Active Queue Management (AQM) plays a very important role in congestion control of Transmission Control Protocol/InternetProtocol (TCP/IP) networks. This paper attempts to design an improved proportional-integralproportional-derivative (PI-PD) controller as an active queue manager for TCP routers. The proposed controller scheme controls present congestion reactively and also avoids the incipient congestion proactively. Fast response to the changing traffic is achieved by PD as it maintains the target queue length, high link utilization and low packet loss. We use ns simulation to demonstrate the practical advantage of using PI-PD controller over PI in managing queue utilization and delay. Index Terms--AQM, Network Congestion, PI-PD controller, Round-Trip Time (RTT) and TCP/IP.

Abstract-Active Queue Management (AQM) is a key congestion control mechanism for reducing the packet loss and improving the network utilization in TCP/IP networks. This paper discusses previously developed PI controller for AQM and proposed a new GA-based PI-PD controller. It is able to control present congestion reactively and also avoid the incipient congestion proactively. Fast response to the changing traffic is achieved by PD to maintain a desired queue length, high link utilization and low packet loss. The optimized tuning parameters are determined by selection of an Integral Square Time Error (ISTE) as an objective/fitness function. We use ns simulation to demonstrate the practical advantage of using GA-based PI-PD controller over PI in managing constant queue length.Index Terms-Congestion control, genetic algorithm (GA), integral square time error (ISTE), transmission control protocol (TCP).