Improving reliability of large software systems

Improving field performance of telecommunication systems is the key objective of both telecom suppliers and operators, as an increasing amount of business critical systems worldwide are relying on dependable telecommunication. Early defect detection improves field performance in terms of reduced field failure rates and reduced intrinsic downtime. This paper describes an integrated approach to improve early defect detection and thus field reliability of telecommunication switching systems. The assumptions at the start of the projects discussed in this paper are: Wide application of code inspections and thorough module testing must lead to a lower fault detection density in subsequent phases. At the same time criteria for selecting the most critical components for code reviews, code inspections and module test are provided in order to optimize efficiency. The primary goal is to identify critical components and to make failure predictions as early as possible during the life cycle and hence reduce managerial risk combined with too early or too late release of such a system to the field. During test release time prediction and field performance prediction are both based on tailored and superposed ENHPP reliability models. Experiences from projects of Alcatel's Switching and Routing Division are included to show practical impacts.