The selective extra stage butterfly

Multistage interconnection networks (MINs) have been used extensively as communication networks in parallel machines due to their high bandwidth, low diameter and constant degree switches. The fault-tolerance of multistage networks can be improved by simply adding extra stages to the network. A novel method of attaching the extra stages in MINs so that they are used in the absence of faults but not necessarily by all messages is suggested. Messages can adaptively select the shortest path to their destination or use one of the longer paths going through the extra stages. Performance results for the method (obtained through simulation), using various traffic loads both in the presence and absence of faults, are presented.<>