Video-conferencing (VC) is a well established educational tool. Using a grounded theory approach, this study explored the experience of medical students studying remotely by VC. A convenience sample of 11 students participated in semi-structured interviews. Constant comparative analysis identified three emerging themes which were refined and verified by a focus group. The key themes were: the effect of VC on the students’ classroom experience, the development of a strong social cohesion between the students, and the impact on student learning. The participants adapted well to VC lectures but expressed reluctance to ask or answer questions in class. Participants felt they became more self-directed and better collaborative learners. Moore’s theory of transactional distance provides a possible explanation for these observations. High transactional distance was evident with less instructor-student interaction, more student-student interaction, and greater student autonomy. Understanding the transactional dynamics in the VC classroom will inform future research and faculty development. / 2011 May

In the last decade the world has seen a steadily increasing number of Cube Satellites deployed to Low Earth Orbit. Traditionally, these cubesats rely on Amateur Radio communications technology that are proven to work from space. However, as data volumes increase, the existing Amateur Radio protocols, combined with the restrictions of use for the Amateur Radio Spectrum, as well as the trend to build one control station per cubesat, result in a bottle neck effect whereby existing communications methods are no longer sufficient to support the increasing data volumes of the spacecraft. This Masters Thesis work explores the concept of deploying a network of distributed ground station receiver nodes for the purposes of increasing access time to the spacecraft, and thereby increasing the potential amount of data that can be transferred from orbit to the ground. The current trends in cubesat communications will be analyzed and an argument will be made in favor of transitioning to more modern digital communications approaches for on orbit missions. Finally, a candidate ground station receiver node design is presented a possible design that could be used to deploy such a network. / Master of Science

Allocating resources in computer systems is a significant challenge due to constraints on resources, coordinating access to those resources, and tolerating malicious behavior. This dissertation investigates two fundamental problems concerning resource allocation. The first addresses the general challenge of sharing server resources among multiple clients, where an adversary may deny the availability of these resources; this is known as a denial-of-service (DoS) attack. Here, we propose a deterministic algorithm that employs resource burning (RB)—the verifiable expenditure of a network resource—to defend against DoS attacks. Specifically, our solution forces an adversary to incur higher RB costs compared to legitimate clients. Next, we develop a general policy-driven framework that utilizes machine learning classification to tune the amount of RB used for mitigating DoS attacks. Finally, we expand the application of RB to defend against DoS attacks on hash tables, which are a popular data structure in network applications. The second problem deals with resource allocation in wireless systems; specifically, the sharing of the wireless medium among multiple participants competing to transmit data. While modern WiFi and cellular standards do solve this problem, several recent theoretical results suggest that superior solutions are possible. Here, we investigate the viability of these solutions and discover that they fall short of their promised performance in practice. Consequently, we identify the cause of this shortcoming and quantify the discrepancy through a combination of analytical and simulation work. Ultimately, we propose a revised theoretical model that aligns better with practical observations.

International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California / This paper describes a distributed network client-server system developed for researchers to perform real-time or near-real-time analyses on ensembles of telemetry data previously done in post-flight. The client-server software approach provides extensible computing and real-time access to data at multiple remote client sites. Researchers at remote sites can share similar information as those at the test site. The system has been used successfully in numerous commercial, academic and NASA wide aircraft flight testing.

Future electrical power networks should support the integration of distributed renewable energy sources, which may be contributed by individual customers instead of utility companies. Such a demand poses new challenges to power distribution network design, since the energy generation, energy consumption, and power flow all become highly dynamic. An inappropriate network design may not only waste much energy in power distribution but also incur high cost in network construction. In this thesis, we study the optimal network design problem under a dynamic current injection model. We investigate different optimization methods to obtain the optimal network structure that can better adapt to dynamic energy generation/consumption requirements and is more efficient than traditional tree-structured power networks. By predicting users' potential load in the network, network design with our method results in significant energy saving. / Graduate / 0984

There are many different database management systems (DBMSs) on the market today. They all have different strengths and weaknesses. What if all of these different DBMSs could be used together in a heterogeneous network? The purpose of this thesis is to explore ways of connecting the many different DBMSs together. This thesis will explore suitable architectures, features, and performance of such a network. This is all done in the context of Ericsson’s wireless communication network. This has not been done in this context before, and a big part of the thesis is exploring if it is even possible. The result of this thesis shows that it is not possible to find a solution that can fulfill the requirements of such a network in this context

Com o crescimento em número e diversidade dos componentes das redes de computadores, surge a necessidade de buscar uma maneira consistente de realizar seu gerenciamento para, com isso, manter toda sua estrutura funcionando de forma suave e atendendo às necessidades de seus usuários e às expectativas de seus administradores. Em aspectos gerais, as abordagens centralizadas têm se mostrado inadequadas para o gerenciamento de redes de computadores com um grande número de nós ou com grande diversidade de dispositivos. A necessidade de distribuição da gerência torna-se, assim, evidente, onde vários operadores administram cooperativamente a rede, cada um sendo responsável por um segmento da mesma, mas que precisam poder inspecionar os demais segmentos para poder resolver problemas distintos. Por isso a necessidade de um sistema de suporte ao gerenciamento cooperativo, que forneça suporte à interação dos administradores, independente de tempo e da localização dos participantes. É esse sistema que determinará como os administradores vão se comunicar, distribuir responsabilidades, compartilhar informações, e utilizar as ferramentas disponíveis. Nesse contexto, esta dissertação de mestrando apresenta a proposta de um ambiente de gerenciamento distribuído e cooperativo, baseado na tecnologia P2P. Esse ambiente oferece quatro serviços: compartilhamento de arquivos de configuração de dispositivos, compartilhamento de registros de dispositivos, configuração de dispositivos e solicitação de reserva de banda. A partir da proposta do ambiente foi implementada em Java, utilizando a plataforma de desenvolvimento JXTA, uma aplicação para a realização de testes, com o objetivo de confirmar a possibilidade de utilização da aplicação para realizar o gerenciamento de redes. Os parâmetros observados nas avaliações de desempenho foram o tráfego gerado e o tempo de resposta. Os resultados dos testes comprovaram a possibilidade da utilização de sistemas P2P para facilitar o gerenciamento cooperativo de redes e foram bastante satisfatórios com relação aos parâmetros avaliados. / With the increasing number and diversity of components of the computer networks, comes the necessity to find a consistent way to manage modern networks. This is required in order to keep all network infrastructures working in a proper and smooth way, while taking care of to the network users’ necessities and filling the network administrators’ expectations. In general aspects, the centralized management approaches are inadequate for the management of networks with a great number of nodes or great diversity of devices. The necessity of a distributed management thus becomes evident. In such distributed management, a group of administrators manages a single network in a cooperative fashion, each administrator being responsible for a segment of the managed network but at the same time being able to inspect other remote segments in order to solve non-overlapping problems. That is the motivation for having management systems with proper cooperative management support that allows interactions among administrators independent of time and location. Such a system will determine how administrators will communicate to delegate responsibilities, share information, and use the available tools. In this context, this dissertation presents the proposal of a distributed and cooperative management environment based on P2P technology. This environment offers four services: sharing of device configuration files, sharing of registered devices, configuration of devices, and bandwidth reservation. Based on the proposed environment, a Java application, using the JXTA development platform, has been implemented. This application allowed us to test and confirm the possibility of using P2P technologies for network management. In addition, the performance of the implemented solution has been measured considering the generated management traffic and response time. The results from the evaluation tests had proven the possibility of the use of P2P systems to facilitate the cooperative network management and had been sufficiently satisfactory in relation to the evaluated parameters.

Com o crescimento em número e diversidade dos componentes das redes de computadores, surge a necessidade de buscar uma maneira consistente de realizar seu gerenciamento para, com isso, manter toda sua estrutura funcionando de forma suave e atendendo às necessidades de seus usuários e às expectativas de seus administradores. Em aspectos gerais, as abordagens centralizadas têm se mostrado inadequadas para o gerenciamento de redes de computadores com um grande número de nós ou com grande diversidade de dispositivos. A necessidade de distribuição da gerência torna-se, assim, evidente, onde vários operadores administram cooperativamente a rede, cada um sendo responsável por um segmento da mesma, mas que precisam poder inspecionar os demais segmentos para poder resolver problemas distintos. Por isso a necessidade de um sistema de suporte ao gerenciamento cooperativo, que forneça suporte à interação dos administradores, independente de tempo e da localização dos participantes. É esse sistema que determinará como os administradores vão se comunicar, distribuir responsabilidades, compartilhar informações, e utilizar as ferramentas disponíveis. Nesse contexto, esta dissertação de mestrando apresenta a proposta de um ambiente de gerenciamento distribuído e cooperativo, baseado na tecnologia P2P. Esse ambiente oferece quatro serviços: compartilhamento de arquivos de configuração de dispositivos, compartilhamento de registros de dispositivos, configuração de dispositivos e solicitação de reserva de banda. A partir da proposta do ambiente foi implementada em Java, utilizando a plataforma de desenvolvimento JXTA, uma aplicação para a realização de testes, com o objetivo de confirmar a possibilidade de utilização da aplicação para realizar o gerenciamento de redes. Os parâmetros observados nas avaliações de desempenho foram o tráfego gerado e o tempo de resposta. Os resultados dos testes comprovaram a possibilidade da utilização de sistemas P2P para facilitar o gerenciamento cooperativo de redes e foram bastante satisfatórios com relação aos parâmetros avaliados. / With the increasing number and diversity of components of the computer networks, comes the necessity to find a consistent way to manage modern networks. This is required in order to keep all network infrastructures working in a proper and smooth way, while taking care of to the network users’ necessities and filling the network administrators’ expectations. In general aspects, the centralized management approaches are inadequate for the management of networks with a great number of nodes or great diversity of devices. The necessity of a distributed management thus becomes evident. In such distributed management, a group of administrators manages a single network in a cooperative fashion, each administrator being responsible for a segment of the managed network but at the same time being able to inspect other remote segments in order to solve non-overlapping problems. That is the motivation for having management systems with proper cooperative management support that allows interactions among administrators independent of time and location. Such a system will determine how administrators will communicate to delegate responsibilities, share information, and use the available tools. In this context, this dissertation presents the proposal of a distributed and cooperative management environment based on P2P technology. This environment offers four services: sharing of device configuration files, sharing of registered devices, configuration of devices, and bandwidth reservation. Based on the proposed environment, a Java application, using the JXTA development platform, has been implemented. This application allowed us to test and confirm the possibility of using P2P technologies for network management. In addition, the performance of the implemented solution has been measured considering the generated management traffic and response time. The results from the evaluation tests had proven the possibility of the use of P2P systems to facilitate the cooperative network management and had been sufficiently satisfactory in relation to the evaluated parameters.

O gerenciamento de redes é realizado seguindo diversos modelos, baseados em diferentes paradigmas. Os paradigmas tradicionais de gerenciamento compreendem o paradigma centralizado e o paradigma hierárquico fracamente distribuído. Tais paradigmas, contudo, apresentam limitações para o gerenciamento de diversas redes atuais, em virtude de fatores como o aumento em tamanho, em complexidade e em heterogeneidade destas redes. Em adição a estes fatores, existem atualmente contextos de rede que, por apresentarem certas peculiaridades, não podem ser gerenciados de modo apropriado por tais modelos. Estas limitações e requisitos diferenciados encontrados nas redes atuais trazem a necessidade do emprego de modelos de gerenciamento inovadores, baseados nos paradigmas fortemente distribuídos. Neste contexto, uma tecnologia que se mostra promissora para o desenvolvimento de um modelo de gerenciamento com tais características é a tecnologia peer-to-peer (P2P). Esta Tese versa sobre estes tópicos. Discute, como primeiro objetivo, as limitações dos modelos tradicionais para o gerenciamento de contextos modernos de rede, isto é, contextos de redes atuais que possuem particularidades distintas e, com isto, demandam requisitos de gerenciamento específicos, não identificados nas redes tradicionais. Define e investiga, então, como segundo objetivo, um modelo de gerenciamento fortemente distribuído baseado na tecnologia P2P. Este modelo visualiza a rede P2P como uma infra-estrutura que provê suporte para que as operações de gerenciamento sejam desempenhadas com forte distribuição. Por fim, como terceiro objetivo, analisa como as soluções de gerenciamento para redes atuais baseadas neste modelo podem ser classificadas segundo os paradigmas de gerenciamento das principais taxonomias propostas na literatura. Tal análise proporciona a identificação das limitações destas taxonomias para a classificação das soluções de gerenciamento requeridas para os contextos de redes atuais e deu origem à definição de uma taxonomia para soluções de gerenciamento que destaca as características e os requisitos demandados dos modelos de gerenciamento modernos. / Network management is carried out following several models, based on different paradigms. Traditional management paradigms consist of centralized and weakly distributed hierarchical ones. However, such paradigms present limitations to be applied to the management of several today networks. This occurs because of some issues such as the grown in size, complexity and heterogeneity of such networks. Additionally, nowadays, there are network contexts that can not be appropriately managed by such models because of some context peculiarities. Those today’s networks drawbacks and requirements demand the employment of innovative models, based on strongly distributed paradigms. A technology that seems promising in addressing such needs is peer-to-peer (P2P). This Thesis discusses about those topics. As its first objective, the Thesis discusses traditional models drawbacks to the management of modern network contexts, this is, current network contexts that have some different peculiarities and, because of them, demand specific management requirements not existent in traditional networks. As its second objective, the Thesis defines and investigates a strongly distributed management model based on P2P technology. Such model looks at P2P network as an infrastructure that can be used as support to management operations be accomplished in a strongly distributed way. Finally, as its third objective, the Thesis analyses how the management solutions based on such model can be classified according the management paradigms of the main literature taxonomies. Such analysis provides the identification of taxonomies limitations to the classification of management solutions required by today’s network contexts. It has originated the definition of a management solution taxonomy that emphasizes the features and requirements demanded of modern management models.

O gerenciamento de redes é realizado seguindo diversos modelos, baseados em diferentes paradigmas. Os paradigmas tradicionais de gerenciamento compreendem o paradigma centralizado e o paradigma hierárquico fracamente distribuído. Tais paradigmas, contudo, apresentam limitações para o gerenciamento de diversas redes atuais, em virtude de fatores como o aumento em tamanho, em complexidade e em heterogeneidade destas redes. Em adição a estes fatores, existem atualmente contextos de rede que, por apresentarem certas peculiaridades, não podem ser gerenciados de modo apropriado por tais modelos. Estas limitações e requisitos diferenciados encontrados nas redes atuais trazem a necessidade do emprego de modelos de gerenciamento inovadores, baseados nos paradigmas fortemente distribuídos. Neste contexto, uma tecnologia que se mostra promissora para o desenvolvimento de um modelo de gerenciamento com tais características é a tecnologia peer-to-peer (P2P). Esta Tese versa sobre estes tópicos. Discute, como primeiro objetivo, as limitações dos modelos tradicionais para o gerenciamento de contextos modernos de rede, isto é, contextos de redes atuais que possuem particularidades distintas e, com isto, demandam requisitos de gerenciamento específicos, não identificados nas redes tradicionais. Define e investiga, então, como segundo objetivo, um modelo de gerenciamento fortemente distribuído baseado na tecnologia P2P. Este modelo visualiza a rede P2P como uma infra-estrutura que provê suporte para que as operações de gerenciamento sejam desempenhadas com forte distribuição. Por fim, como terceiro objetivo, analisa como as soluções de gerenciamento para redes atuais baseadas neste modelo podem ser classificadas segundo os paradigmas de gerenciamento das principais taxonomias propostas na literatura. Tal análise proporciona a identificação das limitações destas taxonomias para a classificação das soluções de gerenciamento requeridas para os contextos de redes atuais e deu origem à definição de uma taxonomia para soluções de gerenciamento que destaca as características e os requisitos demandados dos modelos de gerenciamento modernos. / Network management is carried out following several models, based on different paradigms. Traditional management paradigms consist of centralized and weakly distributed hierarchical ones. However, such paradigms present limitations to be applied to the management of several today networks. This occurs because of some issues such as the grown in size, complexity and heterogeneity of such networks. Additionally, nowadays, there are network contexts that can not be appropriately managed by such models because of some context peculiarities. Those today’s networks drawbacks and requirements demand the employment of innovative models, based on strongly distributed paradigms. A technology that seems promising in addressing such needs is peer-to-peer (P2P). This Thesis discusses about those topics. As its first objective, the Thesis discusses traditional models drawbacks to the management of modern network contexts, this is, current network contexts that have some different peculiarities and, because of them, demand specific management requirements not existent in traditional networks. As its second objective, the Thesis defines and investigates a strongly distributed management model based on P2P technology. Such model looks at P2P network as an infrastructure that can be used as support to management operations be accomplished in a strongly distributed way. Finally, as its third objective, the Thesis analyses how the management solutions based on such model can be classified according the management paradigms of the main literature taxonomies. Such analysis provides the identification of taxonomies limitations to the classification of management solutions required by today’s network contexts. It has originated the definition of a management solution taxonomy that emphasizes the features and requirements demanded of modern management models.