network models

Network Models


A network is a combination of hardware and software that sends data from one location
to another. The hardware consists of the physical equipment that carries signals from
one point of the network to another. The software consists of instruction sets that make
possible the services that we expect from a network.
We can compare the task of networking to the task of solving a mathematics problem
with a computer. The fundamental job of solving the problem with a computer is done
by computer hardware. However, this is a very tedious task if only hardware is involved.
We would need switches for every memory location to store and manipulate data. The
task is much easier if software is available. At the highest level, a program can direct
the problem-solving process; the details of how this is done by the actual hardware can
be left to the layers of software that are called by the higher levels.
Compare this to a service provided by a computer network. For example, the task
of sending an e-mail from one point in the world to another can be broken into several
tasks, each performed by a separate software package. Each software package uses the
services of another software package. At the lowest layer, a signal, or a set of signals, is
sent from the source computer to the destination computer.
In this chapter, we give a general idea of the layers of a network and discuss the
functions of each. Detailed descriptions of these layers follow in later chapters.