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For the purpose of designing more reliable networks, we extend the traditional reliability analysis from wired networks to wireless networks with imperfect components. Wireless network systems, such as wireless CORBA, inherit the unique handoff characteristic which leads to different communication structures with various components & links. Therefore, the traditional definition of two-terminal reliability is not applicable any more. We propose a new term, end-to-end expected instantaneous reliability, to integrate those different communication structures into one metric, which includes not only failure parameters but also service parameters. Nevertheless, it is still a monotonously decreasing function of time. The end-to-end expected instantaneous reliability, and its corresponding MTTF, are evaluated quantitatively in different wireless communication schemes. To observe the gain in overall reliability improvement, the reliability importance of imperfect components are also evaluated. The results show that the failure parameters of different components take different effects on MTTF & reliability importance. With different expected working time of a system, the focus of reliability improvement should change from one component to another in order to receive the highest reliability gain. Furthermore, the number of engaged components during a communication state is more critical than the number of system states. For simplicity, we assume that the wired & wireless communication links are perfect, and omit them in the reliability analysis. If these two are engaged into the proposed end-to-end expected instantaneous reliability, it can give a more detailed & complete reliability assessment of a wireless network system. Our quantitative measurements are conducted as an example with the assumption that the failure & service rate are constant; however, in practice, failure & service processes may follow other distributions. After all, our investigation provides an initial yet overall approach to measure the reliability of wireless networks. Although our analysis is conducted on wireless CORBA platforms, it is easily extensible to generic wireless network systems.
Date of Publication: June 2005