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The Advanced Research Projects Agency Network (ARPANET) of the U.S. DoD 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
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
independently of 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.
The ARPANET and nuclear attacks
The Internet Society writes about this merge of technologies 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
The myth that 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. ARPANET was later extended to survive network losses,
but the main reason was actually that the apparatus and network links were
sensitive, even without any nuclear attacks.
Origins of the ARPANET
While all this was happening, ARPA and Taylor continued to be interesting in
creating a computer communication network, in part to allows 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
At the end of 1966, Taylor brought Lawrence G. Roberts to ARPA from MIT's
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 4 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 awared to Bolt, Beranek and Newman
(BBN) early in 1969.
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 were connected to each other using modems and performed the function of
a router. 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 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:
"...it 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.