Report Number: CSL-TR-73-56
Institution: Stanford University, Computer Systems Laboratory
Title: Reliability modeling of NMR networks
Author: Abraham, Jacob
Author: Siewiorek, Daniel P.
Date: 1973
Abstract: A survey of the literature in the area of redundant system reliability modeling is presented with special emphasis on Triple Modular Redundancy (TMR). Areas where the classical method of TMR reliability prediction may prove inadequate are identified, like the interdependence of fault patterns at points of network fan-in and fan-out. This is especially true if the assumption of highly reliable subsystems, which is frequently made by the modeling techniques, is dropped. It is also not clear if the methods give an upper or a lower bound to the reliability. As a solution, a method of partitioning an arbitrary network into cells so that the faults in a cell are independent of faults in other cells is proposed. An algorithm is then given to calculate a tight lower bound on the reliability of any such cell, by considering only the structure of the interconnections within the cells. The value of reliability found is exact if TMR is assumed to be a coherent system. An approximation to the algorithm is also described; this can be used to find a lower bound to the reliability without extensive calculation. Modifications to the algorithm to improve it and to take care of special cases are given. Finally, the algorithm is extended to N-Modular Redundant (NMR) networks.