Design of TCP traffic controllers for AQM routers based on phase margin specification

We propose proportional and proportional-integral (PI) controllers for active queue management (AQM) in the Internet. Classical control theory is applied in the design to meet the frequency domain specification - phase margin. The user can specify the phase margin to achieve good performance of AQM. The PI controller can regulate the source window size based on the knowledge of the queue size to clamp the steady state value of queue size to the specified reference queue size. Our controllers are verified by OPNET simulation and our PI controller is shown to outperform RED significantly.