Chapter 1 evolution of computer networks

mission networks
, or backbones. Such networks do not serve end users; rather, they
represent the foundation upon which high-speed “point-to-point” digital channels are
based. These channels connect the equipment of another network (the overlay network)
that serves end users.
Initially, transmission networks represented exclusively internal technology used only
by telephone companies. Gradually, however, these companies started to lease part of
their digital channels, connected into transmission networks, to companies that used them
for creating their own telephone networks and WANs. Nowadays, transmission networks
have raised data transmission speeds to hundreds of Gigabits per second (Gbps) and, in
some cases, to several Terabits per second; these networks cover the territories of all main
industrial states.
Both variety and quality of services have helped WANs catch up with LANs, which had
been the leaders despite their relatively late arrival.
1.3.2 First Local Area Networks (LANs)
In the early 1970s, an event took place that has had the greatest influence on the evolution of
computer networks. As a result of technological advances in the field of computer-compo-
nents manufacturing, large-scale integrated circuits (LSI devices) appeared. LSI devices were
characterized by relatively low cost and advanced functional capabilities. This led to the
development of minicomputers, which became the real competitors for mainframes. Grosch’s
Law ceased to represent reality, since a dozen minicomputers, having the same cost as one
mainframe, were capable of accomplishing some tasks (especially ones that could be exe-
cuted in parallel) much faster.
From that moment, even small companies could enjoy the possibility of having their
own computers. Minicomputers could carry out tasks such as controlling technical equip-
ment or managing stocks. This was the origin of the distributed computing concept, with
computing resources becoming distributed over the entire enterprise. All computers within
the same organization, however, continued to operate independently (Figure 1.4).
With time, the needs of computer users evolved. End users were no longer satisfied
with isolated work on a standalone computer. For instance, they needed to exchange com-

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CHAPTER 1 EVOLUTION OF COMPUTER NETWORKS
17
Enterprise
Minicomputer
Minicomputer
p
Minicom uter
Minicomputer
Department 1
Department 2
Department 4
p
De artment 3
Terminal
Figure 1.4
Independent operation of several minicomputers within the same enterprise
Minicomputer
Minicomputer-to-minicomputer
interface unit
Terminals
Minicomputer
Personal computers
Minicomputer
Personal computers
Terminals
Minicomputer-to-PC
interface unit
Figure 1.5 
Types of links in the first LANs

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