A system composed of unreliable components can experience different levels of performance as its configuration changes due to failures and repairs. One approach used to measure overall system performance is to weight the level of performance measured for each system state by the probability that the system is in that state and then sum across all system states. Many performance measures have a transient behavior following a change in the state of the system. Because of the difficulty associated with transient analysis, the system is often assumed to be in steady state when measuring the performance for each system state. When this approach is used to analyze packet-switched communication networks, which consist of highly reliable high-speed links and switching nodes, it is argued that the steady-state assumption is justified on the basis of the large difference in rates of traffic-related events, such as call completions and packet transmissions, compared to component-related events, such as failures and repairs. To investigate the validity of this assumption, we define lower bounds for the length of the transient phase fol1owing link failures and repairs. For both cases, we obtain a distribution for the length of the lower bound. The transient phase is significant when its length exceeds a given fraction of the time until the next change in network state. Using the distributions for these lengths, we derive an expression for the probability that the transient phase is significant in terms of the amount of traffic on the link and the ratio of the rates for traffic-related events and network state changes. These results show that the difference in rates between traffic-related events and component related events is not enough by itself to justify the steady-state assumption. The amount of traffic carried on the link and the size of the network must also be considered. These results indicate some situations where the steady-state assumption is inappropriate. We also obtain sufficient conditions for transient-phase significance following link failures. Although these results do not indicate when it is safe to use the steady-state assumption, they provide a measure of the risk associated with using it. / Ph. D.

Numerous power electronics building blocks (PEBB) based power conversion systems have been developed to explore modular design, scalable voltage and current ratings, low-cost operations, etc. This paper further extends the modular concept from the power stage to the control system. The communication network in SiC-based modular power converters is becoming significant for distributed control architecture, with the requirements of tight synchronization and low latency. The influence of the synchronization accuracy on harmonics under the phase-shifted carrier pulse width modulation (PSC-PWM) is evaluated. When the synchronization is accurate, the influence of an increase in harmonics can be ignored. Thus, a synchronous distributed control and communication protocol with well-performed synchronization of 25 ns accuracy is proposed and verified for a 120 kHz SiC-based impedance measurement unit (IMU) with cascaded H-bridge PEBBs. An improved synchronization method with additional analog circuits is further implemented and verified with sub-ns synchronization accuracy. / The power electronics building block (PEBB) concept is proposed for medium-voltage converter applications in order to realize the modular design of the power stage. Traditionally, the central control architecture is popular in converter systems. The voltage and current are sensed and then processed in one central controller. The control hardware interfaces and software have to be customized for a specified number of power cells, and the scalability of controller is lost. In stead, in the distributed control architecture, a local controller in each PEBB can communicate with the sensors, gate drivers, etc. A high-level controller collects the information from each PEBB and conducts the control algorithm. In this way, the design can be more modular, and the local controller can share the computation burden with the high-level controller, which is good for scalability. In such distributed control architecture, a synchronous communication system is required to transmit data and command between the high-level controller and local controllers. A power converter always requires a highly synchronized operation to turn on or turn off the devices. In this work, a synchronous communication protocol is proposed and experimentally validated on a SiC-based modular power converter.

This thesis seeks to identify and explain some technology in order to more fully understand modern communication. This study makes use of metaphoric cluster analysis to examine the technological rhetoric of Nicholas Negroponte.

>Magister Scientiae - MSc / This thesis validates that packet aggregation is a viable technique to increase call ca-pacity for Voice over Internet Protocol over wireless mesh networks. Wireless mesh networks are attractive ways to provide voice services to rural communities. Due to the ad-hoc routing nature of mesh networks, packet loss and delay can reduce voice quality.Even on non-mesh networks, voice quality is reduced by high overhead, associated with the transmission of multiple small packets. Packet aggregation techniques are proven to increase VoIP performance and thus can be deployed in wireless mesh networks. Kernel level packet aggregation was initially implemented and tested on a small mesh network of PCs running Linux, and standard baseline vs. aggregation tests were conducted with a realistic voice tra c pro le in hop-to-hop mode. Modi cations of the kernel were then transferred to either end of a nine node 'mesh potato' network and those tests were conducted with only the end nodes modi ed to perform aggregation duties. Packet ag- gregation increased call capacity expectedly, while quality of service was maintained in both instances, and hop-to-hop aggregation outperformed the end-to-end con guration. However, implementing hop-to-hop in a scalable fashion is prohibitive, due to the extensive kernel level debugging that must be done to achieve the call capacity increase.Therefore, end-to-end call capacity increase is an acceptable compromise for eventual scalable deployment of voice over wireless mesh networks.

Made available in DSpace on 2016-04-26T18:15:40Z (GMT). No. of bitstreams: 1 cordel-tese.pdf: 19944319 bytes, checksum: fdeb5bc2cabec8f5e2fd7dd144672288 (MD5) Previous issue date: 2006-07-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The first fair pamphlets were printed in Brazil just over one hundred years ago. Between tradition and invention a wider network was spread around the country and was called cordel . A cordel network, index of memory and collective creation has also expanded in time. Its production knew other communication technologies until the interconnected computer network. This research objective is to understand cordel as a shared memory and network communication solution. A production network which spreads throughout poets, singers, graphics men, editors, agents, readers and listeners. Roles that can be exchanged and superimposed in a material and information exchange network. Knowledge that circulates and stays through oral cultural practices and also by constant development in communication technology. These related aspects overlap and are revealed in a network of ideas. The ideas circulate in precarious materials. If the ideas stay is throughout the recurrence operated by the numerous and finest capillarity network choices in a social memory process. The investigation lines that weave the research are distinct: the line that concerns cordel and questions about its imaginary, about the way to map its production and observe its practice; the line that includes cordel but also corresponds to following and bringing up-to-date different natures of communication networks and their technological mediations. There are still other more general lines that refer to communication problems which go from the representation of knowledge to their relation to supports of memory. On the subject of cordel , among the theoretical areas and authors, we point out, Camara Cascudo, Rute Terra, Genevieve Bolleme and the oral culture studies of Paul Zumthor, Jerusa Pires Ferreira, Gilmar de Carvalho; from network theory and general system theory: Michel Serres, Pierre Rosentiehl e Jorge Vieira; from studies related to network investigation methodology, communication networks and digital culture: Barry Wellman, Wasserman and Faust, and Rogério da Costa. Cordel pamphlets cataloged along this research, give support to the thesis of a cordel network. Exchange network maps are drawn through indexes recorded on the fourth cover. An idea network hypothesis is sketched from themes, narratives and images settled in fair pamphlets. Structuring the data base is itself an experience of establishing connections more than making an excluding classification. Over this experience, we understand how ideas expressed in cordel survive technology updates and connect people / Há pouco mais de cem anos eram impressos os primeiros folhetos de feira no Brasil. Entre a tradição e a invenção se estendeu por partes do país uma rede de divulgadores do que veio a ser chamado cordel. A rede de cordéis, índice de memória e criação coletivas, se estendeu também no tempo. Sua oficina conheceu outras tecnologias de comunicação até a rede de computadores interconectados. O objetivo desta pesquisa é entender o cordel como uma solução de comunicação em rede e de memória compartilhada. Uma rede de produção que se dissemina através de poetas, cantadores, gráficos, editores, agentes, leitores e ouvintes. Papéis que podem ser permutados e sobrepostos em uma rede de trocas materiais e de informações. Saberes que circulam e permanecem através das práticas de cultura oral e até das constantes atualizações das tecnologias de comunicação. Os aspectos relacionados se imbricam e se revelam em uma rede de idéias. As idéias circulam embaladas em um material precário. Se idéias permanecem é pela recorrência operada pelas escolhas da capilaridade mais fina e numerosa da rede, em um processo de memória social. São distintas as linhas de investigação que tecem a pesquisa. A linha que concerne ao cordel e interroga-se sobre seu imaginário, sobre a forma de cartografar sua produção e observar suas práticas. A linha que inclui o cordel mas também corresponde ao acompanhamento e atualização das formas de comunicação em rede e suas mediações tecnológicas. Ainda, linhas mais gerais, referem-se aos problemas da comunicação, da representação do conhecimento e sua relação com os suportes da memória. Dentre as áreas teóricas e autores destacamos, sobre o cordel, Câmara Cascudo, Rute Terra, Geneviéve Bolleme e os estudos da cultura oral de Paul Zumthor, Jerusa Pires Ferreira, Gilmar de Carvalho. Da teoria das redes e teoria geral dos sistemas: Michel Serres, Pierre Rosentiehl e Jorge Vieira. Em metodologia de estudos de redes, redes de comunicação e cultura digital: Barry Wellman, Wasserman e Faust, e Rogério da Costa. Um coletivo de folhetos de cordel, catalogados durante a pesquisa, dá suporte à tese da rede de cordéis. Através de índices gravados na quarta capa são desenhados os mapas da rede de trocas. Dos temas, narrativas e imagens, fixados em folheto, se esboça a hipótese da rede de idéias. A estruturação da base de dados é em si uma experiência de estabelecer conexões mais que classificações excludentes. Para além desta experiência, entende-se como as idéias do cordel sobrevivem através das atualizações tecnológicas e conectam pessoas

Submitted by Erika Demachki (erikademachki@gmail.com) on 2015-10-22T17:54:48Z No. of bitstreams: 2 Dissertação - Rosana de Paula Lucas - 2014.pdf: 2188388 bytes, checksum: 3657f86e73f4c67924c818227205f5d6 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Erika Demachki (erikademachki@gmail.com) on 2015-10-22T17:56:21Z (GMT) No. of bitstreams: 2 Dissertação - Rosana de Paula Lucas - 2014.pdf: 2188388 bytes, checksum: 3657f86e73f4c67924c818227205f5d6 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2015-10-22T17:56:21Z (GMT). No. of bitstreams: 2 Dissertação - Rosana de Paula Lucas - 2014.pdf: 2188388 bytes, checksum: 3657f86e73f4c67924c818227205f5d6 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2014-12-04 / In this thesis, we present an algorithm for adaptive estimation of the parameter (Hurst parameter) that measures the selfsimilar degree of the network traffic process. Using this parameter, called the Global Scale parameter, we developed an adaptive bandwidth allocation scheme. We evaluate the performance of this transmission rate allocation scheme with adaptive global parameter, comparing its performance to that of another algorithm that uses only one value for the Hurst parameter. Additionally, using the concepts of Network Calculus, specifically the Effective envelope, we obtain estimates for the quality of service (QoS) parameters. That is, we present a proposal for estimating average queue size (backlog) and delay for different network traffic traces. To this end, we derive an equation for the effective envelope of network traffic trace that can be seen as a generalization of the Multifractal Bounded Arrival Process (MFBAP). Comparisons between the real backlog and delay values are carried out to those estimated by using the proposed Effective Envelope for various violation probabilities and with those obtained by other Envelop Processes. / Nesta dissertação, apresentamos um algoritmo para estimação adaptativa do parâmetro que mede o grau de autossimilaridade do processo de tráfego. Utilizando esse parâmetro, denominado de Parâmetro de Escala Global, elaboramos um esquema de alocação adaptativo de banda. Avaliamos o desempenho deste esquema de alocação de banda com parâmetro de escala global adaptativo comparando seu desempenho com outro algoritmo que utiliza apenas um valor para o parâmetro de Hurst. Além disso, utilizando os conceitos de Cálculo de Rede (Network Calculus), mais especificamente de Envelope Efetivo, obtemos estimativas para parâmetros de qualidade de serviço. Ou seja, apresentamos uma proposta de método para estimação de tamanho médio da fila (backlog) e retardo (delay) para diferentes séries de tráfego de redes. Para tal, deduzimos uma equação para o Envelope Efetivo de séries de tráfego, que pode ser vista como uma generalização do Processo Envelope do modelo Processo de Chegada com Limitante (MFBAP-Multifractal Multifractal Bounded Arrival Process). São realizadas comparações entre os valores de backlog e delay reais (séries de tráfego reais) com os valores limitantes estimados utilizando o Envelope Efetivo proposto para vários valores de probabilidade de violação e com obtidos por outros Processos Envelopes.

Ce mémoire de thèse est consacré à l’étude d’une liaison tout-optique longue de 10 km dédiée à l’extension d’un observatoire câblé de fond de mer existant afin d’atteindre de nouvelles zones d’exploration. Les travaux de recherche qui y sont rapportés démontrent la faisabilité de cette liaison tout-optique entre un instrument déporté et une station terrestre avec une seule fibre optique longue de 10 km, qui transmet simultanément la puissance, nécessaire à l’alimentation de l’instrument (quelques centaines de milliwatts), et des données bidirectionnelles en temps réel.Le contexte de cette thèse est présenté au travers d’un état de l’art sur les observatoires câblés et sur la puissance sur fibre. Le choix de la fibre unique et la présence de fortes puissances optiques complexifient la mise en oeuvre de cette extension tout-optique, et sont à l’origine de l’apparition d'interactions entre l’énergie optique dédiée à l'alimentation (@1480 nm) et les données échangées (@1550 nm). Tout au long de ce document, les choix technologiques retenus sont argumentés et les effets optiques non linéaires tels que les diffusions Raman, Brillouin, Rayleigh, l’Émission Spontanée Amplifiée (ASE) sont décrits, modélisés et analysés expérimentalement. L’extension tout-optique proposée a été caractérisée à la fois en régimes statique et dynamique par des mesures du bilan de liaison, du rapport signal à bruit (SNR) et du taux d’erreur binaire (BER). Les résultats obtenus montrent la possibilité de fournir 160 mW électrique à l’instrument déporté en utilisant une source optique continue de 33 dBm sans dégrader excessivement les données bidirectionnelles transmises simultanément (BER<10-7). / This thesis is devoted to the study of a 10 km long all-optical network dedicated to extend a current cabled seafloor observatory, in order to reach new exploration areas. The research work described in this thesis demonstrates the feasibility of this all-optical link between a remote instrument and a shore station with a single 10 km long optical fiber, which simultaneously transmits the energy required to supply the instrument (several hundred milliwatts) and bidirectional data in real time.The thesis context is presented trough an analysis of the cabled seafloor observatories and of the power-over-fiber. The choice of a single optical fiber and the presence of high optical power complicate the implementation of this all-optical extension, and they cause the appearance of interactions between the optical energy dedicated to the power supply (@1480 nm) and the exchanged data (@1550 nm). Throughout this document, the technological choices are explained and the optical nonlinear effects are described, simulated and analyzed experimentally, such as Raman, Brillouin, and Rayleigh scattering and Amplified Spontaneous Emission (ASE). The proposed all-optical extension has been characterized in static and dynamic regimes with measures of the optical link budget, the Signal-to-Noise Ratio (SNR), and the Bit Error Ratio (BER). The results show the possibility to power the remote instrument with 160 mW, when using a continuous high optical laser source of 33 dBm without huge degradation of the bidirectional data transmitted simultaneously (BER<10-7).

Cette thèse traite de la dissémination de messages dans les réseaux tolérants aux délais (DTNs). Ce type d'environnements très contraints ouvre de nombreux défis parmi lesquels le routage qui exploite au mieux les critères de mobilité des noeuds, le routage utilisant un nombre réduit de copies du message à disséminer, le routage de messages respectant la vie privée des noeuds, le routage en présence de nœuds égoïstes. Ce sont ces défis que nous adressons dans le cadre de cette thèse. La première contribution de cette thèse consiste en un protocole de routage adaptatif pour les DTNs exploitant au mieux les critères de mobilité des nœuds. En particulier, ce protocole permet de déterminer à chaque fois qu'une décision de routage doit être prise, quel critère de mobilité augmente la probabilité que le message soit délivré à sa destination. Cette décision est prise grâce à une fonction d'utilité calculée par les nœuds après normalisation des valeurs décrivant les différents critères de mobilité. Le protocole est validé par des simulations faites en utilisant des traces de mobilité réelles et en comparaison avec des protocoles de l'état de l'art. Les résultats montrent de meilleures performances en terme de taux de délivrance de messages mais à coût plus élevé. La seconde contribution de cette thèse consiste en un protocole dont le but est d'adapter dynamiquement le nombre de copies de messages disséminés dans le réseau. Le protocole proposé dans cette thèse résout ce problème en pré-calculant un nombre de copies nécessaire pour atteindre une certaine probabilité de délivrance, puis en augmentant dynamiquement ce nombre au fur et à mesure que le délai d'expiration du message approche. Les résultats montrent que le protocole proposé offre un taux de délivrance équivalent aux protocoles les plus performants à un cout bien inférieur. La troisième contribution de cette thèse consiste en un protocole de routage dans les DTNs qui protège la vie privée des nœuds. En particulier, ce protocole protège les informations relatives à la mobilité des nœuds. Ceci est fait en se basant sur l'organisation des nœuds en communautés. En particulier, au lieu de comparer leur propres probabilités de rencontrer la destination d'un message donné, dans le protocole proposé, les nœuds comparent la probabilité qu'un nœud de leur communauté rencontre la destination. Afin de calculer cette probabilité au sein de la communauté de manière à préserver les valeurs individuelle, le protocole se base sur des algorithmes de cryptographie afin de calculer des produits de probabilité de manière à protéger les valeurs individuelles. Les résultats montrent que le protocole exhibe des performances équivalentes aux protocoles existants tout en étant le seul à respecter les informations confidentielles des usagers. / Mobile Delay Tolerant Networks (MDTNs) are wireless mobile networks in which a complete routing path between two nodes that wish to communicate cannot be guaranteed. A number of networking scenarios have been categorized as MDTNs, such as vehicular ad hoc networks, pocket switched networks, etc. The network asynchrony, coupled with the limited resources of mobile devices make message dissemination (also called routing) one of the fundamental challenges in MDTNs. In the literature, a large body of work has been done to deal with routing in MDTNs. However, most of the existing routing protocols are based on at least one of the following three assumptions: (1) all messages can be routed by relying on a single mobility property; (2) all messages can be routed using a single message allocation strategy; (3) users are willing to disclose their mobility information and relationships to others in order to improve the quality of the routing. We argue that the above three assumptions are not realistic because: (1) users can exhibit various social behaviors and consequently various mobility properties (e.g., they can have regular movements during week-days and exhibit non-predictable movements during week-ends); (2) some messages might need more or less copies to be delivered according to the localization of the source and the destination and to the urgency of the message; and (3) users mobility data can disclose sensitive information about the users. In this thesis, we relieve MDTN routing from the above three restrictive assumptions. Firstly, we propose an adaptive routing protocol for mobile delay tolerant networks. The proposed protocol can dynamically learn the social properties of nodes based on their mobility patterns, and exploit the most appropriate routing strategy each time an intermediate node is encountered. Simulations performed on real mobility traces show that our protocol achieves a better delivery ratio than existing state-of-the-art routing protocols that rely on a single mobility property. Secondly, we present a delay and cost balancing protocol for efficient routing in mobile delay tolerant networks. The presented protocol reasons on the remaining time-to-live of a message to dynamically allocate the minimum number of copies that are necessary to achieve a given delivery probability. Evaluation results show that the protocol can achieve a good balance between message delivery delay and delivery cost, compared with most of the existing routing protocols in the literature. Lastly, we propose an efficient privacy preserving prediction-based routing protocol for mobile delay tolerant networks. This protocol preserves the mobility patterns of a node from being disclosed by exploiting the mobility pattern of communities that node belongs to. Evaluation results demonstrate that this protocol can obtain comparable routing performance to prediction-based protocols while preserving the mobility pattern of nodes.

Effective decision support plays vital roles in people's daily life, as well as for professional practitioners such as health care providers. Without correct information and timely derived knowledge, a decision is often suboptimal and may result in signi cant nancial loss or compromises of the performance. In this dissertation, we study text mining and topic modeling and propose to use text mining methods, in combination with topic models, to discover knowledge from texts popularly available from a wide variety of sources, such as research publications, news, medical diagnose notes, and further employ discovered knowledge to assist social and medical decision support. Examples of such decisions include hospital patient readmission prediction, which is a national initiative for health care cost reduction, academic research topics discovery and trend modeling, and social preference modeling for friend recommendation in social networks etc. To carry out text mining, our research, in Chapter 3, first emphasizes on single document analyzing to investigate textual stylometric features for user pro ling and recognition. Our research confirms that by using properly designed features, it is possible to identify the authors who wrote the article, using a number of sample articles written by the author as the training data. This study serves as the base to assert that text mining is a powerful tool for capturing knowledge in texts for better decision making. In the Chapter 4, we advance our research from single documents to documents with interdependency relationships, and propose to model and predict citation relationship between documents. Given a collection of documents with known linkage relationships, our research will discover e ective features to train prediction models, and predict the likelihood of two documents involving a citation relationships. This study will help accurately model social network linkage relationships, and can be used to assist e ective decision making for friend recommendation in social networking, and reference recommendation in scienti c writing etc. In the Chapter 5, we advance a topic discovery and trend prediction principle to discover meaningful topics from a set of data collection, and further model the evolution trend of the topic. By proposing techniques to discover topics from text, and using temporal correlation between trend for prediction, our techniques can be used to summarize a large collection of documents as meaningful topics, and further forecast the popularity of the topic in a near future. This study can help design systems to discover popular topics in social media, and further assist resource planning and scheduling based on the discovered topics and the their evolution trend. In the Chapter 6, we employ both text mining and topic modeling to the medical domain for effective decision making. The goal is to discover knowledge from medical notes to predict the risk of a patient being re-admitted in a near future. Our research emphasizes on the challenge that re-admitted patients are only a small portion of the patient population, although they bring signficant financial loss. As a result, the datasets are highly imbalanced which often result in poor accuracy for decision making. Our research will propose to use latent topic modeling to carryout localized sampling, and combine models trained from multiple copies of sampled data for accurate prediction. This study can be directly used to assist hospital re-admission assessment for early warning and decision support. The text mining and topic modeling techniques investigated in the dissertation can be applied to many other domains, involving texts and social relationships, towards pattern and knowledge based e ective decision making. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

Federated approach for the distributed simulation of a network, is an alternative method that aims to combine existing simulation models and software together using a Run Time Infrastructure (RTI), rather than building the whole simulation from scratch. In this study, an approach that significantly reduces the inter-federate communication load in federated simulation of communication networks is proposed. Rather than communicating packet-level information among federates, characteristics of packet flows in individual federates are dynamically identified and communicated. Flow characterization is done with the Gaussian Mixtures Algorithm (GMA) using a Self Organizing Mixture Network (SOMN) technique. In simulations of a network partitioned into eight federates in space parallel manner, it is shown that significant speedups are achieved with the proposed approach without unduly compromising accuracy.