Fault Tolerance Aspects Research Articles

Experimental Performance Evaluation of Smoothing Predictive Redundancy Using Embedded Microcontroller Unit

The dependence of numerous systems on electronic devices is causing rapidly increasing concern over fault tolerance. For example, a car with electronically controlled steering and no mechanical linkage from the steering wheel to the front tires (x-by-wire) must be fault tolerant because a critical failure could arise without warning. Fault-tolerant systems have been studied in detail, mainly in the field of aeronautics. This paper presents a smoothing predictive redundancy system that can remove the effect of faults. In addition, this paper introduces an implementation of such a system using an embedded microcontroller unit to show that the smoothing predictive redundancy system outperforms the well-known average and median voters. The experimental results show that the smoothing predictive redundancy system can be a viable choice for the fault-tolerant aspects of safety-critical systems.

Current Challenges in Embedded Communication Systems

This article defines and analyses key challenges met in future embedded systems in networked multimedia and communication applications. Self-awareness, interoperability and embedded security are used to characterize different aspects of designing and implementing next generation embedded systems. The dynamic nature of applications and implementations as well as possible technological faults and variations need to be considered in system verification and modeling. A new design layer needs to be added to current NoC platforms in order to build procedures that take into account dynamic system reconfigurations, fault-tolerance aspects and flexible portability. Increased modularity and networked implementations create a need for trust management mechanisms between system components and technology for analyzing validity and correctness of received application and system configuration information.

Optimization of checkpointing-related I/O for high-performance parallel and distributed computing

Checkpointing, the process of saving program/application state, usually to a stable storage, has been the most common fault-tolerance methodology for high-performance applications. The rate of checkpointing (how often) is primarily driven by the failure rate of the system. If the checkpointing rate is low, fewer resources are consumed but the chance of high computational loss is increased and vice versa if the checkpointing rate is high. It is important to strike a balance, and an optimum rate of checkpointing is required. In this paper, we analytically model the process of checkpointing in terms of mean-time-between-failure of the system, amount of memory being checkpointed, sustainable I/O bandwidth to the stable storage, and frequency of checkpointing. We identify the optimum frequency of checkpointing to be used on systems with given specifications thereby making way for efficient use of available resources and maximum performance of the system without compromising on the fault-tolerance aspects. Further, we develop discrete-event models simulating the checkpointing process to verify the analytical model for optimum checkpointing. Using the analytical model, we also investigate the optimum rate of checkpointing for systems of varying resource levels ranging from small embedded cluster systems to large supercomputers.

Multiagent technology for fault tolerance and flexible control

One of the main characteristics of multiagent systems (MAS) is fault tolerance. When an agent is unavailable for some reason, another agent with similar capabilities can theoretically compensate for this loss. The system can be designed not only for this kind of fault tolerance but also for others. Many key aspects of fault tolerance in MAS are described in this correspondence including social knowledge and physical distribution. We present a MAS framework that has been designed for control applications, in which fault tolerance and flexibility are key parts of the system

MODELLING OF VERTICAL GYROSCOPES WITH CONSIDERATION OF FAULTS

This paper deals with fault analysis of a vertical gyroscope. A parametric model providing flexibility for inducing common faults is presented first. The fault patterns considered are: bias, random drift, systematic drift, lag, gain degradation, and floating. The simulations are conducted to illustrate the fault patterns, as well as to determine the root causes behind the faults. The study is carried out with engineering details of vertical gyroscopes in mind. The results are of significance to the investigation of fault-tolerant aspects of flight control systems.

Failure Resilient Heterogeneous Parallel Computing Across Multidomain Clusters

We propose lightweight middleware solutions that facilitate and simplify the execution of failure-resilient Message Passing Interface (MPI) programs across multidomain clusters. The system described in this paper leverages H2O, a distributed metacomputing framework, to route MPI message passing across heterogeneous aggregates located in different administrative or network domains. MPI communication is aided by a specially written H2O pluglet; messages that are destined for remote sites are intercepted and transparently forwarded to their final destinations. We demonstrate that the proposed technique is indeed effective in enabling communication by MPI programs across distinct clusters and across firewalls. Only marginally lowered performance was observed in our tests, and we believe the substantially increased functionality would compensate for this overhead in most situations. In addition to enabling multicluster communications, we note that with the increasing size and distribution of metacomputing environments, fault tolerance aspects become critically important. We argue that the fault tolerance model proposed by FT-MPI fits well in geographically distributed environments, even though its current implementation is confined to a single administrative domain. We describe extensions to overcome these limitations by combining FT-MPI with the H2O framework. Our holistic approach allows users to run fault-tolerant MPI programs on heterogeneous, geographically distributed shared machines, without sacrificing performance and with minimal involvement of resource providers.

A SOLUTION TO THE THREE DISJOINT PATH PROBLEM ON HONEYCOMB TORI

In a previous paper we solved an open problem named as the three disjoint path problem on honeycomb meshes. In this paper we extend the technique used to solve the related problem on honeycomb tori. The result gives the minimum possible length of the longest of any three disjoint paths between two given nodes in a torus. The problem has practical benefits in the fault tolerant aspects of interconnection topologies.

Fault-Tolerant Recursive Least-Squares Computations on a Mesh-Connected Parallel Processor

Recursive least squares (RLS) is a popular iterative method used for the modeling of systems while in operation. RLS provides an estimate for unknown parameters of a system based on some known parameters and inputs and outputs of that system. This technique is used frequently in digital signal processing and control applications, where it is not possible to completely determine the current state of the system. The RLS procedure incurs intensive computations in every iteration of the algorithm. To implement RLS in situ at a reasonable sampling rate, the complexity of the system's model must be reduced, or the available computing power must be increased. This paper examines methods for increasing the computing power by implementing RLS algorithms on a parallel processing platform. While there has been a large body of research on using parallel processors for the computation of adaptive algorithms, little of this research has examined fault tolerant aspects. As fault tolerance is a critical aspect of any real-time system, this work will examine some factors that should be considered when implementing a real-time adaptive algorithm on a parallel processor system.

The EFTOS approach to dependability in embedded supercomputing

Industrial embedded supercomputing applications benefit from a systematic approach to fault tolerance. The EFTOS (embedded fault-tolerant supercomputing) framework provides a flexible and adaptable set of fault-tolerance tools from which the application developer can choose to make an embedded application on a parallel or distributed system more dependable. A high-level description (recovery language) helps the developer specify the fault-tolerance strategies of the application as a second application layer; this separates functional from fault-tolerance aspects of an application, thus shortening the development cycle and improving maintainability. The framework incorporates a backbone (to hook a set of fault-tolerance tools onto, and to coordinate the fault-tolerance actions) and a presentation layer (to monitor and test the fault tolerance behavior). A practical implementation is described with its performance evaluation, using an industrial case study from the energy-transport area, as well as an analytic deduction of the appropriateness of fault-tolerance techniques for various application profiles.

Safety Analysis on Reconfigurable Systems using an External Model of Intelligent Components

This paper presents the design of an architecture automation system obtained by the interconnection of elementary smart instruments. An approach of design of such architecture is based on the concept of external model. It permits to designers to analyse the fault tolerance aspects.

Maximum delivery time and hot spots in ServerNet TM topologies

This paper will center on analysis of the performance characteristics of ServerNet topologies, concentrating on the prediction, through simulation and statistical analysis, of the maximum two-way delivery time, the identification of congested links (hot spots) and tree saturation. ServerNet TM, developed by Tandem Computers Inc., is a wormhole-routed, packet-switched, point-to-point network, with special attention paid to reducing latency and to assuring reliability. ServerNet uses multiple high-speed, low-cost routers to rapidly switch data directly between data sources and destinations. The maximum two-way delivery time is necessary for determining the values of timeout counters, which are relevant to the fault-tolerant aspect of the system, and the QoS guarantees. Hot spots may cause the occurrence of tree saturation in the network i.e., where an individual tree will become congested (tree saturation) while all other trees are mostly idle, which leads to significant performance degradation. Our study is based on data generated by a simulation tool. Statistical analysis and inference methods were used to process the samples generated by the simulator and to obtain estimates for the maximum two-way packet delivery time. These methods were also used to determine the number of the samples that were required to produce estimates of the desired accuracy. Both the degree of confidence and the percentage of packets are determined by the number of samples generated by the simulator. This allows us to control the quality and accuracy of the estimate to suit our needs. Link usage statistics were recorded by the simulator for the purpose of performing a detailed investigation of congestion effects and hot spots. The study of the static and dynamic link usage statistics revealed that the extreme values of the two-way maximum delivery time were caused by links operating under heavy traffic loads and that under certain traffic patterns a tree saturation effect occurs.

Configurable Time-Redundant Task Execution for Fault-Tolerant Real-Time Systems

The design of fault-tolerant real-time systems is characterized by a trade-off between performance considerations and fault-tolerance aspects. This paper presents a design approach that provides three strategies for time-redundant execution of the tasks of an application. The three execution strategies differ in their faulttolerance and performance properties such that a software designer can tailor the structure of the application software to the performance and fault-tolerance needs of an application. The paper describes the three time-redundant execution strategies and compares them with respect to fault tolerance, CPU-time requirements, and schedulability.

Primary flight computers for the Boeing 777

This paper follows one on the Boeing 777 primary flight computers, which was presented at ERA's 1992 Avionics Conference. The current paper focuses on the system requirements software implementation, and operational consequences of a fault-tolerant system. Beginning with the reasons for fly-by-wire, the paper goes on to describe the overall architecture of the Boeing 777 primary flight computer system. Particular emphasis is placed on the control modes and the way in which envelope protection functions are implemented. After a brief description of the hardware, the paper describes the software life-cycle process, including design, coding and test, highlighting the way in which the integrity of the software has been achieved. The fault-tolerant aspects of the design, and the advantages that these provide to operators, conclude the paper

Fault tolerant queries in computer networks

In computer networks with decentralized control, it is necessary to provide a distributed query mechanism, whereby a node can dynamically discover the location of a remote resource. The authors propose a query mechanism based on flooding with feedback, which uses no more than two messages over any link. They examine the fault tolerant aspects of this distributed query mechanism, operating in a network where links and nodes may fail and show that, under certain conditions, the resource is indeed found. They then construct enhancements to this mechanism, where the conditions under which the resource is found are substantially relaxed, at the cost of some increase in message complexity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Fault tolerance aspects of a highly reliable microprocessor-based water turbine governor

A highly reliable fault tolerant microprocessor-based governor with high performance is being developed. In this system, techniques such as redundancy, fault detection, fault location, fault isolation, and self-recovery have been applied successfully to achieve high reliability. The hardware architecture of this system and its fault tolerance aspects are described. The software structure and the redundancy architecture are presented. The fault detection, the fault location, and the fault isolation techniques applied to this system are studied. The self-recovery and reconfiguration of the system and the switch-over control based on the fault detection results are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Properties of a class of trivalent network graphs and optimal routing

In the presence paper we investigate various structural properties fo a class of trivalent network graphs, known as Moebius graphs, and then propose an O( N) optimal routing algorithm where N is the number of nodes in the graph. We also discuss the fault-tolerance aspects of such families of graphs.

Tolerating failures of continuous-valued sensors

One aspect of fault-tolerance in process control programs is the ability to tolerate sensor failure. This paper presents a methodology for transforming a process control program that cannot tolerate sensor failures into one that can. Issues addressed include modifying specifications in order to accommodate uncertainty in sensor values and averaging sensor values in a fault-tolerant manner. In addition, a hierarchy of sensor failure models is identified, and both the attainable accuracy and the run-time complexity of sensor averaging with respect to this hierarchy is discussed.

Assessment of reconfiguring algorithms for MIMD architectures

Some issues of reconfigurable computing systems with MIMD architecture are considered. A number of reconfiguring algorithms are analyzed by simulation from the aspect of the attainable fault tolerance.

Software fault tolerance in architectures with hierarchical protection levels

The effect on software fault tolerance of hardware features such as hierarchical privilege levels (rings), the use of descriptors for memory protection, separated virtual address spaces, and ring crossings that enforce specific energy points is considered. A strategy that uses a separate programming layer, the recovery layer, to handle fault-tolerant aspects of process interactions is discussed. The recovery metaprogram (RPM) which monitors the run-time behavior of the application program and coordinates error detection, recovery, and reconfiguration, is examined, focusing on privilege levels, which provide protection against error propagation, RMP implementation, and conversations. The intel 80286 has been used as a sample implementation vehicle, but most of the discussion applies to any machine with a similar range of features. Extension to multiprocessor systems is indicated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A tutorial on the principles of fault tolerance

The paper begins by examining the four aspects of fault tolerance — error detection, damage assessment, error recovery and fault treatment — and describes how these aspects can be incorporated in systems. Following this, a methodology for the construction of robust software systems is presented, covering the topics of design fault tolerance and software implemented fault tolerance. Some aspects of modelling faulty behaviour of components is presented and the notion of a family of fault-tolerant algorithms is introduced.