four were regarded as in the top rank. By the end of the year, the field had been narrowed to two, and after negotiations, a final choice was made, and the contract was awarded to Bolt, Beranek and Newman (BBN) early in 1969 (see: 7 april 1969 and Request for Comments).

Initial ARPANET deployment

There were four nodes on the initial ARPANET. Each was connected to a small computer known as an Interface Message Processor or IMP. The IMPs at each site performed the function of a router, and were to be connected to each other using 64 kbit/second digital links over leased lines. The first four were installed at UCLA (where Kleinrock had established a Network Measurement Center), the Stanford Research Institute (where Doug Engelbart had worked on his "NLS" project, an early hypertext system), UCSB, and University of Utah.

The first ARPANET link was established on November 21 1969, between an IMP at UCLA and another at the Stanford Research Institute in Menlo Park. By December 5, 1969, the entire 4-node network was connected.

The ARPANET and nuclear attacks

The Internet Society writes about the merger of technical ideas that produced the ARPANET in A Brief History of the Internet, and states in a note:

It was from the RAND study that the false rumor started claiming that the ARPANET was somehow related to building a network resistant to nuclear war. This was never true of the ARPANET, only the unrelated RAND study on secure voice considered nuclear war. However, the later work on Internetting did emphasize robustness and survivability, including the capability to withstand losses of large portions of the underlying networks.

The myth that the ARPANET was built to withstand nuclear attacks however remains such a strong and apparently appealing idea - and of course "a good story" - that many people refuse to believe it is not true. However it is not, unless one means that these ideas influenced the ARPANET development by way of the RAND research papers. The ARPANET was designed to survive network losses, but the main reason was actually that the switching nodes and network links were not highly reliable, even without any nuclear attacks.


The support and style of management by ARPA was crucial to the success of ARPANET. As the Internet develops and the struggle over the role the Internet plays unfolds, it will be important to remember how the network developed and the culture that it was connected with. (As a facilitator of communication, the culture of the Net is an important feature to acknowledge.) The ARPANET Completion Report, as published jointly by BBN of Cambridge, Mass., and ARPA concludes by stating:

" is somewhat fitting to end on the note that the ARPANET program has had a strong and direct feedback into the support and strength of computer science, from which the network itself sprung." (Chapter III, pg.132, Section 2.3.4)

In order to understand the wonder that the Internet, and various parts of the Net, represent, we need to understand why the ARPANET Completion report ends with the suggestion that the ARPANET is fundamentally connected to and born of computer science.

See also

Further reading

  • Paul Baran, On Distributed Communications
  • Paul Baran, On Distributed Communications Networks (IEEE Transactions on Communications Systems, March 1964)
  • Leonard Kleinrock, Communication Nets: Stochastic Message Flow and Design (McGraw-Hill, 1964)
  • Arthur Norberg, Judy E. O'Neill, Transforming Computer Technology: Information Processing for the Pentagon, 1962-1982 (Johns Hopkins University, 1996) pp. 153-196
  • A History of the ARPANET: The First Decade (Bolt, Beranek and Newman, 1981)
  • Katie Hafner, Where Wizards Stay Up Late (Simon and Schuster, 1996)

External links

Last updated: 11-06-2004 06:48:03