An approach to the controller design of AQM routers supporting TCP flows

In this paper, we aim at developing an H ∞ approach to the design of an active queue management (AQM) based congestion controller for the Internet Protocol. In the approach, the available link bandwidth is modelled as a nominal constant value, which is known to the link, plus a time-variant disturbance, which is unknown. The design objective is to minimize the ratio, denoted as γ , between the norm of the perturbed queue length and that of the disturbance. An important feature of the approach is that the system performances, including the disturbance rejection ratio γ and hence the stability of closed-loop systems, are guaranteed for all round-trip times that are less than a known value. The design is described by matrix inequalities, which can be efficiently solved by the linear matrix inequality toolbox in Matlab.