Cristian Martín

Implementing the Omega failure detector in the crash-recovery failure model

Unreliable failure detectors are mechanisms providing information about process failures, that allow to solve several problems in asynchronous systems, e.g., Consensus. A particular failure detector, Omega, provides an eventual leader election functionality. This paper addresses the implementation of Omega in the crash-recovery failure model. We first propose an algorithm assuming that processes are reachable from the correct process that crashes and recovers a minimum number of times. Then, we propose two algorithms which assume only that processes are reachable from some correct process. Besides this, one of the algorithms requires the membership to be known a priori, while the other two do not.

Hierarchical and fault-tolerant data aggregation in wireless sensor networks

This paper presents three hierarchical algorithms for data aggregation in wireless sensor networks where sensors can crash and recover. The network is divided in several regions. The algorithms ensure (i) the selection of a common data aggregator sensor within each region, in charge of the collection of local data, and (ii) the selection of a unique super-aggregator sensor, in charge of the collection of global data, among all the aggregators. Both selections are achieved by implementing the Omega failure detector, which provides a self-organizing and fault-tolerant leader election service. We also introduce a battery depletion threshold to provide wireless sensor network QoS.

Communication-efficient leader election in crash-recovery systems

Abstract: This work addresses the leader election problem in partially synchronous distributed systems where processes can crash and recover. More precisely, it focuses on implementing the Omega failure detector class, which provides a leader election functionality, in the crash-recovery failure model. The concepts of communication efficiency and near-efficiency for an algorithm implementing Omega are defined. Depending on the use or not of stable storage, the property satisfied by unstable processes, i.e., those that crash and recover infinitely often, varies. Two algorithms implementing Omega are presented. In the first algorithm, which is communication-efficient and uses stable storage, eventually and permanently unstable processes agree on the leader with correct processes. In the second algorithm, which is near-communication-efficient and does not use stable storage, processes start their execution with no leader in order to avoid the disagreement among unstable processes, that will agree on the leader with correct processes after receiving a first message from the leader.

On the implementation of the Omega failure detector in the crash-recovery failure model

Unreliable failure detectors are mechanisms providing information about process failures that allow solving several problems in asynchronous systems, e.g., Consensus. A particular class of failure detectors, Omega, provides an eventual leader election functionality. This paper addresses the implementation of Omega in the crash-recovery failure model. Recently we have proposed an algorithm assuming that eventually the correct process with the smallest identifier and minimum incarnation number can communicate timely with the rest of processes. Here we propose two Omega algorithms which assume only that processes are reachable from some correct process, independently of its identifier and incarnation number. The first one requires the membership to be known a priori, while the second one relaxes this assumption too

A simple and communication-efficient Omega algorithm in the crash-recovery model

This paper presents a new algorithm implementing the Omega failure detector in the crash-recovery model. Contrary to previously proposed algorithms, this algorithm does not rely on the use of stable storage and is communication-efficient, i.e., eventually only one process (the elected leader) keeps sending messages. The algorithm relies on a nondecreasing local clock associated with each process. Since stable storage is not used to keep the identity of the leader in order to read it upon recovery, unstable processes, i.e., those that crash and recover infinitely often, output a special @? value upon recovery, and then agree with correct processes on the leader after receiving a first message from it.

Eventual Leader Election in the Crash-Recovery Failure Model

Unreliable failure detectors provide information about process failures. A particular failure detector called Omega has been shown to be the weakest for solving consensus with a majority of correct processes. This work addresses the implementation of Omega in the crash-recovery failure model. Firstly, the definition of Omega is adapted to that model, assuming that processes do not use stable storage. After that, an algorithm implementing Omega under some weak assumptions on communication reliability and synchrony is proposed.

Fault-tolerant aggregator election and data aggregation in wireless sensor networks

This paper presents three algorithms for aggregator election and data aggregation in wireless sensor networks where sensors can crash and recover. The network is divided in several regions. The algorithms ensure the election of a common data aggregator sensor within each region, in charge of the collection of local data and the election of a unique super-aggregator sensor, in charge of the collection of global data, among all the aggregators. Both elections are achieved by implementing the Omega failure detector, which provides a self-organising and fault-tolerant leader election service. Each algorithm is based on a different connectivity assumption. The first algorithm assumes that every pair of sensors in a region can communicate directly. The second algorithm only requires some correct sensor to communicate directly with the rest of sensors. Finally, the third algorithm only requires the existence of a multi-hop bidirectional path from some correct sensor to the rest of sensors. We also introduce a battery depletion threshold to enhance the quality of service of the wireless sensor network.

Coordinated data aggregation in wireless sensor networks using the Omega failure detector

We present an algorithm implementing the failure detector class omega (Ω) in the crash-recovery model to coordinate data aggregation in wireless sensor networks. The algorithm ensures the agreement on a common aggregator by all sensors of a region, as well as on a common super-aggregator among the set of aggregators of the network, hence providing a hierarchical energy-efficient data aggregation mechanism. We also introduce a battery depletion threshold to enhance the quality of service of the wireless sensor network

Quiescent Leader Election in Crash-Recovery Systems

This work addresses the leader election problem in distributed systems where processes can crash and recover. More precisely, it focuses on implementing the Omega failure detector class, which provides a leader election functionality, in the crash-recovery failure model. The concepts of quiescence and near-quiescence for an algorithm implementing Omega are defined. Depending on the use or not of stable storage, the property satisfied by unstable processes, i.e., those that crash and recover infinitely often, varies. Two algorithms implementing Omega are presented. In the first algorithm, which is quiescent and uses stable storage, eventually and permanently unstable processes agree on the leader with correct processes. In the second algorithm, which is near-quiescent and does not use stable storage, unstable processes agree on the leader with correct processes after receiving a first message from a correct process. An adaptation of this second algorithm that avoids the disagreement of unstable processes by providing instability awareness is also presented.

Implementing the \Omega Failure Detector in the Crash-Recovery Model with partial Connectivity and/or Synchrony

Unreliable failure detectors are mechanisms providing information about process failures, that allows to solve several problems in asynchronous systems, e.g., consensus. A particular class of failure detectors, Omega, provides an eventual leader election functionality. Recently, an algorithm implementing Omega with unknown membership and weak synchrony has been proposed by Jimenez et al. In that work, a crash failure model and a system in which every process has a direct communication link with every other process are assumed. In this paper, we adapt this algorithm to the crash-recovery failure model, and show that it also works in systems with partial connectivity and/or synchrony