Internet运输层协议设计.ppt

* * * * * * * * * * * REM Match rate clear buffer: It attempts to match user rates to network capacity while clearing buffers (or stabilize queues around a small target), regardless of the number of users. * * * * * * * * * * 。 * * * . ， * * * * * * * 检验时，结果为0 * * Hardin于1968年发表于Science的文章“公用的悲剧”(The Tragedy of the Commons)可以说是迄今为止描述资源两难问题的最有影响力的文章。在文中Hardin认为现代人过度使用资源的后果将是面临类似于使用同一牧场的牧 人所面临的悲剧：在公用牧场之中放牧的牧人尽可能地多饲养牲口以使自己的利益最大化，而这种行为导致的长期后果是牲口的总数超出了牧场所能容纳的极限，草资源很快枯竭。所有的牲口也因为没有足够的食物而面临饿死的境地。 Resource 包括链路的带宽，缓冲区的大小，处理器的处理速度 * 根据V. Jacobson在Sigcomm88上的记载 – 1986年10月第一次报告 – LBL（Lawrence Berkeley Lab）与UC Berkeley的 吞吐量从32Kbps降到了40bps – 自此 ? 拥塞控制（Congestion Control）成为研究热点 ? 一直持续到现在 * D.-M. Chiu and R. Jain, Analysis of the Increase and Decrease Algorithms for Congestion Avoidance in Computer Networks, Computer Networks and ISDN Systems, Vol. 17, 1989, pp. 1-14. This heterogeneity has resulted in a mismatch of arrival and serice rates in the intermediate nodes in the network casusing increased queuing and congestion 1.If the load is small, throughput generally keeps up with the load. As the laod increases, throughput increases. 3.After the load reaches the network capacity, throughput stops increasing. 4.If the load is increased any further .the queues start building ,potentially resulting in packers being dropped. Throughput may suddenly drop when the load increases beyond this point and the network is said to be congested. The response-time cure follows a similiar pattern. 1.At first the reponse time increased little with load. 2.When the queues start building up ,the reponse time increase linearly 3.Finally,as the queuses start overflowing,the reponse time increases drastically The point at which the packets start getting lost is called a cliff. due to the fact that the throughput falls off rapidly after this point. We use the term Knee to describe the point after which the increase in the throughput is small but when a significant increase in the response time res