Calculating the system steady-state availability as a function of subsystem steady-state availability

The number of large complex applications requiring highly availability is increasing. A divide an conquer approach is used to construct these types of systems where subsystems are designed and built independently of one another. This practice is very common for large government projects such as the space shuttle, air traffic control system, and most complex military systems. Oftentimes, the manufacturer of the subsystem must show a certain level of steady-state availability has been achieved during the design/build phase of the subsystem. The overall builder of the complex system must integrate the subsystems together to produce the required functionality and also demonstrate that the system steady-state availability meets or exceeds a certain threshold. This estimation of system availability (A_sssys)is greatly simplified if the known subsystem availability values (A_sssubi) could be used to calculate system availability. Oftentimes, the subsystem manufacturer does not provide the subsystem failure rate and/or repair rate. Thus, the only the subsystem availability is on hand to assist in the calculation of system level availability. This paper presents a novel technique for calculating A_sssys as a function of n subsystem availabilities {A_sssub1, A_sssub2,...,A_sssubn}.