Introduction

Rapid advances in microelectronics and networking technology have lead to penetration of computers and networks into almost every aspect of our life. When these system are used in critical applications, such as, nuclear power plant, avionics, process plants and automobiles etc., failure of these systems could result in loss of huge investment, effort, life and damage to environment. In such case, dependability analysis becomes an important tool for decision making at all stages of system life-cycle – design, development, operation and phaseout. In fact for systems concerned with safety of critical facilities such as nuclear plants, demonstration of dependability through analysis is a mandatory requirement before system can be deployed. Real-time systems refer to reactive computer-based systems, used in various control and on line processing applications requiring responses in real-time [1]. These computer systems are usually a part of a big system or network. Examples of such systems are fly-by-wire system of an aircraft, safety systems of a nuclear reactor, control system of vehicles (such as cars) and network routers to mention a few.