Sharing Memory in Banyan-Based ATM Switches

Debashis Basak Fore Systems Warrendale, PA, USA Abhijit K. Choudhury Bell Laboratories Holmdel, NJ, USA Ellen L. Hahne Bell Laboratories Holmdel, NJ, USA Abstract We study a multistage ATM switch in which shared-memory switching elements are arranged in a banyan topology. By \shared-memory", we mean that each switching element uses output queueing and shares its local cell bu er memory among all its output ports. We apply a bu er management technique called Delayed Pushout that was originally designed for multistage ATM switches with hierarchical topologies. Delayed Pushout combines a pushout mechanism, for sharing memory e ciently among queues within the same switching element, and a backpressure mechanism, for sharing memory across switch stages. The backpressure component has a threshold to restrict the amount of sharing between stages. A synergy emerges when pushout, backpressure, and this threshold are all employed together. Using a computer simulation of the switch under bursty tra c, we study Delayed Pushout as well as several simpler pushout and backpressure schemes under a variety of tra c conditions. Of the ve schemes we simulate, Delayed Pushout is the only one that performs well under all load conditions.