Design a PID Controller for Active Queue Management in NS2

As an enhancement mechanism for the end-to-end congestion control, active queue management (AQM) can keep smaller queuing delay and higher throughput by purposefully dropping the packets at the intermediate nodes. Comparing with RED algorithm, although the PI (proportional-integral) controller for AQM designed by C. Hollot improves the stability, the transient performance of the PI controller is not perfect, such as the regulating time is too long. In order to overcome this drawback, in this paper, the PID (proportional-integral-differential) controller is proposed to speed up the responsiveness of AQM system. The controller parameters are tuned based on the determined gain and phase margins. The simulation results show that the integrated performance of the PID controller is obviously superior to that of the PI controller.