A Basic Requirement for the Policing Function in ATM Networks

Since ATM networks will have to cope with a wide range of applications, some of them producing highly variable tra c, congestion control plays a crucial role for such networks. In this context, the policing function has been introduced to monitor the relevant tra c characteristics of any connection, and several policing mechanisms have been proposed in the literature. They will be called pick-up policing mechanisms because either cells pass transparently through or else they are picked-up either discarded or tagged. In the present paper, we draw attention to the fact that cell clusters of a given connection can pass transparently at the multiplex rate through such a mechanism, giving rise to a bursty component entering the network. The impact of this bursty component on network performance is analyzed in a possible ATM network con guration, involving a switch based upon an output queueing architecture. It turns out that even slightly bursty tra c can induce severe degradation. Consequently, a suitable policing function must strictly avoid cell clusters entering the network.