An improved active queue management scheme using a two-degree-of-freedom feedback controller

In this paper a Two-Degree-Of-Freedom (2DOF) feedback system for Active Queue Management (AQM) in a communication network is presented. The principal advantage of this new design methodology is that robust end-to-end congestion performance is feasible. By utilising fundamental Quantitative Feedback Theory (QFT) results, a pre-filter is added to a conventional AQM control framework thus introducing an independent parameter which supports tracking improvements in uncertain network conditions. A novel incorporation of tracking performance requirements into the pre-filter design is described. A feature of the technique is that the uncertain phase information and time-delay that are inherent to the system dynamics are fully addressed in the design equations, resulting in a minimally conservative over-design. The digital implementation of the design is discussed and simulation results using the ns2 simulator are provided.