121 research outputs found
Routage adaptatif et stabilité dans les réseaux maillés sans fil
GrĂące Ă leur flexibilitĂ© et Ă leur facilitĂ© dâinstallation, les rĂ©seaux maillĂ©s sans fil (WMNs) permettent un dĂ©ploiement dâune infrastructure Ă faible coĂ»t. Ces rĂ©seaux Ă©tendent la couverture des rĂ©seaux filaires permettant, ainsi, une connexion nâimporte quand et nâimporte oĂč. Toutefois, leur performance est dĂ©gradĂ©e par les interfĂ©rences et la congestion. Ces derniers causent des pertes de paquets et une augmentation du dĂ©lai de transmission dâune façon drastique. Dans cette thĂšse, nous nous intĂ©ressons au routage adaptatif et Ă la stabilitĂ© dans ce type de rĂ©seaux.
Dans une premiĂšre partie de la thĂšse, nous nous intĂ©ressons Ă la conception dâune mĂ©trique de routage et Ă la sĂ©lection des passerelles permettant dâamĂ©liorer la performance des WMNs. Dans ce contexte nous proposons un protocole de routage Ă la source basĂ© sur une nouvelle mĂ©trique. Cette mĂ©trique permet non seulement de capturer certaines caractĂ©ristiques des liens tels que les interfĂ©rences inter-flux et intra-flux, le taux de perte des paquets mais Ă©galement la surcharge des passerelles. Les rĂ©sultats numĂ©riques montrent que la performance de cette mĂ©trique est meilleure que celle des solutions proposĂ©es dans la littĂ©rature.
Dans une deuxiĂšme partie de la thĂšse, nous nous intĂ©ressons Ă certaines zones critiques dans les WMNs. Ces zones se trouvent autour des passerelles qui connaissent une concentration plus Ă©levĂ© du trafic ; elles risquent de provoquer des interfĂ©rences et des congestions. Ă cet Ă©gard, nous proposons un protocole de routage proactif et adaptatif basĂ© sur lâapprentissage par renforcement et qui pĂ©nalise les liens de mauvaise qualitĂ© lorsquâon sâapproche des passerelles. Un chemin dont la qualitĂ© des liens autour dâune passerelle est meilleure sera plus favorisĂ© que les autres chemins de moindre qualitĂ©. Nous utilisons lâalgorithme de Q-learning pour mettre Ă jour dynamiquement les coĂ»ts des chemins, sĂ©lectionner les prochains nĆuds pour faire suivre les paquets vers les passerelles choisies et explorer dâautres nĆuds voisins. Les rĂ©sultats numĂ©riques montrent que notre protocole distribuĂ©, prĂ©sente de meilleurs rĂ©sultats comparativement aux protocoles prĂ©sentĂ©s dans la littĂ©rature.
Dans une troisiĂšme partie de cette thĂšse, nous nous intĂ©ressons aux problĂšmes dâinstabilitĂ© des rĂ©seaux maillĂ©s sans fil. En effet, lâinstabilitĂ© se produit Ă cause des changements frĂ©quents des routes qui sont causĂ©s par les variations instantanĂ©es des qualitĂ©s des liens dues Ă la prĂ©sence des interfĂ©rences et de la congestion. Ainsi, aprĂšs une analyse de lâinstabilitĂ©, nous proposons dâutiliser le nombre de variations des chemins dans une table de routage comme indicateur de perturbation des rĂ©seaux et nous utilisons la fonction dâentropie, connue dans les mesures de lâincertitude et du dĂ©sordre des systĂšmes, pour sĂ©lectionner les routes stables. Les rĂ©sultats numĂ©riques montrent de meilleures performances de notre protocole en comparaison avec dâautres protocoles dans la littĂ©rature en termes de dĂ©bit, dĂ©lai, taux de perte des paquets et lâindice de Gini.Thanks to their flexibility and their simplicity of installation, Wireless Mesh Networks (WMNs) allow a low cost deployment of network infrastructure. They can be used to extend wired networks coverage allowing connectivity anytime and anywhere. However, WMNs may suffer from drastic performance degradation (e.g., increased packet loss ratio and delay) because of interferences and congestion. In this thesis, we are interested in adaptive routing and stability in WMNs.
In the first part of the thesis, we focus on defining new routing metric and gateway selection scheme to improve WMNs performance. In this context, we propose a source routing protocol based on a new metric which takes into account packet losses, intra-flow interferences, inter-flow interferences and load at gateways together to select best paths to best gateways. Simulation results show that the proposed metric improves the network performance and outperforms existing metrics in the literature.
In the second part of the thesis, we focus on critical zones, in WMNs, that consist of mesh routers which are located in neighborhoods of gateways where traffic concentration may occur. This traffic concentration may increase congestion and interferences excessively on wireless channels around the gateways. Thus, we propose a proactive and adaptive routing protocol based on reinforcement learning which increasingly penalizes links with bad quality as we get closer to gateways. We use Q-learning algorithm to dynamically update path costs and to select the next hop each time a packet is forwarded toward a given gateway; learning agents in each mesh router learn the best link to forward an incoming packet and explore new alternatives in the future. Simulation results show that our distributed routing protocol is less sensitive to interferences and outperforms existing protocols in the literature.
In the third part of this thesis, we focus on the problems of instability in WMNs. Instability occurs when routes flapping are frequent. Routes flapping are caused by the variations of link quality due to interferences and congestion. Thus, after analyzing factors that may cause network instability, we propose to use the number of path variations in routing tables as an indicator of network instability. Also, we use entropy function, usually used to measure uncertainty and disorder in systems, to define node stability, and thus, select the most stable routes in the WMNs. Simulation results show that our stability-based routing protocol outperforms existing routing protocols in the literature in terms of throughput, delay, loss rate, and Gini index
7. GI/ITG KuVS FachgesprÀch Drahtlose Sensornetze
In dem vorliegenden Tagungsband sind die BeitrĂ€ge des FachgesprĂ€chs Drahtlose Sensornetze 2008 zusammengefasst. Ziel dieses FachgesprĂ€chs ist es, Wissenschaftlerinnen und Wissenschaftler aus diesem Gebiet die Möglichkeit zu einem informellen Austausch zu geben â wobei immer auch Teilnehmer aus der Industrieforschung willkommen sind, die auch in diesem Jahr wieder teilnehmen.Das FachgesprĂ€ch ist eine betont informelle Veranstaltung der GI/ITG-Fachgruppe âKommunikation und Verteilte Systemeâ (www.kuvs.de). Es ist ausdrĂŒcklich keine weitere Konferenz mit ihrem groĂen Overhead und der Anforderung, fertige und möglichst âwasserdichteâ Ergebnisse zu prĂ€sentieren, sondern es dient auch ganz explizit dazu, mit Neueinsteigern auf der Suche nach ihrem Thema zu diskutieren und herauszufinden, wo die Herausforderungen an die zukĂŒnftige Forschung ĂŒberhaupt liegen.Das FachgesprĂ€ch Drahtlose Sensornetze 2008 findet in Berlin statt, in den RĂ€umen der Freien UniversitĂ€t Berlin, aber in Kooperation mit der ScatterWeb GmbH. Auch dies ein Novum, es zeigt, dass das FachgesprĂ€ch doch deutlich mehr als nur ein nettes Beisammensein unter einem Motto ist.FĂŒr die Organisation des Rahmens und der Abendveranstaltung gebĂŒhrt Dank den beiden Mitgliedern im Organisationskomitee, Kirsten Terfloth und Georg Wittenburg, aber auch Stefanie Bahe, welche die redaktionelle Betreuung des Tagungsbands ĂŒbernommen hat, vielen anderen Mitgliedern der AG Technische Informatik der FU Berlin und natĂŒrlich auch ihrem Leiter, Prof. Jochen Schiller
Recent Trends in Communication Networks
In recent years there has been many developments in communication technology. This has greatly enhanced the computing power of small handheld resource-constrained mobile devices. Different generations of communication technology have evolved. This had led to new research for communication of large volumes of data in different transmission media and the design of different communication protocols. Another direction of research concerns the secure and error-free communication between the sender and receiver despite the risk of the presence of an eavesdropper. For the communication requirement of a huge amount of multimedia streaming data, a lot of research has been carried out in the design of proper overlay networks. The book addresses new research techniques that have evolved to handle these challenges
Evaluating Thread protocol in the framework of Matter
Internet of Things is a technology which produced one of the biggest, and with most impact on the society, change in connectivity and automation solutions. It has a lot of new features and advantages, but also has its constraints. For this purpose, many standard have been developed, and IoT solutions designed. A Home Automation system is an application of IoT. It consist of IP-enabled embedded devices connected to the Internet using IPv6.The technology improved when IETF designed 6LoWPAN as a interface to link IPv6 to IEEE 802.15.4, a low-power wireless network standard Untill now, the IoT market is very dispersed with many solutions based in different standards, which make them incompatible between themselves. Appart from that, Home Automation technologies and solutions do not meet the requirements of low power, IP-based, security and friendly use. In order to profit from, and accelerate it, the IoT technology emergence, a unification of the standards used and the requirements needed by the different IoT solutions must be designed. The goal of this thesis was to study a new Home Automation standard called Matter. Matter is an application layer standard which aims to simplify the development for manufacturers and increase compatibility for the consumers, enabling communication across smart home devices, mobile apps, and cloud services. As Matter was to be released in the summer of 2021 but was delayed, instead of that, the Thread architecture has been studied. Thread is, with Wi-Fi, the core of the operational communications supported by Matter. Thread is a simplified, IPv6-based mesh networking architecture developed for efficient communication between energy-constrained devices around the home. As Thread is a royalty-free but closed-documentation standard, Nest Labs developed an open source implementation Called OpenThread. This study is composed by an overview of the architecture, a detailed explanation of each layer of the stack, and a implementation of the network through OpenThread. Furthermore, some test will be evaluated to provide to the reader an introduction to some of the Thread functionalities, specially related with routing
Queueing-Theoretic End-to-End Latency Modeling of Future Wireless Networks
The fifth generation (5G) of mobile communication networks is envisioned to enable a variety of novel applications. These applications demand requirements from the network, which are diverse and challenging. Consequently, the mobile network has to be not only capable to meet the demands of one of these applications, but also be flexible enough that it can be tailored to different needs of various services. Among these new applications, there are use cases that require low latency as well as an ultra-high reliability, e.g., to ensure unobstructed production in factory automation or road safety for (autonomous) transportation. In these domains, the requirements are crucial, since violating them may lead to financial or even human damage. Hence, an ultra-low probability of failure is necessary.
Based on this, two major questions arise that are the motivation for this thesis. First, how can ultra-low failure probabilities be evaluated, since experiments or simulations would require a tremendous number of runs and, thus, turn out to be infeasible. Second, given a network that can be configured differently for different applications through the concept of network slicing, which performance can be expected by different parameters and what is their optimal choice, particularly in the presence of other applications.
In this thesis, both questions shall be answered by appropriate mathematical modeling of the radio interface and the radio access network. Thereby the aim is to find the distribution of the (end-to-end) latency, allowing to extract stochastic measures such as the mean, the variance, but also ultra-high percentiles at the distribution tail. The percentile analysis eventually leads to the desired evaluation of worst-case scenarios at ultra-low probabilities. Therefore, the mathematical tool of queuing theory is utilized to study video streaming performance and one or multiple (low-latency) applications. One of the key contributions is the development of a numeric algorithm to obtain the latency of general queuing systems for homogeneous as well as for prioritized heterogeneous traffic. This provides the foundation for analyzing and improving end-to-end latency for
applications with known traffic distributions in arbitrary network topologies and consisting of one or multiple network slices.Es wird erwartet, dass die fĂŒnfte Mobilfunkgeneration (5G) eine Reihe neuartiger Anwendungen ermöglichen wird. Allerdings stellen diese Anwendungen sowohl sehr unterschiedliche als auch ĂŒberaus herausfordernde Anforderungen an das Netzwerk. Folglich muss das mobile Netz nicht nur die Voraussetzungen einer einzelnen Anwendungen erfĂŒllen, sondern auch flexibel genug sein, um an die Vorgaben unterschiedlicher Dienste angepasst werden zu können. Ein Teil der neuen Anwendungen erfordert hochzuverlĂ€ssige Kommunikation mit niedriger Latenz, um beispielsweise unterbrechungsfreie Produktion in der Fabrikautomatisierung oder Sicherheit im (autonomen) StraĂenverkehr zu gewĂ€hrleisten. In diesen Bereichen ist die ErfĂŒllung der gestellten Anforderungen besonders kritisch, da eine Verletzung finanzielle oder sogar personelle SchĂ€den nach sich ziehen könnte. Eine extrem niedrige Ausfallwahrscheinlichkeit ist daher von gröĂter Wichtigkeit.
Daraus ergeben sich zwei wesentliche Fragestellungen, welche diese Arbeit motivieren. Erstens, wie können extrem niedrige Ausfallwahrscheinlichkeiten evaluiert werden. Ihr Nachweis durch Experimente oder Simulationen wĂŒrde eine extrem groĂe Anzahl an DurchlĂ€ufen benötigen und sich daher als nicht realisierbar herausstellen. Zweitens, welche Performanz ist fĂŒr ein gegebenes Netzwerk durch unterschiedliche Konfigurationen zu erwarten und wie kann die optimale Konfiguration gewĂ€hlt werden. Diese Frage ist insbesondere dann interessant, wenn mehrere Anwendungen gleichzeitig bedient werden und durch sogenanntes Slicing fĂŒr jeden Dienst unterschiedliche Konfigurationen möglich sind.
In dieser Arbeit werden beide Fragen durch geeignete mathematische Modellierung der Funkschnittstelle sowie des Funkzugangsnetzes (Radio Access Network) adressiert. Mithilfe der Warteschlangentheorie soll die stochastische Verteilung der (Ende-zu-Ende-) Latenz bestimmt werden. Dies liefert unterschiedliche stochastische Metriken, wie den Erwartungswert, die Varianz und insbesondere extrem hohe Perzentile am oberen Rand der Verteilung. Letztere geben schlieĂlich Aufschluss ĂŒber die gesuchten schlimmsten FĂ€lle, die mit sehr geringer Wahrscheinlichkeit eintreten können. In der Arbeit werden Videostreaming und ein oder mehrere niedriglatente Anwendungen untersucht. Zu den wichtigsten BeitrĂ€gen zĂ€hlt dabei die Entwicklung einer numerischen Methode, um die Latenz in allgemeinen Warteschlangensystemen fĂŒr homogenen sowie fĂŒr priorisierten heterogenen Datenverkehr zu bestimmen. Dies legt die Grundlage fĂŒr die Analyse und Verbesserung von Ende-zu-Ende-Latenz fĂŒr Anwendungen mit bekannten Verkehrsverteilungen in beliebigen Netzwerktopologien mit ein oder mehreren Slices
Techniques for mitigating congestion in wireless sensor networks
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2005.Includes bibliographical references (p. 99-105).Network congestion occurs when offered traffic load exceeds available capacity at any point in a network. In wireless sensor networks, congestion causes overall channel quality to degrade and loss rates to rise, leads to buffer drops and increased delays (as in wired networks), and tends to be grossly unfair toward nodes whose data has to traverse a larger number of radio hops. Congestion control in wired networks is usually done using end-to-end and network-layer mechanisms acting in concert. However, this approach does not solve the problem in wireless networks because concurrent radio transmissions on different "links" interact with and affect each other, and because radio channel quality shows high variability over multiple time-scales. In this thesis, we examine three techniques that span different layers of the traditional protocol stack: hop-by-hop flow control, rate limiting source traffic when transit traffic is present, and a prioritized medium access control (MAC) protocol. We implement these techniques and present experimental results from a 55-node in-building wireless sensor network. We demonstrate that the combination of these techniques can improve network efficiency by a factor of three under realistic workloads.by Bret Warren Hull.S.M
Efficient hardware and software assist for many-core performance
In recent years, the number of available cores in a processor are increasing rapidly while the pace of performance improvement of an individual core has been lagged. It led application developers to extract more parallelism from a number of cores to make their applications run faster. However, writing a parallel program that scales well with the increasing core counts is challenging. Consequently, many parallel applications suffer from performance bugs caused by scalability limiters.
We expect core counts to continue to increase for the foreseeable future and hence, addressing scalability limiters is important for better performance on future hardware. With this thesis, I propose both software frameworks and hardware improvements that I developed to address three important scalability limiters: load imbalance, barrier latency and increasing on-chip packet latency.
First, I introduce a debugging framework for load imbalance called LIME. The LIME framework uses profiling, statistical analysis and control flow graph analysis to automatically determine the nature of load imbalance problems and pinpoint the code where the problems are introduced.
Second, I address scalability problem of the barrier, which has become costly and difficult to achieve scalable performance. To address this problem, I propose a transmission line (TL) based hardware barrier support, called TLSync, that is orders of magnitude faster than software barrier implementation while supports many (tens) of barriers simultaneously using a single chip-spanning network.
Third and lastly, I focus on the increasing packet latency in on-chip network, and propose a hybrid interconnection where a low-latency TL based interconnect is synergistically used with a high-throughput switched interconnect. Also, a new adaptive packet steering policy is created to judiciously use the limited throughput available on the low-latency TL interconnect.Ph.D
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Design of rate-adaptive MAC and medium aware routing protocols for multi-rate, multi-hop wireless networks
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The IEEE 802.11 standard conformant wireless communication stations have multi-rate transmission capability. To achieve greater communication efficiency, multi-rate capable stations use rateadaptation to select appropriate transmission rate according to variations in the channel quality. The
thesis presents two rate-adaptation schemes, each belonging to one of the two classes of rateadaptation schemes i.e.(1) the frame-transmission statistics based schemes, and (2) Signal-to-Noise Ratio (SNR) based, closed loop schemes. The SNR-based rate-adaptation scheme, proposed in this thesis uses a novel mechanism of delivering a receiverâs feedback to a transmitter; without requiring any modification in the standard frames as suggested by existing research. The frame-transmissionstatistics
based rate adaptation solution uses an on-demand incremental strategy for selecting a
rate-selection threshold. This solution is based on a cross-layer communication framework, where the rate-adaptation module uses information to/from the Application layer along with relevant information from the Medium Access Control (MAC) sub-layer. The proposed solutions are highly responsive when compared with existing rate-adaptation schemes; responsiveness is one of the key
factors in the design of such protocols. The novel feedback mechanism makes it possible to achieve frame-loss differentiation with just three frames, avoiding the use of Request To Send/ Clear To Send (RTS/CTS) frames and further delays in this process. Performance tests have affirmed that the
proposed rate-adaptation schemes are energy efficient; with efficiency up to 19% in specific test scenarios. In terms of throughput and frame loss-differentiation mechanisms, the proposed schemes have shown significantly better performance.Routing protocols for Mobile Ad-Hoc Networks (MANETs) use broadcast frames during the
route discovery process. The 802.11 mandates the use of different transmission rates for broadcast
and unicast (data-) frames. In many cases it causes creation of communication gray zones, where stations which are marked as âreachable neighboursâ using the broadcast frames (using lower transmission rate) are not accessible during normal, unicast communication (mainly at a higher
rate). Similarly, higher device density, interference and mobility cause variable medium access delays. The IEEE 802.11e introduces four different MAC level queues for four access categories, maintaining service priority within the queues; which implies that frames from a higher priority
queue are serviced more frequently than those belonging to lower priority queues. Such an enhancement at the MAC sub-layer introduces uneven queuing delays. Conventional routing protocols are unaware of such MAC specific constraints and as a result these factors are not considered which result in severe performance deterioration. To meet such challenges, the thesis presents a medium aware distance vector (MADV) routing protocol for MANETs. MADV uses MAC and physical layer (PHY) specific information in the route metric and maintains a separate route per-AC-per-destination in its routing tables. The MADV-metric can be incorporated into various routing rotocols and its applicability is determined by the possibility of provision of MAC dependent arameters that are used to determine the hop-by-hop MADV-metric values. Simulation tests and omparison with existing MANET protocols demonstrate the effectiveness of incorporating the medium dependent parameters and show that MADV is significantly better in terms of end-to-end
delay and throughput
Discrete Event Simulations
Considered by many authors as a technique for modelling stochastic, dynamic and discretely evolving systems, this technique has gained widespread acceptance among the practitioners who want to represent and improve complex systems. Since DES is a technique applied in incredibly different areas, this book reflects many different points of view about DES, thus, all authors describe how it is understood and applied within their context of work, providing an extensive understanding of what DES is. It can be said that the name of the book itself reflects the plurality that these points of view represent. The book embraces a number of topics covering theory, methods and applications to a wide range of sectors and problem areas that have been categorised into five groups. As well as the previously explained variety of points of view concerning DES, there is one additional thing to remark about this book: its richness when talking about actual data or actual data based analysis. When most academic areas are lacking application cases, roughly the half part of the chapters included in this book deal with actual problems or at least are based on actual data. Thus, the editor firmly believes that this book will be interesting for both beginners and practitioners in the area of DES
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Cross-Layer Pathfinding for Off-Chip Interconnects
Off-chip interconnects for integrated circuits (ICs) today induce a diverse design space, spanning many different applications that require transmission of data at various bandwidths, latencies and link lengths. Off-chip interconnect design solutions are also variously sensitive to system performance, power and cost metrics, while also having a strong impact on these metrics. The costs associated with off-chip interconnects include die area, package (PKG) and printed circuit board (PCB) area, technology and bill of materials (BOM). Choices made regarding off-chip interconnects are fundamental to product definition, architecture, design implementation and technology enablement. Given their cross-layer impact, it is imperative that a cross-layer approach be employed to architect and analyze off-chip interconnects up front, so that a top-down design flow can comprehend the cross-layer impacts and correctly assess the system performance, power and cost tradeoffs for off-chip interconnects. Chip architects are not exposed to all the tradeoffs at the physical and circuit implementation or technology layers, and often lack the tools to accurately assess off-chip interconnects. Furthermore, the collaterals needed for a detailed analysis are often lacking when the chip is architected; these include circuit design and layout, PKG and PCB layout, and physical floorplan and implementation. To address the need for a framework that enables architects to assess the system-level impact of off-chip interconnects, this thesis presents power-area-timing (PAT) models for off-chip interconnects, optimization and planning tools with the appropriate abstraction using these PAT models, and die/PKG/PCB co-design methods that help expose the off-chip interconnect cross-layer metrics to the die/PKG/PCB design flows. Together, these models, tools and methods enable cross-layer optimization that allows for a top-down definition and exploration of the design space and helps converge on the correct off-chip interconnect implementation and technology choice. The tools presented cover off-chip memory interfaces for mobile and server products, silicon photonic interfaces, 2.5D silicon interposers and 3D through-silicon vias (TSVs). The goal of the cross-layer framework is to assess the key metrics of the interconnect (such as timing, latency, active/idle/sleep power, and area/cost) at an appropriate level of abstraction by being able to do this across layers of the design flow. In additional to signal interconnect, this thesis also explores the need for such cross-layer pathfinding for power distribution networks (PDN), where the system-on-chip (SoC) floorplan and pinmap must be optimized before the collateral layouts for PDN analysis are ready. Altogether, the developed cross-layer pathfinding methodology for off-chip interconnects enables more rapid and thorough exploration of a vast design space of off-chip parallel and serial links, inter-die and inter-chiplet links and silicon photonics. Such exploration will pave the way for off-chip interconnect technology enablement that is optimized for system needs. The basis of the framework can be extended to cover other interconnect technology as well, since it fundamentally relates to system-level metrics that are common to all off-chip interconnects
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