10 research outputs found

    Análisis del rendimiento del protocolo TCP en redes de acceso wireless

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    El presente trabajo tiene como objetivo comparar distintas variantes del protocolo TCP en WLAN. Dentro del espectro de variantes, se pone especial énfasis en las que mantienen la filosofía extremo a extremo de TCP, lo que implica que no recibe ningún tipo de información explicita de la red. Para conseguir este objetivo, se utiliza el simulador de eventos discretos NS-2, con el propósito de realizar modelos simples que permitieran observar las estrategias de los diferentes controles de congestión implementados en las distintas variantes del protocolo TCP. Los modelos utilizados intentan recrear redes de acceso inalámbricas y escenarios donde la ruta de un extremo al otro incluye distintos tipos de redes y enlaces. Estas redes heterogéneas están conformadas por enlaces tanto cableados como inalámbricos. Por lo que resulta relevante analizar el comportamiento de algunas de las variantes del protocolo en estos modelos, concebidas para distintos tipos de escenarios. En las simulaciones se recrearon eventos frecuentes de los enlaces inalámbricos, como las desconexiones de distintos tiempos de duración y los errores en ráfaga de longitudes diferentes. Además, se definieron algunas métricas que permiten la comparación de los diversos mecanismos de control de congestión de las variantes de TCP ensayadas y se analizó cómo es la competencia por la utilización del ancho de banda (equidad) entre distintas variantes de TCP, cuando comparten un mismo canal de transmisión de datos.Facultad de Informátic

    End-to-End Resilience Mechanisms for Network Transport Protocols

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    The universal reliance on and hence the need for resilience in network communications has been well established. Current transport protocols are designed to provide fixed mechanisms for error remediation (if any), using techniques such as ARQ, and offer little or no adaptability to underlying network conditions, or to different sets of application requirements. The ubiquitous TCP transport protocol makes too many assumptions about underlying layers to provide resilient end-to-end service in all network scenarios, especially those which include significant heterogeneity. Additionally the properties of reliability, performability, availability, dependability, and survivability are not explicitly addressed in the design, so there is no support for resilience. This dissertation presents considerations which must be taken in designing new resilience mechanisms for future transport protocols to meet service requirements in the face of various attacks and challenges. The primary mechanisms addressed include diverse end-to-end paths, and multi-mode operation for changing network conditions

    Mitigating TCP Degradation over Intermittent Link Failures Using Intermediate Buffers

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    This thesis addresses the improvement of data transmission performance in a challenged network. It is well known that the popular Transmission Control Protocol degrades in environments where one or more of the links along the route is intermittently available. To avoid this degradation, this thesis proposes placing at least one node along the path of transmission to buffer and retransmit as needed to overcome the intermittent link. In the four-node, three-link testbed under particular conditions, file transmission time was reduced 20 fold in the case of an intermittent second link when the second node strategically buffers for retransmission opportunity

    A Rate-based TCP Congestion Control Framework for Cellular Data Networks

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    Ph.DDOCTOR OF PHILOSOPH

    The 1995 Research Reports: NASA/ASEE Summer Faculty Fellowship Program

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    This document is a collection of technical reports on research conducted by the participants in the 1995 NASA/ASEE Summer Faculty Fellowship Program at the Kennedy Space Center (KSC). This was the eleventh year that a NASA/ASEE program has been conducted at KSC. The 1995 program was administered by the University of Central Florida in cooperation with KSC. The program was operated under the auspices of the American Society for Engineering Education (ASEE) with sponsorship and funding from the Office of Educational Affairs, NASA Headquarters, Washington, D.C. The KSC Program was one of nine such Aeronautics and Space Research Programs funded by NASA Headquarters in 1995. The NASA/ASEE Program is intended to be a two-year program to allow in-depth research by the University faculty member

    ECOS 2012

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    The 8-volume set contains the Proceedings of the 25th ECOS 2012 International Conference, Perugia, Italy, June 26th to June 29th, 2012. ECOS is an acronym for Efficiency, Cost, Optimization and Simulation (of energy conversion systems and processes), summarizing the topics covered in ECOS: Thermodynamics, Heat and Mass Transfer, Exergy and Second Law Analysis, Process Integration and Heat Exchanger Networks, Fluid Dynamics and Power Plant Components, Fuel Cells, Simulation of Energy Conversion Systems, Renewable Energies, Thermo-Economic Analysis and Optimisation, Combustion, Chemical Reactors, Carbon Capture and Sequestration, Building/Urban/Complex Energy Systems, Water Desalination and Use of Water Resources, Energy Systems- Environmental and Sustainability Issues, System Operation/ Control/Diagnosis and Prognosis, Industrial Ecology

    Etude d'une architecture IP intégrant un lien satellite géostationnaire

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    Cette thèse aborde les problèmes relatifs à l'intégration des satellites géostationnaires dans les réseaux IP. Une première étape de ce travail consiste en une analyse critique des systèmes utilisant le Digital Video Broadcating pour véhiculer des flux IP. Cette étude souligne les faiblesses des solutions actuelles : tandis que les solutions classiques souffrent de limites inhérentes à la technologie et aux protocoles utilisées, les propositions reposant sur les satellites de nouvelles génération impliquent un système spécifique et à fortes contraintes financières. Ces limites engendrent des difficultés d'interopérabilité, témoignant de la nécessité d'une démarche plus globale qui viserait à dessiner une architecture plus large qui ne reposerait pas sur des contraintes techniques. La thèse propose alors de suivre cette démarche, et de concevoir une architecture pour intégrer ces différentes solutions dans un seul système et pouvoir supporter des services porteurs comme l'accès Internet, la vidéo à la demande et l'interconnexion de réseaux privés. Au coeur de cette architecture se trouve la notion de charge utile hybride, c'est-à-dire intégrant une partie transparente traditionnelle et une partie régénérative utilisant une intelligence embarquée plus ou moins évoluée. Ses objectifs sont alors d'assurer l'intégration de services porteurs sur satellite, d'offrir une transition entre les systèmes transparents et les satellites de nouvelle génération, et enfin de s'adapter aux évolutions protocolaires. Dans ce contexte, cette proposition est décrite à plusieurs niveaux, en insistant sur le lien entre le niveau réseau et la couche liaison. Cette description implique des choix technologiques témoignant des solutions actuelles, mais reste ouverte aux technologies à venir par son intégration d'IP comme un élément fédérateur. Enfin l'analyse du système hybride permet de légitimer les services choisis, et de souligner sa flexibilité offerte par la coexistence de ces deux modes et la possibilité de choisir pour chaque type de trafic celui qui permet les meilleurs performances. ABSTRACT : This thesis studies issues related to the integration of geostationary satellites in IP networks. A first part of this work presents an analysis of today and future DVB systems for IP support. The limits of standard solutions are underlined. However new technologies and protocols adaptations allow satellite systems to be more compliant to IP services, but at several costs: high complexity and specificity. As there is a real need of a global solution, an architecture based on two different payloads (a transparent one and an on-board-processing) in a same system is proposed for service integration. This solution, called a hybrid system, is defined according to different service needs. It proposes to undertake the transition between today systems and next generation satellites, as to integrate different services and protocols. The study describes such a solution, underlining that the technologic choices have been made according to today solutions, and may be changed in future days. Eventually this architecture is evaluated. The analysis of the system overhead for IP support shows that the architecture proposes a light way to manage IP streams and hybrid mode. The study of service integration concludes on the flexibility of managing two modes for different traffic streams, allowing the best performances for each one
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