Strong Performance Guarantees for Asynchronous Crossbar Schedulers

Abstract

Crossbar-based switches are commonly used to implement routers with throughputs up to about 1 Tb/s. The advent of crossbar scheduling algorithms that provide strong performance guarantees now makes it possible to engineer systems that perform well, even under extreme traffic conditions. Up to now, such performance guarantees have only been developed for crossbars that switch cells rather than variable length packets. Cell-based schedulers may fail to deliver the expected performance guarantees when used in routers that forward packets of variable length. We show how to obtain performance guarantees for asynchronous crossbars that are directly comparable to the performance guarantees previously available only for synchronous, cell-based crossbars. In particular we define derivatives of the Group by Virtual Output Queue (GVOQ) scheduler of Chuang et. al. and the Least Occupied Output First Scheduler of Krishna et. al. and show that both can provide strong performance guarantees in systems with speedups ≥2. We also show that there are schedulers for segment-based crossbars, (introduced recently by Katevenis and Passas) that can deliver strong performance guarantees with small buffer requirements and no bandwidth fragmentation.