We will learn how they are organized, how they
work, and some of the applications they can provide.
REFERENCE MODEL
As with any complicated technology, networks are often divided into a number of layers in order to make
it easier to understand how they work and to make them easier to build. Each layer is responsible for a different
part of the communication process. One of the advantages of using layers is that in order to use a layer you do
not need to understand how it works inside, you simply need to know what services it provides and how to ask
for them. For example, consider making a call on a cell phone. You only need to know how to make the call and
how to speak into the phone. You do not have to understand the technical mechanisms that convert your voice
into a form suitable for transmission using public airwaves.
Several reference models have been developed to define a standard way to split the functionality of a network
into a series of layers. This layered approach has resulted in casual talk of ???the network protocol stack.???
The reference model most commonly used in networking was developed by the International Standards
Organization (ISO) and is called the Open Systems Interconnection (OSI) model, or the ISO OSI model
(How??™s that for acronym reuse!?).
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