Robust Stability Analysis of a class of Smith Predictor-based Congestion Control algorithms for Computer Networks

Congestion control is a fundamental building block in packet switching networks such as the Internet due to the sharing of communication resources. It has been shown that the plant dynamics is essentially made of an integrator plus time delay and that the a proportional controller plus a Smith predictor is a simple and effective controller. It has been also shown that the today running TCP congestion control can me modeled using a Smith predictor plus a proportional controller [8]. Due to the importance of this control structure in the field of data network congestion control, we analyze the robust stability of this controller in the face of delay uncertainties that in data networks are present due to queuing. In particular, by applying a simple geometric approach [3], we derive a bound on the proportional controller gain which is necessary and sufficient to guarantee stability given a bound on delay uncertainty.