Each end of a Telnet connection is assumed to be a Network Virtual Terminal (NVT). This is a virtual device which maps the local terminal characteristics to a well-defined NVT interface. Figure 2.1 shows a model of the NVT system. Each character generated by the local Keyboard is sent to the remote Printer. The host which initiated the Telnet connection is called the client host, and the other end is called the server (the server is usually providing some kind of service to the client). The capabilities of the NVT was originally designed to compromise between terminals with modest capabilities and more advanced terminals.
Figure 2.1: The Network Virtual Terminal concept
The model is symmetric; there is no difference between the server process and the client process. The Telnet protocol could be used for both terminal-terminal, and process-process communication, as well as for terminal-process communication (most common).