General solutions for MTTF and steady-state availability of NMR systems

Voting redundancy is a well-known technique to improve the fault tolerance of digital systems. Calculation of reliability and availability is a necessary part of every fault tolerant system design. Conventional techniques, including block diagram method, are unsuccessful when there is dependent failure, repair, or standby operation in the system. Use of Markov models also almost fails when system is composed of many elements or is repairable. However, the alternatives to reliability and availability, i.e. mean time to failure and steady state availability, respectively, are easily measurable using Markov graphs. In this paper, novel general form solutions for calculation of mean time to failure and steady-state availability of N-modular redundancy systems are presented.