Lesson 3 - The OSI Model

   Introduction

The OSI reference model describes a theoretical protocol stack that consists of seven layers of services and protocols. At the bottom, the concrete Physical Layer contains protocols that transmit bits over physical media. At the top, the abstract Application Layer contains programs such as electronic mail (e-mail).

The OSI model is not a protocol, but an abstract structure that describes the functions and interactions of various data communication protocols. It provides a conceptual framework that helps us discuss and compare network functions and components.

   Objectives

At the end of this lesson you should be able to:

1.	Describe the primary function of each layer of the OSI model
2.	List the two main types of addresses found in most computer networks
3.	Understand why three types of addresses are used to move information from source to destination

Key Point
Each layer of the OSI model uses the services of the layer below it and provides services to the layer above.

[ Previous Lesson ] [ Unit Contents ] [ Next Section ]