AQM controller design for IP routers supporting TCP flows based on pole placement

The simple pole placement technique in classical control theory is exploited to propose two kinds of controllers for active queue management (AQM) in IP routers: the proportional controller based on pole placement (P_PP controller) and the proportional-plus-integral controller based on pole placement (PI_PP controller). The damping ratio ξ and the undamped natural frequency ω_n are appropriately chosen such that the transient response of the system is satisfied and all the poles lie in the left-half s-plane to guarantee the stability of the system. The authors verify the effectiveness of the controllers via extensive simulations using OPNET, including the case of different time-varying round-trip times (RTTs) for different connections. Simulation results show that choosing appropriate values of ξ and ω_n can successfully satisfy the transient response of the system. The impact of different values of ξ and ω_n on the system performance is also investigated.