TELNET is an application protocol that relies on the services of TCP/IP for delivery. This is also considered a peer-to-peer protocol, residing only in the origination and destination hosts.

The TELNET protocol allows terminals or PCs acting as terminals (terminal emulation) to communicate with remote hosts. The remote host may be a server running an application or a mainframe. Terminals are proprietary and are usually not compatible with one another. DEC terminals use a different terminal protocol than IBM terminals do. These differences must be resolved when connections are established with remote hosts. This is the task of TELNET. This protocol provides a means for all terminal types to communicate with remote hosts regardless of the terminal type. It allows the host to determine the characteristics of various terminals.

This is done using a series of commands to negotiate services the host can support. The host must agree to each of the services before the session can begin. All commands are sent using a format defined by TELNET. One example of services to be provided by the remote host is echo, where all data is echoed by the remote host back to the terminal. Other services include control character mapping (defining which keyboard keys will emulate specific control characters) and how flow control is to be managed.

The terminal characteristics supported by the TELNET protocol depend on the terminal emulation being used. However, the main purpose of TELNET is to allow a mechanism by which the remote host...