Necessary and sufficient condition-based stability analysis for Proportional-Integral TCP/AQM networks

This article addresses the stability analysis for TCP networks with proportional-integral (PI) AQM scheme based on a graphical necessary and sufficient stability criterion. A linearized second-order fluid-flow TCP model is adopted and the stability region is drawn in the proportional-integral gain space of PI AQM strategy. Then, we relate the network parameters with the PI controller parameters, and the boundaries relations between these two kinds of parameters are obtained, which do not have any conservatism and exhibit how the PI parameters affect the stability of networks. Finally, different stability conditions are compared using both Matlab and NS-2 simulations to show the superiority of our necessary and sufficient condition-based stability analysis over the Lyapunov sufficient condition-based results.