This link has been bookmarked by 3 people . It was first bookmarked on 07 Sep 2006, by Daniel Ulfe.
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31 Mar 11
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By changing the window size that a device advertises to a peer on a TCP connection, the device can increase or decrease the rate at which its peer sends it data. This is how the TCP sliding window system implements flow control between the two connected devices
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Flow control is a very important part of regulating the transmission of data between devices, but it is limited in the following respect: it only considers what is going on within each of the devices on the connection, and not what is happening in devices between them. In fact, this “self-centeredness” is symptomatic of architectural layering. Since we are dealing with how TCP works between a typical server and client at layer four, we don't worry about how data gets between them; that's the job of the Internet Protocol at layer three.
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n practice, what is going on at layer three can be quite important. Considered from an abstract point of view, our server and client may be connected “directly” using TCP, but all the segments we transmit are carried across an internetwork of networks and routers between them. These networks and routers are also carrying data from many other connections and higher-layer protocols. If the internetwork becomes very busy, the speed at which segments are carried between the endpoints of our connection will be reduced, and they could even be dropped. This is called congestion.
Again, at the TCP level, there is no way to directly comprehend what is causing congestion or why. It is perceived simply as inefficiencies in moving data from one device to another, through the need for some segments to be retransmitted. However, even though TCP is mostly oblivious of what is happening on the internetwork, it must be smart enough to understand how to deal with congestion and not exacerbate it.
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07 Sep 06
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