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 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 Reliability and Flow Control Features and Protocol Modifications

TCP Adaptive Retransmission and Retransmission Timer Calculations 1 2 3 4 TCP Window Management Issues

Closing the Send Window

The process of window adjustment can continue, and of course, can be done by both devices—we are just only considering the client-sends-to-server side of the equation here. If the server continues to receive data from the client faster than it can pump it out to the application, it will continue to reduce the size of its receive window. To continue our example above, suppose that after the send window is reduced to 80, the client sends a third request, this one 80 bytes in length, but the server is still busy. The server then reduces its window all the way down to 0, which is called closing the window. This tells the client the server is very overloaded, and it should stop routine sending of data entirely, as shown in the bottom third of Figure 226. Later on, when the server is less loaded down, it can increase the window size for this connection back up again, permitting more data to be transferred.

While conceptually simple, flow control using window size adjustment can be very tricky. If we aren't careful about how we make changes to window size, we can introduce serious problems in the operation of TCP. There are also special situations that can occur, especially in cases where the window size is made small in response to a device becoming busy. The next two topics explore window management issues, as well as changes that need to be made to the basic sliding windows system to address them.

TCP Adaptive Retransmission and Retransmission Timer Calculations 1 2 3 4 TCP Window Management Issues