Chapter 8 - Application Layer Protocols

Abstract

This chapter discusses application layer protocols. The main purpose of this chapter is to allow the software designer to get a mental map of the higher-layer protocols, how they operate and how to implement them. Telnet provides a very useful byte-by-byte, simple, two-way communication path between two stations. Telnet gives users the illusion that they have a single, dedicated connection to another user or computer. Electronic mail (e-mail) is one of the most convenient ways for sending simple messages over a LAN or over the Internet. An embedded data logger can use e-mail to transmit updates over the Internet anywhere round the world; the only thing it needs is a dial-up modem and an ISP account. The simple mail transfer protocol (SMTP) is used for simple e-mail transmission; SMTP can only be used to transmit mail. The hypertext transfer protocol (HTTP) follows a simple client‑server methodology. The server simply sits there waiting until a client makes a request, and then supplies the requested information. All HTTP requests are handled one at a time, and are responded to individually. HTTP has many options and additions in order to transfer complex objects such as images. File transfer protocol (FTP) was one of the original protocols developed for the Internet. It was developed for the transmission of files and fixed blocks of data.