12 research outputs found
A Stable Fountain Code Mechanism for Peer-to-Peer Content Distribution
Most peer-to-peer content distribution systems require the peers to privilege
the welfare of the overall system over greedily maximizing their own utility.
When downloading a file broken up into multiple pieces, peers are often asked
to pass on some possible download opportunities of common pieces in order to
favor rare pieces. This is to avoid the missing piece syndrome, which throttles
the download rate of the peer-to-peer system to that of downloading the file
straight from the server. In other situations, peers are asked to stay in the
system even though they have collected all the file's pieces and have an
incentive to leave right away.
We propose a mechanism which allows peers to act greedily and yet stabilizes
the peer-to-peer content sharing system. Our mechanism combines a fountain code
at the server to generate innovative new pieces, and a prioritization for the
server to deliver pieces only to new peers. While by itself, neither the
fountain code nor the prioritization of new peers alone stabilizes the system,
we demonstrate that their combination does, through both analytical and
numerical evaluation.Comment: accepted to IEEE INFOCOM 2014, 9 page
Supra-extensibilité des réseaux P2P
International audienceUne des clés du succès du pair-à -pair (P2P) est la faculté de passer à l'échelle, ou extensibilité (scalability) : la capacité de service augmente avec le nombre de participants. Pour la distribution de contenu, l'extensibilité P2P est fortement liée au fait que le principal goulot d'étranglement vient des vitesses d'accès individuelles. Mais avec l'augmentation des accès très haut débit, la congestion pourrait, dans le futur, se déplacer ailleurs. Qu'arriverait-il alors ? Pour aborder ce problème, nous proposons un modèle stochastique où les pairs sont plongés dans un espace métrique qui détermine les vitesses point-à -point. Notre principal résultat est la description, pour un scénario simple inspiré de BitTorrent, des performances du régime stationnaire. Un phénomène contre-intuitif apparaît : la supra-extensibilité, ou l'augmentation sur-linéaire de la capacité de service ! La supra-extensibilité apparaît naturellement dès que le nombre de pairs permet de choisir des voisins locaux, et continue jusqu'à un point de rupture où le réseau sous-jacent devient subitement incapable de supporter la charge. Enfin, nous construisons à partir du scénario de base un "couteau suisse" d'extensions du modèle pour lesquelles nous donnons des formules de performances
On Spatial Point Processes with Uniform Births and Deaths by Random Connection
This paper is focused on a class of spatial birth and death process of the
Euclidean space where the birth rate is constant and the death rate of a given
point is the shot noise created at its location by the other points of the
current configuration for some response function . An equivalent view point
is that each pair of points of the configuration establishes a random
connection at an exponential time determined by , which results in the death
of one of the two points. We concentrate on space-motion invariant processes of
this type. Under some natural conditions on , we construct the unique
time-stationary regime of this class of point processes by a coupling argument.
We then use the birth and death structure to establish a hierarchy of balance
integral relations between the factorial moment measures. Finally, we show that
the time-stationary point process exhibits a certain kind of repulsion between
its points that we call -repulsion
Intelligent query processing in P2P networks: semantic issues and routing algorithms
P2P networks have become a commonly used way of disseminating content on the Internet. In this context, constructing efficient and distributed P2P routing algorithms for complex environments that include a huge number of distributed nodes with different computing and network capabilities is a major challenge. In the last years, query routing algorithms have evolved by taking into account different features (provenance, nodes' history, topic similarity, etc.). Such features are usually stored in auxiliary data structures (tables, matrices, etc.), which provide an extra knowledge engineering layer on top of the network, resulting in an added semantic value for specifying algorithms for efficient query routing. This article examines the main existing algorithms for query routing in unstructured P2P networks in which semantic aspects play a major role. A general comparative analysis is included, associated with a taxonomy of P2P networks based on their degree of decentralization and the different approaches adopted to exploit the available semantic aspects.Fil: Nicolini, Ana LucÃa. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - BahÃa Blanca. Instituto de Ciencias e IngenierÃa de la Computación. Universidad Nacional del Sur. Departamento de Ciencias e IngenierÃa de la Computación. Instituto de Ciencias e IngenierÃa de la Computación; ArgentinaFil: Lorenzetti, Carlos Martin. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - BahÃa Blanca. Instituto de Ciencias e IngenierÃa de la Computación. Universidad Nacional del Sur. Departamento de Ciencias e IngenierÃa de la Computación. Instituto de Ciencias e IngenierÃa de la Computación; ArgentinaFil: Maguitman, Ana Gabriela. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - BahÃa Blanca. Instituto de Ciencias e IngenierÃa de la Computación. Universidad Nacional del Sur. Departamento de Ciencias e IngenierÃa de la Computación. Instituto de Ciencias e IngenierÃa de la Computación; ArgentinaFil: Chesñevar, Carlos Iván. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - BahÃa Blanca. Instituto de Ciencias e IngenierÃa de la Computación. Universidad Nacional del Sur. Departamento de Ciencias e IngenierÃa de la Computación. Instituto de Ciencias e IngenierÃa de la Computación; Argentin
QoS provision in a dynamic channel allocation based on admission control decisions
El PDF se corresponde a la versión de los autores, no obstante los datos de la cita son los de la versión definitiva, tal cual figuran en la página web de la revista.PostprintCognitive Radio Networks have emerged in the last decades as a solution of two problems: spectrum underutilization and spectrum scarcity. In this work, we propose a dynamic spectrum sharing mechanism, where primary users have strict priority over secondary ones in order to improve the mean spectrum utilization with the objective of providing to secondary users a satisfactory grade of service with a small interruption probability. We study a stochastic model for Cognitive Radio Networks with fluid limits techniques. Our main findings consist in a Gaussian limit theorem in the sub-critical case, and a non-Gaussian limit theorem, under a different scaling scheme, in the critical case. These results provide us practical QoS criteria for sharing policies. We support our analysis with representative simulated examples in both scenarios
Stochastic models for cognitive radio networks
During the last decade we have seen an explosive development of wireless technologies. Consequently the demand for electromagnetic spectrum has been growing dramatically resulting in the spectrum scarcity problem. In spite of this, spectrum utilization measurements have shown that licensed bands are vastly underutilized while unlicensed bands are too crowded. In this context, Cognitive Radio emerges as an auspicious paradigm in order to solve those problems. Even more, this concept is envisaged as one of the main components of future wireless technologies, such as the fifth-generation of mobile networks. In this regard, this thesis is founded on cognitive radio networks. We start considering a paid spectrum sharing approach where secondary users (SUs) pay to primary ones for the spectrum utilization. In particular, the first part of the thesis bears on the design and analysis of an optimal SU admission control policy, i.e. that maximizes the long-run profit of the primary service provider. We model the optimal revenue problem as a Markov Decision Process and we use dynamic programming (and other techniques such as sample-path analysis) to characterize properties of the optimal admission control policy. We introduce different changes to one of the best known dynamic programming algorithms incorporating the knowledge of the characterization. In particular, those proposals accelerate the rate of convergence of the algorithm when is applied in the considered context. We complement the analysis of the paid spectrum sharing approach using fluid approximations. That is to say, we obtain a description of the asymptotic behavior of the Markov process as the solution of an ordinary differential equation system. By means of the fluid approximation of the problem, we propose a methodology to estimate the optimal admission control boundary of the maximization profit problem mentioned before. In addition, we use the deterministic model in order to propose some tools and criteria that can be used to improve the mean spectrum utilization with the commitment of providing to secondary users certain quality of service levels. In wireless networks, a cognitive user can take advantage of either the time, the frequency, or the space. In the first part of the thesis we have been concentrated on timefrequency holes, in the second part we address the complete problem incorporating the space variable. In particular, we first introduce a probabilistic model based on a stochastic geometry approach. We focus our study in two of the main performance metrics: medium access probability and coverage probability. Finally, in the last part of the thesis we propose a novel methodology based on configuration models for random graphs. With our proposal, we show that it is possible to calculate an analytic approximation of the medium access probability (both for PUs and, most importantly, SUs) in an arbitrary large heterogeneous random network. This performance metric gives an idea of the possibilities offered by cognitive radio to improve the spectrum utilization. The introduced robust method, as well as all the results of the thesis, are evaluated by several simulations for different network topologies, including real scenarios of primary network deployments. Keywords: Markov decision process, fluid limit, stochastic geometry, random graphs,dynamic spectrum assignment, cognitive radi