On Control Gain Selection in PI-RED

Abstract

Active queue management (AQM) is an effective method used in Internet routers to enhance congestion control, and to achieve a trade off between link utilization and delay. The de facto standard, the random early detection (RED) AQM scheme, and most of its variants use queue length as a congestion indicator to trigger packet dropping. Random early detection (RED) is a widely studied active queue management (AQM) scheme implemented in routers for Internet congestion control. Although certain stability conditions for various RED controllers are discussed, no efficient method for dynamically adapting control gains or result on control gain optimization has been proposed so far. Therefore based on control theory, this paper proposes proportional and integral RED (PI-RED) algorithm, that not only considers the average queue length at the current time slot, but also takes into consideration the past average queue lengths within a round trip time. We provide guidelines for the selection of the feedback gains (the proportional parameter and the integral parameter) for TCP/RED system to stabilize the dynamics, make the congested queue converge at a certain target and hence to improve network performance. Simulations demonstrate that indeed satisfactory performance can be achieved if the control gains are selected based on the guidelines. Based on the stability condition and control gains selection method, extensive simulations with ns2 demonstrate that indeed satisfactory performance can be achieved in terms of robustness, drop probability and stability if the control gains are selected based on the guidelines