Performanz ist ein zentraler Bestandteil des Designs von Anonymisierungsdiensten. Ihre zunehmende Popularität führt jedoch zu einer hohen Netzwerklast, die unzulängliche Entwurfsentscheidungen imminent macht. Die Anforderungen und die vielschichtige Architektur von Anonymisierungsdiensten machen die Thematik zu einem anspruchsvollen und zugleich inspirierenden Forschungsgegenstand. Die vorliegende Arbeit diskutiert das Design von sogenannten Niedriglatenz-Anonymisierungsdiensten im Allgemeinen und dem Tor-Netzwerk als relevantesten Vertreter im Speziellen. Es werden Lösungen für eine Reihe von Forschungsfragen entwickelt, die allesamt das Ziel verfolgen, diese Overlay-Netzwerke zu verbessern und sicherer zu gestalten. Es entsteht ein fundamentales Verständnis zu Netzwerkaspekten in Anonymisierungs-Overlays, das die Netzwerklast, als vorherrschende Ursache für die schwache Performanz, thematisiert. / Performance is a pivot point in the design of anonymity overlays. Due to their growing popularity, they are faced with increasing load, which makes design problems imminent. The special requirements and complex architecture of anonymity overlays renders the topic a challenging but likewise inspiring object of research. In this work, we discuss the design of low-latency anonymous communication systems in general and the Tor network as the de-facto standard in particular. We develop solutions to a number of research questions, all collectively following the aim of enhancing and securing such networks. By doing this we create a fundamental technical understanding of networking aspects in anonymity overlays and tackle the most prevalent performance issue experienced today: network congestion.

Avanços nas tecnologias de comunicação e processamento de sinais além de mudar a forma de como realizar negócios em todo o mundo, têm motivado o surgimento de serviços e aplicações multimídia na Internet de forma crescente. Como conseqüência, é possível conceber, desenvolver, implantar e operar serviços de distribuição de vídeo digital na Internet, tanto na abordagem sob-demanda quanto ao vivo. Com o aumento das aplicações multimídia na rede, torna-se cada vez mais complexo e necessário definir um modelo eficiente que possa realizar o gerenciamento efetivo e integrado de todos os elementos e serviços que compõe um sistema computacional. Pensando assim, este trabalho propõe uma arquitetura de gerenciamento baseado em políticas aplicada à distribuição de conteúdo multimídia com controle de QoS (Quality of Service) em redes de sobreposição (overlay). A arquitetura é baseada nos padrões de gerenciamento por políticas definida pela IETF (Internet Engineering Task Force) que, através de informações contextuais (rede e clientes) administra os serviços disponíveis no sistema. Faz uso dos requisitos de QoS providos pela rede de distribuição e os compara com os requisitos mínimos exigidos pelos perfis das aplicações previamente mapeados em regras de políticas. Dessa forma é possível controlar e administrar os elementos e serviços do sistema, afim de melhor distribuir recursos aos usuários deste sistema. / Advances in communication technologies and signal processing have not only changed the way business is conducted around the world, but have also driven the development of services and multimedia applications on the Internet. As a result, it is possible to design, develop, deploy and operate services for digital video distribution on the Internet, both according to an on-demand approach and live. Because of the increase in multimedia applications on the network, it has become increasingly more complex and necessary to define an efficient architecture that can achieve the effective and integrated management of all the elements and services that compose a computer system. With this in mind, this study proposes developing a robust and efficient architecture based on IETF (Internet Engineering Task Force) policy management standards applied to multimedia distribution content with QoS (Quality of Service) control in Overlay Networks. This architecture makes use of QoS requirements provided by the distribution network and compares them to the minimum requirements demanded by each type of application previously mapped in the policy rules. This system makes it possible to control and manage system information and services and also to distribute resources to system users better.

Redes sobrepostas são consideradas uma forma fácil e eficaz de implantar serviços de Internet de valor agregado através da extensão do serviço de entrega de melhor esforço oferecido pela camada de rede IP. No entanto, para aproveitar-se de seus benefícios, um projeto cuidadoso torna-se necessário. Como ainda não existem padrões para redes sobrepostas, com frequência estas são projetadas de forma independente, o que significa que cada uma aplica sua própria descoberta de topologia e toma suas próprias decisões de roteamento. Como resultado, elas podem afetar negativamente umas às outras, através da geração de uma sobrecarga de informações de controle ou através da criação de gargalos na rede física. Portanto, para evitar tais situações, este trabalho propõe uma arquitetura e organização de middleware para serviços em redes sobrepostas. Dentre os possíveis serviços, um esquema de multidifusão sobreposta foi projetado e implantado, no qual um protocolo de middleware baseado em padrões internacionais implementa tanto um cenário intradomínio quanto interdomínio. Validamos o sistema proposto através de dois tipos de análise: uma análise de desempenho e uma análise funcional. A primeira análise mostra que o desempenho do protocolo aqui proposto pode ser comparado ao desempenho dos protocolos tradicionais de multidifusão IP, a menos de uma métrica: a latência. Entretanto, o modelo analítico desenvolvido mostra a possibilidade de se traçar heurísticas para um projeto de serviço sobreposto com latência controlada. Além disso, a análise funcional utiliza-se de medidas experimentais no sistema real para confirmar a funcionalidade de multidifusão interdomínio, facilidade antes inviável em ambientes de rede pública utilizando-se as técnicas tradicionais. / Overlay networks are considered an easy and effective way to deploy value-added Internet services by extending the best-effort delivery service supported by IP layer. However, a careful design is needed in order to take advantage of these benefits. Since there are no standards for overlay networks yet, they are often independently designed, which means that each one applies its own topology discovery and takes its own routing decisions. As a result, they may negatively affect each other by generating control overhead and by creating bottlenecks in the physical network. In order to avoid such a situation, this work proposes an overlay network organization and architecture for overlay network services. Among possible services, an overlay multicast scheme was projected and deployed, on which a middleware protocol based on international standards implements both intradomain and interdomain scenarios. We validate the proposed system by two kind of analysis: performance analysis and functional analysis. The first one shows the performance of the proposed protocol can be compared with performance of traditional IP multicast protocols, except for one metric: latency. Nevertheless, the developed analytical modeling shows the possibility to outline heuristics for a controlled-latency overlay service project. Moreover, functional analysis uses experimental measurements on real system to confirm interdomain multicast functionality, facility before unfeasible in public network environments when using traditional techniques.

Avanços nas tecnologias de comunicação e processamento de sinais além de mudar a forma de como realizar negócios em todo o mundo, têm motivado o surgimento de serviços e aplicações multimídia na Internet de forma crescente. Como conseqüência, é possível conceber, desenvolver, implantar e operar serviços de distribuição de vídeo digital na Internet, tanto na abordagem sob-demanda quanto ao vivo. Com o aumento das aplicações multimídia na rede, torna-se cada vez mais complexo e necessário definir um modelo eficiente que possa realizar o gerenciamento efetivo e integrado de todos os elementos e serviços que compõe um sistema computacional. Pensando assim, este trabalho propõe uma arquitetura de gerenciamento baseado em políticas aplicada à distribuição de conteúdo multimídia com controle de QoS (Quality of Service) em redes de sobreposição (overlay). A arquitetura é baseada nos padrões de gerenciamento por políticas definida pela IETF (Internet Engineering Task Force) que, através de informações contextuais (rede e clientes) administra os serviços disponíveis no sistema. Faz uso dos requisitos de QoS providos pela rede de distribuição e os compara com os requisitos mínimos exigidos pelos perfis das aplicações previamente mapeados em regras de políticas. Dessa forma é possível controlar e administrar os elementos e serviços do sistema, afim de melhor distribuir recursos aos usuários deste sistema. / Advances in communication technologies and signal processing have not only changed the way business is conducted around the world, but have also driven the development of services and multimedia applications on the Internet. As a result, it is possible to design, develop, deploy and operate services for digital video distribution on the Internet, both according to an on-demand approach and live. Because of the increase in multimedia applications on the network, it has become increasingly more complex and necessary to define an efficient architecture that can achieve the effective and integrated management of all the elements and services that compose a computer system. With this in mind, this study proposes developing a robust and efficient architecture based on IETF (Internet Engineering Task Force) policy management standards applied to multimedia distribution content with QoS (Quality of Service) control in Overlay Networks. This architecture makes use of QoS requirements provided by the distribution network and compares them to the minimum requirements demanded by each type of application previously mapped in the policy rules. This system makes it possible to control and manage system information and services and also to distribute resources to system users better.

Overlay networks have been the subject of significant research and practical interest recently in addressing the inefficiency and ossification of the current Internet. In this thesis, we cover various aspects of overlay network design, including overlay routing algorithms, overlay network assignment and multihomed overlay networks. We also examine the behavior of overlay networks under a wide range of network settings and identify several key factors that affect the performance of overlay networks. Based on these findings, practical design guidelines are also given. Specifically, this thesis addresses the following problems: 1) Dynamic overlay routing: We perform an extensive simulation study to investigate the performance of available bandwidth-based dynamic overlay routing from three important aspects: efficiency, stability, and safety margin. Based on the findings, we propose a hybrid routing scheme that achieves good performance in all three aspects. We also examine the effects of several factors on overlay routing performance, including network load, traffic variability, link-state staleness, number of overlay hops, measurement errors, and native sharing effects. 2) Virtual network assignment: We investigate the virtual network (VN) assignment problem in the scenario of network virtualization. Specifically, we develop a basic VN assignment scheme without reconfiguration and use it as the building block for all other advanced algorithms. Subdividing heuristics and adaptive optimization strategies are presented to further improve the performance. We also develop a selective VN reconfiguration scheme that prioritizes the reconfiguration for the most critical VNs. 3) Overlay network configuration tool for PlanetLab: We develop NetFinder, an automatic overlay network configuration tool to efficiently allocate PlanetLab resources to individual overlays. NetFinder continuously monitors the resource utilization of PlanetLab and accepts a user-defined overlay topology as input and selects the set of PlanetLab nodes and their interconnection for the user overlay. 4) Multihomed overlay network: We examine the effectiveness of combining multihoming and overlay routing from the perspective of an overlay service provider (OSP). We focus on the corresponding design problem and examine, with realistic network performance and pricing data, whether the OSP can provide a network service that is profitable, better (in terms of round-trip time), and less expensive than the competing native ISPs.

Numerous studies have demonstrated the potential efficacy of percutaneous image-guided interventions over open surgical interventions. The conventional image-guided procedures are limited by the freehand technique, requiring mental 3D registration and hand-eye coordination for needle placement. The outcomes of these procedures are associated with longer duration and increased patient discomfort with high radiation exposure. Previously, a static image overlay system was proposed for aiding needle interventions. Certain drawbacks associated with the static system limited the clinical translation. To overcome the ergonomic issues and longer calibration duration associated with static system, an adjustable image overlay system was proposed. The system consisted of monitor and semi-transparent mirror, attached together to an articulated mobile arm. The 90-degree mirror-monitor configuration was proposed to improve the physician access around the patient. MicronTracker was integrated for dynamic tracking of the patient and device. A novel method for auto-direct calibration of the virtual image overlay plane was proposed. Due to large mechanical structure, the precise movement was limited and consumed useful space in the procedure room. A mobile image overlay system with reduced system weight and smaller dimensions was proposed to eliminate the need for mechanical structure. A tablet computer and beamsplitter were used as the display device and mirror respectively. An image overlay visualization module of the 3D Slicer was developed to project the correct image slice upon the tablet device. The system weight was reduced to 1 kg and the image overlay plane tracking precision (0.11mm STD=0.05) was similar to the printed physical markers. The auto-calibration of the image overlay plane can be done in two simple steps, away from the patient table and without additional phantom. Based on the successful pre-clinical testing of the previous static system, the mobile image overlay system with reduced weight, increased tracking precision and easier maneuverability, can be possibly hand-held by the physician to explore the image volume over the patient and be used for a wide range of procedures. The mobile image overlay system shall be classified as Class II device as per FDA regulations, do not require extensive verification and validation efforts and further improves the commercialization opportunities. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2014-06-26 18:51:03.958

Made available in DSpace on 2015-03-26T14:01:02Z (GMT). No. of bitstreams: 1 texto completo.pdf: 2835217 bytes, checksum: b3fc87e9e63a523c32790c1de91c6b8a (MD5) Previous issue date: 2010-06-14 / Most of the Kraft pulp produced in the world come from continuous digesters. Digester corrosion has become a significant topic for the pulp and paper industry since it brought about the need for high expenditures with repairs, replacement of components and upgrade of materials, as well as losses in connection with unplanned outages. Risks to life and property are also significant, as catastrophic failure of pressure bearing equipment may also result. From the Eighties to present days, corrosion problems in many pulp and paper mills around the world have been increasing, for reasons ranging from materials and design aspects of the digesters themselves, to process modifications introduced ever since. The present work examines this scenario, studies the corrosive behavior of continuous digesters in its several forms, and seeks to indicate the main causes. Actual corrosion cases are presented and the main current protective technologies are discussed. Electrochemical testing, metallurgical analyses, corrosivity testing and field inspections are used to support the discussions and conclusions. Highlight is given to the field experience with a type 316 stainless-clad digester, the only known continuous cooker built in such material in the industry, whose prospective corrosion hazards prompted the execution of studies and protective measures that are unique for stainless cooking vessels. The risks to carbon or austenitic stainless steel digesters running on modern cooking processes are demonstrated to be significant. The effectiveness of the main protective technologies, as well as the compatibility among them, was proved. The need to include these technologies in cooking plant retrofit projects was established. / A maior parte da celulose Kraft produzida no mundo provém de digestores contínuos. A corrosão destes digestores tornou-se uma questão relevante para a indústria de celulose, na medida em que trouxe a necessidade de elevados gastos com reparos, substituições de componentes e melhoria de materiais, bem como prejuízos por paralisações imprevistas e prolongadas da produção. O risco ao patrimônio e à vida humana é também considerável, já que há possibilidade real de falhas catastróficas em equipamentos pressurizados. Desde a década de 80 até os dias atuais, os problemas de corrosão em digestores de muitas fábricas de celulose Kraft vêm se acentuando, por razões que vão desde materiais e aspectos construtivos dos próprios digestores até mudanças nos processos desde então introduzidas. O presente trabalho examina este cenário, estuda o comportamento corrosivo dos digestores contínuos em suas diversas formas e procura evidenciar as principais causas. Casos reais de corrosão e proteção são apresentados e as principais tecnologias protetoras atualmente disponíveis são discutidas. Testes eletroquímicos, análises metalúrgicas, testes de corrosividade e inspeções de campo são utilizados para suportar as discussões e conclusões. Destaca-se a experiência com um digestor revestido em aço inoxidável tipo 316,sem similar conhecido, cujos riscos potenciais de corrosão instaram a execução de estudos e a adoção de providências inéditas para digestores em material inoxidável. Os riscos de corrosão dos digestores em aço carbono ou inoxidável austenítico operando com processos atuais são evidenciados como sendo significativos. A eficácia das principais tecnologias protetoras, bem como a compatibilidade entre elas, foi comprovada. A necessidade de inclusão destas tecnologias em projetos de retrofit de cozimento foi estabelecida.

Made available in DSpace on 2014-12-17T14:55:03Z (GMT). No. of bitstreams: 1 MarcosCMAP.pdf: 634837 bytes, checksum: 4a0393d7f7dbe297fda66b1ed1859c99 (MD5) Previous issue date: 2006-02-20 / There are some approaches that take advantage of unused computational resources in the Internet nodes - users? machines. In the last years , the peer-to-peer networks (P2P) have gaining a momentum mainly due to its support for scalability and fault tolerance. However, current P2P architectures present some problems such as nodes overhead due to messages routing, a great amount of nodes reconfigurations when the network topology changes, routing traffic inside a specific network even when the traffic is not directed to a machine of this network, and the lack of a proximity relationship among the P2P nodes and the proximity of these nodes in the IP network. Although some architectures use the information about the nodes distance in the IP network, they use methods that require dynamic information. In this work we propose a P2P architecture to fix the problems afore mentioned. It is composed of three parts. The first part consists of a basic P2P architecture, called SGrid, which maintains a relationship of nodes in the P2P network with their position in the IP network. Its assigns adjacent key regions to nodes of a same organization. The second part is a protocol called NATal (Routing and NAT application layer) that extends the basic architecture in order to remove from the nodes the responsibility of routing messages. The third part consists of a special kind of node, called LSP (Lightware Super-Peer), which is responsible for maintaining the P2P routing table. In addition, this work also presents a simulator that validates the architecture and a module of the Natal protocol to be used in Linux routers / Entre as diversas abordagens para se aproveitar os recursos computacionais ociosos existentes nas folhas da Internet, ou seja, nas m?quinas dos usu?rios, as redes peer-to-peer (P2P) v?m ganhando destaque especial nos ?ltimos anos devido principalmente ? sua escalabilidade, desempenho e toler?ncia ? falhas. As arquiteturas P2P atuais, entretanto, ainda apresentam alguns problemas como a sobrecarga nos n?s devido ? realiza??o do roteamento de mensagens, o n?mero elevado de n?s reconfigurados devido ? mudan?as de topologia da rede, a exist?ncia de tr?fego de roteamento dentro das redes das organiza??es que n?o ? destinado a nenhuma de suas m?quinas e ? aus?ncia de rela??o entre a proximidade dos n?s na rede P2P e a proximidade desses n?s na rede IP. Embora algumas arquiteturas considerem essas dist?ncias na rede IP, o fazem atrav?s de m?todos que requerem a troca de informa??es constantemente. Nesse trabalho n?s propomos uma arquitetura P2P para resolver os problemas citados. Essa arquitetura ? composta por tr?s partes. A primeira parte consiste em uma arquitetura P2P b?sica, chamada SGrid, que mant?m a rela??o dos n?s na rede P2P com suas posi??es na rede IP e atribui regi?es de chaves adjacentes para n?s de uma mesma organiza??o. A segunda parte consiste em um protocolo chamado NATal (Routing and NAT application layer) que estende a arquitetura b?sica para retirar dos n?s a fun??o de roteamento de mensagens. A terceira parte consiste de um tipo especial de n?, chamado LSP (Lightware Super-Peer), que ? o respons?vel pela manuten??o das tabelas de roteamento P2P. Al?m da descri??o da arquitetura proposta e da especifica??o dos protocolos SGrid e NATal, esse trabalho apresenta o simulador desenvolvido para validar a arquitetura e um m?dulo para ser utilizado em roteadores Linux que implementa o protocolo Natal

Made available in DSpace on 2014-12-17T14:57:58Z (GMT). No. of bitstreams: 1 MoacirBR_DISSERT.pdf: 4521415 bytes, checksum: c98edffad04a3e49fed259b6f659f5f2 (MD5) Previous issue date: 2009-12-04 / Universidade Federal do Rio Grande do Norte / In general, the designs of equipment takes into account the effects and processes of deterioration it will undergo and arrives at an approximate useful life. However, changes in operational processes and parameters, the action of external agents, the kind of maintenance conducted, the means of monitoring, and natural and accidental occurrences completely modify the desired performance of the equipment. The discontinuities that occur in anisotropic materials often and due to different factors evolve from being subcritical to critical acquiring the status of defect and compromising the physical integrity of the equipment. Increasingly sophisticated technological means of detection, monitoring and assessment of these discontinuities are required to respond ever more rapidly to the requirements of industry. This paper therefore presents a VPS (Virtual Pipe System) computational tool which uses the results of ultrasonic tests on equipment, plotting the discontinuities found in models created in the CAD and CAE systems, and then simulates the behavior of these defects in the structure to give an instantaneous view of the final behavior. This paper also presents an alternative method of conventional ultrasonic testing which correlates the integrity of an overlay (carbon steel and stainless steel attached by welding) and the reflection of ultrasonic waves coming from the interface between the two metals, thus making it possible to identify cracks in the casing and a shift of the overlay / Os projetos de equipamentos em geral j? contemplam os esfor?os e os mecanismos de de processo e de par?metros operacionais, a??o de agentes externos, esp?cie de manuten??o aplicada, forma de acompanhamento, ocorr?ncias naturais e acidentes modificam completamente deteriora??o a que estes est?o submetidos, prevendo aproximadamente sua vida ?til, por?m, mudan?as o comportamento esperado dos equipamentos. As descontinuidades em materiais anisotr?picos muitas vezes e, por diversos fatores, evoluem da condi??o de subcr?ticas para cr?ticas assumindo o status de defeito e comprometendo a integridade f?sica do equipamento. Meios de detec??o, monitora??o e avalia??o dessas descontinuidades, cada vez mais tecnol?gicos, s?o requeridos para responderem de forma mais eficaz ? exig?ncia da ind?stria. Assim, este trabalho apresenta uma ferramenta computacional VPS (Virtual Pipe System) que utiliza o resultado de ensaios de ultrassom em equipamentos plotando essas descontinuidades encontradas em modelos criados em sistemas CAD e CAE e, ainda, simula o comportamento desses defeitos na estrutura possibilitando a visualiza??o instant?nea do comportamento final. Apresenta-se ainda neste trabalho um m?todo alternativo de ensaio ultrass?nico convencional que correlaciona a integridade de um overlay (a?o carbono e a?o inoxid?vel depositado por solda) com as reflex?es de ondas de ultra-som provindas da interface entre os dois metais, possibilitando a identifica??o de trincas no revestimento e de descolamento do overlay

Au cours des dernières années, la révolution numérique a continué sa progression. Les technologies de l'information et des communications (TIC) ont totalement changé la vie quotidienne des gens à leur domicile (concept de « maison numérique »). Pendant ce temps, non seulement le volume des émissions de CO2 produit par les TIC, ce qu'on appelle l'empreinte carbone, est sans cesse en croissance mais elle s'accompagne également d'une hausse du prix de l'électricité, augmentant fortement la part des équipements numériques dans la budget global des ménages. Ainsi, pour des raisons environnementale et économique, réduire la consommation d'énergie dans les nombreux équipements du réseau domestique est devenu un enjeu majeur. Dans ce contexte, la thèse porte sur la conception, l'évaluation et la mise en œuvre d'un ensemble de mécanismes dans le but de répondre aux problèmes de consommation d'énergie sur les réseaux locaux rassemblant les équipements numériques domestiques. Nous proposons un réseau de contrôle qui est formé par des noeuds de contrôle de l'énergie placés au-dessus du réseau traditionnel. Chaque nœud de contrôle est relié à un dispositif en vue de coordonner les états d'alimentation de l'équipement domestique associé.. Un démonstrateur pour un système Home Power Efficiency (HOPE) a également été mis en œuvre. Il démontre la faisabilité de la solution technique que nous proposons pour le contrôle de l'énergie dans un réseau domestique réel avec des scénarios réels qui sont souvent utilisées par utilisateur. Après avoir analysé le mode d'utilisation des équipements du réseau domestique, nous proposons un système de gestion d'énergie qui contrôle ces équipements minimisant ainsi que leur consommation. Le système est basé sur l'analyse des services collaboratifs, chaque service est découpé en blocs fonctionnels atomiques, distribués dans les différents équipements. Cela permet de gérer avec plus de précision les besoins énergétiques de chaque équipement de manière à n'alimenter que les composants nécessaires au service demandé. Pour conclure ces travaux, nous avons également cherché à minimiser les impacts de l'économie d'énergie sur la qualité d'expérience perçue par l'utilisateur (notamment le délai d'activation des services). Nous proposons un système de gestion d'énergie pour des services collaboratifs offrant plusieurs compromis possibles entre la consommation d'énergie et le délai d'activation des services dans un réseau domestique. Il est complété par un algorithme d'apprentissage du comportement des utilisateurs domestiques. / In recent years, Information and Communications Technology (ICT) has totally changed the people daily life in the Digital Home. Meanwhile, not only the amount of CO2 emission of ICT, so called ''footprint'', is increasing without cease, but also the price of electricity is constantly rising. Thus, it is quite important to reduce energy consumption in the home network and home devices for the environmental and economic reasons. In order to cope with this context, the thesis concerns the design, the evaluation, and the implementation of a novel set of mechanisms with the purpose of responding to home network energy consumption problems. We proposed firstly an Overlay Energy Control Network which is formed by the overlay energy control nodes. Each node is connected to one device which forms an overlay control network to coordinate the power states of the device. Then, a testbed for HOme Power Efficiency system (HOPE) is implemented to demonstrate the technical solution for energy control in a real home network environment with several frequently used scenarios. After analyzing user's way of use of their home network equipment, we propose a power management which controls the devices based on the analysis of the collaborative services. These frequently used collaborative services require different functional blocks in different devices. This model provides the possibility to turn on the right requested functional blocks in the right device at the right moment. Finally, based on the former contribution, the collaborative overlay power management offers several possible tradeoffs between the power consumption and the waiting delay in the home network.