Rede P2P sobre WLANs em modo ad hoc

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para a obtenção do grau de Mestre em Engenharia Electrotécnica e de ComputadoresNa dissertação é realizado um estudo à partilha de recursos em redes sem fios muito dinâmicas, com o objectivo de identificar alguns dos seus problemas e apresentar soluções para estes. É complicado manter a conectividade entre equipamentos presentes numa rede sem fios não. A mobilidade e instabilidade introduz dificuldades no de informação entre os diferentes nós presentes na rede. Foi idealizado e implementado um algoritmo de localização assíncrona de recursos para operar em redes muito dinâmicas, que permite uma melhor gestão da difusão de pesquisas. Para demonstrar a eficácia do algoritmo implementado, foi desenvolvida uma aplicação de pesquisa e partilha de ficheiros. A tecnologia JXTA foi estendida com a implementação do algoritmo de gestão de pesquisas. Durante a implementação deste algoritmo foi criado um novo módulo, com objectivo ser uma base para todas as implementações de suporte a redes dinâmicas sem fios. Para melhorar o débito na comunicação foi implementado um módulo de transporte independente da plataforma

Walkabout : an asynchronous messaging architecture for mobile devices

Modern mobile devices are prolific producers and consumers of digital data, and wireless networking capabilities enable them to transfer their data over the Internet while moving. Applications running on these devices may perform transfers to upload data for backup or distribution, or to download new content on demand. Unfortunately, the limited connectivity that mobile devices experience can make these transfers slow and impractical as the amount of data increases. This thesis argues that asynchronous messaging supported by local proxies can improve the transfer capabilities of mobile devices, making it practical for them to participate in large Internet transfers. The design of the Walkabout architecture follows this approach: proxies form store-and-forward overlay networks to deliver messages asynchronously across the Internet on behalf of devices. A mobile device uploads a message to a local proxy at rapid speed, and the overlay delivers it to one or more destination devices, caching the message until each one is able to retrieve it from a local proxy. A device is able to partially upload or download a message whenever it has network connectivity, and can resume this transfer at any proxy if interrupted through disconnection. Simulation results show that Walkabout provides better throughput for mobile devices than is possible under existing methods, for a range of movement patterns. Upload and end-to-end to transfer speeds are always high when the device sending the message is mobile. In the basic Walkabout model, a message sent to a mobile device that is repeatedly moving between a small selection of connection points experiences high download and end-to-end transfer speeds, but these speeds fall as the number of connection points grows. Pre-emptive message delivery extensions improve this situation, making fast end-to-end transfers and device downloads possible under any pattern of movement. This thesis describes the design and evaluation of Walkabout, with both practical implementation and extensive simulation under real-world scenarios

Session Mobility in the Mockets Communication Middleware

Taking advantage of the benefits of modern networking, a growing number of users are exhibiting mobile behavior. As they roam between different network localities, they access the Internet and the Web exploiting both wired and wireless communications and using several heterogeneous devices. Mobile users want to access their subscribed services anywhere, anytime, and want to preserve their currently opened service sessions as they roam between different network localities or switch between different devices. Mobile userspsila requirements call for novel middlewares to provide support for mobility on top of the traditional Internet infrastructure. In this context, we have developed Mockets, a communication middleware specifically designed to address the challenges of wireless networks and mobile computing. In particular, Mockets supports session mobility in terms of seamless handover for preservation of end-to-end connectivity in spite of node mobility, automatic detection and exploitation of best available connectivity, and migration of service session endpoints from one node to another