Credit-Flow-Controlled ATM versus Wormhole Routing

ATM has been adopted as the main high speed technology in both wide and local area networks. When ATM is combined with credits −the flow control mechanism that is particularly suitable for local data communication− it becomes appropriate for multiprocessor interconnection networks as well. Actually, credit-flowcontrolled ATM has similarities with wormhole routing, one of the most popular architectures for MP networks: they both use credits and fixed size cells/flits, and their hardware complexity is comparable. In this paper, we show that ATM with credits performs better than wormhole routing, because ATM uses lanes more efficiently: ATM provides high throughput and low latency with much less buffer space than that required by wormhole routing; also, ATM demonstrates little sensitivity to bursty traffic, and, unlike wormhole, it is fair in terms of latency in hot-spot configurations. Our simulation uses detailed and realistic switch models, which operate at clock-cycle granularity and track closely ‘‘ATLAS I’’, a single-chip ATM switch under development.