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.
TCP Sliding Window Data Transfer and Acknowledgement Mechanics
(Page 6 of 6)
Real-World Complications of the Sliding Window Mechanism
I'm sure this seems rather complicated,
but in fact, the example is highly simplified, to show
you how the basic data transfer mechanism works without too much going
on. Scary, isnt it? J
A real world connection would include several complications:
- Overlapping Transmissions: I intentionally
showed only one request from the client and the response from the server.
In reality, the client and server could be pumping many requests and
responses at each other in rapid-fire succession; the client would be
acknowledging segments received from the server with segments that themselves
contained new requests, and so on.
- Acknowledgment of Multiple Segments: I
also didn't show a case where two segments are received by a device
and acknowledged with a single acknowledgment, though this can certainly
happen. Suppose that in the example above, the two parts of the 280-byte
file were sent at once and received by the client at the same time.
The client would acknowledge both by sending a single segment with an
Acknowledgment Number of 601. Remember, this field is a cumulative
acknowledgment of all segments containing data through the number preceding
it, so this would acknowledge all data up to byte 600.
- Fluctuating Window Sizes For Flow Control:
The window sizes in the example above remained constant, but in a real
connection this will not always be the case. A very busy server may
not be able to process and remove data from its buffer as fast as it
acknowledges it. It may need to reduce its receive window to reduce
the amount of data the client sends it, and then increase the window
when more space becomes available. This
is how TCP implements flow control.
- Lost Transmissions: In a real connection,
some transmitted segments will be lost and need to be retransmitted.
This is handled by TCP's
- Avoiding Small Window Problems: I hinted
in the table above that we don't necessarily always want to send data
as fast as we can, when it means we have to send a very small segment.
The reason is that this can lead to performance degradation, including
a phenomenon called silly
window syndrome. This too will be explored
in the section that follows, where we will see how handling it requires
that we change
the simple sliding windows scheme we have
seen until the point.
- Congestion Handling and Avoidance: The
basic sliding window mechanism has been changed over the years to avoid
having TCP connections cause internetwork congestion and to have them
handle congestion when it is detected. Congestion issues are discussed,
you guessed it, in
the next 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!|
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.