En aquesta tesi proposem dos esquemes de xarxa amb control d'admissió per al trànsit elàstic TCP amb mecanismes senzills. Ambdós esquemes són capaços de proporcionar throughputs diferents i aïllament entre fluxos, on un "flux" es defineix com una seqüència de paquets relacionats dins d'una connexió TCP. Quant a l'arquitectura, ambdós fan servir classes de paquets amb diferents prioritats de descart, i un control d'admissió implícit, edge-to-edge i basat en mesures. En el primer esquema, les mesures són per flux, mentre que en el segon, les mesures són per agregat. El primer esquema aconsegueix un bon rendiment fent servir una modificació especial de les fonts TCP, mentre que el segon aconsegueix un bon rendiment amb fonts TCP estàndard. Ambdós esquemes han estat avaluats satisfactòriament a través de simulació en diferents topologies de xarxa i càrregues de trànsit. / In this thesis we propose two network schemes with admission control for TCP elastic traffic using simple mechanisms. Both schemes are able to provide different throughputs and isolation between flows, where a flow is defined as a sequence of related packets within a TCP connection. Regarding to the architecture, both use packet classes with different discarding priorities and an admission control that is implicit, edge-to-edge and based on measurements. In the first scheme, measurements are per-flow, while in the second one, measurements are per-aggregate. The first scheme achieves a good performance using a special modification of TCP sources, while the second scheme achieves a good performance with standard TCP sources. Both schemes have been evauated succesfully through simulation in different network topologies and traffic loads.

In recent years, there has been a rapid growth in deployment and usage of realtime network applications, such as Voice-over-IP, video calls/video conferencing, live network seminars, and networked gaming. The continued increase in the popularity of realtime applications requires a more intense focus on the provision of strict guarantees for Quality of Service (QoS) parameters such as delay, jitter and packet loss in access networks. At the same time, wireless networking technologies have become increasingly popular with a wide array of devices such as laptop computers, Personal Digital Assistants (PDAs), and cellular phones being sold with built-in WiFi and WiMAX interfaces. For realtime applications to be popular over wireless networks, simple, robust and effective QoS mechanisms suited for a variety of heterogeneous wireless networks must be devised. Implementing the same QoS mechanisms across multiple neighbouring networks aids seamless handover by ensuring that a flow will be treated in the same way, both before and after handover. To provide guaranteed QoS, an access network should limit load using an admission control algorithm. In this research, we propose a method to provide effective admission control for variable bit rate realtime flows, based on the Central Limit Theorem. Our objective is to estimate the percentage of packets that will be delayed beyond a predefined delay threshold, based on the mean and variance of all the flows in the system. Any flow that will increase the percentage of delayed packets beyond an acceptable threshold can then be rejected. Using simulations we have shown that the proposed method provides a very effective control of the total system load, guaranteeing the QoS for a set of accepted flows with negligible reductions in the system throughput. To ensure that flow data is transmitted according to the QoS requirements of a flow, a scheduling algorithm must handle data intelligently. We propose methods to allow more efficient scheduling by utilising existing Medium Access Control mechanisms to exchange flow information. We also propose a method to determine the delay-dependent "value" of a packet based on the QoS requirements of the flow. Using this value in scheduling is shown to increase the number of packets sent before a predetermined deadline. We propose a measure of fairness in scheduling that is calculated according to how well each flow's QoS requirements are met. We then introduce a novel scheduling paradigm, Delay Loss Controlled-Earliest Deadline First (DLC-EDF), which is shown to provide better QoS for all flows compared to other scheduling mechanisms studied. We then study the performance of our admission control and scheduling methods working together, and propose a feedback mechanism that allows the admission control threshold to be tuned to maximise the efficient usage of available bandwidth in the network, while ensuring that the QoS requirements of all realtime flows are met. We also examine heterogeneous/vertical handover, providing an overview of the technologies supporting seamless handover. The issues studied in this area include a method of using the Signal to Noise Ratio to trigger handover in heterogeneous networks and QoS Mapping between heterogeneous networks. Our proposed method of QoS mapping establishes the minimum set of QoS parameters applicable to individual flows, and then maps these parameters into system parameter formats for both 802.11e and 802.16e networks.

A tecnologia WDM (Wavelength Division Multiplexing) e a introdução de OXCs (Optical Cross Connect) e OADMs (Optical Add/Drop Multiplexer) puramente ópticos podem dotar as redes ópticas da função de networking, ou seja, da capacidade de manipular comprimentos de onda de forma a implementar o roteamento destes. Esta possibilidade implica em uma nova forma de relacionamento das aplicações com a camada física, sendo a arquitetura GMPLS candidata a estabelecer tal relacionamento. Soluções eficientes para o problema de alocação de recursos e roteamento de tráfego tornam-se uma necessidade imperiosa em projeto, expansão e gerenciamento de redes ópticas. A contribuição desta tese consiste em relacionar funcionalidades tais como: agregação (grooming) de tráfego, mecanismo de controle de admissão de chamadas (CAC), mecanismos de restauração e alocação de conversores em redes ópticas heterogêneas, avaliando-se as métricas de probabilidade de bloqueio, probabilidade do tráfego bloqueado e imparcialidade (fairness). Tais funcionalidades são tratadas separadamente na literatura. Com este objetivo em mente modela-se a rede com duas camadas: a camada física e a camada virtual. Estabelecem-se duas políticas de agregação de tráfego MrTV (minimização da rota na topologia virtual) e MrTF (minimização da rota na topologia física) e analisa-se o desempenho destas em relação à porcentagem de tráfego bloqueado. Em seguida um mecanismo de controle de admissão de chamadas (CAC) é implementado e sua influência em termos de imparcialidade (fairness) e probabilidade de bloqueio é analisada. A simulação e análise de redes ópticas, como a Rede NSFnet e a Rede Nacional Italiana são executadas por meio da implementação de um grafo baseado em Zhu e Mukherjee [28]. Como resultado, a política MrTF apresenta menor porcentagem de tráfego bloqueado do que a política MrTV para as redes simuladas e a implementação de um mecanismo de janela deslizante (rolling window) tornou o mecanismo de CAC mais otimizado. A utilidade de se implantar conversores de comprimento de onda apenas em alguns nós da rede (conversão esparsa) é estudada e uma análise sobre a probabilidade de bloqueio e a imparcialidade da rede desta distribuição de conversores é apresentada. Finalmente, técnicas de restauração na camada física e virtual são implementadas e uma análise da influência destes sobre a probabilidade de bloqueio e a imparcialidade da rede é executada. / The Wavelength Division Multiplexing (WDM) technology as well as both the introduction of all optical OXCs (Optical Cross Connect) and OADMs (Optical Add/Drop Multiplexer) may provide the optical network with the networking function, i.e, the capacity to manipulate wavelengths in order to implement their routing. This possibility implies a new type of relationship between applications and the physical layer. The likely candidate to establish such relationships is GMPLS architecture. Efficient solutions to both the problems of allocating resources and traffic routing become an enhanced requirement in the design, expansion and management of optical networking. The present study focus at the relationship between functionalities such as traffic grooming, network fairness improvement, protection/restoring mechanisms and wavelength conversion in heterogeneous optical networks, evaluating the metrics of blocking probability, probability of traffic blocked and fairness. These functionalities are separately treated in literature. With this goal in mind, a two-layer representation is used in order to model the network: the physical and virtual layers, respectively. Two policies on traffic grooming are set up, as follows: MrTV (route minimizing on virtual topology) and MrTF (route minimizing on physical topology). The performance of such policies is analyzed regarding the percentage of blocked traffic. Next, a mechanism for call admission control (CAC) is implemented and its influence in terms of fairness and blocking probability is discussed. The simulations of optical networks such as NSFnet and the Italian National Network are carried out through a graph based in Zhu and Mukherjee [28]. As a result, MrTF policy presents a smaller percentage of blocked traffic than the MrTV for the simulated networks and the rolling window mechanism has allowed the optimization of the call admission control (CAC) mechanism. The usefulness of placing wavelength converters in a few networks nodes (spare conversion) is studied and an analysis on the blocking probability is presented. Next, the network fairness for this distribution of wavelength converters is presented. Finally, techniques for restoring both physical and virtual layers are also implemented and an analysis regarding their influence on the blocking probability and the network fairness is carried out.

O crescente aumento da demanda de tráfego nas redes celulares vem aumentando a necessidade de uma melhor utilização dos recursos do sistema, já que sua expansão é custosa. Nas estações rádio base (ERB), a disponibilidade de largura de faixa de freqüências é limitada e desta maneira, em uma rede de comunicação móvel celular, o controle de admissão de chamadas exerce grande influência no desempenho do sistema, pois determina a utilização de banda das ERBs e se uma determinada quantidade de recursos (banda) será alocado ou não para uma determinada chamada. O desempenho da rede pode ser atrelado a determinados parâmetros, como a probabilidade de bloqueio de novas chamadas, probabilidade de bloqueio de chamadas handoff e a utilização de banda da rede. Este trabalho propõe um controle de admissão de chamadas que, no atendimento de uma chamada, faz o empréstimo de banda de chamadas em andamento na célula no caso de banda insuficiente. O sistema adota um mecanismo heurístico que determina a banda disponível para novas chamadas conforme os valores de certos parâmetros do sistema. O empréstimo de banda é realizado em chamadas em andamento nas células até níveis mínimos estabelecidos para cada tipo de chamada, que se diferenciam pelas necessidades de banda de cada uma. O algoritmo foi aplicado às bandas e características de uma rede de terceira geração (3G), que possui chamadas de voz, videoconferência, interação multimídia, e-mail, downloads e transferência de arquivos e a uma rede GSM/GPRS (global system for mobile communications/ general packet radio service), que possui chamadas de voz e de dados. Os resultados mostram melhorias na probabilidade de bloqueio de novas chamadas, probabilidade de bloqueio de handoff e na utilização de banda do sistema. / The recent growth in traffic loads in cellular networks has seen the need for a better use of system resources as its expansion is expensive. In the base transceiver station (BTS), the bandwidth availability is limited. Thus, in cellular networks the call admission control greatly influences the system performance because it determines the bandwidth use of the BTSs and if an amount of resources will or will not be allocated to a call. The network performance can be evaluated by parameters such as blocking probability of new calls, dropping probability of handoff calls and bandwidth use. This work proposes a call admission control that carries out the bandwidth borrowing when a call arrives and there is not enough bandwidth. The system makes use of a heuristic mechanism that determines the available bandwidth for the new calls according to some parameter values of the system. The bandwidth borrowing is applied to the cell ongoing calls until the minimum levels for each type are met. The algorithm was applied to the bandwidths and characteristics of a third generation cellular network, which supports voice calls, videoconference, multimedia interaction, e-mails, downloads and file transfers. It was also applied to a GSM/GPRS (global system for mobile communications/ general packet radio service), which supports voice and data calls. The results show improvements in the blocking probability of new calls, dropping probability of handoff calls and in the bandwidth use of the system.

Abstract Communication networks are experiencing a significant growth of data traffic posing new challenges to the overall systems that should become more reactive and adaptive towards dynamically changing traffic, connections and network conditions. This thesis examines adaptive traffic management solutions within heterogeneous communication networks, which can be utilized to improve network performance, provide Quality of Service (QoS) for traffic paths and share resources in a fair way. The developed adaptive methods include solutions for fuzzy flow scheduling (AWFQ, FWQ) and regressive admission control (REAC) to provide stable network performance and efficient resource control. Such techniques for adaptive traffic management continuously balance and control traffic usage and recover from network faults and attacks. The results utilize traffic monitoring for estimating the overall network conditions, applying cognition to learn from previous actions, and adapting to the current traffic conditions for resource optimization. The thesis researches how to distribute these computing mechanisms towards network edges closer to the actual application users for more efficient resource usage, and to provide better performance for delay-sensitive applications. The methods developed have been applied to vehicular communications to assess and improve the messaging between vehicles and vulnerable road users (VRUs). These mechanisms are able to react faster to data traffic changes and guarantee better quality for prioritized traffic and users while at the same time they preserve fairness to other flows compared to traditional control and scheduling methods without adaptive characteristics. The overall system reacts to changes in the network QoS by determining decision-making procedures on possible flow rejection, marking, or allowed bandwidth weight assignment, thus bringing cognition to the network path. / Tiivistelmä Merkittävä liikennemäärien kasvu aiheuttaa tietoverkoille uusia haasteita, minkä vuoksi niiden täytyy tukea reaktiivisuutta ja adaptiivisuutta vastatakseen muuttuviin liikenne- sekä verkko-olosuhteisiin että yhteyksiin. Väitöskirjassa kehitetään heterogeenisten tietoverkkojen adaptiivisia liikenteenhallintaratkaisuja, joita voidaan hyödyntää verkon suorituskyvyn parantamiseen, tarjoamaan liikenteen palvelunlaatua (QoS) sekä tasapuolista resurssien jakoa. Kehitetyt adaptiiviset menetelmät sisältävät ratkaisuja sumeaan logiikkaan perustuvaan skedulointiin sekä regressiiviseen verkon pääsynhallintaan pohjautuen, jotka takaavat vakaamman verkon suorituskyvyn ja resurssien hallinnan. Nämä menetelmät tasapainottavat ja kontrolloivat liikennettä sekä pyrkivät palautumaan verkon häiriöistä ja hyökkäyksistä. Tulokset hyödyntävät liikenteen monitorointia verkon tilan arviointiin, soveltavat kognitiivisuutta oppiakseen aiemmista toiminnoista sekä adaptoituvat nykytilanteeseen resurssien optimoimiseksi. Väitöskirja tutkii, miten kyseisiä laskentamenetelmiä voidaan hajauttaa verkon reunoille lähemmäksi sovellusten käyttäjiä resurssien käytön tehostamiseksi sekä tarjoamaan parempaa suorituskykyä viiveherkille sovelluksille. Kehitettyjä menetelmiä sovelletaan autoverkkoihin autojen sekä suojattomien tienkäyttäjien viestinnän määrittämiseen sekä parantamiseen. Nämä menetelmät reagoivat nopeammin dataliikenteen muutoksiin, takaavat paremman laadun priorisoidulle liikenteelle sekä samalla tasapuolisuutta muulle liikenteelle verrattuna perinteisiin kontrollointi- ja skedulointimenetelmiin. Kehitetty järjestelmä reagoi verkon palvelunlaadun muutoksiin määrittelemällä päätöksentekomalleja mahdolliseen tietovuon hylkäämiseen, merkitsemiseen tai kaistankäytön painokertoimen määrittämiseen, täten luoden kognitiivisuutta verkon reitille.

La thèse s'intéresse à la réalisation d'une architecture de Qualité de Service en rupture avec les approches classiques, permettant d'offrir des garanties de bout en bout pour le trafic. L'approche Flow-Aware Networking considère le trafic au niveau des flux applicatifs, pour lesquels des modèles de trafic simples mais robustes conduisent à une relation fondamentale entre ressources offertes par le réseau, la demande générée, et la performance obtenue. En particulier, l'architecture de routeur Cross-Protect propose la combinaison d'un ordonnancement fair queueing et d'un contrôle d'admission afin d'assurer de manière implicite la performance des flots streaming et élastique, sans nécessiter ni marquage ni procotole de signalisation. Dans un tel contexte, nous considérons le dimensionnement des buffers au sein des routeurs, l'introduction d'un ordonnancement de type fair queueing dans le réseau et son impact sur la performance des protocoles TCP, ainsi que la réalisation d'un algorithme de contrôle d'admission approprié. Pour terminer, une déclinaison de cette architecture pour le réseau d'accès est proposée. / The thesis deals with the realization of a Quality of Service architecture that breaks with traditional approaches, and allows end-to-end performance guarantees for the traffic. The Flow-Aware Networking approach considers the traffic at the flow level, for which simple but robust traffic models lead to a fundamental relationship between the resources offered by the network, the demand and the obtained performance. In particular, the Cross-Protect router architecture proposes the combination of a fair queueing scheduler, and an admission control so as to implicitly ensure the performance of both streaming and elastic flows, without the need for any marking nor signalization protocol. In such a context, we consider the sizing of router buffers, the introduction of fair queueing scheduling inside the network and its impact on the performance of TCP protocols, as well as the realization of a suitable admission control algorithm. Finally, a declination of this architecture for the access network is proposed.

When designing architectures and protocols for data traffic requiring real-time services, one of the major design goals is to guarantee that traffic deadlines can be met. However, many real-time applications also have additional requirements such as high throughput, high reliability, or energy efficiency. High-performance embedded systems communicating heterogeneous traffic with high bandwidth and strict timing requirements are in need of more efficient communication solutions, while wireless industrial applications, communicating control data, require support of reliability and guarantees of real-time predictability at the same time. To meet the requirements of high-performance embedded systems, this thesis work proposes two multi-wavelength high-speed passive optical networks. To enable reliable wireless industrial communications, a framework in­corporating carefully scheduled retransmissions is developed. All solutions are based on a single-hop star topology, predictable Medium Access Control algorithms and Earliest Deadline First scheduling, centrally controlled by a master node. Further, real-time schedulability analysis is used as admission control policy to provide delay guarantees for hard real-time traffic. For high-performance embedded systems an optical star network with an Arrayed Waveguide Grating placed in the centre is suggested. The design combines spatial wavelength re­use with fixed-tuned and tuneable transceivers in the end nodes, enabling simultaneous transmis­sion of both control and data traffic. This, in turn, permits efficient support of heterogeneous traf­fic with both hard and soft real-time constraints. By analyzing traffic dependencies in this mul­tichannel network, and adapting the real-time schedulability analysis to incorporate these traffic dependencies, a considerable increase of the possible guaranteed throughput for hard real-time traffic can be obtained. Most industrial applications require using existing standards such as IEEE 802.11 or IEEE 802.15.4 for interoperability and cost efficiency. However, these standards do not provide predict­able channel access, and thus real-time guarantees cannot be given. A framework is therefore de­veloped, combining transport layer retransmissions with real-time analysis admission control, which has been adapted to consider retransmissions. It can be placed on top of many underlying communication technologies, exemplified in our work by the two aforementioned wireless stan­dards. To enable a higher data rate than pure IEEE 802.15.4, but still maintaining its energy saving properties, two multichannel network architectures based on IEEE 802.15.4 and encompassing the framework are designed. The proposed architectures are evaluated in terms of reliability, utiliza­tion, delay, complexity, scalability and energy efficiency and it is concluded that performance is enhanced through redundancy in the time and frequency domains.

Depuis quelques années, la recherche dans le domaine des réseaux maillés sans fil ("Wireless Mesh Network (WMN)" en anglais) suscite un grand intérêt auprès de la communauté des chercheurs en télécommunications. Ceci est dû aux nombreux avantages que la technologie WMN offre, telles que l'installation facile et peu coûteuse, la connectivité fiable et l'interopérabilité flexible avec d'autres réseaux existants (réseaux Wi-Fi, réseaux WiMax, réseaux cellulaires, réseaux de capteurs, etc.). Cependant, plusieurs problèmes restent encore à résoudre comme le passage à l'échelle, la sécurité, la qualité de service (QdS), la gestion des ressources, etc. Ces problèmes persistent pour les WMNs, d'autant plus que le nombre des utilisateurs va en se multipliant. Il faut donc penser à améliorer les protocoles existants ou à en concevoir de nouveaux. L'objectif de notre recherche est de résoudre certaines des limitations rencontrées à l'heure actuelle dans les WMNs et d'améliorer la QdS des applications multimédia temps-réel (par exemple, la voix). Le travail de recherche de cette thèse sera divisé essentiellement en trois principaux volets: le contrôle d‟admission du trafic, la différentiation du trafic et la réaffectation adaptative des canaux lors de la présence du trafic en relève ("handoff" en anglais). Dans le premier volet, nous proposons un mécanisme distribué de contrôle d'admission se basant sur le concept des cliques (une clique correspond à un sous-ensemble de liens logiques qui interfèrent les uns avec les autres) dans un réseau à multiples-sauts, multiples-radios et multiples-canaux, appelé RCAC. Nous proposons en particulier un modèle analytique qui calcule le ratio approprié d'admission du trafic et qui garantit une probabilité de perte de paquets dans le réseau n'excédant pas un seuil prédéfini. Le mécanisme RCAC permet d‟assurer la QdS requise pour les flux entrants, sans dégrader la QdS des flux existants. Il permet aussi d‟assurer la QdS en termes de longueur du délai de bout en bout pour les divers flux. Le deuxième volet traite de la différentiation de services dans le protocole IEEE 802.11s afin de permettre une meilleure QdS, notamment pour les applications avec des contraintes temporelles (par exemple, voix, visioconférence). À cet égard, nous proposons un mécanisme d'ajustement de tranches de temps ("time-slots"), selon la classe de service, ED-MDA (Enhanced Differentiated-Mesh Deterministic Access), combiné à un algorithme efficace de contrôle d'admission EAC (Efficient Admission Control), afin de permettre une utilisation élevée et efficace des ressources. Le mécanisme EAC prend en compte le trafic en relève et lui attribue une priorité supérieure par rapport au nouveau trafic pour minimiser les interruptions de communications en cours. Dans le troisième volet, nous nous intéressons à minimiser le surcoût et le délai de re-routage des utilisateurs mobiles et/ou des applications multimédia en réaffectant les canaux dans les WMNs à Multiples-Radios (MR-WMNs). En premier lieu, nous proposons un modèle d'optimisation qui maximise le débit, améliore l'équité entre utilisateurs et minimise le surcoût dû à la relève des appels. Ce modèle a été résolu par le logiciel CPLEX pour un nombre limité de noeuds. En second lieu, nous élaborons des heuristiques/méta-heuristiques centralisées pour permettre de résoudre ce modèle pour des réseaux de taille réelle. Finalement, nous proposons un algorithme pour réaffecter en temps-réel et de façon prudente les canaux aux interfaces. Cet algorithme a pour objectif de minimiser le surcoût et le délai du re-routage spécialement du trafic dynamique généré par les appels en relève. Ensuite, ce mécanisme est amélioré en prenant en compte l‟équilibrage de la charge entre cliques. / In the last few years, Wireless Mesh Networks (WMNs) area brought a new field of advanced research among network specialized scientists. This is due to the many advantages which WMN technology offers, such as: easy and inexpensive installation, reliable connectivity and flexible interoperability with other existing networks (Wi-Fi, WiMax, Cellular, Sensors, WPAN networks, etc.). However, several problems still remain to be solved such as the scalability, the security, the quality of service (QoS), the resources management, etc. These problems persist for WMNs, therefore the researchers propose to improve the existing protocols or to conceive new protocols for WMNs. In order to solve some of the current limitations met in the wireless networks and to improve QoS of real time multimedia applications in such networks, our research will be divided primarily into three parts: traffic admission control, traffic differentiation and handoff-aware channel assignment schemes. In the first part, we propose a distributed admission control scheme for WMNs, namely, Routing on Cliques (a clique is defined as a subset of logical links that interfere with each other) Admission Control (RCAC). Particularly, we propose an analytical model to compute the appropriate acceptance ratio and guarantee that the packet loss probability in the network does not exceed a threshold value. The model also allows computing end-to-end delay to process flow requests with delay constraints. In the second part, we design an efficient scheduler for Mesh Deterministic Access (MDA) in IEEE 802.11s-based WMNs, called Enhanced Differentiated-MDA (ED-MDA) to support voice and video applications with strict requirements on delay and on blocking/dropping probability. ED-MDA together with Enhanced Admission Control, namely EAC, reserves the minimum amount of necessary resources while maintaining an acceptable handoff call dropping and high resource utilization. The final section addresses handoff-aware channel assignment (CA) problem in Multiple Radios WMNs (MR-WMNs). In this section, we first propose a multi-objective optimization model that, besides maximizing throughput, improves fairness and handoff experience of mesh clients. In this model, the Jain’s index is used to maximize users’ fairness and to allow same channel assignments to links involved in the same high handoff traffic, thus reducing handoff-triggered re-routing characterized by its high latency. Second, we solved this model to obtain exact solutions by the CPLEX software for a limited number of nodes. We therefore propose to use centralized heuristics/meta-heuristics algorithms as an offline CA process to obtain near-optimal solutions for larger instances (real size network). Moreover, in order to adapt to traffic dynamics caused especially by user handoffs, an online CA scheme is proposed that carefully re-assigns channels to interfaces with the purpose of continuously minimizing the re-routing overhead/latency during user handoffs. This online scheme is improved using load balancing.

Depuis quelques années, la recherche dans le domaine des réseaux maillés sans fil ("Wireless Mesh Network (WMN)" en anglais) suscite un grand intérêt auprès de la communauté des chercheurs en télécommunications. Ceci est dû aux nombreux avantages que la technologie WMN offre, telles que l'installation facile et peu coûteuse, la connectivité fiable et l'interopérabilité flexible avec d'autres réseaux existants (réseaux Wi-Fi, réseaux WiMax, réseaux cellulaires, réseaux de capteurs, etc.). Cependant, plusieurs problèmes restent encore à résoudre comme le passage à l'échelle, la sécurité, la qualité de service (QdS), la gestion des ressources, etc. Ces problèmes persistent pour les WMNs, d'autant plus que le nombre des utilisateurs va en se multipliant. Il faut donc penser à améliorer les protocoles existants ou à en concevoir de nouveaux. L'objectif de notre recherche est de résoudre certaines des limitations rencontrées à l'heure actuelle dans les WMNs et d'améliorer la QdS des applications multimédia temps-réel (par exemple, la voix). Le travail de recherche de cette thèse sera divisé essentiellement en trois principaux volets: le contrôle d‟admission du trafic, la différentiation du trafic et la réaffectation adaptative des canaux lors de la présence du trafic en relève ("handoff" en anglais). Dans le premier volet, nous proposons un mécanisme distribué de contrôle d'admission se basant sur le concept des cliques (une clique correspond à un sous-ensemble de liens logiques qui interfèrent les uns avec les autres) dans un réseau à multiples-sauts, multiples-radios et multiples-canaux, appelé RCAC. Nous proposons en particulier un modèle analytique qui calcule le ratio approprié d'admission du trafic et qui garantit une probabilité de perte de paquets dans le réseau n'excédant pas un seuil prédéfini. Le mécanisme RCAC permet d‟assurer la QdS requise pour les flux entrants, sans dégrader la QdS des flux existants. Il permet aussi d‟assurer la QdS en termes de longueur du délai de bout en bout pour les divers flux. Le deuxième volet traite de la différentiation de services dans le protocole IEEE 802.11s afin de permettre une meilleure QdS, notamment pour les applications avec des contraintes temporelles (par exemple, voix, visioconférence). À cet égard, nous proposons un mécanisme d'ajustement de tranches de temps ("time-slots"), selon la classe de service, ED-MDA (Enhanced Differentiated-Mesh Deterministic Access), combiné à un algorithme efficace de contrôle d'admission EAC (Efficient Admission Control), afin de permettre une utilisation élevée et efficace des ressources. Le mécanisme EAC prend en compte le trafic en relève et lui attribue une priorité supérieure par rapport au nouveau trafic pour minimiser les interruptions de communications en cours. Dans le troisième volet, nous nous intéressons à minimiser le surcoût et le délai de re-routage des utilisateurs mobiles et/ou des applications multimédia en réaffectant les canaux dans les WMNs à Multiples-Radios (MR-WMNs). En premier lieu, nous proposons un modèle d'optimisation qui maximise le débit, améliore l'équité entre utilisateurs et minimise le surcoût dû à la relève des appels. Ce modèle a été résolu par le logiciel CPLEX pour un nombre limité de noeuds. En second lieu, nous élaborons des heuristiques/méta-heuristiques centralisées pour permettre de résoudre ce modèle pour des réseaux de taille réelle. Finalement, nous proposons un algorithme pour réaffecter en temps-réel et de façon prudente les canaux aux interfaces. Cet algorithme a pour objectif de minimiser le surcoût et le délai du re-routage spécialement du trafic dynamique généré par les appels en relève. Ensuite, ce mécanisme est amélioré en prenant en compte l‟équilibrage de la charge entre cliques. / In the last few years, Wireless Mesh Networks (WMNs) area brought a new field of advanced research among network specialized scientists. This is due to the many advantages which WMN technology offers, such as: easy and inexpensive installation, reliable connectivity and flexible interoperability with other existing networks (Wi-Fi, WiMax, Cellular, Sensors, WPAN networks, etc.). However, several problems still remain to be solved such as the scalability, the security, the quality of service (QoS), the resources management, etc. These problems persist for WMNs, therefore the researchers propose to improve the existing protocols or to conceive new protocols for WMNs. In order to solve some of the current limitations met in the wireless networks and to improve QoS of real time multimedia applications in such networks, our research will be divided primarily into three parts: traffic admission control, traffic differentiation and handoff-aware channel assignment schemes. In the first part, we propose a distributed admission control scheme for WMNs, namely, Routing on Cliques (a clique is defined as a subset of logical links that interfere with each other) Admission Control (RCAC). Particularly, we propose an analytical model to compute the appropriate acceptance ratio and guarantee that the packet loss probability in the network does not exceed a threshold value. The model also allows computing end-to-end delay to process flow requests with delay constraints. In the second part, we design an efficient scheduler for Mesh Deterministic Access (MDA) in IEEE 802.11s-based WMNs, called Enhanced Differentiated-MDA (ED-MDA) to support voice and video applications with strict requirements on delay and on blocking/dropping probability. ED-MDA together with Enhanced Admission Control, namely EAC, reserves the minimum amount of necessary resources while maintaining an acceptable handoff call dropping and high resource utilization. The final section addresses handoff-aware channel assignment (CA) problem in Multiple Radios WMNs (MR-WMNs). In this section, we first propose a multi-objective optimization model that, besides maximizing throughput, improves fairness and handoff experience of mesh clients. In this model, the Jain’s index is used to maximize users’ fairness and to allow same channel assignments to links involved in the same high handoff traffic, thus reducing handoff-triggered re-routing characterized by its high latency. Second, we solved this model to obtain exact solutions by the CPLEX software for a limited number of nodes. We therefore propose to use centralized heuristics/meta-heuristics algorithms as an offline CA process to obtain near-optimal solutions for larger instances (real size network). Moreover, in order to adapt to traffic dynamics caused especially by user handoffs, an online CA scheme is proposed that carefully re-assigns channels to interfaces with the purpose of continuously minimizing the re-routing overhead/latency during user handoffs. This online scheme is improved using load balancing.

This thesis presents a cross-layer design and optimization for emerging wideband wireless networks supporting multimedia applications, considering the interactions of the wireless channel characteristics, the physical and link layer protocols, and the user-perceived Quality-of-Service (QoS). As wireless channels are error-prone and broadcast in nature, both the error control mechanisms and the Media Access Control (MAC) protocols are critical for resource utilization and QoS provisioning. How to analyze, design and optimize the high-rate wireless networks by considering the characteristics of the propagation channels and wideband communication technologies is an open, challenging issue. In this thesis, we consider two important wideband wireless systems, the Ultra-Wideband (UWB) and the Orthogonal Frequency-Division Multiplexing (OFDM) systems. First, we propose the packet-level channel models based on Finite State Markov Chains (FSMCs) for the two systems, which present the statistical properties of the propagation channels and the transmission systems. Second, by incorporating the proposed packet-level channel models, we develop analytical frameworks for quantifying the performance of the high-rate wireless networks, combining the channel fading, physical- and link-layer error-control mechanisms and MAC protocols. Third, to mitigate the impact of channel fading and impairments, a cross-layer joint error-control mechanism is proposed. In addition, we also investigate the impact of channel fading on the video streaming applications, and propose a simple admission control algorithm to ensure QoS. As considering the physical-layer characteristics is critical for ensuring QoS and efficiency of resource utilization, the packet-level channel models, cross-layer analytical frameworks, networking protocols and simulation methodologies proposed in this dissertation are essential for future proliferation of high-rate wireless networks.