Nearest Neighbors Graph Construction: Peer Sampling to the Rescue

International audienceIn this paper, we propose an efficient KNN service, called KPS (KNN-Peer-Sampling). The KPS service can be used in various contexts e.g. recommendation systems, information retrieval and data mining. KPS borrows concepts from P2P gossip-based clustering protocols to provide a localized and efficient KNN computation in large-scale systems. KPS is a sampling-based iterative approach, combining ran-domness, to provide serendipity and avoid local minimum, and clustering , to ensure fast convergence. We compare KPS against the state of the art KNN centralized computation algorithm NNDescent, on multiple datasets. The experiments confirm the efficiency of KPS over NNDescent: KPS improves significantly on the computational cost while converging quickly to a close to optimal KNN graph. For instance, the cost, expressed in number of pairwise similarity computations, is reduced by ≈ 23% and ≈ 49% to construct high quality KNN graphs for Jester and MovieLens datasets, respectively. In addition, the randomized nature of KPS ensures eventual convergence, not always achieved with NNDescent

A Distributed Polling with Probabilistic Privacy

In this paper, we present PDP, a distributed polling protocol that enables a set of participants to gather their opinion on a common interest without revealing their point of view. PDP does not rely on any centralized authority or on heavyweight cryptography. PDP is an overlay-based protocol where a subset of participants may use a simple sharing scheme to express their votes. In a system of $M$ participants arranged in groups of size $N$ where at least $2k-1$ participants are honest, PDP bounds the probability for a given participant to have its vote recovered with certainty by a coalition of $B$ dishonest participants by $pi(B/N)^(k+1)$, where $pi$ is the proportion of participants splitting their votes, and $k$ a privacy parameter. PDP bounds the impact of dishonest participants on the global outcome by $2(k&alpha + BN), where represents the number of dishonest nodes using the sharing scheme

ANALYSE DU COMPORTEMENT DU HANDOVER VERTICAL SELON UNE VARIETE DE PROTOCOLES DE TRANSPORT

Ce travail s’inscrit dans un projet visant à assurer une continuité de service pour une application de Voix IP (Internet Protocol) lors de la traversée de deux réseaux mobiles différents. Dans cet article nous nous intéressons à évaluer l’utilisation de différents protocoles de transport TCP (Transport Control Protocol) : TCP New-Reno et TCP Vegas, en considérant différents paramètres liés à la QoS (Quality of Service). Cette évaluation s’effectue dans un contexte de mobilité d’un utilisateur entre deux réseaux mobiles hétérogènes (Wifi et Wimax). La plateforme NS2 (Network Simulator) sera utilisée pour effectuer les mesures nécessaires à cette évaluation de protocoles

A game theory-based approach for robots deploying wireless sensor nodes

International audienceWireless Sensor Networks (WSNs) are deployed in many fields of application. Depending on the application requirements, sensor nodes can either be mobile and autonomous or static. In both cases, they are able to cooperate together in order to monitor a given area or some given Points of Interest (PoIs). Static sensor nodes need one or several agent(s) (humans or robots) to deploy them. In this paper, we focus on the deployment of static sensor nodes in an area containing obstacles, using two mobile robots. We want to minimize the time needed by the two robots to deploy all the sensor nodes and to return to their starting position. We require that each sensor node is placed at a PoI position, no PoI position is empty and no PoI position is occupied by more than one sensor node. The problem consists in determining the best strategy for each robot in order to meet these constraints. We adopt a game theory approach to solve this problem

Measurements of Photon Beam Flattening Filter Using an Anisotropic Analytical Algorithm and Electron Beam Employing Electron Monte Carlo

Introduction: This study aimed to report the measurement of photon and electron beams to configure the Analytical Anisotropic Algorithm and Electron Monte Carlo used in clinical treatment. Material and Methods: All measurements were performed in a large water phantom using a 3-dimensional scanning system (PTW, Germany). For photon beams, the data were measured with a 0.125cc cylindrical chamber. For electron, the data were performed with a Roos chamber. Results: In photon beams, flatness and symmetry for reference field size 10×10cm2 were within the tolerance intervals. Flatness were 0.79% and 1.55% for X6MV and X18MV, respectively. Symmetry were 0.57 and 0.25 for X6MV and X18MV, respectively. The output factor vary between 0.83 and 1.11 for X6MV. Moreover, it varies between 0.74 and 1.09 for X18MV. The leaf transmission factors were 0.97% for X6MV and1.14% for X18MV. The DLG were 1.31 and 1.34 for X6MV and X18MV, respectively. For electron beams, the quality index R50 for applicator 15×15cm2 were in the tolerance. Maximum depth dose for 6, 9, 12, 16 and 20MeV were 1.2, 1.9, 2.7, 2.99 and 2.4cm, respectively. Bremsstrahlung tail were 6MeV–2.86cm, 9MeV–4.32cm, 12MeV–5.96cm, 16MeV–7.93cm, and 20MeV–10.08cm per energy levels. Conclusion: The obtained results and international recommendations were in a good agremen

An SDL Specification of Coordination within a Teleconferencing System

Rapport interne.Advances in multimedia technology and highspeed networks leads to new types of applications. Especially, teleconferencing and collaborative work has emerged as new type of communication. Teleconferencing denotes synchronous collaboration, among a conference participants, that combine shared workspaces and live media (audio, video). Such media are computed and transported through a video conferencing system. Some of the problems, that the teleconferencing systems designers are faced with, we find synchronisation, session management and coordination, floor control and human habits to work in collaborative groups. Such problems are most of the time due to the complexity of these systems. Abstraction combined with the use of Formal Description Techniques, are ones of the most prevalent techniques to deal with complexity. In this work, we define an architecture of a teleconferencing system. This architecture consists in a coordination level and a videconferencing level. Then we present our experiment using SDL to describe the behaviors corresponding to the coordination and videoconferencing system components. We present also the interaction between such components

A formal basis for the design and analysis of firewall security policies

A firewall is the core of a well defined network security policy. This paper presents an automata-based method to study firewall security policies. We first propose a procedure that synthesizes an automaton that describes a security policy given as a table of rules. The synthesis procedure is then used to develop procedures to detect: incompleteness, anomalies and discrepancies in security policies. A method is developed to represent the automaton by a policy qualified as mixable and that has practical utilities, such as ease to determine the whitelist and the blacklist of the policy. The developed procedures have been deeply evaluated in terms of time and space complexities. Then, a real case study has been investigated. The obtained results confirm that the developed procedures have reasonable complexities and that their actual execution times are of the order of seconds. Finally, proofs of all results are provided

Dynamic Evolution of Distributed Systems Speci cations Using Re Language

RÉSUMÉ. Récemment, les spécifications orientées objets des systèmes distribués ont suscité beaucoup d'interêt. L'approche orientée objet offre beaucoup de flexibilité pour la construction des systèmes. Cependant, un des problèmes culminant est d'effectuer des modifications de façon dynamique durant le processus de développement d’exploitation et de maintenance. Nous nous intéressons dans cet article, aux techniques de description formelle qui permettent le développement et la modification dynamique des spécifications exécutables. Nous introduisons un modèle à deux niveaux pour l'évolution des spécifications orientées objets. Le premier niveau concerne la modification dynamique des types (classes), alors que le second niveau est consacré à la modification dynamique des modules. Pour chacun des niveaux, nous définissons un ensemble de contraintes, structurelles et comportementales, qui assurent la consistence de la spécification après sa modification. Pour effectuer les modifications de façon dynamique, nous avons développé un langage réflexif de spécification orientée objet. Ce langage permet de définir les opérations de modifications à un meta-niveau en utilisant des meta-objets. Dans ce langage, les types et les modules sont des objets. MOTS-CLES. Spécification orientée objet, évolution de logiciel, modification des types, compatibilité des modules, réflection, modification dynamique