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!

Get The TCP/IP Guide for your own computer.
The TCP/IP Guide

Custom Search







Table Of Contents  The TCP/IP Guide
 9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
      9  TCP/IP Transport Layer Protocols
           9  Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)
                9  TCP/IP Transmission Control Protocol (TCP)
                     9  TCP Message Formatting and Data Transfer

Previous Topic/Section
TCP Immediate Data Transfer: "Push" Function
Previous Page
Pages in Current Topic/Section
1
2
Next Page
TCP Reliability and Flow Control Features and Protocol Modifications
Next Topic/Section

TCP Priority Data Transfer: "Urgent" Function
(Page 2 of 2)

Prioritizing Data For Transfer

TCP provides a means for a process to prioritize the sending of data in the form of its “urgent” feature. To use it, the process that needs to send urgent data enables the function and sends the urgent data to its TCP layer. TCP then creates a special TCP segment that has the URG control bit set to 1. It also sets the Urgent Pointer field to an offset value that points to the last byte of urgent data in the segment. So, for example, if the segment contained 400 bytes of urgent data followed by 200 bytes of regular data, the URG bit would be set and the Urgent Pointer field would have a value of 400.

Upon receipt of a segment with the URG flag set to 1, the receiving device looks at the Urgent Pointer and from its value determines which data in the segment is urgent. It then forwards the urgent data to the process with an indication that the data is marked as urgent by the sender. The rest of the data in the segment is processed normally.

Since we typically want to send urgent data, well, urgently, it makes sense that when such data is given to TCP, the “push” function is usually also invoked. This ensures that the urgent data is sent as soon as possible by the transmitting TCP and also forwarded up the protocol stack right away by the receiving TCP. Again, we need to remember that this does not guarantee the contents of the urgent segment. Using the “push” function may mean the segment contains only urgent data with no non-urgent data following, but again, an application cannot assume that this will always be the case.

Key Concept: To deal with situations where a certain part of a data stream needs to be sent with a higher priority than the rest, TCP incorporates an “urgent” function. When critical data needs to be sent, the application signals this to its TCP layer, which transmits it with the URG bit set in the TCP segment, bypassing any lower-priority data that may have already been queued for transmission.


 


Previous Topic/Section
TCP Immediate Data Transfer: "Push" Function
Previous Page
Pages in Current Topic/Section
1
2
Next Page
TCP Reliability and Flow Control Features and Protocol Modifications
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.