This unit discusses the functions of application layer protocols and describes the services they need from other network layers. The unit also explains HTTP, FTP, and SMTP, illustrates the client-server model for network applications, and shows how client and server interact in a network application.
The application layer discussed in this unit is of the Internet protocol (TCP/IP) stack. An understanding of application layer protocols is essential not only for network programmers, but also for users wishing to understand how network applications work. The application layer directly supports network applications in accomplishing their functions.