Archive for February 11th, 2008
TCP congestion control and queueing
TCP mechanisms for traffic regulation and congestion-control
Standard TCP implementations have several mechanisms for congestion-avoidance:
- TCP Slow-start - this is the standard method for increasing the amount of data being transported - starting exponentially at one segment, and after a certain point - in a linear way (congestion-avoidance behaviour), and for regulating this amount in cases of congestion after the traffic source;
- TCP congestion-avoidance - works together with TCP Slow-start and defines a means of regulating the volume of data to be sent in TCP - de facto providing something like flow-control at the source;
- TCP Fast retransmit - defines an accelerated retransmission of part of the data, upon receipt of a minimum of 3 duplicate acknowledgements, without waiting for the TCP retransmission timeout to expire;
- TCP Fast recovery - after sending the missing segment of the fast-restransmit mechanism, TCP goes on with linear growing of the amount of information in transport (congestion avoidance), instead of starting a new slow-start from the beginning;
TCP Slow-start
During a TCP session establishment one of the variables being initialized at the end nodes is the cwnd - congestion window. › Continue reading
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