Robustness evaluation of disturbance observer-based active queue management supporting TCP flows

Implementation of active queue management (AQM) at routers can prevent serious congestion of transmission control protocol (TCP) flows. We previously proposed a disturbance observer (DOB)-based AQM controller to cope with modeling errors of network systems. However, the robustness of the controller against parameter fluctuations, e.g., the number of TCP connections and round-trip time (RTT) delay between terminal devices, has not been investigated sufficiently. This letter evaluates the robustness of the DOB-based AQM controller when the number of TCP connections and the RTT delay vary. Simulation results show that the DOB-based proportional-derivative (PD) controller provides better robustness than a classical proportional-integral-derivative (PID) controller.