Chapter 4. The OSI Model

OBJECTIVES

This chapter covers the following CompTIA-specified objectives for the “Protocols and Standards” section of the Network+ exam:

Identify the seven layers of the OSI model and their functions.

• The OSI reference model provides a theoretical framework that is used to describe the processes and technologies associated with networking.

Identify the OSI layers at which various network components operate including:

• Hubs

• Switches

• Bridges

• Routers

• Network interface cards (NICs)

• Understanding how devices' functions relate to the OSI model can provide a greater understanding of networking principles.

OUTLINE

Introduction

Why Do We Need a Network Model?

OSI Reference Model 101

Layer 1: The Physical Layer

Layer 2: The Data-Link Layer

Layer 3: The Network Layer

Switching Methods

Network-Layer Addressing

Layer 4: The Transport Layer

Connection-Oriented Protocols

Connectionless Protocols

Flow Control

Layer 5: The Session Layer

Layer 6: The Presentation Layer

Layer 7: The Application Layer

OSI Model Summary

The Layers at Which Devices Operate

Hubs

Switches

Bridges

Routers

NICs

Summary of the Layers at Which Devices Operate

Chapter Summary

Apply Your Knowledge

STUDY STATEGIES

• Read the objectives at the beginning of the chapter.

• Study the information in the chapter, paying special attention to the tables, which summarize key information.

• Review the objectives again.

• Answer the exam questions at the end of the chapter and check your results.

• Use the ExamGear test on the CD-ROM that accompanies this book to answer additional exam questions concerning this material.

• Review the notes and exam tips in this chapter. Make sure you understand the information in the exam tips. If you don't understand the topic referenced in an exam tip, refer to the information in the chapter text and then read the exam tip again.