Adaptive message routing in a class of fault-tolerant multistage interconnection networks

Abstract

Multistage interconnection networks (MINs) are often used to provide interconnections in multiprocessor systems. A unique path MIN usually has lower hardware complexity and simple control algorithm, but it lacks fault-tolerance. This paper proposes a class of multipath MINs, which are obtained by adding auxiliary links at the final stage in quad tree networks so that they can provide more paths between each source-destination pair, and presents their routing algorithm which is both destination tag based and adaptive. Starting with the routing tag for the minimum path between a given source-destination pair, the routing algorithm uses a set of rules to select switches and modify routing tag. In addition to trying the auxiliary link when both of the output links are unavailable, the second output link is tried before the auxiliary link when the first output link is unavailable. This feature distinguishes the proposed routing algorithm from the one for quad tree networks and makes better use of all the possible paths between the given source-destination pair. At the end of this paper, an index of performance called capacity is introduced to compare different kinds of MINs. Comparison shows that the proposed MINs have better capacity than quad tree networks.