Egomunities, Exploring Socially Cohesive Person-based Communities

In the last few years, there has been a great interest in detecting overlapping communities in complex networks, which is understood as dense groups of nodes featuring a low outbound density. To date, most methods used to compute such communities stem from the field of disjoint community detection by either extending the concept of modularity to an overlapping context or by attempting to decompose the whole set of nodes into several possibly overlapping subsets. In this report we take an orthogonal approach by introducing a metric, the cohesion, rooted in sociological considerations. The cohesion quantifies the community-ness of one given set of nodes, based on the notions of triangles - triplets of connected nodes - and weak ties, instead of the classical view using only edge density. A set of nodes has a high cohesion if it features a high density of triangles and intersects few triangles with the rest of the network. As such, we introduce a numerical characterization of communities: sets of nodes featuring a high cohesion. We then present a new approach to the problem of overlapping communities by introducing the concept of ego-munities, which are subjective communities centered around a given node, specifically inside its neighborhood. We build upon the cohesion to construct a heuristic algorithm which outputs a node's ego-munities by attempting to maximize their cohesion. We illustrate the pertinence of our method with a detailed description of one person's ego-munities among Facebook friends. We finally conclude by describing promising applications of ego-munities such as information inference and interest recommendations, and present a possible extension to cohesion in the case of weighted networks

Triangles to Capture Social Cohesion

Although community detection has drawn tremendous amount of attention across the sciences in the past decades, no formal consensus has been reached on the very nature of what qualifies a community as such. In this article we take an orthogonal approach by introducing a novel point of view to the problem of overlapping communities. Instead of quantifying the quality of a set of communities, we choose to focus on the intrinsic community-ness of one given set of nodes. To do so, we propose a general metric on graphs, the cohesion, based on counting triangles and inspired by well established sociological considerations. The model has been validated through a large-scale online experiment called Fellows in which users were able to compute their social groups on Face- book and rate the quality of the obtained groups. By observing those ratings in relation to the cohesion we assess that the cohesion is a strong indicator of users subjective perception of the community-ness of a set of people

Capacity and interference modeling of CSMA/CA networks using SSI point processes

International audienceThe relative location of simultaneous transmitters, i.e. the set of nodes transmitting a frame at a given time, has a crucial impact on the performance of multi hop wireless networks. Two fundamental aspects of wireless network performances are related to these locations: capacity and interference. Indeed, as interference results from the summation of signals stemmed by concurrent transmitters, it directly depends on the transmitters' location. On the other hand, the network capacity is proportional to the number of simultaneous transmitters. In this paper, we investigate original point processes that can be used to model the location of transmitters that comply with the CSMA/CA policies, i.e. the Medium Access Control protocol used in 802.15.4 and 802.11 families of wireless technologies. We first propose the use of the Simple Sequential Inhibition point process to model CSMA/CA networks where clear channel assessment depends on the strongest emitter only. We then extend this point process to model a busy medium detection based on the strength of all concurrent signals. We finally compare the network capacity obtained through realistic simulations to a theoretical capacity estimated using the intensity of the SSI point process. It turns out that the proposed model is validated by the simulations

Biais dans les mesures obtenues par un réseau de capteurs sans fil

International audienceIn the area of complex networks, research has been stimulated by the availability of important data sets obtained through automatic measurement. In this article, we focus on interaction data in a hospital, gathered through the use of a wireless sensor network. We highlight the bias introduced by the measurement system and propose a method to reconstruct the original signal which evidences phenomenon which were not visible on the raw data

Demonstration of worldsens: a fast prototyping and performance evaluation of wireless sensor network applications & protocols

International audienceWe present Worldsens, a complete environment for fast prototyping of wireless sensor protocols and applications. Our environment proposes a full simulation platform with both embedded software instruction and radio packet accuracy. We propose a demonstration including a full software design, simulation, performance estimation and deployment on a set of nodes within the same design environment. Through these first experimentations, we show that accurate sensor network simulation is feasible and that complex application design and deployment is affordable

Communautés : Arrêtons de ne compter que les arêtes

International audienceDans cet article, nous souhaitons revenir sur la question de la définition d'une communauté en tant qu'ensemble de sommets U sans avoir à en juger la qualité au regard des autres communautés, recouvrantes ou non. Ce qui importe c'est uniquement l'ensemble U considéré et le graphe sous-jacent et ce indépendamment de tout découpage global. À dessein, nous introduisons la " cohésion " qui repose sur la relation forte qui existe entre des triplets de sommets lorsqu'ils forment un triangle ou au contraire sur la non présence de triangle traduisant la présence de lien faible (notion de "weak tie" introduite par A. Rapoport en 1957 et reprise par M.S. Granovetter en 1973). La notion de communauté découle de cette mesure confinée à un sous-ensemble de sommets plongé dans son graphe d'origine : une communauté est un ensemble de sommets offrant une forte cohésion. Après avoir introduit la métrique de cohésion, nous illustrons son application sur la découverte de communautés egocentrées dans des réseaux sociaux en utilisant un algorithme se basant sur la cohésion et donnons quelques résultats sur l'application de ce calcul d'egomunautés

Energy aware unicast geographic routing

Abstract — In this paper, we are investigating the optimal radio range minimizing the energy globally consummed by a geographical routing process. Considering a geographical greedy routing protocol and a uniform distribution of nodes in the network area, we analytically evaluate the energy cost of a multi-hop communication. This cost evaluation corresponds to the asymptotic behavior of the routing protocol and turns out to be very accurate compared to the results obtained by simulations. We show that this cost is function of the node intensity and we use this result to deduce the optimal radio range. We evaluate this range with two energy consumption models, the first one considering the energy consumed by transmission operations only and the second one considering both transmission and reception operations. These results can be used in two ways. First, the nodes range can be tuned in advance as a function of the expected node intensity during an off-line planning. Second, we propose an adaptative algorithm where nodes tune their powers according to an on-line evaluation of the local node intensity. I

Worldsens: development and prototyping tools for application specific wireless sensors networks

International audienceIn this paper we present Worldsens, an integrated environment for development and rapid prototyping of wireless sensor network applications. Our environment relies on software simulation to help the designer during the whole development process. The refinement is done starting from the high level design choices down to the target code implementation, debug and performance analysis. In the early stages of the design, high level parameters, like for example the node sleep and activity periods, can be tuned using WS-Net, an event driven wireless network simulator. WSNet uses models for applications, protocols and radio medium communication with a parameterized accuracy. The second step of the sensor network application design takes place after the hardware implementation choices. This second step relies on the WSim cycle accurate hardware platform simulator. WSim is used to debug the application using the real target binary code. Precise performance evaluation, including real-time analysis at the interrupt level, are made possible at this low simulation level. WSim can be connected to WSNet, in place of the application and protocol models used during the high level simulation to achieve a full distributed application simulation. WSNet and WSNet+WSim allow a continuous refinement from high level estimations down to low level real-time validation. We illustrate the complete application design process using a real life demonstrator that implements a hello protocol for dynamic neighborhood discovery in a wireless sensor network environment

PFMAC : Routage sans connaissance du voisinage efficace en énergie

Session Réseaux de capteursInternational audienceL'efficacité énergétique constitue l'objectif clef pour la conception des protocoles de communication pour des réseaux de capteurs sans fil. De nombreuses stratégies proposent d'économiser l'énergie à diffé- rents niveaux de la pile protocolaire : couches MAC avec techniques d'ordonnancement et d'endormissement, routage efficace en énergie ou encore des techniques d'agrégation de données. Récemment, le routage géogra- phique sans contrôle a émergé comme une alternative pour prolonger la durée de vie d'un réseau de capteurs. Toutefois, les protocoles proposés ne sont pas adaptés à un environnement radio réel à cause de la stratégie de planarisation utilisée ou d'hypothèses discutables comme la connaissance de la portée radio. En outre, ils souffrent énormément des écoutes passives et involontaires du canal. Dans cet article, nous proposons PFMAC (Pizza-Forwarding Medium Access Control) intégrant, de façon transversale, un routage géographique sans contrôle réactif et un protocole MAC efficace en énergie. PFMAC garantit une grande efficacité énergétique avec un meilleur taux de livraison. PFMAC utilise un routage glouton et un routage basé sur une découverte optimisée du 2-voisinage pour contourner un trou. Une évaluation des performances par simulation est propo- sée afin de mettre en évidence les performances de PFMAC par rapport au protocole BOSS intégré à BMAC

Convergence speed of a link-state protocol for IPv6 router autoconfiguration

This report presents a model for the NAP protocol, dedicated to the auto-configuration of IPv6 routers. If the auto-configuration of hosts is defined by IPv6 and mandatory, IPv6 routers still have to be manually configured. In order to succeed in new networking domains, a full auto-configuration feature must be offered. NAP offers a fully distributed solution that uses a link state OSPFv3-like approach to perform prefix collision detection and avoidance. In this report, we present a model for NAP and analyze the average and maximum autoconfiguration delay as a function of the network size and the prefix space size