On the relative behavior of source and distributed routing in NOWs using Up*/Down* routing schemes

Networks of workstations (NOWs) are arranged as a switch-based network with irregular topology, which makes routing and deadlock avoidance quite complicated. Current proposals use the up*/down* routing algorithm to remove cyclic dependencies between channels and avoid deadlock. Recently, a simple and effective methodology to compute up*/down* routing tables has been proposed by us. The resulting up*/down* routing scheme increases the number of alternative paths between every pair of switches and allows most messages to follow minimal paths. Also, up*/down* routing is suitable to be implemented using source or distributed routing. Source routing provides a safer and lower cost implementation of up*/down* routing than that provided by distributed routing. However distributed routing may benefit from routing messages through alternative paths to reach their destination. In this paper we evaluate the performance of up*/down* routing when using two methodologies to compute routing tables, and when both source and distributed routing are used. Evaluation results show that it is not worth to implement up*/down* routing in a distributed way in a NOW environment, since its performance is very close to that achieved by implementing it with source routing when a traffic-balancing algorithm is used. Moreover it is shown that a greater improvement in performance can be achieved by modifying the method to compute up*/down* routing tables when source routing is used.