I must Create a System, or be enslav’d by another Man’s; I will not
Reason and Compare: my business is to Create.
uppose you want to build a computer network, one that has the potential to
grow to global proportions and to support applications as diverse as telecon-
ferencing, video-on-demand, electronic commerce, distributed computing, and
digital libraries. What available technologies would serve as the underlying building
blocks, and what kind of software architecture would you design to integrate these
Building a Network
building blocks into an effective com-
munication service? Answering this
question is the overriding goal of
this book—to describe the available
building materials and then to show
how they can be used to construct
a network from the ground up.
Before we can understand how to design a computer network, we should
Frst agree on exactly what a computer network is. At one time, the term
meant the set of serial lines used to attach dumb terminals to mainframe com-
puters. To some, the term implies the voice telephone network. To others, the
only interesting network is the cable network used to disseminate video signals.
The main thing these networks have in common is that they are specialized to
handle one particular kind of data (keystrokes, voice, or video) and they typically
connect to special-purpose devices (terminals, hand receivers, and television sets).
What distinguishes a computer network from these other types of networks? Prob-
ably the most important characteristic of a computer network is its generality. Com-
puter networks are built primarily from general-purpose programmable hardware, and
they are not optimized for a particular application like making phone calls or deliv-
ering television signals. Instead, they are able to carry many different types of data,
and they support a wide, and ever-growing, range of applications. This chapter looks