Control of ATM networks: fragility and robustness issues

Recently, communication networks, and ATM (asynchronous transfer mode) in particular, received a growing attention in the control community. Several problems have been studied from the control system point of view, including traffic identification with optimization algorithms, adaptive bandwidth estimation, decentralized and robust flow control. In this paper, we continue this line of research studying the problem of robustly controlling the information flow in a single communication channel of an ATM network. We consider a simplified model already existing in literature in which the main features are the existence of a buffer representing the congestion and a delay time in the communication between the source and the destination nodes. We show that searching for optimal control policies are fragile if the delay time is allowed to vary (possibly of an arbitrarily small amount) with respect to the nominal value on which the design is based. Subsequently, we suggest a classical design procedure which is robust with respect to variations in the delay which does not exceed a prescribed upper bound.