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BGP by Iljitsch van Beijnum

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Queuing, Traffic Shaping, and Policing

Traffic engineering works only if you have bandwidth to spare on one of your connections. Even the most sophisticated traffic balancing techniques won’t help you when there is just too much traffic. When the output queues for interfaces start filling up, interactive protocols start noticing delays, and bulk protocols start noticing lower throughput. The best way to handle this would be to get more bandwidth, but with some smart queuing techniques, it’s possible to increase performance for some protocols or sessions without hurting others very much. Or just give way to “important” packets and let less important traffic suffer. There are three ways to accomplish this: special queuing strategies, traffic shaping, and rate limiting. Before choosing one, you should know how each interacts with TCP.

Nearly all applications that run over the Internet use the TCP (RFC 793) “on top of” IP. IP can only transmit packets of a limited size, and the packets may arrive corrupted by bit errors on the communications medium, in the wrong order, or not at all. Also, IP provides no way for applications to address a specific program running on the destination host. All this missing functionality is implemented in TCP. The characteristics of TCP are:

“Stream” interface

Any and all bytes the application writes to the stream come out in the same order at the application running on the remote host. There is no packet size limit: TCP breaks up the communication into packets ...

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