13 research outputs found

    The complexity of resolving conflicts on MAC

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    We consider the fundamental problem of multiple stations competing to transmit on a multiple access channel (MAC). We are given nn stations out of which at most dd are active and intend to transmit a message to other stations using MAC. All stations are assumed to be synchronized according to a time clock. If ll stations node transmit in the same round, then the MAC provides the feedback whether l=0l=0, l=2l=2 (collision occurred) or l=1l=1. When l=1l=1, then a single station is indeed able to successfully transmit a message, which is received by all other nodes. For the above problem the active stations have to schedule their transmissions so that they can singly, transmit their messages on MAC, based only on the feedback received from the MAC in previous round. For the above problem it was shown in [Greenberg, Winograd, {\em A Lower bound on the Time Needed in the Worst Case to Resolve Conflicts Deterministically in Multiple Access Channels}, Journal of ACM 1985] that every deterministic adaptive algorithm should take Ω(d(lgn)/(lgd))\Omega(d (\lg n)/(\lg d)) rounds in the worst case. The fastest known deterministic adaptive algorithm requires O(dlgn)O(d \lg n) rounds. The gap between the upper and lower bound is O(lgd)O(\lg d) round. It is substantial for most values of dd: When d=d = constant and dO(nϵ)d \in O(n^{\epsilon}) (for any constant ϵ1\epsilon \leq 1, the lower bound is respectively O(lgn)O(\lg n) and O(n), which is trivial in both cases. Nevertheless, the above lower bound is interesting indeed when dd \in poly(lgn\lg n). In this work, we present a novel counting argument to prove a tight lower bound of Ω(dlgn)\Omega(d \lg n) rounds for all deterministic, adaptive algorithms, closing this long standing open question.}Comment: Xerox internal report 27th July; 7 page

    An empirical evaluation of techniques for parallel simulation of message passing networks

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    209 p.[EN]In the field of computer design, simulation is an essential tool to validate and evaluate architectural proposals. Conventional simulation techniques, designed for their use in sequential computers, are too slow if the system to simulate is large or complex. The aim of this work is to search for techniques to accelerate simulations exploiting the parallelism available in current, commercial multicomputers, and to use these techniques to study a model of a message router. This router has been designed to constitute the communication infrastructure of a (hypothetical) massively parallel computer. Three parallel simulation techniques have been considered: synchronous, asynchronous-conservative and asynchronous-optimistic. These algorithms have been implemented in three multicomputers: a transputer-based Supernode, an Intel Paragon and a network of workstations. The influence that factors such as the characteristics of the simulated models, the organization of the simulators and the characteristics of the target multicomputers have in the performance of the simulations has been measured and characterized. It is concluded that optimistic parallel simulation techniques are not suitable for the considered kind of models, although they may provide good performance in other environments. A network of workstations is not the right platform for our experiments, because the communication demands of the parallel simulators surpass the abilities of local area networks—the granularity is too fine. Synchronous and conservative parallel simulation techniques perform very well in the Supernode and in the Paragon, specially if the model to simulate is complex or large—precisely the worst case for traditional, sequential simulators. This way, studies previously considered as unrealizable, due to their exceedingly high computational cost, can be performed in reasonable times. Additionally, the spectrum of possibilities of using multicomputers can be broadened to execute more than numeric applications.[ES]En el ámbito del diseño de computadores, la simulación es una herramienta imprescindible para la validación y evaluación de cualquier propuesta arquitectónica. Las ténicas convencionales de simulación, diseñadas para su utilización en computadores secuenciales, son demasiado lentas si el sistema a simular es grande o complejo. El objetivo de esta tesis es buscar técnicas para acelerar estas simulaciones, aprovechando el paralelismo disponible en multicomputadores comerciales, y usar esas técnicas para el estudio de un modelo de encaminador de mensajes. Este encaminador está diseñado para formar infraestructura de comunicaciones de un hipotético computador masivamente paralelo. En este trabajo se consideran tres técnicas de simulación paralela: síncrona, asíncrona-conservadora y asíncrona-optimista. Estos algoritmos se han implementado en tres multicomputadores: un Supernode basado en Transputers, un Intel Paragon y una red de estaciones de trabajo. Se caracteriza la influencia que tienen en las prestaciones de los simuladores aspectos tales como los parámetros del modelo simulado, la organización del simulador y las características del multicomputador utilizado. Se concluye que las técnicas de simulación paralela optimista no resultan adecuadas para trabajar con el modelo considerado, aunque pueden ofrecer un buen rendimiento en otros entornos. La red de estaciones de trabajo no resulta una plataforma apropiada para estas simulaciones, ya que una red local no reúne condiciones para la ejecución de aplicaciones paralelas de grano fino. Las técnicas de simulación paralela síncrona y conservadora dan muy buenos resultados en el Supernode y en el Paragon, especialmente si el modelo a simular es complejo o grande—precisamente el peor caso para los algoritmos secuenciales. De esta forma, estudios previamente considerados inviables, por ser demasiado costosos computacionalmente, pueden realizarse en tiempos razonables. Además, se amplía el espectro de posibilidades de los multicomputadores, utilizándolos para algo más que aplicaciones numéricas.Este trabajo ha sido parcialmente subvencionado por la Comisión Interministerial de Ciencia y Tecnología, bajo contrato TIC95-037

    A Network of One’s Own: Struggles to Domesticate the Internet

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    This thesis is a design research practice-led inquiry into the domesticated Internet. It first seeks to complicate simplistic corporate and academic visions by naming some of the struggles it encounters – not least to assert a private home and network of one's own. It is argued that a century of domestic technologies has emphasised invisibility, ubiquity, and automation in ways that obscure a network of exploited people and finite resources. Furthermore, these technological ambitions are met through machine surveillance, in ways newly enabled by the domesticated Internet, that threaten the privacy of the home. In response, this thesis seeks some practical ways to design alternatives that assert a network of one's own and makes the work it implicates visible. The methodological approach is broadly Research Through Design supplemented by a practice described as designerly hacking through which hidden technical potential is revealed and given meaning. Two empirical studies are described that together make an account of the technical possibility and social reality of the networked home: an autobiographical technical exploration of the author's home and network with the making of hacks and Research Products privately and in public; and a cultural probe engagement with six rented households surfacing contemporary accounts of the domesticated Internet and in particular the challenges and opportunities of wireless networking. Together this yields a series of technical and social insights for design and two forms are offered to communicate these: a framework for understanding change in the networked home (The Stuff of Home) and a set of 30 design patterns for a network of one's own; each invites different analyses. The conclusion then draws together the multiple threads developed through this thesis and offers some reflection on the complexity of doing contemporary technical design work

    Applications

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    Volume 3 describes how resource-aware machine learning methods and techniques are used to successfully solve real-world problems. The book provides numerous specific application examples: in health and medicine for risk modelling, diagnosis, and treatment selection for diseases in electronics, steel production and milling for quality control during manufacturing processes in traffic, logistics for smart cities and for mobile communications

    Applications

    Get PDF
    Volume 3 describes how resource-aware machine learning methods and techniques are used to successfully solve real-world problems. The book provides numerous specific application examples: in health and medicine for risk modelling, diagnosis, and treatment selection for diseases in electronics, steel production and milling for quality control during manufacturing processes in traffic, logistics for smart cities and for mobile communications

    Telemedicine

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    Telemedicine is a rapidly evolving field as new technologies are implemented for example for the development of wireless sensors, quality data transmission. Using the Internet applications such as counseling, clinical consultation support and home care monitoring and management are more and more realized, which improves access to high level medical care in underserved areas. The 23 chapters of this book present manifold examples of telemedicine treating both theoretical and practical foundations and application scenarios
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