Le " projet de voyage ", un cadre interprétatif des pratiques touristiques en ville ?

http://www.univ-paris1.fr/fileadmin/doctoriales-tourisme/Textes_doctoriales/Simon_doctoriales.pdfNational audienceAlthough the dynamics of the urban tourism phenomenon are widely studied and tourism flows toward certain destinations are considerable, we paradoxically know rather little about what precisely tourists do in cities, even in a city like Paris. This paper highlights how tourists' travel plans are used as an analytical framework for urban practices.Le tourisme urbain est aujourd'hui un phénomène dont les dynamiques sont largement étudiées. L'enjeu de connaissance est paradoxalement peu porté sur ce que font précisément les touristes dans les métropoles, même dans une ville mondialement médiatisée comme Paris. Ce papier développe et discute la notion de " projet de voyage " comme cadre d'analyse des pratiques urbaines des touristes à Paris

Corps, technologies et handicaps dans le logement : comment favoriser la capacité d'action des vieilles personnes ?

Communication en ligne à l'adresse suivante : http://www.marsouin.org/IMG/pdf/gwendal_simon_proposition_communication_Marsouin.pdf. Ensemble des actes et diaporamas à l'adresse suivante : http://www.marsouin.org/spip.php?article359National audienc

A note on the data-driven capacity of P2P networks

We consider two capacity problems in P2P networks. In the first one, the nodes have an infinite amount of data to send and the goal is to optimally allocate their uplink bandwidths such that the demands of every peer in terms of receiving data rate are met. We solve this problem through a mapping from a node-weighted graph featuring two labels per node to a max flow problem on an edge-weighted bipartite graph. In the second problem under consideration, the resource allocation is driven by the availability of the data resource that the peers are interested in sharing. That is a node cannot allocate its uplink resources unless it has data to transmit first. The problem of uplink bandwidth allocation is then equivalent to constructing a set of directed trees in the overlay such that the number of nodes receiving the data is maximized while the uplink capacities of the peers are not exceeded. We show that the problem is NP-complete, and provide a linear programming decomposition decoupling it into a master problem and multiple slave subproblems that can be resolved in polynomial time. We also design a heuristic algorithm in order to compute a suboptimal solution in a reasonable time. This algorithm requires only a local knowledge from nodes, so it should support distributed implementations. We analyze both problems through a series of simulation experiments featuring different network sizes and network densities. On large networks, we compare our heuristic and its variants with a genetic algorithm and show that our heuristic computes the better resource allocation. On smaller networks, we contrast these performances to that of the exact algorithm and show that resource allocation fulfilling a large part of the peer can be found, even for hard configuration where no resources are in excess.Comment: 10 pages, technical report assisting a submissio

Optimized Adaptive Streaming Representations based on System Dynamics

Adaptive streaming addresses the increasing and heterogenous demand of multimedia content over the Internet by offering several encoded versions for each video sequence. Each version (or representation) has a different resolution and bit rate, aimed at a specific set of users, like TV or mobile phone clients. While most existing works on adaptive streaming deal with effective playout-control strategies at the client side, we take in this paper a providers' perspective and propose solutions to improve user satisfaction by optimizing the encoding rates of the video sequences. We formulate an integer linear program that maximizes users' average satisfaction, taking into account the network dynamics, the video content information, and the user population characteristics. The solution of the optimization is a set of encoding parameters that permit to create different streams to robustly satisfy users' requests over time. We simulate multiple adaptive streaming sessions characterized by realistic network connections models, where the proposed solution outperforms commonly used vendor recommendations, in terms of user satisfaction but also in terms of fairness and outage probability. The simulation results further show that video content information as well as network constraints and users' statistics play a crucial role in selecting proper encoding parameters to provide fairness a mong users and to reduce network resource usage. We finally propose a few practical guidelines that can be used to choose the encoding parameters based on the user base characteristics, the network capacity and the type of video content

A quicker way to discover nearby peers

International audienceThe match between a peer-to-peer overlay and the physical Internet infrastructure is a constant issue. Time-constrained peer-to-peer applications such as live streaming systems are even more challenging because participating peers have to discover their closest neighbors as quickly as possible. We propose in this paper an approach based on landmarks and a management server in order to discover, as quickly as possible, its closest neighbors among a large population of peers

Distributed delivery system for time-shifted streaming systems

International audienceIn live streaming systems (IPTV, life-stream services, etc.), an attractive feature consists in allowing users to access past portions of the stream. This is called a time-shifted streaming sys- tem. We address in this paper the design of a large-scale delivery system for a time-shifted streaming application. We highlight the challenging characteristics of time-shifted applications that prevent known delivery systems to be used. Then, we describe the turntable structure, the first structure that has been specifically designed to cope with the properties of time-shifted systems. A set of preliminary simulations confirm the interest for this structure

A Semantic Overlay for Self- Peer-to-Peer Publish/Subscribe

International audiencePublish/Subscribe systems provide a useful platform for delivering data (events) from publishers to subscribers in an anonymous fashion in distributed networks. In this pa-per, we promote a novel design principle for self-* dynamic and reliable content-based publish/subscribe systems and perform a comparative analysis of its probabilistic and de-terministic implementations. More specifically, we present a generic content-based publish/subscribe system, called DPS (Dynamic Publish/Subscribe). DPS combines classi-cal content-based filtering with self-* (self-organizing, self-configuring, and self-healing) subscription-driven cluster-ing of subscribers. DPS gracefully adapts to failures and changes in the system while achieving scalable events deliv-ery. DPS includes a variety of fault-tolerant deterministic and probabilistic content-based publication/subscription schemes. These schemes are targeted toward scalability, and aim at reducing and distributing the number of mes-sages exchanged. Reliability and scalability of our system are shown through analytical and experimental evaluation

Throughput Prediction in Cellular Networks: Experiments and Preliminary Results

International audienceThroughput has a strong impact on user experience in cellular networks. The ability to predict the throughput of a connection, before it starts, will bring new possibilities, particularly to the Internet service providers. They could adapt contents to the quality of service really reachable by users, in order to enhance their experience. First this study highlights the prediction capabilities thanks to different algorithms and data gathered at different network levels. Then we propose a simple approach based on machine learning to predict the throughput using a few data related to the context of use.Le débit d'une connexion possède un impact significatif sur la qualité d'expérience via les réseaux cellulaires. Savoir prédire le débit d'une connexion à venir permettrait d'offrir d'immenses possibilités, notamment aux fournisseurs de services Internet. Ces derniers pourraient ainsi adapter leurs contenus à la qualité de service accessible par l'utilisateur, dans le but de maximiser sa qualité d'expérience. En premier lieu, cette étude illustre les capacités de prédiction atteignables grâce à des données collectées à différents niveaux du réseau. Dans un second temps, nous proposons une approche simple fondée sur des méthodes d'apprentissage pour prédire le débit d'une connexion à partir d'information minimale sur le contexte d'utilisation