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    Optimistic Replication Approach for Transactional Mobile Agent Fault Tolerance
    (Jixin Ma, Liz Bacon, Wencai Du, Miltos Petridis, 2010-06-09) Zeghache, Linda; Badache, Nadjib
    The mobile agent is a computer program that can move between different hosts in heterogeneous networks. This paradigm is advantageous for distributed systems implementation, especially in mobile computing application characterized by low bandwidth, high latency and unreliable networks connections. Mobile agent is also attractive for distributed transactions applications. Although mobile agent has been studied for twenty years for some good reasons, it is not largely used in developing distributed systems for simple reasons: important issues like security and fault tolerance are not solved in effective way. In this paper we address the issue of fault tolerance in mobile agent systems and transactional support. We present the agent system design and describe the protocol of our approach in which we treat infrastructure failures to prevent a partial or complete loss of mobile agent and deal with semantic failures to ensure atomic execution and transactional support for mobile agent.
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    Self-Repairing Clusters for Time-Efficient and Scalable Actor-Fault-Tolerance in Wireless Sensor and Actor Networks
    (Springer, 2011) Amirouche, Loucif; Djenouri, Djamel; Badache, Nadjib
    A new solution for fault-tolerance in wireless sensor and actor networks (WSAN) is proposed. The solution deals with fault-tolerance of actors, contrary to most of the literature that only considers sensors. It considers real-time communication, and ensures the execution of tasks with low latency despite fault occurrence. A simplified MAMS (multiple-actor multiple-sensor) model is used, where sensed events are duplicated only to a limited number of actors. This is different from the basic MAMS model and semi-passive coordination (SPC), which use data dissemination to all actors for every event. Although it provides high level of fault- tolerance, this large dissemination is costly in terms of power consumption and communication overhead. The proposed solution relies on the construction of self-repairing clusters amongst actors, on which the simplified MAMS is applied. This clustering enables actors to rapidly replace one another whenever some actor breaks down, and eliminates the need of consensus protocol execution upon fault detection, as required by the current approaches to decide which actor should replace the faulty node. The extensive simulation study carried out with TOSSIM in different scenarios shows that the proposed protocol reduces the latency of replacing faulty actors compared to current protocols like SPC. The reduction of the overall delay for executing actions reaches 59%, with very close fault-tolerance (action execution success rate). The difference for this metric does not exceed 8% in the worst case. Scenarios of different network sizes confirm the results and demonstrate the protocol’s scalability.