Differential service in high-speed interconnection systems: an algorithm for prioritized access

The requirement to connect high-performance components of supercomputer systems has caused an increasing demand for connection-oriented, high-speed communication in a peer-to-peer environment. The importance of this type of communication is underscored by the advent of the high-performance parallel interface (HIPPI) standard, designed to support the commercial development of interconnection systems for this environment. For such interconnection systems, we present a connection management algorithm that supports priorities to provide preferential access for important classes of traffic, and that assures equitable access for all connections within the same priority class. At the same time, the algorithm utilizes the connection resources efficiently and assures low overhead at the nodes. We demonstrate the algorithm's applicability by outlining a centralized as well as a distributed implementation in an HIPPI-based interconnection system. Furthermore, we introduce an analytic priority model that can be used to evaluate an interconnection system's performance under the algorithm. Using this model, we analyze the efficacy of the nonpreemptive priority discipline and show the load/throughput behavior of a typical system.