Unicast Wormhole Message Routing in Irregular Computer Networks

In this paper we consider the problem of deadlockfree unicast wormhole routing in computer networks with irregular topologies, such as Networks of Workstations (NOWs). The proposed algorithm consists of two stages. At the first stage, we minimize the set of turns in the network graph which should be prohibited for deadlock prevention by breaking all cycles in the channel dependency graph. Proposed approach guarantees that the constructed set of prohibited turns is irreducible and the fraction of the prohibited turns does not exceed 1/3 for any network topology. At the second stage, routing tables are constructed based on the set of prohibited turns that minimize average message path lengths and delivery times in a decentralized manner. Given N, the number of nodes, and d the maximal number of ports in routers, the complexity of the proposed algorithm does not exceed O(Nd). This algorithm is invoked when a change in the topology of the network is detected, which we assume is infrequent. We also present results of simulation experiments of average latency for uniform, transpose and local traffic patterns, saturation points and scalability. These results illustrate the performance and advantages of the proposed approach as compared with the existing up/down techniques [1,2].