An optimal PID controller for AQM supporting TCP with ECN

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 routers. Comparing with RED algorithm, although the PI (Proportional-Integral) or PID(Proportional-Integral-Differential) controller for AQM improves the stability, It is very difficulty in selecting a group of optimal parameters for these controller to guarantee the transient performance. Moreover, the case is much worse especially when the networks parameters are time-varying, i.e. time-varying numbers of the users, uncertain link utilization and heterogeneous delays with different users. In this paper, we use numerical optimization to propose an optimal PID (OPID) controller of AQM for TCP with ECN to improve the robustness and transient performance of the PID controller. The simulation results show that the integrated performance of the controller is obviously superior to those of RED, PI and PID controller.