H2Performance Limitation of Congestion Controller for TCP/AQM Network Systems

In this paper, we deal with congestion control of one bottleneck type for TCP/AQM network systems and investigate the H
2
control performance limitation. To this end, we first represent the dynamics of the congestion window size at source nodes and the queue length at the bottleneck link by a discrete time model. We then prove the stability of the plant and provide the Youla parametrization of all stabilizing controllers. With this parametrization, we consider an H
2
optimization problem of the queue length at the bottleneck link. We derive an explicit form of the best achievable H
2
norm and discuss the control performance limitation with respect to the ratio of the transmission time of the packets from source nodes to the link and the round trip time.