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.
Telnet Interrupt Handling Using Out-Of-Band Signaling: The Telnet Synch Function
(Page 2 of 2)
The Synch Function
When needed, as in the example just
described, the synch function is invoked by the client sending the special
Telnet Data Mark (DM) protocol command, while instructing its
TCP layer to mark that data urgent. The URG bit in
segment carrying this command causes it
to bypass TCPs normal flow control mechanism so it is sent over
to the remote host. The Telnet server software, seeing the synch in
the data stream, then searches through all of the data in its buffer
looking only for Telnet control commands such as Interrupt Process,
Abort Output and Are You There. These commands are then
executed immediately. The server continues to search for important commands
up to the point where the Data Mark command is seen. All intervening
data is discarded; it will need to be retransmitted. After the Data
Mark is processed, the server returns to normal operation.
It is also possible for the server
to use the synch function in communication with the user on the client
device. For example, if the user sends the Abort Output command
to the server, he or she is telling the server to discard all remaining
output from the current process. The server will stop sending that output,
and can also use the synch function to clear all outstanding data that
is waiting in buffers to be sent to the client machine (since it causes
data to be discarded as mentioned above).
Key Concept: Telnet protocol commands are sent in the same stream with user data, which means a problem with the remote host that stops the flow of data might cause user commands to become backed up and never received by the host. Since this may include commands issued by the user to try to fix the problem on the host, this can be a serious problem. To alleviate this situation, Telnet includes the synch function, which uses TCPs urgent data transmission feature to force the receipt of essential commands even when regular data is not being processed.
|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!|
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.