The Research On The Flow Control Of ABR Service Based On ATM Networks

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.