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Whitbeck J.,Thales Alenia | Conan V.,Thales Alenia | De Amorim M.D.,Sorbonne Universits
Proceedings of the Annual International Conference on Mobile Computing and Networking, MOBICOM | Year: 2010

The limitations of contact-logging experiments, particularly those based on periodic Bluetooth neighborhood scans, prevent them from detecting many contact opportunities. This paper highlights recent results on inferring a plausible movement from contact traces and shows how they may be used to identify those missed contacts. This analysis is then applied to the Rollernet contact trace and indicates that these missed contacts have an important impact on protocol performance evaluation. Copyright 2010 ACM.

Dubois S.,Sorbonne Universits | Dubois S.,French Institute for Research in Computer Science and Automation | Potop-Butucaru M.,Sorbonne Universits | Potop-Butucaru M.,French Institute for Research in Computer Science and Automation | And 2 more authors.
Theoretical Computer Science | Year: 2011

Distributed fault-tolerance can mask the effect of a limited number of permanent faults, while self-stabilization provides forward recovery after an arbitrary number of transient faults hit the system. FTSS (Fault-Tolerant Self-Stabilizing) protocols combine the best of both worlds since they tolerate simultaneously transient and (permanent) crash faults. To date, deterministic FTSS solutions either consider static (i.e. fixed point) tasks, or assume synchronous scheduling of the system components. In this paper, we present the first study of deterministic FTSS solutions for dynamic tasks in asynchronous systems, considering the unison problem as a benchmark. Unison can be seen as a local clock synchronization problem as neighbors must maintain digital clocks at most one time unit away from each other, and increment their own clock value infinitely often. We present several impossibility results for this difficult problem and propose an FTSS solution (when the problem is solvable) for the state model that exhibits optimal fault-containment. © 2011 Elsevier B.V. All rights reserved.

Dieudonne Y.,University of Picardie Jules Verne | Petit F.,Sorbonne Universits
Theoretical Computer Science | Year: 2012

In this paper, we investigate the possibility to deterministically solve the gathering problem starting from an arbitrary configuration with weak robots, i.e., anonymous, autonomous, disoriented, oblivious, and devoid of means of communication. By starting from an arbitrary configuration, we mean that robots are not required to be located at distinct positions in the initial configuration. We introduce strong multiplicity detection as the ability for the robots to detect the exact number of robots located at a given position. We show that with strong multiplicity detection, there exists a deterministic algorithm solving the gathering problem starting from an arbitrary configuration for n robots if, and only if, n is odd. © 2011 Elsevier B.V. All rights reserved.

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