Software fault tolerance by design diversity in the classroom

The two bestknown methods of building fault tolerant software are nversion programming 3 and recovery blocks 7. Design diversity is the provision of software components called variants, which have the same or an equivalent specification but with different. Approach to componentbased synthesis of faulttolerant software. Below are 5 ways to promote equity and diversity in your classroom. The need to control software fault is one of the most rising challenges facing. Early experiments with software diversity in the mid 1970s investigated nversion. At present, most of the industrial applications of design diversity fall into the class where. This is certainly more true of software systems than almost any phenomenon, not all software change in the same way so software fault tolerance methods are designed to overcome execution errors by modifying variable values to create an acceptable program state. We aim to support the software architect in the design of faulttolerant. Software diversity approaches to software fault tolerance depend on software diversity where it is assumed that different implementations of the same software specification will fail in different ways.

There can be either hardware fault or software fault, which disturbs the. The cost of softwarefault tolerance fault tolerance introduces additional costs. In order to complement design diversity in the quest for faulttolerance software, there exits several data diversity techniques which are similar to the aforementioned for the design diversity approach. This chapter concentrates on software fault tolerance based on design diversity. An introduction to software engineering and fault tolerance. Abbott suggests instead that fault tolerance should search for alternative recovery options in the manner of his resourceful robot. With design diversity, if a module cannot provide its service, then another module. This chapter focuses specifically on fault tolerance techniques, rather than the myriad of fault avoidance techniques. Design diversity is a solution to software fault tolerance only so far as it is possible. Index termsdesign diversity, fault tolerance, multiple computa tion, nversion programming. When a fault occurs, these techniques provide mechanisms to. Softwarecontrolled fault tolerance 3 cution time by 42. We outline a system that defines recovery goals and subgoals, and errordetection and correction procedures for each goal.

June 6, 2001 nversion programming nvp and acceptance testing at are established methods for obtaining highly reliable results from imperfect software. Software fault tolerance using data diversity attention. Design and analysis of a faulttolerant computer for aircraft control john h. So the goal of the system designer is to ensure that the probability of system failure is acceptably small. Software fault tolerance techniques are designed to allow a system to tolerate software faults that remain in the system after its development. Nair department of computer science and engineering, southern methodist university, dallas, texas providing resiliency from software failures requires design diversity. To tolerate faults, both of these techniques rely on design diversity, i.

Therefore faulttolerance is achieved by using diversity in the data space. Designing a resourceful faulttolerance system sciencedirect. Software fault tolerance in the application layer y. Diversity in the classroom promoting diversity is a goal shared by many in american colleges and universities, but actually achieving this goal in the daytoday classroom is often hard to do. Software fault tolerance is basically the design faults in the computer system. Northholland software fault tolerance for distributed object based computing hyun c. In addition software design faults and even compiler, library, operating system and underlying hardware design faults can be detected.

Techniques for fault tolerance fault tolerance is the ability to continue operating despite the failure of a limited subset of their hardware or software. Pdf software fault tolerance in the application layer. Fault elimination and fault prevention are parts of fault avoidance. Software fault tolerance in the application layer, by huang and kintala. Design diversity is a solution to software fault tolerance only so far as it is possible to create diverse and equivalent specifications so that programmers can create software which has different enough designs that they dont share similar failure modes. Design of dependable computing systems, kluwer academic publishers, 2002.

Software fault tolerance is an immature area of research. The proposed software techniques are either new or never considered systematically for the detection of hardware faults in a general purpose system environment with design diversity. Definition and analysis of hardware and softwarefault. Multiversioning the software com ponents provides the required diversity. Software fault tolerance carnegie mellon university. Unlike hardware faults, all software faults are design and implementation errors. Recovery modules try blocks run different version of the same algorithm. In fact there exist sophisticated computing systems, designed for environments requiring nearcontinuous service, which contain ad hoc checks and checkpointing facilities that provide a measure of tolerance against some software errors as well as hardware failures 11. These principles deal with desktop, server applications andor soa. This belief led to the use of design diversity for supporting fault tolerance. They include the recovery block scheme rbs programming, consensus recovery block programming, nversion programming nvp, n selfchecking programming nscp and data diversity. Bohrbugs and permission to make digital or hard copies of all or part of this work for personal or.

We have several software fault tolerance schemes as proposed in 46,47,48,49,50 are based on software design diversity in order to tolerate software design bugs. If its operating quality decreases at all, the decrease is proportional to the severity of the failure, as compared to a naively designed system, in which even a small failure can cause total breakdown. It would be very difficult to sum it up in one article since there are multiple ways to achieve fault tolerance in software. We suggest the combined utilization of so called systematic diversity and design diversity in a timeredundant system instead of the structural redundant duplex system. Software designers or system integrators who want an introduction to the problems found in designing for fault tolerance and to the range of design solutions.

Fault tolerance through automated diversity in the management of distributed systems jorg prei. In order to complement design diversity in the quest for fault tolerance software, there exits several data diversity techniques which are similar to the aforementioned for the design diversity approach. Designing faulttolerant soa based on design diversity springerlink. In this paper we explore the feasibility of resourceful software fault tolerance. Shostak, abstmtsift softwue implemented fault tolerance is an. Since design diversity affects costs dif ferently according to the lifecycle phases, we start with cost distribution among the various lifecycle activities for classical, nonfaulttolerant, soft ware. Software fault tolerance for distributed object based. The versions are used as alternatives with a separate means of. Therefore, it is reasonable to deal with the remaining software faults bugs during runtime to increase the overall reliability. Architectural issues in software fault tolerance 49 in having several subfunctions implemented by software, supported by the same hardware equipment.

Fault tolerance is the property that enables a system to continue operating properly in the event of the failure of or one or more faults within some of its components. Software fault tolerance professur fur systems engineering. Abstractnowadays the reliability of software is often the main goal in the software development process. Systematic and design diversity software techniques for. Most system designers go to great lengths to limit the impact of a hardware failure on system performance. The cost of software fault tolerance fault tolerance introduces additional costs. Designing faulttolerant soa based on design diversity. Fault tolerance through automated diversity in the. Software fault tolerance cmuece carnegie mellon university. Section 2 describes our methodology and the base library. This book does a very good job in presenting the fundamental concepts of fault tolerance.

That is, it should compensate for the faults and continue to. It is assumed that implementations are a independent and b do not include common errors. Software fault tolerance in computer operating systems r. It is important to focus on diversity and equity because white teachers have to be able to use classroom instruction to support a diverse student population. Another class of related mplex faults is quite different. Approach to componentbased synthesis of faulttolerant. Also there are multiple methodologies, few of which we already follow without knowing. The goal of this teaching module is to highlight a few of the key challenges and concerns in promoting diversity, and illustrate ways to incorporate an.

Diversity in the classroom poorvu center for teaching. Software fault tolerance techniques are employed during the procurement, or development, of the software. Software fault tolerance software fault tolerance is the ability for software to detect and recover from a fault that is happening or has already happened in either the software or hardware in the system in which the software is running to provide service by the specification. Using abstraction to improve fault tolerance 239 the remainder of the paper is organized as follows. A characteristic of the software fault tolerance techniques is that they can, in principle, be applied at any level in a software system. Dec 06, 2018 fault tolerance is the way in which an operating system os responds to a hardware or software failure. To handle faults gracefully, some computer systems have two or more. Therefore fault tolerance is achieved by using diversity in the data space. He holds a laurea cum laude in electronic engineering from the university of pisa, italy 1980. Data diverse software fault tolerance techniques n complements design diversity by compensating for design diversity s limitations n involves obtaining a related set of points in the program data space, executing the same software on those points in the program data space, and then using a decision algorithm to determine the resulting output.

The two bestknown methods of building faulttolerant software are nversion programming 3 and recovery blocks 7. Designfault tolerance by means of design diversity is a concept that traces back to the very early age of informatics. This is really surprising because hardware components have much higher reliability than the software that runs over them. By software fault tolerance in the application layer, we mean a set of application level software components to detect and recover from faults that are not handled in the hardware or operating. If design fault detection is required, design diversity in the software has to be used, too. Software engineers assume that the different implementations use different designs.

Schools must prioritize efforts to promote diversity and equity within their school culture and within the classroom. Design diversity is the provision of software components called variants, which have the same or an equivalent specification but with different designs and implementations gartner 1999. Fault tolerant software architecture stack overflow. As more and more complex systems get designed and built, especially safety critical systems, software fault tolerance and the next generation of hardware fault tolerance will need to evolve to be able to solve the design fault problem. Assessment of data diversity methods for software fault tolerance. Software fault tolerance is the ability for software to detect and recover from a fault that is happening or has already happened in either the software or hardware in the system in which the software is running to provide service by the specification. Software fault tolerance, audits, rollback, exception handling.

Buy only what you need wide range of configurable, fault tolerant, multi function io modules to suit most applications. Software fault tolerance during the development of software, it is infeasible to find all its bugs, which can reach as far back as the design phase. Modeling fault tolerance tactics with reusable aspects. Software engineering software fault tolerance javatpoint. A characteristic of the software fault tolerance techniques is that they can, in principle, be applied at any level in a. Researchers agree that all software faults are design faults. The adoption of software fault tolerance techniques based on design diversity has. It is possible for a limited class of design faults to be recovered from using. Hardware implemented fault tolerance design reduces operating system size, minimises systems software and increases processing speed, offering the end user the safest and simplest design. Fault tol erance is a function of computing systems that serves to as. Fault tolerant software has the ability to satisfy requirements despite failures. The adoption of software fault tolerance techniques based on design diversity has been advocated as a means of coping with residual software design faults in operational software lee and anderson. It also goes into detail on fault avoidance and fault removal. Softwarecontrolled fault tolerance princeton university.

Since design diversity affects costs dif ferently according to the lifecycle phases, we start with cost distribution among the various lifecycle activities for classical, non fault tolerant, soft ware. Because of this, a wide range of issues affects software reliability. The cost effectiveness of telecommunication service dependability y. Nov 06, 2010 an introduction to software engineering and fault tolerance. Sc high integrity system university of applied sciences, frankfurt am main 2. Its function is to prevent system accidents, and mask out faults if possible. Early implementations were developed by randell and hecht in 1975 and 1981 respectively.

Despite more and more improvements in fault preventing techniques, it is a fact that faults remain in every complex software system. Fault tolerance is the way in which an operating system os responds to a hardware or software failure. His research has addressed faulttolerance in multiprocessor and distributed systems, protocols for highspeed networks, software fault tolerance via design diversity, software testing and software reliability assessment. The craft hybrid techniques reduces outputcorrupting faults to 0. Software fault tolerance is the ability of computer software to continue its normal operation despite the presence of system or hardware faults. The term essentially refers to a systems ability to allow for failures or malfunctions, and this ability may be provided by software, hardware or a combination of both. Section 3 explains how we applied the methodology to build the replicated. Such an approach, which can be termed as integration, comes up against software failures, which are due to design faults only. Nversion programming nvp is one of the software fault tolerance techniques based on design. Fault tolerance is the realization that we will have faults in our system hardware andor software and we have to design the system in such a way that it will be tolerant of those faults. Fault tolerance through automated diversity in the management. This course has been developed by the centre for software reliability with funding from the engineering and physical sciences research council grant number 00711eng95 as part of their. Architecture and software fault tolerant technology. Designing fault tolerant applications amazon web services.