Please Whitelist This Site?

I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)

If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.

If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.

Thanks for your understanding!

Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide


NOTE: Using software to mass-download the site degrades the server and is prohibited.
If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

The Book is Here... and Now On Sale!

Read offline with no ads or diagram watermarks!
The TCP/IP Guide

Custom Search







Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Key Applications and Application Protocols
           9  TCP/IP Interactive and Remote Application Protocols
                9  Telnet Protocol

Previous Topic/Section
Telnet Communications Model and the Network Virtual Terminal (NVT)
Previous Page
Pages in Current Topic/Section
1
23
Next Page
Telnet Interrupt Handling Using Out-Of-Band Signaling: The Telnet Synch Function
Next Topic/Section

Telnet Protocol Commands
(Page 1 of 3)

Most of the input that a user enters at a terminal takes the form of data and commands that are sent to the application program he or she is using. However, computer systems also provide a means by which a user can instruct the terminal to send certain commands that control how the terminal itself operates, and how it interacts with the computer to which it is connected. The best example of this is the command to interrupt a process, which is usually sent by pressing a special key or key combination on the user terminal.

Telnet needs to have a way to allow such commands to be entered by the user. However, here we run into the same problem that we saw in the last topic, when we talked about the communication of data between terminals and computers: a lack of uniformity in representation. While all terminals and computers support the ability to interrupt a running program, for example, they may each use a different keystroke to represent it. For example, on most UNIX systems, the key combination “<Ctrl>+C” interrupts a program, but typing this on a Windows system will not (it usually represents instead the “copy data” function!)

Defining a Universal Representation for Standard Command Functions

Since the problem is the same as the one we ran into in representing data flow, it’s not too surprising that the solution is the same: the use of a universal representation for a set of standard commands to be passed between the terminal and host computer. All keystrokes that represent these commands are translated to the standard Telnet codes for transmission, and then translated to the specific needs of the host computer. So to take our example again, if a user presses “<Ctrl>+C” on a UNIX terminal where this is defined as the interrupt function, then instead of sending that exact keystroke, the Telnet client sends the special Telnet Interrupt Process command, which is translated by the Telnet server to the command code appropriate for the connected host.

The Telnet standard includes a number of these special codes to allow a user to control the operation of the remote computer. It also defines a set of commands that are specific to the Telnet protocol itself; these let the Telnet client and Telnet server software communicate. Collectively, these are called Telnet protocol commands.


Previous Topic/Section
Telnet Communications Model and the Network Virtual Terminal (NVT)
Previous Page
Pages in Current Topic/Section
1
23
Next Page
Telnet Interrupt Handling Using Out-Of-Band Signaling: The Telnet Synch Function
Next Topic/Section

If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



Home - Table Of Contents - Contact Us

The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005

© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.