Telnet

Telnet is one of the original Internet application predating even e-mail. Telnet is a text-based application that allows you to log into a remote computer server via your local computer and utilize the resources available on that computer server. FTP allows you to copy information from a remote computer while Telnet allows you to run programs on the remote computer.

How Telnet Works

When using Telnet to access a remote server, your computer becomes a "dumb" terminal and acts analogously to a terminal on any time-sharing computer system. A time-sharing computer system allows one large computer to support multiple users simultaneously. Each user accesses this computer from a terminal consisting of a keyboard, monitor and mouse. The time-sharing computer allocates a particular portion of its resources each terminal to use to run programs. This computer's operating system is constantly switching very quickly between users to ensure that work at each terminal proceeds as if it were the only terminal in operation. When working at one of these terminals, the computer responds to your keyboard input instantly -- you can't tell the difference between the time-sharing computers response and the response you observe on your single user PC. In order to access a time-sharing computer, you must invoke terminal emulation software which causes your local computer to act like a terminal.

Only authorized users can access a time-sharing computer. Thus, the computer requires users to login with a user name and password. Once you are logged onto the remote server, the computer executes any commands that you type on your keyboard. The login procedure allows the computer to keep track of how many authorized users are using its resources at any given time. Although time-sharing computers are designed to allow access to its resources by simultaneous, multiple users, there is a limit to the number of users that can be logged on at the same time.

Using Telnet

A Telnet client program is needed to connect to a Telnet server. Although many Internet services can be accessed with a WWW browser, it cannot directly access a Telnet server. Browsers can only communicate with a Telnet server by using an outside Telnet application.

Telnet provides general access to the programs on the remote computer without requiring any modifications for different local computer operating systems. DOS, Macintosh and UNIX machines can all use the same program at the same time.

Telnet sites are generally easy to use and have online help systems available. Most work best using VT100 teminal emulation. Most available Telnet application programs recognize standard basic commands.

**Telnet Commands**
Command	Use
close	Close the connection. This disconnects the local computer from the remote computer.
help	Displays information about Telnet commands.
open	Establish a connection with a remote server.
quit	Close the connection and exit the Telnet program.
z	Suspend current activity and return to a UNIX shell.

Telnet client programs have two operating modes -- the input mode and the command mode. On start up, Telnet client software puts you in input mode where you can edit the program's parameters. Once you log into a remote site, the program switches to command mode allowing you to send commands to the server.

Connecting to a Telnet Site

To connect to a Telnet site, all you have to do is start your client program and type the address for the site. Every Telnet site has two addresses -- a word address or host name consisting of words separated by periods (good for people to remember) and a numerical address or network address composed of a series of numbers separated by periods (suited for use by a computer.) Some Telnet computers only allow the general public to access them through a specific port. This port information appears as a number following the series of words or numbers in the address. If you do not specify a port, the computer will assume you are an authorized local user and request a valid username and password. This is similar to using anonymous FTP.

After entering the address, wait patiently for the connection to be established. In some cases you will be able to start using the remote computer's resources immediately in others you will need to enter a login name and password. Normally these will be noted on the screen before you log in.

If the remote computer stops responding to your commands, you can usually disconnect from the remote system by simultaneously depressing the control key and the ]. This should return you to the Telnet prompt on your system. You can then close the connection to the remote computer and exit the Telnet program.

Telnet Applications

Many resources are available to you via Telnet. These include:

Free public access databases
Commercial networks and services such as STN (a collection of electronic databases such as Chemical Abstracts) and CompuServe (an electronic bulletin board). An account is needed to access these services -- they are not free!
Libraries. Many libraries such as the Library of Congress have their card catalogs via Telnet.
Special programs such as Archie and WAIS designed for locating Internet information sources.
Special programs for locating people such as Whois and Netfind.
Freenets -- community-based networks offering free access to people who live in that community.

Some Telnet Sites To Try

The Library of Congress site provides access to card catalogs, legislation copywrite information etc. (locis.loc.gov)

The University of Michigan Geographic Name Server (martini.eecs.umich.edu 3000). Try typing in a city name and zip code and see what happens!

NASA Information Online (spacelink.msfcm.nasa.gov)

Weather Underground (madlab.sprl.umich.edu 3000)

Carl UnCover (database.carl.org)

The Global Change Master Directory (gcmd.gsfc.nasa.gov) contains descriptions of earht and space science data holdings including info from DOE, EPA, NASA, NOAA, NSF, etc. This site does not contain actual data, but rather provides pointers to the data sets.

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