Design of a fuzzy controller for active queue management
As an effective mechanism acting on the intermediate nodes to support end-to-end congestion control, active queue management (AQM) takes a trade-off between link utilization and delay experienced by data packets. From the point of view of the control theory, it is rational to regard AQM as a typical regulating system. Although proportional integral (PI) controller for AQM outperforms traditional RED algorithm, the mismatches in simplified TCP flow model inevitably degrades the performance because the design of PI controller is heavily dependent of the accuracy of the plant, such as, for small buffer the system tends to perform poorly. In this paper, the fuzzy logic controller (FLC) for AQM is designed based on the fuzzy logical control. Its superiority is independent of the model of the plant, which is very suitable to the high variability and uncertainty networks. We present the guidelines and highlights to design the parameters of the FLC. We then compare its performance with the PI controller through simulations, and investigate the impact of the network configuration and operating parameters on the stability and responsibility. The results show that the FLC is rather robust against the noise and disturbance caused by the round-trip time, the link capacity, the number of the active flows and the non-responsive UDP flows, etc., which badly degrade the performance of the PI controller. The transient response and tracking capability of the FLC is superior to that of the PI controller, which is beneficial to achieve the goals of AQM scheme. (C) 2002 Published by Elsevier Science B.V.
congestion control active queue management (aqm) fuzzy logic control flow control