Towards a Practical and Fair Rate Allocation for Multihop Wireless Networks based on a Simple Node Model

IEEE 802.11 is often considered as the underlying wireless technology of multihop wireless networks. But the use of 802.11 in such networks raises issues, like efficiency and/or fairness issues. Different kinds of solutions have been proposed to overcome these problems. One approach is to design new MAC protocols that provide alternatives to the IEEE 802.11 MAC protocol. Although these solutions are of some interest, it should probably take some time before new wireless network interface cards based on one of these solutions are developed and released. Another approach is to consider that 802.11 will remain the underlying wireless technology and to design solutions above it. Several solutions based on rate allocation have been proposed so far. The main drawback of the proposed solutions is that they rely on a radio medium sharing model that is difficult to compute in a wireless, distributed and mobile environment. Indeed, very few of these solutions have been derived into a network protocol. In this article, we propose a distributed and dynamic rate allocation solution that is based on a simple sharing model. Due to its simplicity, we can derive a network protocol that can be practically used in multihop wireless networks. This protocol provides a fair bandwidth sharing between end-to-end flows while maintaining an efficient overall throughput in the network. This solution has been implemented in NS2 and evaluated by simulations

Evaluation d'un protocole de régulation de débit dans les réseaux sans fil multisauts

International audienceLe standard IEEE 802.11 est très souvent considéré comme la technologie sans fil sous-jacente dans les réseaux radio multisauts. Il est maintenant bien connu que l'utilisation de ce standard pose des problèmes d'efficacité et d'équité dans de tels réseaux. Ces problèmes proviennent en partie du protocole MAC de 802.11. Une approche possible est de proposer une alternative à ce protocole MAC afin de limiter ou d'éliminer ces problèmes. Néanmoins, il faudra très probablement attendre un certain temps avant de voir apparaître, sur le marché, des cartes sans fil adaptées aux réseaux multisauts. Une autre approche est de considérer que la technologie sous-jacente restera 802.11 pour un certain temps et que les solutions doivent se situer au-dessus de 802.11. Dans [VAN 08], nous avons proposé un algorithme d'allocation de bande passante distribué et dynamique qui reposait sur un modèle simple de partage du médium radio. Dans cet article, nous transformons cet algorithme en un protocole de régulation de débit pour les réseaux sans fil multisauts. Ce protocole, appelé Profiterole, est distribué, asynchrone, dynamique et nécessite peu d'informations sur le réseau. Puis, nous proposons une évaluation détaillée de Profiterole menée sous le simulateur de réseaux NS2. Enfin, nous le comparons à DiffQ, un nouveau protocole de contrôle de congestion dans les réseaux sans fil multisauts

A Utility-based Framework for Assessing Fairness Schemes in Ad-Hoc Networks

Fairness in multihop ad hoc networks has received considerable attention in the literature. A plethora of protocols have been proposed, which compute the ``optimal'' bit rates of the transmitting mobile nodes over short time-scales so that a certain fairness criterion is met. However, there has been limited research on the impact of the varying short-term allocations of these protocols due to nodes mobility on the user-perceived QoS (and social welfare) for services of long duration. In this paper, we introduce a utility-based framework, based on {\em QoS-aware history-dependent} utility functions. These functions quantify the satisfaction that the users of the MANETs obtain from the way their long-lived service sessions are allocated bandwidth, due to the behavior of the fairness protocols proposed for ad hoc networks. Finally, we demonstrate the framework's usefulness, by performing a comparative assessment of the fairness protocol of our previous work with the standard IEEE 802.11

Partage équitable de la bande passante dans les réseaux ad hoc

12 pagesSome previous works have shown that the DCF mode within the IEEE 802.11 standard can be inappropriate for many ad hoc configurations. In some situations, the bandwidth allocation between multiple flows can be extremely unfair. Some solutions have already attempted to solve these problems, either by modifying the MAC layer, or by regulating the flow throughput at a higher level. The latter are usually based upon a complex interference model using link contention graphs, thus making the resulting bandwidth allocation algorithms hard to use practically. In this article, we propose a distributed and dynamic bandwidth allocation algorithm based on a simpler model. We show by simulation that the quality of the resulting allocations are roughly equivalent in both models, even though the algorithms are greatly simplified

Quelle R&D Mener pour le Développement Des Réseaux D'énergie De Demain ? Les Propositions de L'ancre en 2015

Feuille de route sur les réseaux électriques et stockage élaborée par le GP10 Réseaux et Stockages de l'Energie de l'ANCRECette feuille de route concerne les réseaux d’énergie électrique, de chaleur et de froid, les réseaux de gaz (hydrogène, gaz naturel), leurs stockages associés, ainsi que leurs couplages à venir dans le cadre de la transition énergétique et des évolutionsqui l’accompagneront, que ce soit sur les modes de production d’énergie ou sur l’évolution des usages.Le focus est porté sur les réseaux électriques qui seront les premiers impactés par cette transition énergétique. Hormisquelques éléments très spécifiques aux réseaux électriques (et qui seront notés dans le texte par une couleur différente)il est à souligner que la quasi-totalité des considérations et axes de R&D évoqués pour les réseauxélectriques et le développement de leur « intelligence » et/ou de leur flexibilité s’appliquentégalement aux autres réseaux d’énergie. Par ailleurs, si le groupe programmatique« Réseaux et Stockage » de l’ANCRE (GP10) s’est largement appuyé sur les nombreuses feuilles de route émises tant au niveau national, dont celles de l’ADEME, qu’européen, il a également souhaité s’en démarquer en insistantlargement et en détaillant les recherches scientifiques et technologiques à mener face aux verrous actuellement identifiés

LITpro: a model fitting software for optical interferometry

9 pagesInternational audienceLITpro is a software for fitting models on data obtained from various stellar optical interferometers, like the VLTI. As a baseline, for modeling the object, it provides a set of elementary geometrical and center-to-limb darkening functions, all combinable together. But it is also designed to make very easy the implementation of more specific models with their own parameters, to be able to use models closer to astrophysical considerations. So LITpro only requires the modeling functions to compute the Fourier transform of the object at given spatial frequencies, and wavelengths and time if needed. From this, LITpro computes all the necessary quantities as needed (e.g. visibilities, spectral energy distribution, partial derivatives of the model, map of the object model). The fitting engine, especially designed for this kind of optimization, is based on a modified Levenberg-Marquardt algorithm and has been successfully tested on real data in a prototype version. It includes a Trust Region Method, minimizing a heterogeneous non-linear and non-convex criterion and allows the user to set boundaries on free parameters. From a robust local minimization algorithm and a starting points strategy, a global optimization solution is effectively achieved. Tools have been developped to help users to find the global minimum. LITpro is also designed for performing fitting on heterogeneous data. It will be shown, on an example, how it fits simultaneously interferometric data and spectral energy distribution, with some benefits on the reliability of the solution and a better estimation of errors and correlations on the parameters. That is indeed necessary since present interferometric data are generally multi-wavelengths

Study of the atmospheric refraction in a single mode instrument - Application to AMBER/VLTI

International audienceThis paper presents a study of the atmospheric refraction and its effect on the light coupling efficiency in an instrument using single-mode optical fibers. We show the analytical approach which allowed us to assess the need to correct the refraction in J- and H-bands while observing with an 8-m Unit Telescope. We then developed numerical simulations to go further in calculations. The hypotheses on the instrumental characteristics are those of AMBER (Astronomical Multi BEam combineR), the near infrared focal beam combiner of the Very Large Telescope Interferometric mode (VLTI), but most of the conclusions can be generalized to other single-mode instruments. We used the software package caos (Code for Adaptive Optics Systems) to take into account the atmospheric turbulence effect after correction by the ESO system MACAO (Multi-Application Curvature Adaptive Optics). The opto-mechanical study and design of the system correcting the atmospheric refraction on AMBER is then detailed. We showed that the atmospheric refraction becomes predominant over the atmospheric turbulence for some zenith angles z and spectral conditions: for z larger than 30° in J-band for example. The study of the optical system showed that it allows to achieve the required instrumental performance in terms of throughput in J- and H-bands. First observations in J-band of a bright star, alpha Cir star, at more than 30° from zenith clearly showed the gain to control the atmospheric refraction in a single mode instrument, and validated the operating law

Babesiosis in Immunocompetent Patients, Europe

We report 2 cases of babesiosis in immunocompetent patients in France. A severe influenza-like disease developed in both patients 2 weeks after they had been bitten by ticks. Diagnosis was obtained from blood smears, and Babesia divergens was identified by PCR in 1 case. Babesiosis in Europe occurs in healthy patients, not only in splenectomized patients

Social and Hydrological Responses to Extreme Precipitations: An Interdisciplinary Strategy for Postflood Investigation

International audienceThis paper describes and illustrates a methodology to conduct postflood investigations based on interdisciplinary collaboration between social and physical scientists. The method, designed to explore the link between crisis behavioral response and hydrometeorological dynamics, aims at understanding the spatial and temporal capacities and constraints on human behaviors in fast-evolving hydrometeorological conditions. It builds on methods coming from both geosciences and transportations studies to complement existing post-flood field investigation methodology used by hydrometeorologists. The authors propose an interview framework, structured around a chronological guideline to allow people who experienced the flood firsthand to tell the stories of the circumstances in which their activities were affected during the flash flood. This paper applies the data collection method to the case of the 15 June 2010 flash flood event that killed 26 people in the Draguignan area (Var, France). As a first step, based on the collected narratives, an abductive approach allowed the identification of the possible factors influencing individual responses to flash floods. As a second step, behavioral responses were classified into categories of activities based on the respondents' narratives. Then, aspatial and temporal analysis of the sequences made of the categories of action to contextualize the set of coping responses with respect to local hydrometeorological conditions is proposed. During this event, the respondents mostly follow the pace of change in their local environmental conditions as the flash flood occurs, official flood anticipation being rather limited and based on a large-scale weather watch. Therefore, contextual factors appear as strongly influencing the individual's ability to cope with the event in such a situation

AMBER : a near infrared focal instrument for the VLTI

10 pagesInternational audienceAMBER is the General User near-infrared focal instrument of the Very Large Telescope interferometer. Its specifications are based on three key programs on Young Stellar Objects, Active Galactic Nuclei central regions, masses and spectra of hot Extra Solar Planets. It has an imaging capacity because it combines up to three beams and very high accuracy measurement are expected from the spatial filtering of beams by single mode fibers and the comparison of measurements made simultaneously in different spectral channels