Reliability enhancement by time and space redundancy in multistage interconnection networks

The authors present the dynamic full access (DFA) properties of fault tolerant multistage interconnection networks (MINs) which have multiple connections to the inputs and outputs, and thus potentially no hardcore. When full access is lost due to multiple faults, but DFA exists, multiple pass routing could be utilized to achieve graceful degradation. Some efficiency conditions for the existence of DFA in a broad class of fault tolerant MINs are derived. The reliability of four multiple path MINs under DFA is studied. The metrics used are the probability of existence of DFA and the mean time to failure. One particular network (the MD-Omega), which uses a minimum amount of hardware redundancy to provide two connections from each source to the MIN and to each destination from the MIN, shows the most gain in reliability when time redundancy is used. The MD-Omega network has a 2×2 switch as its basic element, but is almost as reliable as another fault tolerant MIN, the ASEN, which uses a 3×3 element, when multiple pass routing is used