【作者】 谢利超；

【导师】 刘宏立；

【作者基本信息】 湖南大学 ， 电路与系统， 2004， 硕士

【摘要】 ATM网络的多业务复用特性及其对QoS的承诺，使得其流量和拥塞控制变得非常复杂。总的来说，ATM网络的流量控制包括开环控制机制和闭环控制机制。开环机制包括连接允许控制，使用参数控制，流量成形等，这些开环机制能够有效地用于CBR，VBR等业务。对于ABR业务，ATM论坛最终确定其流量及拥塞控制是一种基于速率的闭环反馈控制机制，这使得ABR成为五种业务中唯一一种速率可控的业务。这种基于速率的机制和Internet中使用的窗口机制的显著区别在于，前者向源端反馈的是直接的速率信息，而后者反馈的则是窗口的大小。ABR业务的流量控制是本文讨论的主题。 现有的ABR业务流量控制算法，都存在一些问题和需要改进的地方。本文的第三章，针对二进制算法收敛慢和缓存队列长度大幅振荡的缺点，提出一种参数自适应算法。仿真证明，这种算法能够快速解除拥塞并能有效地减小对缓存的依赖。这也说明，根据网络的拥塞状态动态地选择参数可以使得算法的性能得到优化。然后，利用描述函数的方法分析了二进制算法的稳定性，给出了二进制算法绝对稳定的一个充分条件，并就如何改善算法的稳定性提出了一些有用的建议。 第四章讨论了ABR业务流量控制算法面临的问题，包括时延问题，公平性与稳定性问题，多播，多业务背景及TCP over ABR时的流量与拥塞控制等。其中重点讨论了时延问题，并提出了一种可以减小控制时延的算法，以减小由时延引起的控制滞后效应。最后是对本文的总结，其中主要论述了本文提出的两种算法的不足之处和进一步改进的方向。 本文的讨论对ABR业务流量控制算法的优化和高速ATM交换机的设计具有实际的指导意义。更多还原

【Abstract】 The characteristics of multiple service multiplex of ATM networks as well as its promise to QoS, lead to the complexity of its flow and congestion control. Generally speaking, flow control of ATM networks consists of open-looped and close-looped mechanism. Open-looped mechanism includes connection admission control, using parameter control, traffic shaping, and so on. These open-looped mechanisms can be used effectively for CBR and VBR services. Flow control of ABR service is identified by ATM forum as a rate-based close-looped feedback mechanism, which makes ABR service the only one whose rate can be controlled among the five services. This rate-based mechanism is very different from the window-based one used in Internet: in the former one rate is fed back, while in the latter feedback is window size. Flow control of ABR service is the main concert of this thesis.There exist several problems and places to be improved in the existing algorithm. In chapter 3, an algorithm with adaptive parameter is proposed to overcome the defects of converging slowly and cache queue oscillating with large extent in binary algorithm. Simulation indicates that this algorithm can eliminate congestion fast and effectively abate the dependence on cache. It demonstrates that choosing parameter reasonably according to network state can optimize the performance of algorithm. Then description function is used to analyze the stability of binary algorithm. A full term of absolute stability is brought forward and some useful suggestions about how to improve stability are presented.Chapter 4 discusses problems that algorithm are confronted with, including delay, fairness and stability, multicast, TCP over ABR etc.Among these problems, the issue of delay is discussed with emphasis and an algorithm that can decrease the delay is proposed to alleviate the impact of control lag resulted from control delay. Finally, the conclusion is drawn on the defect and direction for the improvement of the two algorithms proposed in this article.The discussion in this thesis has practical guiding significance for the optimization of ABR flow control algorithm and the design of high-speed ATM switch.更多还原