Virtual Networks and Quality of Service for Cluster Computing

Exploiting clusters of workstations as a single computational resource is an attractive alternative to conventional multiprocessor technologies. However, the class of parallel applications that can benefit from clusters is restricted due to their relatively high latency and low throughput - consequences of conventional networking. LANs offer the best performance but also limit the scope for effective clustering to a single room or building. Another major difference remains: multiprocessors carl reasonably be programmed with the "error-free" assumption but applications cannot be run on distributed clusters without programming against the potential for remote faults. Emergent high speed switched networks such as ATM have the potential to reduce latency and increase bandwidth in the distributed scenario, and therefore extend the class of applications suitable for running on clusters. In addition, the virtual network capability of ATM removes some of the geographical constraints from clustering. But can A TM guarantee the type of application-level connection reliability which is taken for granted in multiprocessor environments.' This paper reviews the capabilities of modern high-speed networks as exemplified by ATM and their relevance to parallel and distributed systems. In particular it asks if Quality of Service (QoS) can benefit parallel programming on distributed platforms.