Optimization models for complex recovery block schemes

Abstract In this paper we consider three complex recovery block schemes: (1) nested recovery block; (2) modified recovery block; and (3) nested consensus recovery block. For all the three models: (1) we derive simple expressions for calculating the system reliability; (2) we investigate how to arrange the versions in a nested recovery block and in a nested consensus recovery block; and (3) we develop optimization models where the objective is to optimize the reliability satisfying a budget constraint. The paper also includes efficient branch and bound procedures to solve the optimization problems. Two numerical example problems are solved to illustrate the branch and bound technique. Scope and purposes Software has become an integral part of many systems. For systems such as air traffic control, space shuttle, fighter aircraft and automated-guided missiles, it is usually the reliability of computer software that has the most single significant impact on the performance. Virtually, all major military systems are dependent on the correct operation of defense systems’ software. For systems such as air traffic control, fighter aircraft and automated guided missiles, 80% of the life cycle cost is spent on the software. Traditionally, reliability of any hardware and software is improved by introducing redundancy. However, redundant components require additional resources. Therefore, the redundancy level needed to achieve specified reliability must be carefully determined. The main purpose of this paper is to develop reliability prediction techniques and optimization models for important fault-tolerant software such as nested recovery block, modified recovery block and nested consensus recovery block. The methods have significant use in selection of programs in COTS (commercial-off-the-shelf) environment.