The opportunity to improve software RAMS

Abstract

Software is at the heart of many safety critical systems in the railway sector. The development of systems that include software modules requires the correct evaluation of software RAMS (Reliability, Availability, Maintainability and Safety) in order to obtain the correct value of the overall system RAMS. In order to obtain appropriate software, the standards propose the performance of a set of activities in the different phases of software development, as well as tasks to control their correct accomplishment. They ensure the developed software is of adequate quality. However, it is necessary to go further and try to obtain a quantitative measure of RAMS for each software module as is usually done in hardware development. There are several techniques for the assurance of software reliability and safety that have been in use for years and must be analysed to find their real potential. These techniques are: reliability growth models, artificial intelligence techniques, Markov chains, Software Fault Tree Analysis and Software Failure Mode and Effect Analysis, among others. This paper is an update of the previous one presented at the COMPRAIL XI Conference. Two circumstances emphasize the strategic time the railway sector is undergoing and the opportunity to adopt the most promising software techniques in order to improve reliability and safety. (1) The development of high-performance railway networks that interconnect different countries and the liberalization and opening of the national markets demand new European global agreements. In this regard, the European Railway Agency has asked its Safety Unit to develop the new Common Safety Methods (CSM) and Common Safety Targets (CST) to be used in all European countries. (2) The IEC 61508 standard (from which some parts of CENELEC EN 50128 are derived) is now under Advanced Train Control Systems 91 www.witpress.com, ISSN 1755-8336 (on-line) WIT Transactions on State of the Art in Science and Engineering, Vol 46, © 2010 WIT Press doi:10.2495/978-1-84564/ 494 9 11 revision, with the primary aim of ensuring the safety of the developed software by hardening the requirements and promoting the use of the most promising techniques. Moreover, the CENELEC EN 50128 standard is also under revision.