Nonlinear output feedback control of TCP/AQM networks

An output-feedback active queue management (AQM) scheme is presented for asymptotically stabilizing a class of TCP networks at a desired operating point. In order to design an AQM controller with only an output (queue size) measurement, a novel TCP window size observer is first proposed. Then, the control law is developed by applying an observer-based backstepping design technique. The amplitude limits on the control input is addressed, namely, packet dropping or marking ratio must fall between 0 and 1. An estimation of the domain of attractiveness is given with a Lyapunov level set.