Business Data Communications and Networking

Chapter 2. APPLICATION LAYER

THE APPLICATION layer (also called layer 5) is the software that enables the user to perform useful work. The software at the application layer is the reason for having the network because it is this software that provides the business value. This chapter examines the three fundamental types of application architectures used at the application layer (host-based, client-based, client-server). It then looks at the Internet and the primary software application packages it enables: the Web, e-mail, Telnet, FTP, and Instant Messaging.

OBJECTIVES ▾

• Understand host-based, client-based, and client-server application architectures

• Understand how the Web works

• Understand how e-mail works

• Be aware of how FTP, Telnet, and instant messaging works

CHAPTER OUTLINE ▾

INTRODUCTION

APPLICATION ARCHITECTURES

• Host-Based Architectures

• Client-Based Architectures

• Client-Server Architectures

• Peer-to-Peer Architectures

• Choosing Architectures

WORLD WIDE WEB

• How the Web Works

• Inside an HTTP Request

• Inside an HTTP Response

ELECTRONIC MAIL

• How E-mail Works

• Inside an SMTP Packet

• Listserv Discussion Groups

• Attachments in Multipurpose Internet Mail Extension

OTHER APPLICATIONS

• File Transfer Protocol

• Telnet

• Instant Messaging

• Videoconferencing

IMPLICATIONS FOR MANAGEMENT

SUMMARY

INTRODUCTION

Network applications are the software packages that run in the application layer. You should be quite familiar with many types ...