A framework for the development of tolerant real time applications

This work presents a framework architecture for the development of distributed real-time applications to be integrated into WWW clients. It assumes a WWW environment over networks providing a best-effort delivery service like the internets based on the IP protocol. The framework is that of an application programming interface (API) providing the program developer with the services needed by tolerant realtime applications. Once developed, an application is bundled together with the API to form a WWW plug-in which can subsequently be called from a WWW client interface or browser. The application is then perceived as being integrated into the WWW environment. The design aims to provide real-time applications with a transport service layer assuring near end-to-end isochronism despite the weak guaranties of the underlying network service. The implementation of the mechanisms that allow multistream real-time communications to adapt to the operational conditions of these networks are discussed. In this work, the RTP and RTCP protocols were also implemented as part of the API. Experience with this framework reports the development of a prototype real-time application for multimedia group communication and the analysis of the behaviour of RTP sessions in a real operational situation. The analysis uses protocol state data logged during their operation

Aspect-oriented fault tolerance for real-time embedded systems

Real-time embedded systems for safety-critical applications have to introduce fault tolerance mechanisms in order to cope with hardware and software errors. Fault tolerance is usually applied by means of redundancy and diversity. Redundant hardware implies the establishment of a distributed system executing a set of fault tolerance strategies by software, and may also employ some form of diversity, by using different variants or versions for the same processing. This paper describes our approach to introduce fault tolerance in distributed embedded systems applications, using aspect-oriented programming (AOP). A real-time operating system sup-porting middleware thread communication was integrated to a fault tolerant framework. The introduction of fault tolerance in the system is performed by AOP at the application thread level. The advantages of this approach include higher modularization, less efforts for legacy systems evolution and better configurability for testing and product line development. This work has been tested and evaluated successfully in several fault tolerant configurations and presented no significant performance or memory footprint costs.Fundação para a Ciência e a Tecnologia (FCT

Dynamic fault tolerant grid workflow in the water threat management project

Achieving fault tolerance is an inevitable problem in distributed systems, with it becoming more challenging in decentralized, heterogeneous, and dynamic-environment systems such as a Grid. When deploying applications requires time-criticality, how to allocate resources for jobs in a fault-tolerant manner is an important issue for the delivery of the services. The Water Threat Management project is a research to find solutions for the contamination incidents problems in urban water distribution systems, and it involves the development of the cyberinfrastructure in a Grid environment. To handle such urgent events properly, the deployment of the system demands real-time processing without the failure. Our approach of integrating a fault-tolerant framework into a Water Threat Management system provides fault tolerance at the queuing stage rather than the job-execution stage by scheduling jobs in fault-tolerant ways. This includes the development of the batch queuing system in the Cyberaide Shell project. In addition, we present a dynamic workflow in the Water Threat Management system that can reduce the queue wait time in the changing environment

A Symbiotic Approach to Designing Cross-Layer QoS in Embedded Real-Time Systems

International audienceNowadays there is an increasing need for embedded systems to support intensive computing while maintaining traditional hard real-time and fault-tolerant properties. Extending the principle of multi-core systems, we are exploring the use of distributed processing units interconnected via a high performance mesh network as a way of supporting distributed real-time applications. Fault-tolerance can then be ensured through dynamic allocation of both computing and communication resources. We postulate that enhancing QoS (Quality of Service) for real-time applications entails the development of a cross-layer support of high-level requirements, thus requiring a deep knowledge of the underlying networks. In this paper, we propose a new simulation/emulation/experimentation framework, ERICA, for designing such a feature. ERICA integrates both a network simulator and an actual hardware network to allow implementation and evaluation of different QoS-guaranteeing mechanisms. It also supports real-software-in-the-loop, i.e. running of real applications and middleware over these networks. Each component can evolve separately or together in a symbiotic manner, also making teamwork more flexible. We present in more detail our discrete-event simulation approach and the in-silicon implementation with which we cross-check our solutions in order to bring real performance aspects to our work. We also discuss the challenges of running real-software-in-the-loop in a real-time context, i.e. how to bridge it with a network simulator, and how to deal with time consistency

M-Grid : A distributed framework for multidimensional indexing and querying of location based big data

The widespread use of mobile devices and the real time availability of user-location information is facilitating the development of new personalized, location-based applications and services (LBSs). Such applications require multi-attribute query processing, handling of high access scalability, support for millions of users, real time querying capability and analysis of large volumes of data. Cloud computing aided a new generation of distributed databases commonly known as key-value stores. Key-value stores were designed to extract value from very large volumes of data while being highly available, fault-tolerant and scalable, hence providing much needed features to support LBSs. However complex queries on multidimensional data cannot be processed efficiently as they do not provide means to access multiple attributes. In this thesis we present MGrid, a unifying indexing framework which enables key-value stores to support multidimensional queries. We organize a set of nodes in a P-Grid overlay network which provides fault-tolerance and efficient query processing. We use Hilbert Space Filling Curve based linearization technique which preserves the data locality to efficiently manage multi-dimensional data in a key-value store. We propose algorithms to dynamically process range and k nearest neighbor (kNN) queries on linearized values. This removes the overhead of maintaining a separate index table. Our approach is completely independent from the underlying storage layer and can be implemented on any cloud infrastructure. Experiments on Amazon EC2 show that MGrid achieves a performance improvement of three orders of magnitude in comparison to MapReduce and four times to that of MDHBase scheme --Abstract, pages iii-iv

Operating system fault tolerance support for real-time embedded applications

Tese de doutoramento em Electrónica Industrial (ramo de conhecimento em Informática Industrial)Fault tolerance is a means of achieving high dependability for critical and highavailability systems. Despite the efforts to prevent and remove faults during the development of these systems, the application of fault tolerance is usually required because the hardware may fail during system operation and software faults are very hard to eliminate completely. One of the difficulties in implementing fault tolerance techniques is the lack of support from operating systems and middleware. In most fault tolerant projects, the programmer has to develop a fault tolerance implementation for each application. This strong customization makes the fault-tolerant software costly and difficult to implement and maintain. In particular, for small-scale embedded systems, the introduction of fault tolerance techniques may also have impact on their restricted resources, such as processing power and memory size. The purpose of this research is to provide fault tolerance support for real-time applications in small-scale embedded systems. The main approach of this thesis is to develop and integrate a customizable and extendable fault tolerance framework into a real-time operating system, in order to fulfill the needs of a large range of dependable applications. Special attention is taken to allow the coexistence of fault tolerance with real-time constraints. The utilization of the proposed framework features several advantages over ad-hoc implementations, such as simplifying application-level programming and improving the system configurability and maintainability. In addition, this thesis also investigates the application of aspect-oriented techniques to the development of real-time embedded fault-tolerant software. Aspect- Oriented Programming (AOP) is employed to modularize all fault tolerant source code, following the principle of separation of concerns, and to integrate the proposed framework into the operating system. Two case studies are used to evaluate the proposed implementation in terms of performance and resource costs. The results show that the overheads related to the framework application are acceptable and the ones related to the AOP implementation are negligible.Tolerância a falhas é um meio de obter-se alta confiabilidade para sistemas críticos e de elevada disponibilidade. Apesar dos esforços para prevenir e remover falhas durante o desenvolvimento destes sistemas, a aplicação de tolerância a falhas é normalmente necessária, já que o hardware pode falhar durante a operação do sistema e falhas de software são muito difíceis de eliminar completamente. Uma das dificuldades na implementação de técnicas de tolerância a falhas é a falta de suporte por parte dos sistemas operativos e middleware. Na maioria dos projectos tolerantes a falhas, o programador deve desenvolver uma implementação de tolerância a falhas para cada aplicação. Esta elevada adaptação torna o software tolerante a falhas dispendioso e difícil de implementar e manter. Em particular, para sistemas embebidos de pequena escala, a introdução de técnicas de tolerância a falhas pode também ter impacto nos seus restritos recursos, tais como capacidade de processamento e tamanho da memória. O propósito desta tese é prover suporte à tolerância a falhas para aplicações de tempo real em sistemas embebidos de pequena escala. A principal abordagem utilizada nesta tese foi desenvolver e integrar uma framework tolerante a falhas, customizável e extensível, a um sistema operativo de tempo real, a fim de satisfazer às necessidades de uma larga gama de aplicações confiáveis. Especial atenção foi dada para permitir a coexistência de tolerância a falhas com restrições de tempo real. A utilização da framework proposta apresenta diversas vantagens sobre implementações ad-hoc, tais como simplificar a programação a nível da aplicação e melhorar a configurabilidade e a facilidade de manutenção do sistema. Além disto, esta tese também investiga a aplicação de técnicas orientadas a aspectos no desenvolvimento de software tolerante a falhas, embebido e de tempo real. A Programação Orientada a Aspectos (POA) é empregada para segregar em módulos isolados todo o código fonte tolerante a falhas, seguindo o princípio da separação de interesses, e para integrar a framework proposta com o sistema operativo. Dois casos de estudo são utilizados para avaliar a implementação proposta em termos de desempenho e utilização de recursos. Os resultados mostram que os acréscimos de recursos relativos à aplicação da framework são aceitáveis e os relativos à implementação POA são insignificantes