Mathematical analysis of Westwood+TCP congestion control
Mathematical analysis of Westwood+TCP congestion control
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DOI：
10.1049/ip-cta:20051010
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发表时间：
2005-02
期刊：
影响因子：
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通讯作者：
L. Grieco;S. Mascolo
中科院分区：
文献类型：
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作者：
L. Grieco;S. Mascolo
TCP拥塞控制基于一种加性增/乘性减（AIMD）探测模式，旨在调整TCP数据源的发送速率以匹配互联网随时间变化的可用带宽。最近提出了Westwood+ TCP来改进对经典TCP可用带宽的跟踪。它基于对可用带宽的端到端估计，这种估计是通过对确认分组流进行适当的计数和过滤而获得的。该估计用于在拥塞后自适应地减小拥塞窗口和慢启动阈值，因此可以说Westwood+ TCP用一种自适应减模式替代了经典的乘性减模式。作者提出了对加性增/自适应减（AIADD）模式的数学分析，以分析Westwood+ TCP提供的稳态吞吐量，并研究AIADD模式的协议内公平性以及AIADD和AIMD算法之间的协议间友好性。结果表明：（i）经典TCP和Westwood+ TCP都提供与1/√p成正比的吞吐量，其中p是分段丢弃概率，即它们彼此友好；（ii）Westwood+ TCP的吞吐量与1/√RTT成正比，其中RTT是往返时间，而Reno TCP的吞吐量与1/RTT成正比，即Westwood+ TCP提高了协议内公平性。最后，报告了Ns - 2模拟结果，以便在存在广泛的网络负载、丢失概率和往返时间的情况下验证数学模型。
TCP congestion control is based on an additive-increase/multiplicative-decrease (AIMD) probing paradigm aimed at adapting the sending rate of TCP data sources to match the Internet time-varying available bandwidth. Westwood+ TCP has been recently proposed to improve the tracking of available bandwidth of classic TCP. It is based on an end-to-end estimate of the available bandwidth, which is obtained by properly counting and filtering the stream of acknowledgement packets. The estimate is used to adaptively decrease the congestion window and slow start threshold after congestion so that it can be said that Westwood+ TCP substitutes the classic multiplicative decrease with an adaptive decrease paradigm. The authors propose a mathematical analysis of the additive-increase/adaptive-decrease (AIADD) paradigm to analyse the steady-state throughput provided by Westwood+ TCP and investigate the intra-protocol fairness of the AIADD paradigm and the inter-protocol friendliness between AIADD and AIMD algorithms. It is shown that (i) both classic and Westwood+ TCP provide a throughput that is proportional to 1/√p, where p is the segment drop probability, that is they are friendly to each other; and (ii) the throughput of Westwood+ TCP is proportional to 1/√RTT, where RTT is the round trip time, whereas the throughput of Reno TCP is proportional to 1/RTT, i.e. Westwood+ TCP improves the intra-protocol fairness. Finally, Ns-2 simulations are reported in order to validate the mathematical model in the presence of a wide range of network loads, loss probabilities and round trip times.