CODESIGN-ORIENTED AND USER-PERCEIVED SERVICE AVAILABILITY MEASUREMENT FOR HARDWARE/SOFTWARE SYSTEM

Service availability is one of the customer-oriented attribute and defined as the attribute that the system can successfully satisfy the customers' requests. This paper discusses the stochastic service availability measurement for the computer-based system incorporating the concept of hardware/software codesign. We assume that the computer-based system consists of one hardware subsystem and one software subsystem and consider the situation where one customer intermittently uses the system which is operating and available anytime. From the viewpoint of a customer, occurrence of a system failure is recognized when either one of the following two events arises: A system failure occurs when the customer is using the system, or a usage request occurs when the system is down. We propose and derive three kinds of novel service-oriented system availability assessment measure. These are given as the functions of time and the number of software debuggings. The time-dependent behaviors of the system alternating between up and down states and the customer's request are described by a Markov process. Especially for the software subsystem, we incorporate the dynamic software reliability growth process, the upward tendency of difficulty in debugging, and the imperfect debugging environment into the model. Finally, we present several numerical examples of these measures for system service availability analysis.