Esta tese de doutorado apresenta a investigação de alternativas para melhorar o desempenho de ambientes Web, avaliando o impacto da utilização de mecanismos de diferenciação de serviços em todos os pontos do sistema. Foram criados e modelados no OPNET Modeler cenários com diferentes configurações voltadas tanto para a diferenciação de serviços, quanto para o congestionamento da rede. Foi implementado um servidor cache com suporte à diferenciação de serviços (cache CDF), que constitui uma contribuição dentro deste trabalho, complementando o cenário de diferenciação de serviços de forma positiva, assegurando que os ganhos obtidos em outras etapas do sistema não sejam perdidos no momento da utilização do cache. Os principais resultados obtidos mostram que a diferenciação de serviços introduzida de forma isolada em partes do sistema, pode não gerar os ganhos de desempenho desejados. Todos os equipamentos considerados nos cenários propostos possuem características reais e os modelos utilizados no OPNET foram avaliados e validados pelos seus fabricantes. Assim, os modelos que implementam os cenários considerados constituem também uma contribuição importante deste trabalho, uma vez que o estudo apresentado não se restringe a uma modelagem teórica, ao contrário, aborda aspectos bem próximos da realidade, constituindo um possível suporte de gerenciamento de sistemas Web / This PhD thesis presents the investigation of alternatives to improve the performance of Web environments by evaluating the impact of using differentiated service mechanisms in all points of the system. Several scenarios were created and modeled in the OPNET Modeler, with different configurations of both differentiated services and network overloading. A special cache server supporting differentiated services (CDF cache) was proposed and included in the model, comprising one of the major contributions of this work once it positively complements the differentiated service scenario, making that the gains obtained with other stages of the system do not be spoiled when using the cache. The main results obtained show that the adoption of differentiated services in isolated parts of the system cannot generate the expected performance gains. The features of all the equipments considered in the several scenarios defined in this work are very close to the reality and the models used in the OPNET were evaluated and validated by the companies that produce those equipments. Thus, the models that implement the scenarios considered in this work also comprises an important contribution of this thesis, once the study presented is not just a theoretical modeling exercise but, conversely, it approaches aspects very close to the reality, comprising a possible Web system management support

Esta tese de doutorado apresenta a investigação de alternativas para melhorar o desempenho de ambientes Web, avaliando o impacto da utilização de mecanismos de diferenciação de serviços em todos os pontos do sistema. Foram criados e modelados no OPNET Modeler cenários com diferentes configurações voltadas tanto para a diferenciação de serviços, quanto para o congestionamento da rede. Foi implementado um servidor cache com suporte à diferenciação de serviços (cache CDF), que constitui uma contribuição dentro deste trabalho, complementando o cenário de diferenciação de serviços de forma positiva, assegurando que os ganhos obtidos em outras etapas do sistema não sejam perdidos no momento da utilização do cache. Os principais resultados obtidos mostram que a diferenciação de serviços introduzida de forma isolada em partes do sistema, pode não gerar os ganhos de desempenho desejados. Todos os equipamentos considerados nos cenários propostos possuem características reais e os modelos utilizados no OPNET foram avaliados e validados pelos seus fabricantes. Assim, os modelos que implementam os cenários considerados constituem também uma contribuição importante deste trabalho, uma vez que o estudo apresentado não se restringe a uma modelagem teórica, ao contrário, aborda aspectos bem próximos da realidade, constituindo um possível suporte de gerenciamento de sistemas Web / This PhD thesis presents the investigation of alternatives to improve the performance of Web environments by evaluating the impact of using differentiated service mechanisms in all points of the system. Several scenarios were created and modeled in the OPNET Modeler, with different configurations of both differentiated services and network overloading. A special cache server supporting differentiated services (CDF cache) was proposed and included in the model, comprising one of the major contributions of this work once it positively complements the differentiated service scenario, making that the gains obtained with other stages of the system do not be spoiled when using the cache. The main results obtained show that the adoption of differentiated services in isolated parts of the system cannot generate the expected performance gains. The features of all the equipments considered in the several scenarios defined in this work are very close to the reality and the models used in the OPNET were evaluated and validated by the companies that produce those equipments. Thus, the models that implement the scenarios considered in this work also comprises an important contribution of this thesis, once the study presented is not just a theoretical modeling exercise but, conversely, it approaches aspects very close to the reality, comprising a possible Web system management support

The continuous growth of traffic demand driven by the brisk increase in number of Internet users and emerging online services creates new challenges for communication networks. The latest advances in Wavelength Division Multiplexing (WDM) technology make it possible to build Transparent Optical Networks (TONs) which are expected to be able to satisfy this rapidly growing capacity demand. Moreover, with the ability of TONs to transparently carry the optical signal from source to destination, electronic processing of the tremendous amount of data can be avoided and optical-to-electrical-to-optical (O/E/O) conversion at intermediate nodes can be eliminated. Consequently, transparent WDM networks consume relatively low power, compared to their electronic-based IP network counterpart. Furthermore, TONs bring also additional benefits in terms of bit rate, signal format, and protocol transparency. However, the absence of O/E/O processing at intermediate nodes in TONs has also some drawbacks. Without regeneration, the quality of the optical signal transmitted from a source to a destination might be degraded due to the effect of physical-layer impairments induced by the transmission through optical fibers and network components. For this reason, routing approaches specifically tailored to account for the effect of physical-layer impairments are needed to avoid setting up connections that don’t satisfy required signal quality at the receiver. Transparency also makes TONs highly vulnerable to deliberate physical-layer attacks. Malicious attacking signals can cause a severe impact on the traffic and for this reason proactive mechanisms, e.g., network design strategies, able to limit their effect are required. Finally, even though energy consumption of transparent WDM networks is lower than in the case of networks processing the traffic at the nodes in the electronic domain, they have the potential to consume even less power. This can be accomplished by targeting the inefficiencies of the current provisioning strategies applied in WDM networks. The work in this thesis addresses the three important aspects mentioned above. In particular, this thesis focuses on routing and wavelength assignment (RWA) strategies specifically devised to target: (i) the lightpath transmission quality, (ii) the network security (i.e., in terms of vulnerability to physical-layer attacks), and (iii) the reduction of the network energy consumption. Our contributions are summarized below. A number of Impairment Constraint Based Routing (ICBR) algorithms have been proposed in the literature to consider physical-layer impairments during the connection provisioning phase. Their objective is to prevent the selection of optical connections (referred to as lightpaths) with poor signal quality. These ICBR approaches always assign each connection request the least impaired lightpath and support only a single threshold of transmission quality, used for all connection requests. However, next generation networks are expected to support a variety of services with disparate requirements for transmission quality. To address this issue, in this thesis we propose an ICBR algorithm supporting differentiation of services at the Bit Error Rate (BER) level, referred to as ICBR-Diff. Our approach takes into account the effect of physical-layer impairments during the connection provisioning phase where various BER thresholds are considered for accepting/blocking connection requests, depending on the signal quality requirements of the connection requests. We tested the proposed ICBR-Diff approach in different network scenarios, including also a fiber heterogeneity. It is shown that it can achieve a significant improvement of network performance in terms of connection blocking, compared to previously published non-differentiated RWA and ICBR algorithms.  Another important challenge to be considered in TONs is their vulnerability to physical-layer attacks. Deliberate attacking signals, e.g., high-power jamming, can cause severe service disruption or even service denial, due to their ability to propagate in the network. Detecting and locating the source of such attacks is difficult, since monitoring must be done in the optical domain, and it is also very expensive. Several attack-aware RWA algorithms have been proposed in the literature to proactively reduce the disruption caused by high-power jamming attacks. However, even with attack-aware network planning mechanisms, the uncontrollable propagation of the attack still remains an issue. To address this problem, we propose the use of power equalizers inside the network nodes in order to limit the propagation of high-power jamming attacks. Because of the high cost of such equipment, we develop a series of heuristics (incl. Greedy Randomized Adaptive Search Procedure (GRASP)) aiming at minimizing the number of power equalizers needed to reduce the network attack vulnerability to a desired level by optimizing the location of the equalizers. Our simulation results show that the equalizer placement obtained by the proposed GRASP approach allows for 50% reduction of the sites with the power equalizers while offering the same level of attack propagation limitation as it is possible to achieve with all nodes having this additional equipment installed. In turn, this potentially yields a significant cost saving.    Energy consumption in TONs has been the target of several studies focusing on the energy-aware and survivable network design problem for both dedicated and shared path protection. However, survivability and energy efficiency in a dynamic provisioning scenario has not been addressed. To fill this gap, in this thesis we focus on the power consumption of survivable WDM network with dynamically provisioned 1:1 dedicated path protected connections. We first investigate the potential energy savings that are achievable by setting all unused protection resources into a lower-power, stand-by state (or sleep mode) during normal network operations. It is shown that in this way the network power consumption can be significantly reduced. Thus, to optimize the energy savings, we propose and evaluate a series of energy-efficient strategies, specifically tailored around the sleep mode functionality. The performance evaluation results reveal the existence of a trade-off between energy saving and connection blocking. Nonetheless, they also show that with the right provisioning strategy it is possible to save a considerable amount of energy with a negligible impact on the connection blocking probability. In order to evaluate the performance of our proposed ICBR-Diff and energy-aware RWA algorithms, we develop two custom-made discrete-event simulators. In addition, the Matlab program of GRASP approach for power equalization placement problem is implemented. / <p>QC 20120508</p>