Lesson 2 - Layers of Protocols and Services

   Introduction

When two computers communicate over a network, several different processes may take part in the message transmission. At first, this might seem like an inefficient way to communicate. However, in this lesson we will see that there are real advantages to using several protocols to transmit a message, rather than one protocol that does it all. To understand how this works, let us see how a familiar type of communication (a letter) may use multiple protocols to reach its destination.

   Objectives

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

1.	Explain why a network uses several protocols that each perform part of a job, instead of just one protocol that does it all
2.	Describe how each layer in a protocol stack interacts with other layers
3.	Explain what a peer process is
4.	Explain what a protocol stack is
5.	Explain the processes of encapsulation and decapsulation

Key Point
It takes several layers of protocols to move information across a network.

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