Telnet, which stands for Telecommunications Network, is a protocol that provides a way for users (or clients) to connect to other users via servers on the Internet, this could be in the next building or around the other side of the world. In most cases, users use Telnet to communicate with a remote login service.

Telnet is based on three main principles:

• The concept of the Network Virtual Terminal (NVT).
• The concept of negotiations.
• A symmetrical view of terminals and processes.

Network Virtual Terminal
The Network Virtual Terminal is a device used by Telnet to enable a local computer to communicate with a remote computer. To make Telnet inter-operate between as many systems as possible, it must accommodate the details of heterogeneous computers and operating systems. To accommodate heterogeneity, Telnet defines how data and command sequences are sent across the Internet. The definition is known as the Network Virtual Terminal (NVT). The NVT defines how data and commands are sent across the internet. The NVT is a bi-directional character device that makes use of a printer and a keyboard. The printer responds to incoming data and the keyboard produces outgoing data which is sent over the Telnet connection. The NVT is seen as a half-duplex device.

Concept of Negotiation
The option negotiation mechanism allows the user to set terminal parameters to values other than the default or to negotiate more sophisticated facilities. The Telnet protocol negotiation mechanism can be initiated by either side. Besides negotiating whether or not a particular option is to be in effect, the mechanism also allows one to specify, when appropriate, which side is to perform the function. For example, a user may negotiate the Echo option and specify whether echoing is to be done locally or remotely to the initiator of the negotiation.

Symmetrical View
The third concept of Telnet is one of symmetry in the negotiation syntax. This symmetry allows either the client or server ends of the connection to request a particular option as required, thus optimising the service provided by the other party. A terminal protocol should not only allow a terminal to interact with an application process on a host, but it should also allow process-process and terminal-terminal interactions. Although a majority of the connections established will be of the process-terminal form, the symmetrical forms can be very useful.
www.rad.com/networks/1997/telnet/proj.htm#INTRODUCTION

Uses of Telnet
Telnet is a text-based way of connecting to other computers and networks. It is one of the oldest
forms of the Internet. When you telnet to another computer, it is like you are using a terminal of that
system. Telnet is typically used with Unix-oriented systems.

Telnet operates in a client/server environment in which one host (the computer you are using, running Client (User) Telnet) negotiates opening a session on another computer (the remote host, running Server Telnet). During the behind-the-scenes negotiation process, the two computers agree on the parameters governing the session. One of the first things they decide is the terminal type to be used -- in general, a line-by-line network virtual terminal, for simplicity's sake. Virtual terminal, in this context, refers to a set of terminal characteristics and sequences that both sides of a network connection agree to use to transmit data from terminals across the network, regardless of the terminal used.

Telnet is a program that lets you use the power of the Internet to connect you to databases, library catalouges, and other information resources around the world. Want to see what the weather's like in an American city? Check on crop conditions in Azerbaijan? Get more information about somebody whose name you've seen online? Telnet lets you do this, and more. Alas, there's a big "but!'' Unlike the phone system, Internet is not yet universal; not everybody can use all of its services. Almost all colleges and universities on the Internet provide telnet access. But the Freenet systems do not give you access to every telnet system. The main reason for this is cost. Connecting to the Internet can easily cost US$1,000 or more for a leased, high-speed phone line.
www.lysator.liu.se/etexts/iguide/chap6.telnet.html

Patrick Hilton 9457372