The aim of this work is to analyze the modern radio communication technologies and to formulate a methodology and means for implementing them in customers’ premises networks.

The aim of this work is to analyze the modern radio communication technologies and to formulate a methodology and means for implementing them in customers’ premises networks.

Aquesta tesi suggereix usar un compte enrere determinista després de les transmissions exitoses en les xarxes d'àrea local sense fils. Com que les estacions que han transmès amb èxit en el seu darrer intent no poden col·lisionar entre elles en el seu proper intent, el nombre de col·lisions es redueix. Per tant, anomenem el protocol accés múltiple per detecció de portadora amb evitament de col·lisions millorat. El protocol es modela i es simula en diversos escenaris per a la seva avaluació. S'arriba a la conclusió de que el protocol proposat ofereix un rendiment igual o major que l'existent. / This thesis suggests the use of a deterministic backoff after successful transmissions in the MAC protocol of WLANs. Since those stations that successfully transmitted in their last collision attempt cannot collide among them in their next transmission attempt, the number of collisions is reduced. Hence, the protocol is called Carrier Sense Multiple Access with Enhanced Collision Avoidance. The protocol is modelled and simulations are used to assess its performance in a variety of scenarios. It is concluded that the proposed protocol performs always equal or better than the legacy one.

This thesis is concerned with the development of new mathematical models for the IEEE 802.11??s access mechanisms, with a particular focus on DCF and EDCA. Accurate mathematical models for the DCF and EDCA access mechanisms provide many benefits, such as improved performance analysis, easier network capacity planning, and robust network design. A feature that permeates the work presented in this thesis is the application of our new models to network environments where both saturated and non-saturated traffic sources are present. The scenario in which multiple traffic sources are present is more technically challenging, but provides for a more realistic setting. Our first contribution is the development of a new Markov model for non-saturated DCF in order to predict the network throughput. This model takes into account several details of the protocol that have been hitherto neglected. In addition, we apply a novel treatment of the packet service time within our model. We show how the inclusion of these effects provides more accurate predictions of network throughput than earlier works. Our second contribution is the development of a new analytical model for EDCA, again in order to predict network throughput. Our new EDCA model is based on a replacement of the normal AIFS parameter of EDCA with a new parameter more closely associated with DCF. This novel procedure allows EDCA to be viewed as a modified multi-mode version of DCF. Our third contribution is the simultaneous application of our new Markov models to both the non-saturated and the saturated regime. Hitherto, network throughput predictions for these regimes have required completely separate mathematical models. The convergence property of our model in the two regimes provides a new method to estimate the network capacity of the network. Our fourth contribution relates to predictions for the multimedia capacity of 802.11 networks. Our multimedia capacity analysis, which is based on modifications to our Markov model, is new in that it can be applied to a broad range of quality of service requirements. Finally, we highlight the use of our analysis in the context of emerging location-enabled networks.

Submitted by Santos Davilene (davilenes@ufba.br) on 2016-05-25T13:52:34Z No. of bitstreams: 1 Sergio Gramacho - Dissertacao Mestrado.pdf: 6432983 bytes, checksum: 6c04f369697d8a06c796b55ebf26e4f0 (MD5) / Made available in DSpace on 2016-05-25T13:52:34Z (GMT). No. of bitstreams: 1 Sergio Gramacho - Dissertacao Mestrado.pdf: 6432983 bytes, checksum: 6c04f369697d8a06c796b55ebf26e4f0 (MD5) / As Redes Locais Sem Fio (WLANs) são, cada vez mais, presentes no contexto de pequenas organizações e residências e sua adoção tem sido impulsionada por tendências como o acesso à Internet em banda larga, a computação móvel e a Internet das Coisas. Neste contexto, as WLANs são independentes e sua interação com as demais é não-coordenada. Estas WLANs compartilham mesmo espectro de frequências, o que pode ocasionar interferência entre WLANs vizinhas. Neste trabalho, este problema de interferência foi estudado levando-se em consideração o aspecto dinâmico de mitigação de interferência entre WLANs. Para a seleção de melhores canais, um algoritmo guloso, que tem por características a pró-atividade e permitir “decisão racional” por agentes referenciais das WLANs, foi adotado. A informação usada pelo algoritmo é provida por um modelo de interferência, que consolida os efeitos de contenção e SINR em uma métrica única: velocidade potencial de comunicação. Além disto, a dinâmica de seleção de canais foi modelada como um jogo competitivo extensivo, baseado na Teoria dos Jogos, para análise de propriedades gerais, em especial os estados de equilíbrio de Nash. Um modelo em Cadeias de Markov foi usado para análise dos jogos. Verificou-se que, de forma análoga a outros modelos de jogos competitivos na Teoria dos Jogos, os equilíbrios podem não oferecer o máximo desempenho. Foram propostos algoritmos de cooperação, capazes de computar soluções para a melhoria do desempenho do grupo após um equilíbrio inicial, num equilíbrio posterior específico e intencional.

Dissertação (mestrado)—Universidade de Brasília, Instituto de Ciências Exatas, Departamento de Ciência da Computação, Mestrado Profissional em Computação Aplicada, 2015. / Submitted by Albânia Cézar de Melo (albania@bce.unb.br) on 2016-01-28T11:53:24Z No. of bitstreams: 1 2015_ClaudioXavierOliveira.pdf: 6916242 bytes, checksum: 945503a644d7ced55dd003d0dad373a3 (MD5) / Approved for entry into archive by Raquel Viana(raquelviana@bce.unb.br) on 2016-01-28T18:44:42Z (GMT) No. of bitstreams: 1 2015_ClaudioXavierOliveira.pdf: 6916242 bytes, checksum: 945503a644d7ced55dd003d0dad373a3 (MD5) / Made available in DSpace on 2016-01-28T18:44:42Z (GMT). No. of bitstreams: 1 2015_ClaudioXavierOliveira.pdf: 6916242 bytes, checksum: 945503a644d7ced55dd003d0dad373a3 (MD5) / Nos últimos anos, temos observado um crescimento de uso e evolução das redes padrão IEEE 802.11. Atualmente, a Universidade de Brasília conta com uma infraestrutura de WLAN (do Inglês, Wireless Local Area Network) para atender os usuários de seus campi. Por meio dessa infraestrutura, a Universidade vem buscando alterativas para melhor atender a seus usuários, preferencialmente sem custos adicionais. Uma das alternativas é a implantação do serviço de voz sobre a rede sem fio da Instituição, em que os usuários utilizarão seus dispositivos móveis na comunicação, dispondo da facilidade de mobilidade. Ao se utilizar serviços de voz sobre redes sem fio, é necessário que parâmetros como atraso, variação de atraso e perda de pacotes estejam de acordo com recomendações para uma boa qualidade nas chamadas telefônicas. Além disso, prover mobilidade em redes padrão IEEE 802.11 envolve a transição do usuário móvel entre pontos de acesso, sendo um dos fatores de degradação da qualidade auditiva da voz. A solução de rede sem fio da UnB dispõe de tecnologias, como ClientMatch e os padrões IEEE 802.11k e 802.11r, que auxiliam o usuário móvel no processo de transição. Nesse contexto, o trabalho em questão buscou avaliar o impacto da tecnologia ClientMatch e dos padrões IEEE 802.11k e 802.11r no suporte à mobilidade e tráfego de voz, aferindo a qualidade auditiva da voz e o desempenho dos principais parâmetros de QoS (do Inglês, Quality of Service) em uma rede VoIP (do Inglês, Voice over IP). Mediante os experimentos realizados foi possível verificar que a tecnologia ClientMatch – Sticky Client não está voltada para suporte a mobilidade, apresentando baixo índice de atuação. As tecnologias IEEE 802.11k e 802.11r não produziram os resultados esperados nas avaliações realizadas. Mesmo com baixos índices de atuação da tecnologia ClientMatch – Sticky Client e resultados inesperados das soluções 802.11k e 802.11r, a rede WLAN da UnB permite um bom desempenho para o tráfego de voz mediante mobilidade, com níveis aceitáveis de qualidade da voz, devendo-se atentar para o processo de transição entre pontos de acesso, ClientMatch – Band Steering e o distanciamento entre os pontos de acesso. Além dos experimentos que buscaram avaliar o impacto da tecnologia ClientMatch e dos padrões IEEE 802.11k e 802.11r no suporte à mobilidade e tráfego de voz, foram realizados testes com CODECs (do Inglês, Coder–Decoder) mediante mobilidade do cliente móvel. O codificador–decodificador G711 foi o que apresentou melhores resultados nos experimentos executados com relação a qualidade auditiva da voz. / In recent years, we have observed an increase of use and evolution of the IEEE 802.11 based-networks. Currently, the University of Brasília (UnB) owns and operate a WLAN (Wireless Local Area Network) infrastructure to serve users of its campuses. Through this infrastructure, UnB is seeking alternatives to better serve its users, preferably without increasing its costs. An alternative is the implementation of voice over the wireless network of the Institution, where users utilize their mobile devices for communication while providing mobility. When using voice over wireless networks, parameters such as delay, delay variation and packet loss must comply with the recommendations for reasonable phone calls quality. Furthermore, providing mobility in IEEE 802.11 networks involves the transition of the mobile user between access points and this very process is one of the key factors of voice quality degradation. The UNB wireless networking solution encompasses technologies such as ClientMatch, IEEE 802.11r and 802.11k standards that assist the mobile user in the transition process. In this context, this work evaluates the impact of the ClientMatch technology, IEEE 802.11r and 802.11k standards in supporting mobility and voice traffic, while evaluating the audio quality, performance of the main QoS (Quality of Service) parameters in a VoIP network (Voice over IP). The conducted experiments showed that the ClientMatch – Sticky Client technology is not tailored for mobility support, presenting low rate of action, while the IEEE 802.11r and 802.11k technologies have not produced the expected results. Even with the low rates of operation of ClientMatch – Sticky Client technology and unexpected results of the solutions 802.11k and 802.11r, the UnB WLAN infrastructure provided good performance for voice traffic, even under moderate mobility, attaining acceptable levels of voice quality; nevertheless, the process of transition between access points, ClientMatch – Band Steering and the distance between access points may impact in the results. In addition to the experiments that seek to evaluate the impact of technology ClientMatch and IEEE 802.11r and 802.11k standards in supporting mobility and voice traffic, tests were performed with CODECs (Coder - Decoder) by mobility of mobile client. The encoder – decoder G711 showed the best results in the experiments performed with respect to the voice quality.

Submitted by Patrícia Cerveira (pcerveira1@gmail.com) on 2017-06-13T15:41:09Z No. of bitstreams: 1 Marcelo Dissertação.pdf: 13477166 bytes, checksum: e46f91138593316f4c2c1504aaf297a3 (MD5) / Rejected by Biblioteca da Escola de Engenharia (bee@ndc.uff.br), reason: Boa tarde, Patrícia! Favor acertar o resumo. Atenciosamente, Catarina Ribeiro Bibliotecária BEE - Ramal 5992 on 2017-06-29T16:10:33Z (GMT) / Submitted by Patrícia Cerveira (pcerveira1@gmail.com) on 2017-06-29T19:26:55Z No. of bitstreams: 1 Marcelo Dissertação.pdf: 13477166 bytes, checksum: e46f91138593316f4c2c1504aaf297a3 (MD5) / Approved for entry into archive by Biblioteca da Escola de Engenharia (bee@ndc.uff.br) on 2017-07-03T12:53:35Z (GMT) No. of bitstreams: 1 Marcelo Dissertação.pdf: 13477166 bytes, checksum: e46f91138593316f4c2c1504aaf297a3 (MD5) / Made available in DSpace on 2017-07-03T12:53:35Z (GMT). No. of bitstreams: 1 Marcelo Dissertação.pdf: 13477166 bytes, checksum: e46f91138593316f4c2c1504aaf297a3 (MD5) / O serviço ”Móvel de Voz sobre IP” é a convergência natural da tecnologia de voz sobre IP (VoIP) e a comunicação sem fio, e pode impulsionar o aumento da popularidade da primeira bem como promover constantes avanços da última. Embora seja possível encontrar várias aplicações que oferecem serviço de VoIP na Internet e muitos dispositivos que implementam VoIP em hardware, uma implementação aberta e não-proprietária pode ser integrada aos serviços legados - como PABXs institucionais - o que proporciona uma contribuição significativa. Este trabalho descreve a implementação do serviço Móvel de Voz sobre IP no Instituto Federal Fluminense e destaca os desafios a serem enfrentados em seu gerenciamento e operação, enfatizando a segurança contra ataques. Os principais resultados indicam que este serviço oferece flexibilidade, conforto, redução de custos e mobilidade para o serviço de voz. / A “Mobile Voice over IP” service is the natural convergence of Voice over IP (VoIP) technology and wireless communication, and can leverage the increading popularity of the former and the constant advances of the latter. Although we can find various applications that o er VoIP service on the Internet, and in e ect many devices that implement VoIP in hardware, an open, non-propietary implementation that can be integrated with legacy services such as institutional PABXs is a welcome addition. This works describes the implementation of the Mobile Voice over IP service in the Instituto Federal Fluminense, and the challenges of its management and operation, with emphasis in security against attacks. This services brings flexibility, confort, cost reduction and mobility to the voice service.

The usage of Wireless Local Area Networks is increasing rapidly throughout the world. The technology today is not quality proof for the market’s demands. We want to be able to completely wireless perform our demands, such as confer via video or IP-telephony. This is what we call multimedia real-time traffic. It may be achieved over the physical infrastructure in some areas with good results. The goal of this Master’s Thesis is to analyze the possibilities and give solutions and suggestions to achieve multimedia over the wireless networks, with emphasis on the protocol Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). This Master’s Thesis is a theoretical study and the suggested solutions have not been tested in an actual wireless network. Instead they have been tested by computer simulation to give an indication of improvements. Basic configurations are set to the same as in the IEEE 802.11 standard. Different methods to reach possible improvements of a WLAN are studied, analyzed and simulated. Such methods are: priority, congestion management and multi-channel protocol. Simulations results show how the priority affects the wireless network and how a multi-channel protocol improves the latency and efficiency of the network. The simulation part is concentrated to show improvements of real-time traffic, which is time sensitive. With a multi- channel protocol the network can allow more users, i.e. more traffic. Also, the network will gain improvement in stability.

The IEEE 802.11b standard is today the only commonly used standard in Europe for fast wireless networks. This makes it possible to connect computers to networks in places where it is not possible to use wires. Examples of such situations are internet access at airports, communication in emergency areas or for military communication. Common for all these situations is that network security is important. This thesis consists of two different parts. The first part handles the security mechanisms and the second part is an evaluation of the possibilities to use IEEE 802.11b in embedded applications. The part that handles the security includes the security mechanisms found in the standard, flaws in these mechanisms and methods that try to reduce these problems.

The diploma thesis is focuses on technologies and security of the wireless networks in standard IEEE 802.11, describes the most used standards, definition of physical layer, MAC layer and specific technologies for wireless networks. The diploma thesis is focused on description of selected security protocols, their technologies as well as weaknesses. Also, in the thesis, there are described security threats and vectors of attacks towards wireless networks 802.11. Selected threats were simulated in established experimental network, for these threats were designed detection methods. For testing and implementing designed detection methods, IDS system Zeek is used together with network scripts written in programming language Python. In the end there were trained and tested models of machine learning both supervised and unsupervised machine learning.