Congestion controller design for TCP/AQM network systems

In this paper, we deal with congestion control of one bottleneck type for TCP/AQM network systems. We represent the dynamics of the congestion window size at source nodes and the queue length at the bottleneck link by discrete time systems in order to derive the parametrization of stabilizing controllers for the perturbation systems from equilibrium states. We prove the stability of the plant and give the Youla. parametrization of the stabilizing controllers. With this result, a control performance problem of the queue length at the bottleneck link is considered and H-2 optimization problem under a condition of the throughput at the bottleneck link is solved. We show that there exists a nonzero optimal queue length for this problem.