A Reliability Model for Various Switch Designs in Hybrid Redundancy

Various switch designs for the hybrid redundancy scheme are studied. A reliability model for the switch is developed and the switch is shown to be a significant factor in the overall system reliability. A hybrid redundancy scheme with a triple-modular redundant (TMR) core may have a maximum attainable reliability for only a spare or two. Adding spares complicates the switch enough to cause the system reliability to actually decrease. There exist conditions under which the switch becomes so complex that simple TMR would yield a better solution. Models for fault-tolerant switch designs are also obtained. Finally, various designs are compared via their reliability models.