A stable adaptive PI controller for AQM

Active queue management (AQM) mechanisms have been proposed to support end-to-end congestion control mechanisms of transmission control protocol (TCP) in TCP/IP networks. This paper introduces a new AQM based on a stable adaptive proportional-integral (SAPI) controller. SAPI adaptively adjusts the PI controller parameters based on estimated network parameters to improve the transient performance of a fixed-gain PI controller. We present the SAPI scheme in detail, and provide guidelines for the selection of its parameters. Through extensive simulations, we demonstrate that SAPI maintains satisfactory transient and steady-state performance independent of traffic loads, round trip propagation delay, and bottleneck capacity. The simulation results also demonstrate that SAPI is robust to non-responsive UDP traffic and HTTP traffic, and it is effective for networks with multiple bottlenecks. Comparison with other well-known AQM algorithms like PI, REM and Q-SAPI shows that SAPI achieves faster convergence to queue length target and smaller queue length jitter.