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 Comm Corner 
Telnet/Remote Login 
What does it do?  
by John Woody

Alamo PC Organization: HOME > PC Alamode Magazine > Columns > Comm Corner 
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Telnet is a collective term used when we do remote-login on the Internet. 

Telnet is one of those early client-server applications which is used to remotely log into another computer in order to use it. As all client-server programs, Telnet comes in two parts, the client which resides on our computer and the Telnet server. It has a two part definition: 

     (a) A "terminal emulation" protocol that allows you to log in to another computer system on the Internet. 

     (b) An application program that allows you to log in to another computer system using the TELNET' protocol.

Telnet is the remote login protocol for the Internet. In it's "terminal emulation" role, it is able to use the remote computer keyboard and operating system (OS) completely. Once you have completed the connection to the remote computer, you no longer use your operating system. You have complete control of the remote computer and must use its operating system including key strokes and operating system conventions. 

 In the beginning, 1968ish, Telnet and an account on the remote computer was all that you needed to "surf" the Internet. It goes without saying, that Telnet was part of the Unix operating system. At the remote end, the computer being logged into operated as a Telnet server. 

 

What is Really Going On

Telnet sessions are basic client-server programs. The client, running on the local computer requests server from a remote computer, called a server. The client, upon activation performs several functions including: 
     
  • Create a TCP network connection with a server 
  • Accept input from the local computer in a convenient manner 
  • Reformat the local input to a standard format and send it to a server 
  • Accept output from the server in a standard format 
  • Reformat that output for display to you
The Telnet server program on the remote computer simply resides in the background and waits for the client call. Most servers have these server programs running in the background waiting to be called. UNIX servers, called daemons, run all the time. The server accepts the Telnet request and then performs the following: 
     
  • Informs the networking software (client) it is ready to accept connections 
  • Waits for a request in a standard format 
  • Services the request 
  • Sends the results back to the client in a standard format 
  • Waits again
The servers must be able to handle any type of computer, IBM/PC, Macintosh, or Amigas, whatever makes the call. The set of rules, standards, which cause this to happen are established as a protocol for the application. Everyone who develops client or server programs for this application must follow this protocol for the program to successfully work. 

 Telnet, the application, has grown up over the years. It started as a Unix command line program which was started from Unix by typing the command <Telnet>, or <Telnet ?> if you did not know what the commands were for the particular computer you were attempting to log into. The clients most of use today are Windows-based graphic applications. The client side of Telnet has developed into many stand-alone programs such as EWAN, or have been added as part of the suite of client applications such as the Telnet in my Chameleon suites. 

 

What Telnet Is Used For

For most of us, two types of sessions are important uses of Telnet. One is when we want to remotely login to the San Antonio Public Library, or any other public library. Most libraries which have on-line presence use Telnet to access their card catalogs or other services. The other is when we are traveling, and want to access our home Internet account. In either case, the Telnet client is programmed with the Host address, either the IP or the Domain Name, the type of emulation desired (what the server requires), and the TCP port. With just these client application setup entries, you can log into the remote computer. The remote server will ask for; a user name, and a password. Once these have been satisfied at the remote site, the session can then proceed. 

 Additionally, most stand-alone Telnet client programs have scripting capability which allows you to preset the program with your User name and password. Take the usual precautions with your password. 

 In the case of the Library, we would follow the menu to the desired public subdirectory to find the card catalog data we are looking for. Then, when the session is over, we would follow the menu to find the correct exit command. Exit commands are important in Telnet sessions. Most server programs use Unix which may have a unique exit command. Exit is usually part of the main menu, so take time to write it down so that you can terminate the session properly. 

 In the second case, remote login to your home Internet account, follow the same session setup steps, this time using your ISP IP or Domain Name address. At the prompt, enter your User Name and password, then follow the main menu items to the one which will open your e-mail account. From there, read, re-direct, answer, or otherwise act on your e-mail. The ISP can be reached via a direct long distance phone call or using another account to the Internet. In either dial-in method, the session will connect to your ISP Telnet server. 

 Emulation is the term used in Telnet to describe the remote terminal type. Supported terminal types in most client applications include 

  •  TTY 
  • ANSI 
  • ANSI-BBS 
  • ANSI-SCO 
  • AT386 
  • VT100 
  • VT220 
  • VT320 
  • VT340 
  • TV1950 
  • WYSE50 
  • and WYSE60.
Some of these terminal emulations may be familiar, such as ANSI-BBS which the Wildcat BBS works under. My Telnet application has three modes which are Telnet TCP/IP protocol, Rlogin, and Async communications protocol. The Telnet and Rlogin are Internet connections. The Async communications protocol can be an Internet connection, or it can be used to connect to a regular BBS such as the Alamo PC BBS. 

 There is also another emulation which may be used, and that is the IBM mainframe printing commands. This emulation setting is called the TN3270 application establishes the complete IBM mainframe protocol as a TCP/IP client application. My suite gives this application its own program. 

 

The Chameleon Telnet Connection Profile Setup

Quick connections may be made from the main Telnet window by clicking on <connect>, then entering the Host IP address or Domain Name. Then set the emulation type; the default is VT320. Next, set the Port, again the default is 23. Try the default settings first, then change them if you get feedback information. If the remote site is one which you will return to, then setting the Telnet Connection Profile with a program description, Host IP address, Port, and adding information concerning the host Login Prompt, and your Password competes it. This screen is then saved (added) the Telnet .CFG file and will be available until deleted. 

 The Asynchronous Communications Settings for dialing directly into BBS sites establishes the regular direct dialing parameters for the modem and the host file transfer protocols such as Z-Modem. Again the Telnet Connection Profile can be setup for this mode of operation. Select Async for the type of connection. 

 

Conclusion

Knowing Telnet can be of real benefit when you want to get back to your home ISP during travel. 

JOHN WOODY IS A TELECOMMUNICATIONS CONSULTANT SPECIALIZING IN SMALL BUSINESS COMMUNICATIONS, NETWORKS, AND INTERNET BUSINESS TRAINING.