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Internetworking Models

communication system is designed in this manner, it's known as

layered

architecture

Think of it like this: You and some friends want to start a company. One

of the first things you'd do is sit down and think through what tasks must be
done, who will do them, what order they will be done in, and how they relate
to each other. Ultimately, you might group these tasks into departments.
Let's say you decide to have an order-taking department, an inventory
department, and a shipping department. Each of your departments has its
own unique tasks, keeping its staff members busy and requiring them to
focus on only their own duties.

In this scenario, departments are a metaphor for the layers in a commu-

nication system. For things to run smoothly, the staff of each department will
have to trust and rely heavily on the others to do their jobs and competently
handle their unique responsibilities. In your planning sessions, you would
probably take notes, recording the entire process to facilitate later discus-
sions about standards of operation that will serve as your business blueprint,
or reference model.

Once your business is launched, your department heads, armed with the

part of the blueprint relating to their department, will need to develop prac-
tical methods to implement their assigned tasks. These practical methods, or
protocols, will need to be compiled into a standard operating procedures
manual and followed closely. Each of the various procedures in your manual
will have been included for different reasons and have varying degrees of
importance and implementation. If you form a partnership or acquire
another company, it will be imperative for its business protocols--its busi-
ness blueprint--to match yours (or at least be compatible with it).

Similarly, software developers can use a reference model to understand

computer communication processes and see what types of functions need to
be accomplished on any one layer. If they are developing a protocol for a
certain layer, all they need to concern themselves with is the specific layer's
functions, not those of any other layer. Another layer and protocol will
handle the other functions. The technical term for this idea is

binding

. The

communication processes that are related to each other are bound, or grouped
together, at a particular layer.

Advantages of Reference Models

The OSI model is hierarchical, and the same benefits and advantages can
apply to any layered model. The primary purpose of all models, and espe-
cially the OSI model, is to allow different vendors' networks to interoperate.

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