Design of feedback controller for TCP/AQM networks

In this paper, we propose a novel proportional-differential-type feedback controller called Novel-PD as new active queue management (AQM) to regulate the queue length with small oscillation. It measures the current queue length and uses the current queue length and differential error signals to adjust packet drop probability dynamically. We provide control theoretic analysis of system stability and develop guidelines to select control gain parameters of Novel-PD. The design of Novel-PD for TCP/AQM system is given in details. NS2 is used for conducting extensive simulation. The proposed controller is compared with random early detection (RED), random exponential marking (REM), proportional integrator (PI) and proportional derivative (PD) controller. Result shows that, Novel-PD is stable and achieves faster response in dynamic environments where number of TCP connections, bottleneck capacity, round trip time (RTT) keeps changing. The proposed controller outperforms other AQM schemes.