Replication and fault-tolerance in real-time systems

PhD ThesisThe increased availability of sophisticated computer hardware and the corresponding decrease in its cost has led to a widespread growth in the use of computer systems for realtime plant and process control applications. Such applications typically place very high demands upon computer control systems and the development of appropriate control software for these application areas can present a number of problems not normally encountered in other applications. First of all, real-time applications must be correct in the time domain as well as the value domain: returning results which are not only correct but also delivered on time. Further, since the potential for catastrophic failures can be high in a process or plant control environment, many real-time applications also have to meet high reliability requirements. These requirements will typically be met by means of a combination of fault avoidance and fault tolerance techniques. This thesis is intended to address some of the problems encountered in the provision of fault tolerance in real-time applications programs. Specifically,it considers the use of replication to ensure the availability of services in real-time systems. In a real-time environment, providing support for replicated services can introduce a number of problems. In particular, the scope for non-deterministic behaviour in real-time applications can be quite large and this can lead to difficultiesin maintainingconsistent internal states across the members of a replica group. To tackle this problem, a model is proposed for fault tolerant real-time objects which not only allows such objects to perform application specific recovery operations and real-time processing activities such as event handling, but which also allows objects to be replicated. The architectural support required for such replicated objects is also discussed and, to conclude, the run-time overheads associated with the use of such replicated services are considered.The Science and Engineering Research Council

Creation of a Support Software for the Development of a System for Sending and Visualizing FBG Sensor Data for Aerospace Application

Optical fiber-based sensors have rapidly increased their application fields across multiple engineering sectors. Their physical characteristics, including low weight, electrical passivity, immunity to electromagnetic disturbances, and high sensitivity, make them highly suitable for aerospace applications. A flying test bench was recently developed at the Politecnico di Torino to evaluate the performance of optical sensors applied to an aircraft model. To allows their fruition in near real-time, it was necessary to develop a pipeline of software capable of transmitting, saving, and displaying them on the ground. To carry out in-depth tests on their reliability it is necessary to carry out more tests with different sensors and configurations. However, doing flight tests for the sole purpose of testing the data acquisition system is too expensive and impractical. Therefore, it was developed an emulator software that can generate data like that obtained from the real system, saving time and resources. Thanks to it, it is now possible to exploit the complete test bench on the aircraft for the final verification campaign only. The results are therefore very positive and demonstrate the potential of the emulator also for the most recent applications

Wireless reconfigurability of fault-tolerant processing systems

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 55-56).This thesis examines the use of wireless data buses for communication in a real-time computer system designed for applications with high reliability requirements. This work is based on the Draper Laboratory Software Based Redundancy Management System (SBRMS), which is a fault-tolerant system architecture that uses data exchange and voting via Ethernet connections between redundant hardware components to detect and recover from faults. For this thesis, a triplex redundant system was developed that utilized the key features from the SBRMS design, including commercial-off-the-shelf hardware components and robust software partitioning, while replacing the standard Ethernet connection with a wireless Ethernet connection. The implementation of this system is presented and the benefits and potential applications of such a system are discussed.by Melinda Y. Tang.M.Eng

Fast, reliable and efficient database search motion planner (FREDS-MP) for repetitive manipulator tasks

University of Technology Sydney. Faculty of Engineering and Information Technology.This thesis presents FREDS-MP, a motion planning framework that leverages state of the art methods for solving a set of practical agricultural manipulator applications. Current methods exhibit unacceptably slow planning and execution times, hence FREDS-MP aims to bridge this gap by speeding up planning times whilst maintaining high reliability and solution efficiency. While only a specific set of applications are explored, FREDS-MP can be adopted for other similar applications seamlessly due to its general interface. FREDS-MP consists of three planning phases: offline, task and online. The offline planner pre-computes trajectories and cost information based on special cases that anticipate the real world. This pre-computed information is used by the task planner to compute accurate heuristics for sequencing tasks. The pre-computed trajectories are used as initial seeds by the online planner which utilises state of the art trajectory optimisers to adapt them in real-time to online tasks. Software simulations are performed to validate FREDS-MP and compare it to other state of the art planners. Further, the suitability of two commercial manipulators, six-DOF and seven-DOF, are compared for the intended applications. Several unconstrained and constrained tasks, commonly seen in agricultural applications, are tested under diverse obstacle configurations. Statistical results based on planner performance metrics are presented. From these results it was found that FREDS-MP significantly outperformed other state of the art planners when using a seven-DOF manipulator. Hence, an active perception experiment was carried out on a real Rethink Robotics Sawyer robot arm which was tasked to seek out apples on an artificial trellis and inspect them individually. The results from these experiments are presented and validate the practicality of FREDS-MP

Evaluation of software dependability

It has been said that the term software engineering is an aspiration not a description. We would like to be able to claim that we engineer software, in the same sense that we engineer an aero-engine, but most of us would agree that this is not currently an accurate description of our activities. My suspicion is that it never will be. From the point of view of this essay – i.e. dependability evaluation – a major difference between software and other engineering artefacts is that the former is pure design. Its unreliability is always the result of design faults, which in turn arise as a result of human intellectual failures. The unreliability of hardware systems, on the other hand, has tended until recently to be dominated by random physical failures of components – the consequences of the ‘perversity of nature’. Reliability theories have been developed over the years which have successfully allowed systems to be built to high reliability requirements, and the final system reliability to be evaluated accurately. Even for pure hardware systems, without software, however, the very success of these theories has more recently highlighted the importance of design faults in determining the overall reliability of the final product. The conventional hardware reliability theory does not address this problem at all. In the case of software, there is no physical source of failures, and so none of the reliability theory developed for hardware is relevant. We need new theories that will allow us to achieve required dependability levels, and to evaluate the actual dependability that has been achieved, when the sources of the faults that ultimately result in failure are human intellectual failures

Reasoning About the Reliability of Multi-version, Diverse Real-Time Systems

This paper is concerned with the development of reliable real-time systems for use in high integrity applications. It advocates the use of diverse replicated channels, but does not require the dependencies between the channels to be evaluated. Rather it develops and extends the approach of Little wood and Rush by (for general systems) by investigating a two channel system in which one channel, A, is produced to a high level of reliability (i.e. has a very low failure rate), while the other, B, employs various forms of static analysis to sustain an argument that it is perfect (i.e. it will never miss a deadline). The first channel is fully functional, the second contains a more restricted computational model and contains only the critical computations. Potential dependencies between the channels (and their verification) are evaluated in terms of aleatory and epistemic uncertainty. At the aleatory level the events ''A fails" and ''B is imperfect" are independent. Moreover, unlike the general case, independence at the epistemic level is also proposed for common forms of implementation and analysis for real-time systems and their temporal requirements (deadlines). As a result, a systematic approach is advocated that can be applied in a real engineering context to produce highly reliable real-time systems, and to support numerical claims about the level of reliability achieved

Software reliability and dependability: a roadmap

Shifting the focus from software reliability to user-centred measures of dependability in complete software-based systems. Influencing design practice to facilitate dependability assessment. Propagating awareness of dependability issues and the use of existing, useful methods. Injecting some rigour in the use of process-related evidence for dependability assessment. Better understanding issues of diversity and variation as drivers of dependability. Bev Littlewood is founder-Director of the Centre for Software Reliability, and Professor of Software Engineering at City University, London. Prof Littlewood has worked for many years on problems associated with the modelling and evaluation of the dependability of software-based systems; he has published many papers in international journals and conference proceedings and has edited several books. Much of this work has been carried out in collaborative projects, including the successful EC-funded projects SHIP, PDCS, PDCS2, DeVa. He has been employed as a consultant t