Leader election in synchronous networks

Worst, best and average number of messages and running time of leader election algorithms of different distributed systems are analyzed. Among others the known characterizations of the expected number of messages for LCR algorithm and of the worst number of messages of Hirschberg-Sinclair algorithm are improve

New protocols for the election of a leader in a ring

AbstractIn this paper we investigate the impact of time for the election of a leader in a distributed environment. We propose a new protocol schema that can be specialized to obtain several protocols with different communication-time characteristics when the network is ring-shaped and the communications between processors are synchronous

Fairness Properties of the Trusting Failure Detector

In 1985 it was shown by Fischer et al. that consensus, a fundamental problem in distributed computing, was impossible in asynchronous distributed systems in the presence of even just one process failure. This result prompted a search for alternative system models that were capable of solving such problems and culminated in the development of two helpful constructs: partially synchronous system models and failure detectors. Partially synchronous system models seek to solve the problem of identifying process crashes by constraining the real-time behavior of the underlying system. In the resulting models, crashed processes can be detected indirectly through the use of timeouts. Failure detectors, on the other hand, address process crashes by directly providing (potentially inaccurate) information on failures. As a result, failure detectors were viewed as abstractions of real-time information. Pike et al. proposed a different perspective on failure detectors; as abstracting fairness properties. Fairness in a system imposes bounds on the relative frequencies of communication and execution between processes in a system, and it was shown that four frequently-used failure detectors from the Chandra-Toueg hierarchy (P, ♢P, S, ♢S) encapsulate these fairness properties. This discovery suggests that failure detectors may be better understood as abstractions of fairness rather than real-time properties as well as demonstrates the possibility to communicate results between systems augmented with failure detectors and partially synchronous system models. In this thesis, we will be discussing an extension of the Pike et al. result to the trusting failure detector. The trusting failure detector is the weakest failure detector to implement the problem of fault-tolerant mutual exclusion: a fundamental primitive for distributed computing

Leader election in distributed networks using agent based self-stabilizing technique

There are many variants of leader election algorithm in distributed networks. In this research, an agent based approach to leader election in distributed networks is investigated. Agents have shown to be useful in several ways. In the theoretical perspective, agents sometime help in reducing the message complexity of the system and sometimes help in lowering time complexity. In a more practical sense, agents perform operations independent of the processors, thereby lending a more flexible algorithm supporting different types of networks

Robust network computation

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 91-98).In this thesis, we present various models of distributed computation and algorithms for these models. The underlying theme is to come up with fast algorithms that can tolerate faults in the underlying network. We begin with the classical message-passing model of computation, surveying many known results. We give a new, universally optimal, edge-biconnectivity algorithm for the classical model. We also give a near-optimal sub-linear algorithm for identifying bridges, when all nodes are activated simultaneously. After discussing some ways in which the classical model is unrealistic, we survey known techniques for adapting the classical model to the real world. We describe a new balancing model of computation. The intent is that algorithms in this model should be automatically fault-tolerant. Existing algorithms that can be expressed in this model are discussed, including ones for clustering, maximum flow, and synchronization. We discuss the use of agents in our model, and give new agent-based algorithms for census and biconnectivity. Inspired by the balancing model, we look at two problems in more depth.(cont.) First, we give matching upper and lower bounds on the time complexity of the census algorithm, and we show how the census algorithm can be used to name nodes uniquely in a faulty network. Second, we consider using discrete harmonic functions as a computational tool. These functions are a natural exemplar of the balancing model. We prove new results concerning the stability and convergence of discrete harmonic functions, and describe a method which we call Eulerization for speeding up convergence.by David Pritchard.M.Eng

Contributions on agreement in dynamic distributed systems

139 p.This Ph.D. thesis studies the agreement problem in dynamic distributed systems by integrating both the classical fault-tolerance perspective and the more recent formalism based on evolving graphs. First, we developed a common framework that allows to analyze and compare models of dynamic distributed systems for eventual leader election. The framework extends a previous proposal by Baldoni et al. by including new dimensions and levels of dynamicity. Also, we extend the Time-Varying Graph (TVG) formalism by introducing the necessary timeliness assumptions and the minimal conditions to solve agreement problems. We provide a hierarchy of time-bounded, TVG-based, connectivity classes with increasingly stronger assumptions and specify an implementation of Terminating Reliable Broadcast for each class. Then we define an Omega failure detector, W, for the eventual leader election in dynamic distributed systems, together with a system model, , which is compatible with the timebounded TVG classes. We implement an algorithm that satisfy the properties of W in M. According to our common framework, M results to be weaker than the previous proposed dynamic distributed system models for eventual leader election. Additionally we use simulations to illustrate this fact and show that our leader election algorithm tolerates more general (i.e., dynamic) behaviors, and hence it is of application in a wider range of practical scenarios at the cost of a moderate overhead on stabilization times

The changing geomagnetic field from the ionosphere to the core-mantle boundary

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