Business Data Communications and Networking, Eleventh Edition

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, email, Telnet, and instant messaging.

OBJECTIVES

• Understand host-based, client-based, and client-server application architectures
• Understand how the Web works
• Understand how email works
• Be aware of how Telnet and instant messaging works

CHAPTER OUTLINE

2.1 INTRODUCTION

2.2 APPLICATION ARCHITECTURES

2.2.1 Host-Based Architectures

2.2.2 Client-Based Architectures

2.2.3 Client-Server Architectures

2.2.4 Peer-to-Peer Architectures

2.2.5 Choosing Architectures

2.3 WORLD WIDE WEB

2.3.1 How the Web Works

2.3.2 Inside an HTTP Request

2.3.3 Inside an HTTP Response

2.4 ELECTRONIC MAIL

2.4.1 How Email Works

2.4.2 Inside an SMTP Packet

2.4.3 Attachments in Multipurpose Internet ...