An empirical study of TCP's fairness

Pao Yue-kong Library Electronic Theses Database

An empirical study of TCP's fairness

 

Author: Ng, Ping-wing
Title: An empirical study of TCP's fairness
Degree: M.Sc.
Year: 1999
Subject: TCP/IP (Computer network protocol)
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Computing
Pages: viii, 76 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1479277
URI: http://theses.lib.polyu.edu.hk/handle/200/3116
Abstract: It has been reported that TCP connection discriminates against long round trip times with regards to the throughput. The cause of the unfairness is the "slow start" and "congestion avoidance" algorithms used by TCP, which result in unfair bandwidth allocation when multiple connections with different round trip times share a congested gateway. This fairness problem is particularly severe for networks with long round trip delay. An experimental approach is used in this project to identify this fairness problem. To solve this problem, two algorithms have been proposed by some researchers. These algorithms, termed as the "linear rate policy" and "constant rate policy", have been implemented and studied. The result is that these algorithms solve the problem to a certain extent but with some shortcomings. During the experiment, a new factor is discovered based on the measurement data. This finding reveals that there is a positive correlation between the round trip time and the congestion window during the congestion phase. Based on this finding, a new algorithm is then devised and implemented to address this problem together with experimental measurements of how well this algorithm performs. Judging from the measured result, it is found that the "linear rate policy" and "constant rate policy" suffer from a fundamental disadvantage of inducing more congestion during the congestion phase. Hence additional insight about the nature of congestion is gained from the measurements. The new algorithm is found to be very promising because it do not suffer from the mentioned fundamental disadvantage in addition to its capability to restore fairness. This sheds light on future improvement and implementation of TCP, and there is plenty of rooms for future work.

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