Information Technology Reference
In-Depth Information
exchange of programs and data.
2
This view of the computer as a device to improve
communication was in stark contrast to the mind-set of computer manufacturers, which
continued to think of computers as number-crunching machines.
Conventional, circuit-switched telephone networks were not a good foundation
upon which to build a global computer network (Figure 1.15a). Between 1961 and 1967,
three research teams independently came up with an alternative to circuit-switched
networks. These teams were led by Donald Davies and Roger Scantlebury at NPL in
England, Paul Baran at RAND, and Leonard Kleinrock at MIT. Eventually the new design
came to be called a packet-switched network (Figure 1.15b).
In 1967 ARPA initiated the design and construction of the ARPANET. Fear of a
nuclear attack led to the crucially important design decision that the network should
be decentralized. In other words, the loss of any single computer or communication link
would not prevent the rest of the network from working. Every computer on the network
would have the ability to make decisions about how message traffic should be routed.
Packet-switched networks met this condition; circuit-switched networks did not.
BBN in Boston was responsible for the Interface Message Processor (IMP) that
connected a computer to the telephone network. In 1969 BBN delivered its first four
IMPs to UCLA, the Stanford Research Institute, the University of California at Santa
Barbara, and the University of Utah.
During the earliest years of ARPANET, the networked computers could transfer pro-
grams and data only. ARPANET users still relied upon the telephone for personal com-
munications. In March 1972, Ray Tomlinson at BBN wrote the first software enabling
email messages to be sent and received by ARPANET computers. A few months later,
Lawrence Roberts created the first “killer app” for the network: an email utility that gave
individuals the ability to list their email messages, selectively read them, reply to them,
forward them to others, and save them. Email quickly became the most popular network
application.
Today email is one of the most important communication technologies on the
planet. More than 200 billion email messages are sent each day.
ARPA researchers anticipated the need to connect the ARPANET with other networks
based on different designs. Robert Kahn developed the concept of open architecture
networking, which means individual networks could be quite different as long as they
shared a common “internetworking architecture.” Vinton Cerf and Robert Kahn de-
signed the TCP/IP protocol that would support open architecture networking [36]. TCP
(Transmission Control Protocol) is responsible for dividing a message into packets at the
2. The primary source document for this description of the evolution of the Internet is
A Brief History
of the Internet
by Barry M. Leiner et al. [35].
