MP-Start基于带宽测量的分阶段TCP慢启动机制.doc

MP-Start:基于带宽测量的分阶段TCP慢启动机制
邓晓衡1,2, 陈志刚1, 张连明1, 曾碧卿1
(1. 中南大学信息科学与工程学院,湖南长沙 410083;2. 国防科学技术大学计算机学院, 湖南长沙 410073)
摘要:针对TCP慢启动机制门限值参数难于设置以及突发流量引起网络抖动的问题,提出了一种基于带宽测量及分阶段实施的TCP慢启动改进算法。该方法利用在线网络带宽测量技术,探测出网络带宽,从而根据网络状态的动态变化实现慢启动门限值的动态更新,同时,采用分阶段方法调节拥塞窗口的增加,在拥塞窗口大于门限值一半时,拥塞窗口增幅为门限值和拥塞窗口差值的一半,逐步迭代逼近门限值,使拥塞窗口在连接启动和过渡到拥塞避免阶段增加幅度比较小,而在中间阶段窗口增加幅度比较大。有效避免了多个分组丢失现象的发生,实现了连接的平滑接入和过渡到拥塞避免阶段;为提高改进算法的性能,设计了一种灵活的参数化的模型和自适应参数设置方案。大量仿真实验结果表明MP-Start能在多种网络环境下有效改善网络性能,如降低分组丢弃数、减少数据传输时间、降低共享链路分组队列长度、保持连接的传输平滑性。
关键词:TCP;拥塞控制;慢启动;测量;分阶段
中图分类号:TP393 文献标识码:B 文章编号:1000-436X(2007)11-0092-11
MP-Start: bandwidth measurement based and
phase-divided TCP slow start mechanism
DENG Xiao-heng1,2, CHEN Zhi-gang1, ZHANG Lian-ming1, ZENG Bi-qing1
( of Information Science and Technology, Central South University,Changsha 410083,China;
puter, National University of Defense Technology, Changsha 410073,China)
Abstract: To set appropriate threshold value(ssthresh) of slow start and work oscillation caused by bursty traffic, a new measurement-based and phase-divided slow start mechanism was proposed, which was called MP-Start. MP-Start employs effective online bandwidth measurement technology to update the ssthresh with appropriate value dynamically, and adjusts the increment of congestion window(cwnd) in different phase of the startup. MP-Start increases cwnd with half of the difference between ssthesh and cwnd, iterates and gradually closes up ssthresh, of which the increment is small at start phase and end phase paratively large at the middle phase of the startup of a connection, the largest increment is no more than one quarter of ssthresh. In order to improve the performance of this algorithm, a flexible parameterized model and an adaptive parameter setting solution are designed. And series simulation experiments indicate that MP-Start significantly decreases dropped packets, data transforming time, packet queue length of shared link, and also work performance and smoothness o