A Generic Fault Tolerant Architecture For Real Time Dependable Systems

The design of computer systems to be embedded in critical real-time applications is a complex task. Such systems must not only guarantee to meet hard real-time deadlines imposed by their physical environment, they must guarantee to do so dependably, despite both physical faults (in hardware) and design faults (in hardware or software). A fault-tolerance approach is mandatory for these guarantees to be commensurate with the safety and reliability requirements of many life- and mission-critical applications. This book explains the motivations and the results of a collaborative project', whose objective was to significantly decrease the lifecycle costs of such fault tolerant systems. The end-user companies participating in this project already deploy fault-tolerant systems in critical railway, space and nuclear-propulsion applications. However, these are proprietary systems whose architectures have been tailored to meet domain-specific requirements. This has led to very costly, inflexible, and often hardware-intensive solutions that, by the time they are developed, validated and certified for use in the field, can already be out-of-date in terms of their underlying hardware and software technology.

Delta-4 is a 5-nation, 13-partner project that has been investigating the achievement of dependability in open distributed systems, including real-time systems. This book describes the design and validation of the distributed fault-tolerant architecture developed within this project. The key features of the Delta-4 architecture are: (a) a distributed object-oriented application support environment; (b) built-in support for user-transparent fault tolerance; (c) use of multicast or group communication protocols; and (d) use of standard off the-shelf processors and standard local area network technology with minimum specialized hardware. The book is organized as follows: The first 3 chapters give an overview of the architecture's objectives and of the architecture itself, and compare the proposed solutions with other approaches. Chapters 4 to 12 give a more detailed insight into the Delta-4 architectural concepts. Chapters 4 and 5 are devoted to providing a firm set of general concepts and terminology regarding dependable and real-time computing. Chapter 6 is centred on fault-tolerance techniques based on distribution. The description of the architecture itself commences with a description of the Delta-4 application support environment (Deltase) in chapter 7. Two variants of the architecture - the Delta-4 Open System Architecture (OSA) and the Delta-4 Extra Performance Architecture (XPA) - are described respectively in chapters 8 and 9. Both variants of the architecture have a common underlying basis for dependable multicasting, i. e.

As software systems become ubiquitous, the issues of dependability become more and more crucial. This state-of-the-art survey contains 18 expanded and peer-reviewed papers based on the carefully selected contributions to the Workshop on Architecting Dependable Systems (WADS 2006) organized at the 2006 International Conference on Dependable Systems and Networks (DSN 2006), held in Philadelphia, PA, USA, in June 2006.

As software systems become more and more ubiquitous, the issues of dependability become more and more critical. Given that solutions to these issues must be planned at the beginning of the design process, it is appropriate that these issues be addressed at the architectural level. This book is inspired by the ICSE 2002 Workshop on Architecting Dependable Systems; it is devoted to current topics relevant for improving the state of the art for architecting dependability. Some of the 13 peer-reviewed papers presented were initially presented at the workshop, others were invited in order to achieve competent and complete coverage of all relevant aspects. The papers are organized in topical sections on - architectures for dependability - fault tolerance in software architectures - dependability analysis in software architectures - industrial experience.

As software systems become increasingly ubiquitous, issues of dependability become ever more crucial. Given that solutions to these issues must be considered from the very beginning of the design process, it is clear that dependability and security have to be addressed at the architectural level. This book, as well as its six predecessors, was born of an effort to bring together the research communities of software architectures, dependability, and security. This state-of-the-art survey contains expanded, peer-reviewed papers based on selected contributions from the Workshop on Architecting Dependable Systems (WADS 2009), held at the International Conference on Dependable Systems and Networks (DSN 2009), as well as a number of invited papers written by renowned experts in the area. The 13 papers are organized in topical sections on: mobile and ubiquitous systems, architecting systems, fault management, and experience and vision.

Foundations of Dependable Computing: Models and Frameworks for Dependable Systems presents two comprehensive frameworks for reasoning about system dependability, thereby establishing a context for understanding the roles played by specific approaches presented in this book's two companion volumes. It then explores the range of models and analysis methods necessary to design, validate and analyze dependable systems. A companion to this book (published by Kluwer), subtitled Paradigms for Dependable Applications, presents a variety of specific approaches to achieving dependability at the application level. Driven by the higher level fault models of Models and Frameworks for Dependable Systems, and built on the lower level abstractions implemented in a third companion book subtitled System Implementation, these approaches demonstrate how dependability may be tuned to the requirements of an application, the fault environment, and the characteristics of the target platform. Three classes of paradigms are considered: protocol-based paradigms for distributed applications, algorithm-based paradigms for parallel applications, and approaches to exploiting application semantics in embedded real-time control systems. Another companion book (published by Kluwer) subtitled System Implementation, explores the system infrastructure needed to support the various paradigms of Paradigms for Dependable Applications. Approaches to implementing support mechanisms and to incorporating additional appropriate levels of fault detection and fault tolerance at the processor, network, and operating system level are presented. A primary concern at these levels is balancing cost and performance against coverage and overall dependability. As these chapters demonstrate, low overhead, practical solutions are attainable and not necessarily incompatible with performance considerations. The section on innovative compiler support, in particular, demonstrates how the benefits of application specificity may be obtained while reducing hardware cost and run-time overhead.

When architecting dependable systems, fault tolerance is required to improve the overall system robustness. Many studies have been proposed, but the solutions are usually commissioned late during the design and implementation phases of the software life-cycle (e.g., Java and Windows NT exception handling), thus reducing the error recovery effectiveness. Since the system design typically models only normal behaviors of the system while ignoring exceptional ones, the generated system implementation is unable to handle abnormal events. Consequently, the system may fail in unexpected ways due to some faults. Researchers have advocated that fault tolerance management during the entire life-cycle improves the overall system robustness and that different classes of exceptions must be identified for each identified phase of software development, depending on the abstraction level of the software system being modeled. This book builds on this trend and investigates how fault tolerance mechanisms can be used when engineering a software system. New problems will arise, new models are needed at different abstraction levels, methodologies for mode driven engineering of such systems must be defined, new technologies are required, and new validation and verification environments are necessary.

As software systems become ubiquitous, the issues of dependability become more and more critical. Given that solutions to these issues must be taken into account from the very beginning of the design process, it is appropriate that dependability is addressed at the architectural level. This book results from an effort to bring together the research communities of software architectures and dependability. Inspired by the ICSE 2003 Workshop on Software Architectures for Dependable Systems, the book focuses on topics relevant to improving the state of the art in architecting dependable systems. The 15 thoroughly reviewed papers originate partly from the workshop; others were solicited in order to achieve complete coverage of all relevant aspects. The papers are organized into topical sections on architectures for dependability, fault-tolerance in software architectures, dependability analysis in software architectures, and industrial experience.