Protocolo Híbrido de Ordem Total Uniforme com entrega Optimista

Broadcast algorithms with total uniform order simplify the development of applications that use replication as a fault-tolerance technique. This paper presents and compares three alternatives to implement an optimistic delivery service in total order uniform broadcast protocols for large-scale systems

An Indulgent Uniform Total Order Algorithm with Optimistic Delivery

A total order algorithm is a fundamental building block in the construction of distributed fault-tolerant applications. Unfortunately, the implementation of such a primitive can be expensive both in terms of communication steps and of number of messages exchanged. This problem is exacerbated in large-scale systems, where the performance of the algorithm may be limited by the presence of high-latency links. Typically, the most efficient total order algorithms do not provide uniform delivery and assume the availability of a perfect failure detector. Such algorithms may provide inconsistent results if the system assumptions do not hold. On the other hand, algorithms that assume an unreliable failure detector always provide consistent results but exhibit higher costs. This paper presents a new algorithm that combines the advantages of both approaches. On good periods, when the system is stable and processes are not suspected, the algorithm operates as if a perfect failure detector is assumed. Yet, the algorithm is indulgent, since it never violates consistency, even in runs where processes are suspecte

Middleware for transparent TCP connection migration : masking faulty TCP-based services

Masteroppgave i informasjons- og kommunikasjonsteknologi 2004 - Høgskolen i Agder, GrimstadMission critical TCP-based services create a demand for robust and fault tolerant TCP communication. Sense Intellifield monitors drill operations on rig sites offshore. Critical TCP-based services need to be available 24 hours, 7 days a week, and the service providers need to tolerate server failure. How to make TCP robust and fault tolerant without modifying existing infrastructure like existing client/server applications, services, TCP stacks, kernels, or operating systems is the motivation of this thesis. We present a new middleware approach, first of its kind, to allow TCP-based services to survive server failure by migrating TCP connections from failed servers to replicated surviving servers. The approach is based on a proxy technique, which requires modifications to existing infrastructure. Our unique middleware approach is simple, practical, and can be built into existing infrastructure without modifying it. A middleware approach has never been used to implement the proxy based technique. Experiments for validation of functionality and measurement of performance of the middleware prototype are conducted. The results show that our technique adds significant robustness and fault tolerance to TCP, without modifying existing infrastructure. One of the consequences of using a middleware to make TCP communication robust and fault tolerant is added latency. Another consequence is that TCP communication can survive server failure, and mask it. Companies providing robust and fault tolerant TCP, is no longer dependant of third party hardware and/or software. By implementing our solution, they can gain economical advantages. A main focus of this report is to present a prototype that demonstrates our technique and middleware approach. We present relevant background theory which has lead to the design architecture of a middleware approach to make TCP communication fault tolerant. Finally we conduct experiments to uncover the feasibility and performance of the prototype, followed by a discussion and conclusion

Totally Ordered Broadcast and Multicast Algorithms: A Comprehensive Survey

Total order multicast algorithms constitute an important class of problems in distributed systems, especially in the context of fault-tolerance. In short, the problem of total order multicast consists in sending messages to a set of processes, in such a way that all messages are delivered by all correct destinations in the same order. However, the huge amount of literature on the subject and the plethora of solutions proposed so far make it difficult for practitioners to select a solution adapted to their specific problem. As a result, naive solutions are often used while better solutions are ignored. This paper proposes a classification of total order multicast algorithms based on the ordering mechanism of the algorithms, and describes a set of common characteristics (e.g., assumptions, properties) with which to evaluate them. In this classification, more than fifty total order broadcast and multicast algorithms are surveyed. The presentation includes asynchronous algorithms as well as algorithms based on the more restrictive synchronous model. Fault-tolerance issues are also considered as the paper studies the properties and behavior of the different algorithms with respect to failures

Forschungs- und Arbeitsgebiete des Instituts für Telematik

Dieser Interne Bericht gibt einen Ueberblick ueber aktuelle Forschungsarbeiten des Instituts fuer Telematik der Universitaet Karlsruhe in den Bereichen Hochleistungskommunikation, verteilte Systeme, Cooperation&Management und Telekooperation. Er ist in zwei Teile gegliedert. Der erste beschreibt die persoenlichen Interessensgebiete der wissenschaftlichen Mitarbeiter. Danach folgt eine Darstellung der Kooperationsprojekte des Instituts. Im Anhang finden sich die referenzierten Literaturstellen sowie aktuelle Eigenveroeffentlichungen der Mitarbeiter des Instituts. Der Bericht entstand im Rahmen der Klausurtagung des Instituts in Rothenburg ob der Tauber im Oktober 1996

Experiências com tolerância a faltas no CORBA e extensões ao FT-CORBA para sistemas distribuidos de larga escala

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Elétrica.Esta tese apresenta nossas experiências com tolerância a faltas no CORBA e uma proposta de extensão das especificações Fault-Tolerant CORBA para sistemas distribuídos de larga escala. A motivação deste trabalho foi a inadequação ou a falta de definições nas especificações FT-CORBA que permitissem atender a requisitos de tolerância a falta para sistemas de larga escala, tal como a Internet. Neste trabalho é apresentado um conjunto de soluções, englobando detecção de falhas, membership e comunicação de grupo, que visam principalmente atender aspectos de escalabilidade, necessários quando são tratados sistemas desta natureza. A principal contribuição desta trabalho é a proposta de um modelo de hierarquia de domínios de tolerância a faltas que facilita o gerenciamento e comunicação de grupo interdomínio

Totally ordered multicast in large-scale systems

Totally ordered multicast protocols have proved to be extremely useful in supporting fault-tolerant distributed applications. This paper compares the performance of the two main classes of protocols providing total order in large-scale systems: token-site and symmetric protocols. The paper shows that both classes of protocols can exhibit a latency close to 2D, where D is the message transit delay between two processes. In face of these observations, the paper makes the following contributions: it presents a rate-synchronization scheme for symmetric protocols that exhibits a latency close to D+ t, where t is the largest inter-message transmission time; it proposes a new hybrid protocol and shows that the hybrid scheme for heterogeneous topologies performs better than any of the previous classes of protocols in isolation; finally, the paper presents an algorithm that allows a process to dynamically adapt to changes in throughput and in network delays. The combination of these three techniques results in a dynamic hybrid scheme that, when applied to systems where the topology/traffic patterns are not known a priori, offers a much lower latency than non-hybrid approaches