Redes em malha virtuais para optimização de conectividade

Mestrado em Engenharia Electrónica e TelecomunicaçõesActualmente, os utilizadores têm necessidades muito distintas, assim como os serviços a que acedem. Essas necessidades são constituídas por vários parâmetros, que se designam por contexto do utilizador e dos seus serviços, tais como, padrões de mobilidade, requisitos de qualidade de serviço, disponibilidade, confiança, segurança, custo, etc. A dissertação apresentada encontra-se no âmbito de um nova abordagem de rede que permite ter redes em malha sem fios muito adaptativas através do suporte de várias redes lógicas construídas sobre a mesma rede física. Nesta abordagem as redes em malha sem fios são virtualizadas, e cada rede virtual é específica para diferentes características de contexto mapeadas em níveis. De entre diversos desafios associados a esta nova abordagem, esta dissertação propõese a simular os seguintes mecanismos: i) configuração/mapeamento dos recursos/topologias de cada rede virtual, de acordo com as características de contexto dos utilizadores e aplicações a que se destinam; ii) associação de um determinado utilizador à rede virtual mais apropriada, introduzindo mecanismos de comparação entre o contexto do utilizador e as características das redes virtuais; iii) procura de um ponto de ligação à rede virtual através de mecanismos de descoberta locais ou globais (distribuídos), que envolvem diferentes mecanismos para mapeamento da informação de contexto nos elementos de rede. De forma a implementar a proposta apresentada recorreu-se ao simulador de redes NS-2. Os resultados da avaliação do desempenho da rede foram obtidos usando diferentes cenários com a variação de diferentes parâmetros, tais como o número de redes virtuais e de utilizadores, o tamanho da rede física e das redes virtuais, os padrões de mobilidade e o tipo de tráfego dos utilizadores. Através das simulações efectuadas é possível concluir que aplicando a solução proposta, são fornecidos diferentes serviços aos utilizadores mediante os seus requisitos de contexto, sem que haja impacto significativo no desempenho da rede.Currently, users have different needs, as well as the services they access. These needs consist of various parameters designated by the user’s context and its services, such as mobility patterns, requirements of quality of service, availability, reliability, safety, cost, etc. This Thesis is in the scope of a new network approach that allows wireless mesh networks to be very adaptive through the support of multiple logical networks built on the same physical network. In this approach the wireless mesh networks are virtualized, and each virtual network is specific to different context requirements that are mapped in levels. Among the various challenges associated with this new approach, this dissertation proposes to simulate the following mechanisms: i) configuration/mapping of resources/topologies for each virtual network, according to the characteristics of the context of its users and applications; ii) association of a particular user to the most appropriate virtual network, introducing mechanisms to compare the user’s context against the characteristics of virtual networks; iii) searching for a connection point to the virtual network through mechanisms for local or global (distributed) discovery, which involves different mechanisms for context information mapping in network elements. In order to implement this architecture, the network simulator NS-2 was used. The evaluation results of the network performance were obtained using different scenarios with the variation of different parameters, such as the number of virtual networks and users, the WMN size and the size of the virtual networks, mobility patterns and traffic of the users. Through the implemented simulation setup, it is possible to conclude that with the deployment of the proposed solution, different services are provided to users without a significant impact on the network performance

Bohacek S. Performance of urban mesh networks

Currently, large-scale deployments of mesh networks are being planned for Philadelphia as well as other cities. The performance of such networks has never been examined through simulation or through any other means. In this paper we perform detailed simulations of mesh networks in several urban environments and evaluate the performance of these networks. The simulations utilize realistic ray-tracing and other propagation models. The mobility of nodes is based on models derived from several movement and time use surveys including the US Department of Labor’s recent time use study that includes travel diaries from over 20,000 people. Basic performance issues such as connectivity, capacity, and several application oriented performance metrics as a function of the density infrastructure (base stations and fix wireless relays) are examined. It is found that a high density infrastructure is required to achieve reasonable coverage, in particular, the density must be higher than is currently considered by most deployments. While allowing mobile nodes to act as relays improves coverage, it does not necessarily improve the performance received by the application. It is found that in general, there is a significant difference between the fraction of nodes that are able to communicate with a base station and the fraction of nodes that received acceptable application layer performance