Desempenho de QoS e mobilidade de sessões multicast em redes dinâmicasMes

Mestrado em Engenharia Electrónica e TelecomunicaçõesThe increasing demand in multimedia group services, contextawareness and seamless mobility implies strict requirements that cannot be satisfactorily addressed by the traditional transport control architectures for session content delivery. Moreover, context-aware networks introduce personalized concepts: any change in context can change the overall services and network environments, requiring the network and multicast sessions to be completely restructured in a very dynamic way. Regarding the complexity of maintaining scalability in context-aware networks, this Thesis has as main goal the development of an intelligent module, included in C-CAST architecture, capable of managing the entire network scheme. This mechanism depending on the scenario and the context of users and sources, and in cooperation with other network entities, must decide the most suitable network transport path in order to provide the best multiparty content delivery to the users, and manage the dynamicity of the network whenever changes occur. To perform its implementation, it was used an approach based in the interaction of different network components, exchanging context information between them. The intelligent module, using the updated network information, decides the better network connection to serve each user. In order to simulate the network behaviour in various situations, several scenarios were tested to evaluate its performance. The network is evaluated according to the several configured parameters, evaluating the improvements achieved in the network performance concerning different metrics, e.g. delay, lost packets ratio, overhead introduced by the architecture signalling. Through the implemented simulation setup, it is possible to conclude that the deployment of the solution proposed effectively provides an enhanced service to the users, distributing the multiparty content with QoS assurance using context information.O aumento da exigência em serviços de grupo, redes baseadas em contexto e mobilidade transparente implicam requisitos rígidos que não podem ser satisfeitos pelas arquitecturas tradicionais de controlo de transporte para entrega de conteúdos de sessão. Não obstante, redes baseadas em contexto introduzem conceitos personalizados: qualquer mudança no contexto pode mudar completamente os serviços e a própria rede, sendo necessário que a rede e as sessões multicast sejam completamente reestruturadas de uma forma dinâmica. Tendo em conta a complexidade de manter a escalabilidade em redes baseadas em contexto, esta Tese tem como principal objectivo o desenvolvimento de um módulo inteligente, que faz parte da arquitectura do projecto C-CAST, capaz de gerir toda a rede. Este mecanismo, dependendo do cenário da rede e do contexto dos utilizadores e das fontes, e em cooperação com outras entidades da rede, deve seleccionar a o caminho mais apropriado da rede de modo a fornecer da melhor forma o conteúdo aos utilizadores, e gerir a dinâmicidade da rede sempre que ocorrem mudanças. Para o implementar foi usada um método baseado na interacção de vários componentes, que trocam informação sobre contextos entre eles. O componente inteligente, usando informação actualizada da rede decide qual a melhor conexão da rede para servir cada utilizador. De forma a simular o comportamento da rede em várias situações, foram testados diversos cenários para avaliar a sua performance. A rede é avaliada de acordo com os vários parâmetros configurados, avaliando as melhorias conseguidas na performance da rede, por exemplo em termos de atrasos, rácio de pacotes perdidos e a carga imposta pelas mensagens de controlo da arquitectura. Através das simulações efectuadas é possível concluir que aplicando a arquitectura proposta, é fornecido de forma eficiente um serviço melhorado aos utilizadores, distribuindo o serviço de grupo com garantias de Qualidade de Serviço e usando informação de contexto

Process-aware web programming with Jolie

We extend the Jolie programming language to capture the native modelling of process-aware web information systems, i.e., web information systems based upon the execution of business processes. Our main contribution is to offer a unifying approach for the programming of distributed architectures on the web, which can capture web servers, stateful process execution, and the composition of services via mediation. We discuss applications of this approach through a series of examples that cover, e.g., static content serving, multiparty sessions, and the evolution of web systems. Finally, we present a performance evaluation that includes a comparison of Jolie-based web systems to other frameworks and a measurement of its scalability.Comment: IMADA-preprint-c

Controlo do transporte de sessões multicast em redes dinâmicas

Mestrado em Engenharia Electrónica e TelecomunicaçõesHoje em dia assiste-se a um aumento considerável da procura de serviços ou aplicações para múltiplos utilizadores (multiparty), como streaming de conteúdos media, partilha de informações, colaboração entre utilizadores, entre outros. O suporte de tais serviços pela Internet mostra-se extremamente exigente para as actuais arquitecturas de rede, requerendo recursos e funcionalidades completamente fora do alcance de serem suportadas. Desta forma, é necessário investigar e desenvolver novos mecanismos que possibilitem simultaneamente um melhor e maior controlo a este nível. Neste âmbito, tem-se observado actualmente um aumento no número de arquitecturas propostas, capazes de integrar as vantagens do protocolo IP multicast na entrega e transporte de conteúdos multimédia a grupos de utilizadores. Por outro lado, a inclusão de informação de contexto da rede, ambiente e utilizadores proporciona uma maior personalização e adaptação nas decisões de controlo necessárias à rede. É neste sentido que o projecto C-Cast abordado nesta tese se enquadra, procurando especificar uma arquitectura capaz de integrar uma quantidade abrangente de informação de contexto por forma a fornecer personalização nas sessões de entrega de conteúdos multimédia. Para a gestão dos recursos de rede é também proposto um mecanismo de transporte dos conteúdos baseado em IP multicast, juntamente com a possibilidade de adaptação dos caminhos escolhidos na rede de core baseada na informação de contexto da rede e do utilizador. A junção destes factores visa então possibilitar uma melhor gestão dos recursos disponibilizados pela rede. O principal objectivo desta Tese é então focado no desenvolvimento de um módulo inteligente, capaz de permitir o transporte multiparty e reserva de recursos, permitindo a entrega dos conteúdos de uma forma personalizada e independente das capacidades da rede e do utilizador, melhorando não só a qualidade de serviço, como também a qualidade de experiência. De forma a implementar a proposta apresentada, recorreu-se à criação de um novo componente organizado segundo uma arquitectura interna hierarquizada e centralizada, na qual um único módulo (IPT Controller) central comanda vários outros módulos (IPT Node) distribuídos ao longo de toda a rede. Após concluída a implementação, provou-se que o componente é capaz de criar e remover várias reservas de recursos por forma a permitir o transporte multiparty por caminhos específicos na rede. Este mecanismo é também capaz de modificar reservas previamente efectuadas, permitindo que as sessões multimédia sejam capazes de responder às modificações de contexto na rede, actualizando possíveis sessões já existentes com um mínimo de interrupção de serviço possível para utilizadores que não tenham sofrido alterações. Avaliando os resultados obtidos, pode-se também concluir que o impacto do IPT na rede é ligeiro e menor em relação ao dos restantes componentes, pelo que não é um factor decisivo no desempenho global da arquitectura.Today we are witnessing a considerable increase in the demand for services or applications for multiple users (multiparty), such as streaming media content, information sharing, collaboration among users, among others. The support of such services over the Internet proves to be extremely demanding for the existing network architectures, requiring features and functionality completely out of reach of the current networks. Thus, investigation and development of new mechanisms that enable a superior management at this level is necessary. In this context, it is possible to observe an increase in the number of architectures proposed, which are able of integrating the advantages of the IP multicast protocol in the transport and delivery of multimedia content to user groups. Moreover, the inclusion of context information from the network, environment and users, provides a greater customization and adaptation in the decisions necessary to control the network. It in this context that the C-CAST project discussed in this dissertation is included, which tries to specify an architecture capable of integrating a comprehensive amount of context information in order to be able to provide superior dynamic sessions to deliver multimedia content. For the management of the network resources, it is also proposed a mechanism for the transport of multimedia content based on IP multicast. The possibility of path adaptation in the core network based on context information of both users and network is also considered. Is it with the combination of these factors that this project seeks to enable an improved management of the network’s resources. The main objective of this dissertation is then focused on the latter point of the C-CAST project architecture. It proposed the development of an intelligent module capable of allowing multiparty transport and resource reservation, enabling the delivery of multimedia content in a personalized way, independent of network and users capabilities, improving not only the quality of service, as well as quality of experience. In order to implement the proposed solution, a new component was developed, organized according to a hierarchical and centralized architecture in which a single central unit (IPT Controller) is able to command several other modules (IPT Node) deployed throughout the network. It was verified that the developed component is capable of creating and removing the necessary enforcements on the network to enable the multiparty transport through specific data paths. It is also capable of modifying previous enforcements, allowing the multimedia sessions to adapt themselves to context changes avoiding as much as possible to disrupt the existing services to users that were not subjected to modifications. Evaluating the obtained results, it is possible to conclude that the overall impact of the IPT component in the network is reduced and considerably less than the one of the remaining components. Hence, the IPT does not have a direct impact on the overall architecture performance

Avaliação de controlo de sessões multicast em redes com contexto

Mestrado em Engenharia Electrónica e TelecomunicaçõesOs utilizadores pretendem aceder, cada vez mais, a serviços multimédia com requisitos mais exigentes e personalizados. As limitações impostas pelos ambientes existentes (internet, 3G) para fornecer estes serviços levam à procura de melhores soluções, nomeadamente uma gestão eficaz das sessões multiparty. Neste tipo de soluções é normalmente utilizado o multicast, já que este permite reduzir os recursos utilizados, diminuindo o número de pacotes na rede. Contudo, o multicast não está consistente ao nível dos cenários de mobilidade, fundamentais nas redes de próxima geração. Actualmente existe uma vasta gama de tecnologias de acesso sem fios como WiFi, GPRS, UMTS e WiMAX. No futuro estas tecnologias diferentes complementar-se-ão convergindo numa infra-estrutura heterogénea capaz de fornecer um melhor serviço aos utilizadores, denominadas de redes 4G. A evolução dos terminais móveis também permitirá que estes se liguem simultaneamente a várias redes de acesso. Para uma melhor distribuição dos serviços dos utilizadores pelas redes de acesso disponíveis são necessários novos mecanismos de selecção. Uma nova selecção da rede baseada em informação de contexto (entidades e ambiente) tem tido grande relevo na comunidade científica. Assim, aplicações e rede reagem a alterações de contexto para uma melhor selecção da mesma. A dissertação apresentada encontra-se no âmbito do transporte multiparty com informação de contexto e reserva de recursos, permitindo a entrega do conteúdo de uma forma personalizada e com Qualidade de Serviço a vários utilizadores móveis, independentemente da tecnologia de acesso de cada um e da própria tecnologia da rede. Em suma, é utilizada uma arquitectura de rede baseada em informação de contexto e que reage eficazmente a alterações do mesmo. De forma a implementar a proposta apresentada recorreu-se à criação de várias entidades no simulador de redes NS-2. Os resultados foram obtidos usando diferentes cenários, avaliando a influência de cada parâmetro individualmente. Demonstrou-se que a arquitectura implementada permite suportar uma entrega dos conteúdos de uma maneira personalizada e independente da tecnologia utilizada. Obteve-se ainda uma boa gestão dos recursos da rede e uma melhoria na experiência percepcionada pelo utilizador através da selecção total da rede com base numa entidade de controlo central. A introdução do overlay de transporte multiparty melhora o comportamento geral da rede, minimizando as reconfigurações frequentes necessárias.Nowadays, more and more users want to access multimedia services with strong and personalized requirements. The limitations intrinsic to current environments (Internet and 3G) to provide this type of services motivate the research for an efficient management of multiparty sessions. The solution can also be based on multicast implementation, since it reduces resources utilization, decreasing the number of packets in the network. However, current multicast is not a strong solution in mobility scenarios, essential in next generation networks. Currently there is a wide range of wireless access technologies such as WiFi, GPRS, UMTS and WiMAX. In the future, these different technologies will converge in a complementary manner forming a heterogeneous infrastructure able to offer a better service to its users, usually named 4G. The evolution of mobile terminals will also allow them to connect simultaneously to several access networks. In order to a better distribution of the users services throughout available access networks, new selection mechanisms are required. A new network selection based on context information (entities and environments) is having a relevant role in scientific community. So, applications and networks react according to context changes, improving network selection. This Thesis is in the scope of context-aware multiparty transport with resources allocation, allowing the delivery of content in a personalized way with Quality of Service to several users, independently of the technology and the network. Resuming, the solution implements a context-aware network architecture that reacts efficiently to its changes. In order to implement this architecture, new entities were created in the network simulator NS-2. The results were obtained using different scenarios, evaluating the influence of each parameter independently. It was demonstrated that the integration of several components, allows a delivery of contents in a personalized manner and independently of the technology. The results showed a better management of the network resources and users experience, throughout the total network selection, based on a central control unit. The multiparty transport overlay improves the network behaviour, minimizing the necessary frequent reconfigurations

Hybrid session veri cation through endpoint API generation

This paper proposes a new hybrid session veri cation method- ology for applying session types directly to mainstream languages, based on generating protocol-speci c endpoint APIs from multiparty session types. The API generation promotes static type checking of the be- havioural aspect of the source protocol by mapping the state space of an endpoint in the protocol to a family of channel types in the tar- get language. This is supplemented by very light run-time checks in the generated API that enforce a linear usage discipline on instances of the channel types. The resulting hybrid veri cation guarantees the absence of protocol violation errors during the execution of the session. We have implemented our methodology for Java as an extension to the Scrib- ble framework, and used it to implement compliant clients and servers for real-world protocols such as HTTP and SMTP. The API genera- tion methodology additionally provides a platform for applying further features from session type theory: our implementation supports choice subtyping through branch interface generation, and safe permutation of I/O actions and a ne inputs through input future generation

An investigation into a distributed virtual reality environment for real-time collaborative 4D construction planning and simulation

The use and application of 4 Dimensional Computer Aided Design (4D CAD) is growing within the construction industry. 4D approaches have been the focus of many research efforts within the last decade and several commercial tools now exist for the creation of construction simulations using 4D approaches. However, there are several key limitations to the current approaches. For example, 4D models are normally developed after the initial planning of a project has taken place using more traditional techniques such as Critical Path Method (CPM). Furthermore, mainstream methodologies for planning are based on individual facets of the construction process developed by discrete contractors or sub-contractors. Any 4D models generated from these data are often used to verify work flows and identify problems that may arise, either in terms of work methods or sequencing issues. Subsequently, it is perceived that current 4D CAD approaches provide a planning review mechanism rather than a platform for a novel integrated approach to construction planning. The work undertaken in this study seeks to address these issues through the application of a distributed virtual reality (VR) environment for collaborative 4D based construction planning. The key advances lie in catering for geographically dispersed planning by discrete construction teams. By leveraging networked 4D-VR based technologies, multidisciplinary planners, in different places, can be connected to collaboratively perform planning and create an integrated and robust construction schedule leading to a complete 4D CAD simulation. Establishing such a complex environment faces both technological and social challenges. Technological challenges arise from the integration of traditional and recent 4D approaches for construction planning with an ad hoc application platform of VR linked through networked computing. Social challenges arise from social dynamics and human behaviours when utilizing VR-based applications for collaborative work. An appropriate 4D-based planning method in a networked VR based environment is the key to gaining a technical advancement and this approach to distributed collaborative planning tends to promote computer-supported collaborative work (CSCW). Subsequently, probing suitable CSCW design and user interface/interaction (UI) design are imperative for solutions to achieve successful applicability. Based on the foregoing, this study developed a novel robust 4D planning approach for networked construction planning. The new method of interactive definition was devised through theoretical analysis of human-computer interaction (HCI) studies, a comparison of existing 4D CAD creation, and 3D model based construction planning. It was created to support not only individual planners’ work but multidisciplinary planners’ collaboration, and lead to interactive and dynamic development of a 4D simulation. From a social perspective, the method clarified and highlighted relevant CSCW design to enhance collaboration. Applying this rationale, the study specified and implemented a distributed groupware solution for collaborative 4D construction planning. Based on a developed system architecture, application mode and dataflow, as well as a real-time data exchange protocol, a prototype system entitled ‘4DX’ was implemented which provides a platform for distributed multidisciplinary planners to perform real-time collaborative 4D construction planning. The implemented toolkit targeted a semi-immersive VR platform for enhanced usability with compatibility of desktop VR. For the purpose of obtaining optimal UI design of this kind of VR solution, the research implemented a new user-centred design (UCD) framework of Taguchi-Compliant User-Centred Design (TC-UCD) by adapting and adopting the Taguchi philosophy and current UCD framework. As a result, a series of UIs of the VR-based solution for multifactor usability evaluation and optimization were developed leading to a VR-based solution with optimal UIs. The final distributed VR solution was validated in a truly geographically dispersed condition. Findings from the verification testing, the validation, and the feedback from construction professionals proved positive in addition to providing constructive suggestions to further reinforce the applicability of the approach in the future.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Hardware-Assisted Secure Computation

The theory community has worked on Secure Multiparty Computation (SMC) for more than two decades, and has produced many protocols for many settings. One common thread in these works is that the protocols cannot use a Trusted Third Party (TTP), even though this is conceptually the simplest and most general solution. Thus, current protocols involve only the direct players---we call such protocols self-reliant. They often use blinded boolean circuits, which has several sources of overhead, some due to the circuit representation and some due to the blinding. However, secure coprocessors like the IBM 4758 have actual security properties similar to ideal TTPs. They also have little RAM and a slow CPU.We call such devices Tiny TTPs. The availability of real tiny TTPs opens the door for a different approach to SMC problems. One major challenge with this approach is how to execute large programs on large inputs using the small protected memory of a tiny TTP, while preserving the trust properties that an ideal TTP provides. In this thesis we have investigated the use of real TTPs to help with the solution of SMC problems. We start with the use of such TTPs to solve the Private Information Retrieval (PIR) problem, which is one important instance of SMC. Our implementation utilizes a 4758. The rest of the thesis is targeted at general SMC. Our SMC system, Faerieplay, moves some functionality into a tiny TTP, and thus avoids the blinded circuit overhead. Faerieplay consists of a compiler from high-level code to an arithmetic circuit with special gates for efficient indirect array access, and a virtual machine to execute this circuit on a tiny TTP while maintaining the typical SMC trust properties. We report on Faerieplay\u27s security properties, the specification of its components, and our implementation and experiments. These include comparisons with the Fairplay circuit-based two-party system, and an implementation of the Dijkstra graph shortest path algorithm. We also provide an implementation of an oblivious RAM which supports similar tiny TTP-based SMC functionality but using a standard RAM program. Performance comparisons show Faerieplay\u27s circuit approach to be considerably faster, at the expense of a more constrained programming environment when targeting a circuit

The Post-Soviet Voter: Evidence From The Caucasus

In western liberal democracies, voting behavior is often times characterized by sociological and psychological indicators. Party identification and issues such as the economy dominant the vote function of the electorate. In the post-Soviet space, party volatility and the competitive authoritarian nature of regimes may result in voters failing to act as agents of accountability. In this dissertation, I argue that the socio-psychological theory of voting behavior applies to post-Soviet electorate in the Caucasus. I demonstrate that Armenian and Georgian voters rely on partisanship as well as perceptions of the economy when casting electoral judgment on the incumbent party. This research furthers the applicability of the socio-psychological theory beyond countries with mature and durable party structures, and demonstrates that voters in competitive authoritarian regimes can act as agents of electoral accountability

Assessing Electoral Process Challenges Through Poll Workers\u27 Performance in Sub-Saharan Africa-Togo

Contenders disputing electoral results in Sub-Saharan African countries often attribute defects in presidential electoral processes to the implementation of rules and procedures. Yet despite the considerable decision-making authority poll workers are entrusted with and the significance of the tasks performed by therm, scholars have not closely investigated poll workers\u27contributions to elections\u27 management in Sub-Saharan Africa. Using principal-agent theory as the foundation, the purpose of this case study was to examine the challenges encountered in the organization of the presidential election in Togo, held on April 25, 2015, with a particular emphasis on poll workers\u27 job performance. Research questions focused on whether poll workers in Togo have the ability and the resources necessary to carry out quality elections and the perceived effects of poll workers\u27 performance on the integrity of the presidential electoral process. Data were obtained from interviews with 11 purposely selected poll workers and review of social media audio and video records of the election. These data were inductively coded and subjected to thematic analysis. A key finding was that deficiencies in poll workers\u27 performance reflect a complex interplay of ill-conceived legal framework, lack of infrastructure, poor training, personal ineptitude, underfunding, partisanship, and tribalism. Further findings indicated that poll workers performing poorly resulted in long lines of voters, voter suppression, inaccuracies in vote counts, and delay in results announcement. Implications for positive social change include election practitionners\u27 increased awareness that improving the quality of service delivery to voters on election day may foster confidence in and legitimacy of election results, seen as prerequisite to peaceful presidential elections in this part of the world