1. Sounds good to me. What can you tell me about the application layer protocols?

There are many different TCP/IP-based application-layer protocols. Some of the most frequently used ones, and the ones you are probably most familiar with, include the Simple Mail Transfer Protocol (SMTP), the Multipurpose Internet Mail Extensions (MIME), and the Post Office Protocol (POP) for e-mail, the TELNET protocol for virtual terminal connections, the File Transfer Protocol (FTP) for file transfers, and the Hypertext Transfer Protocol (HTTP) for Web applications.

Before we begin discussing them, you might want to review the material we presented in Chapter 1 that distinguished between an application and application protocol. Recall that there is a difference between a network application like e-mail and the application-layer protocol that defines it (e.g., SMTP).

1. Okay. Let's start with electronic mail.

From a general perspective, electronic mail (e-mail) refers to the concept of creating, sending, receiving, and storing messages or documents electronically. Nearly every computer system has a program that serves as an interface for e-mail service. This interface provides users with a utility to, among others, compose, read, save, forward, and print mail messages. In addition to providing a user interface, a local system's e-mail service also supports background processes that govern how incoming and outgoing e-mail messages are stored, how users are presented with incoming e-mail, and how often delivery of outgoing messages is attempted. A generic diagram of how local e-mail service...