Broadcasting is an essential and effective data propagation mechanism with several important applications, such as route discovery, address resolution and many other network services. Though data broadcasting has many advantages, it can also cause a high degree of contention, collision and congestion, leading to what is known as ¿broadcast storm problems¿. Broadcasting has traditionally been based on the flooding protocol, which simply overflows the network with a high number of rebroadcast messages until these reach all the network nodes. A good probabilistic broadcast protocol can achieve high saved rebroadcast (SRB), low collision and a lower number of relays. When a node is in a sparse region of the network, rebroadcasting is relatively more important while the potential redundancy of rebroadcast is low because there are few neighbours which might rebroadcast the packet unnecessarily. Further, in such a situation, contention over the wireless medium resulting from Redundant broadcasts is not as serious as in scenarios with medium or high density node populations. This research proposes a dynamic probabilistic approach that dynamically fine-tunes the rebroadcast probability according to the number of neighbouring nodes distributed in the ad-hoc network for routing request packets (RREQs) without requiring the assistance of distance measurements or location-determination devices. The main goal of this approach is to reduce the number of rebroadcast packets and collisions in the network. The performance of the proposed approach is investigated and compared with simple AODV, fixed-probabilistic and adjusted-probabilistic flooding [1] schemes using the GloMoSim network simulator and a number of important MANET parameters, including node speed, traffic load and node density under a Random Waypoint (RWP) mobility model. Performance results reveal that the proposed approach is able to achieve higher SRB and less collision as well as a lower number of relays than fixed probabilistic, simple AODV and adjusted-probabilistic flooding. In this research, extensive simulation experiments have been conducted in order to study and analyse the proposed dynamic probabilistic approach under different mobility models. The mobility model is designed to describe the movement pattern of mobile customers, and how their position, velocity and acceleration change over time. In this study, a new enhanced dynamic probabilistic flooding scheme is presented. The rebroadcast probability p will be calculated dynamically and the rebroadcasting decision will be based on the average number of nodes in the ad-hoc networks. The performance of the new enhanced algorithm is evaluated and compared to the simple AODV, fixed-probabilistic, adjusted-probabilistic and dynamic-probabilistic flooding schemes. It is demonstrated that the new algorithm has superior performance characteristics in terms of collision, relays and SRB. Finally, the proposed schemes are tested and evaluated through a set of experiments under different mobility models to demonstrate the relative merits and capabilities of these schemes.

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Dans les réseaux mobiles spontanés (en anglais, Mobile Ad hoc NETworks ou MANETs), la gestion de groupe partitionnable est un service de base permettant la construction d'applications réparties tolérantes au partitionnement. Aucune des spécifications existantes ne satisfait les deux exigences antagonistes suivantes : 1) elle doit être assez forte pour fournir des garanties utiles aux applications réparties dans les systèmes partitionnables ; 2) elle doit être assez faible pour être résoluble. Dans cette thèse, nous proposons une solution à la gestion de groupe partitionnable en environnements réseaux très dynamiques tels que les MANETs. Pour mettre en œuvre notre solution, nous procédons en trois étapes. Tout d'abord, nous proposons un modèle de système réparti dynamique qui caractérise la stabilité dans les MANETs. Ensuite, nous adaptons pour les systèmes partitionnables l'approche Paxos à base de consensus Synod. Cette adaptation résulte en la spécification d'un consensus abandonnable AC construit au-dessus d'un détecteur ultime des α participants d'une partition ♢PPD et d'un registre ultime par partition ♢RPP. ♢PPD garantit la vivacité dans une partition même si la partition n'est pas complètement stable tandis que ♢RPP préserve la sûreté dans la même partition. Enfin, la gestion de groupe partitionnable est résolue en la transformant en une séquence d'instances de AC. Chacun des modules ♢PPD, ♢RPP, AC et gestion de groupe partitionnable est implanté et prouvé. Par ailleurs, nous analysons les performances de ♢PPD par simulation / In Mobile Ad hoc NETworks or MANETs, partitionable group membership is a basic service for building partition-tolerant applications. None of the existing specifications satisfy the two following antagonistic requirements: 1) it must be strong enough to simplify the design of partition-tolerant distributed applications in partitionable systems; 2) it must be weak enough to be implantable. In this thesis, we propose a solution to partitionable group membership in very dynamic network environment such as MANETs. To this means, we proceed in three steps. First, we develop a dynamic distributed system model that characterises stability in MANETs. Then, we propose a solution to the problem of partitionable group membership by adapting Paxos for such systems. This adatation results in a specification of abortable consensus AC which is composed of an eventual α partition-participants detector ♢PPD and an eventual register per partition ♢RPP. ♢PPD guarantees liveness in a partition even if the partition is not completely stable whereas ♢RPP ensures safety in the same partition. Finally, partitionable group membership is solved by transforming it into a sequence of abortable consensus instances AC. Each of the modules ♢PPD, ♢RPP, AC, and partitionable group membership is implanted and proved. Next, we analyse the performances of ♢PPD by simulation

Les réseaux sans fil 802.11 sont en train d'être considérés comme étant la pierre angulaire des systèmes de communication autonomes. En permettant aux usagers de communiquer les uns avec les autres avec les stations de base fixées a des endroits bien précis par l'intermédiaire de protocoles de communication comme les protocole de routage ad hoc. Le standard IEEE 802.11 propose des spéciations pour les deux couches basses (MAC et Physique) du modelé OSI. La couche MAC (Medium Access Control) introduit deux mécanismes d'accès au médium sans fil qui sont différents l'un de l'autre. Le mécanisme DCF (accès au canal distribue ou Distributed Coordination Function), l'accès au canal s'exécute dans chaque station sans faire appel à une unité centrale. Le mécanisme PCF (Point Coordination Function), contrairement au mécanisme DCF l'accès au canal se fait à l'aide d'une unité centrale. Le mécanisme le plus utilise par la norme 802.11 est DCF vu qu'il ne nécessite pas d'infrastructure au déploiement. Pour améliorer la qualité de service dans les réseaux sans multi- sauts, cette thèse aborde cette problématique dans deux couches de la pile protocolaire, à savoir la couche routage et la couches MAC. Elle améliore le routage a QoS en utilisant le protocole de routage a état de lien optimisé (OLSR) et améliore aussi l'efficacité de l'accès au médium sans fil lors du fonctionnement de la couche MAC en mode le plus courant DCF. Pour l'amélioration de routage, nous proposons une approche basée sur le graphe de conflit pour l'estimation de la bande passante partagée entre les nœuds adjacents. Pour la couche MAC, nous proposons un nouveau schéma de Backoff nomme l'algorithme Backoff de Padovane (PBA), pour améliorer l'efficacité de l'accès au médium sans fil dans les réseaux sans fil mobiles Ad Hoc (MANETs). / IEEE 802.11 based wireless networks are considered the cornerstone of autonomous communication systems. These networks allow users to communicate with each others via base stations deployed in specic locations through a set of dedicated communication protocols like Ad Hoc routing protocols. The IEEE 802.11 standard proposes specications for both physical and MAC layers of the OSI model. MAC layer denes dierent types of access to the wireless medium as explained below. The DCF (Distributed Coordination Function) mechanism, in which the access to the medium is executed localy in each station. The PCF (Point Coordination Function) method, unlike DCF mechanism the access the medium is managed by a central unit. The most widespread mechanism among them is the DCF mode as it does not require any infrastructure deployment. To improve the Quality of Service (QoS) oered to the dierent applications in multihop wireless networks, this thesis proposes original solutions to enhance the eciency of certain protocols in two dierent layers of OSI, i.e., routing and MAC layers. More specically, our proposed solutions enable higher eciency of OLSR protocol and ensure more ecient usage of the available bandwidth through the designed Padovan based medium access scheme operating in DCF mode. The routing approach used in OLSR is improved by applying the conict graphs to acquire more accurate estimation of the bandwidth shared with the adjacent nodes. At MAC layer, the number of collisions in dense networks is signicantly reduced by designing new backo scheme dubbed Padovan Backo Algorithm (BEB).

Atualmente, muitas redes com características dinâmicas estão em funcionamento (por exemplo MANETs, DTNs, redes oportunistas, etc). Neste trabalho, estudamos um modelo para estas redes chamado de Grafos Evolutivos, que permite expressar a dinamicidade das conexões entre nós por meio de uma simples extensão da estrutura comum de grafos. Esta modelagem é utilizada no arcabouço proposto por Casteigts et al. para definir algoritmos distribuídos em redes dinâmicas, que utiliza grafos evolutivos para representar a topologia da rede e renomeação de rótulos para expressar a comunicação entre os nós. Utilizamos esta abordagem para estudar o problema da exclusão mútua distribuída em redes dinâmicas e diversos algoritmos propostos para ele, a fim de definir e validar suas condições necessárias e suficientes de conectividade em redes dinâmicas. Além da formalização de algoritmos, o modelo de grafos evolutivos também pode ser utilizado para analisar redes dinâmicas. Rastros de redes dinâmicas reais são amplamente utilizados na literatura para estudos de algoritmos pois estes geram resultados mais realísticos do que redes simuladas com padrões de movimento. A partir dos detalhes de cada conexão entre nós de um destes rastros, é possível construir um grafo evolutivo, do qual se pode extrair dados como jornadas ótimas entre nós, variação da conectividade no tempo, estabilidade, e periodicidade. Com as informações mencionadas, um pesquisador pode observar com maior precisão as características do rastro, o que facilita na escolha da rede mais apropriada para sua necessidade. Além disso, o conhecimento prévio de tais características de uma rede auxilia no estudo do comportamento de algoritmos executados sobre ela e provém uma validação para suposições geralmente feitas pelos pesquisadores. Para fornecer estas informações, desenvolvemos uma ferramenta Web que analisa rastros de redes dinâmicas e agrega os dados em um formato de fácil visualização. Descrevemos, neste trabalho, a implementação e a utilidade de todos os serviços da ferramenta. / Lately, several networks with dynamic properties (for instance MANETs, DTNs, opportunistic networks, etc) are functioning. In this work, we studied a model for these networks called Evolving Graphs, which allows the expression of the dynamicity of the conections between nodes through a simple extension of the common graph structure. This model is used by the framework proposed by Casteigts et al. to define distributed algorithms in dynamic networks, which uses evolving graphs to represent the network topology and graph relabelling to express the communication between nodes. Using this approach, we study the distributed mutual exclusion problem in dynamic networks and several algorithms proposed to solve it, in order to define and validate their necessary and sufficient connectivity conditions. Apart from the formalization of algorithms, the evolving graphs model can also be used to analyze dynamic networks. Dynamic network traces are widely used in the literature in order to study algorithms, as they generate better results than simulated networks with movement patterns. From the details of every connection between nodes in a trace, it is possible to build an evolving graph, from which a large amount of information can be extracted, such as optimal journeys between nodes, variation of the conectivity over time, stability and periodicity. With the aforementioned information, a researcher might observe the characteristics of a trace more precisely, which facilitates the process of choosing the most appropriate trace for his needs. Furthermore, the early knowledge of such characteristics of a network helps in the study of the behavior of the algorithms exected over it and provides a validation for the assumptions usually made by the researchers. In order to provide this information, we developed a web tool which analyzes dynamic network traces and aggregates the data in an easily readable format. In this work, we describe the implementation and usefulness of every service in the tool.

Les réseaux sans fil 802.11 sont en train d'être considérés comme étant la pierre angulaire des systèmes de communication autonomes. En permettant aux usagers de communiquer les uns avec les autres avec les stations de base fixées a des endroits bien précis par l'intermédiaire de protocoles de communication comme les protocole de routage ad hoc. Le standard IEEE 802.11 propose des spéciations pour les deux couches basses (MAC et Physique) du modelé OSI. La couche MAC (Medium Access Control) introduit deux mécanismes d'accès au médium sans fil qui sont différents l'un de l'autre. Le mécanisme DCF (accès au canal distribue ou Distributed Coordination Function), l'accès au canal s'exécute dans chaque station sans faire appel à une unité centrale. Le mécanisme PCF (Point Coordination Function), contrairement au mécanisme DCF l'accès au canal se fait à l'aide d'une unité centrale. Le mécanisme le plus utilise par la norme 802.11 est DCF vu qu'il ne nécessite pas d'infrastructure au déploiement. Pour améliorer la qualité de service dans les réseaux sans multi- sauts, cette thèse aborde cette problématique dans deux couches de la pile protocolaire, à savoir la couche routage et la couches MAC. Elle améliore le routage a QoS en utilisant le protocole de routage a état de lien optimisé (OLSR) et améliore aussi l'efficacité de l'accès au médium sans fil lors du fonctionnement de la couche MAC en mode le plus courant DCF. Pour l'amélioration de routage, nous proposons une approche basée sur le graphe de conflit pour l'estimation de la bande passante partagée entre les nœuds adjacents. Pour la couche MAC, nous proposons un nouveau schéma de Backoff nomme l'algorithme Backoff de Padovane (PBA), pour améliorer l'efficacité de l'accès au médium sans fil dans les réseaux sans fil mobiles Ad Hoc (MANETs). / IEEE 802.11 based wireless networks are considered the cornerstone of autonomous communication systems. These networks allow users to communicate with each others via base stations deployed in specic locations through a set of dedicated communication protocols like Ad Hoc routing protocols. The IEEE 802.11 standard proposes specications for both physical and MAC layers of the OSI model. MAC layer denes dierent types of access to the wireless medium as explained below. The DCF (Distributed Coordination Function) mechanism, in which the access to the medium is executed localy in each station. The PCF (Point Coordination Function) method, unlike DCF mechanism the access the medium is managed by a central unit. The most widespread mechanism among them is the DCF mode as it does not require any infrastructure deployment. To improve the Quality of Service (QoS) oered to the dierent applications in multihop wireless networks, this thesis proposes original solutions to enhance the eciency of certain protocols in two dierent layers of OSI, i.e., routing and MAC layers. More specically, our proposed solutions enable higher eciency of OLSR protocol and ensure more ecient usage of the available bandwidth through the designed Padovan based medium access scheme operating in DCF mode. The routing approach used in OLSR is improved by applying the conict graphs to acquire more accurate estimation of the bandwidth shared with the adjacent nodes. At MAC layer, the number of collisions in dense networks is signicantly reduced by designing new backo scheme dubbed Padovan Backo Algorithm (BEB).

Atualmente, muitas redes com características dinâmicas estão em funcionamento (por exemplo MANETs, DTNs, redes oportunistas, etc). Neste trabalho, estudamos um modelo para estas redes chamado de Grafos Evolutivos, que permite expressar a dinamicidade das conexões entre nós por meio de uma simples extensão da estrutura comum de grafos. Esta modelagem é utilizada no arcabouço proposto por Casteigts et al. para definir algoritmos distribuídos em redes dinâmicas, que utiliza grafos evolutivos para representar a topologia da rede e renomeação de rótulos para expressar a comunicação entre os nós. Utilizamos esta abordagem para estudar o problema da exclusão mútua distribuída em redes dinâmicas e diversos algoritmos propostos para ele, a fim de definir e validar suas condições necessárias e suficientes de conectividade em redes dinâmicas. Além da formalização de algoritmos, o modelo de grafos evolutivos também pode ser utilizado para analisar redes dinâmicas. Rastros de redes dinâmicas reais são amplamente utilizados na literatura para estudos de algoritmos pois estes geram resultados mais realísticos do que redes simuladas com padrões de movimento. A partir dos detalhes de cada conexão entre nós de um destes rastros, é possível construir um grafo evolutivo, do qual se pode extrair dados como jornadas ótimas entre nós, variação da conectividade no tempo, estabilidade, e periodicidade. Com as informações mencionadas, um pesquisador pode observar com maior precisão as características do rastro, o que facilita na escolha da rede mais apropriada para sua necessidade. Além disso, o conhecimento prévio de tais características de uma rede auxilia no estudo do comportamento de algoritmos executados sobre ela e provém uma validação para suposições geralmente feitas pelos pesquisadores. Para fornecer estas informações, desenvolvemos uma ferramenta Web que analisa rastros de redes dinâmicas e agrega os dados em um formato de fácil visualização. Descrevemos, neste trabalho, a implementação e a utilidade de todos os serviços da ferramenta. / Lately, several networks with dynamic properties (for instance MANETs, DTNs, opportunistic networks, etc) are functioning. In this work, we studied a model for these networks called Evolving Graphs, which allows the expression of the dynamicity of the conections between nodes through a simple extension of the common graph structure. This model is used by the framework proposed by Casteigts et al. to define distributed algorithms in dynamic networks, which uses evolving graphs to represent the network topology and graph relabelling to express the communication between nodes. Using this approach, we study the distributed mutual exclusion problem in dynamic networks and several algorithms proposed to solve it, in order to define and validate their necessary and sufficient connectivity conditions. Apart from the formalization of algorithms, the evolving graphs model can also be used to analyze dynamic networks. Dynamic network traces are widely used in the literature in order to study algorithms, as they generate better results than simulated networks with movement patterns. From the details of every connection between nodes in a trace, it is possible to build an evolving graph, from which a large amount of information can be extracted, such as optimal journeys between nodes, variation of the conectivity over time, stability and periodicity. With the aforementioned information, a researcher might observe the characteristics of a trace more precisely, which facilitates the process of choosing the most appropriate trace for his needs. Furthermore, the early knowledge of such characteristics of a network helps in the study of the behavior of the algorithms exected over it and provides a validation for the assumptions usually made by the researchers. In order to provide this information, we developed a web tool which analyzes dynamic network traces and aggregates the data in an easily readable format. In this work, we describe the implementation and usefulness of every service in the tool.

Les réseaux sans fil 802.11 sont en train d'être considérés comme étant la pierre angulaire des systèmes de communication autonomes. En permettant aux usagers de communiquer les uns avec les autres avec les stations de base fixées a des endroits bien précis par l'intermédiaire de protocoles de communication comme les protocole de routage ad hoc. Le standard IEEE 802.11 propose des spéciations pour les deux couches basses (MAC et Physique) du modelé OSI. La couche MAC (Medium Access Control) introduit deux mécanismes d'accès au médium sans fil qui sont différents l'un de l'autre. Le mécanisme DCF (accès au canal distribue ou Distributed Coordination Function), l'accès au canal s'exécute dans chaque station sans faire appel à une unité centrale. Le mécanisme PCF (Point Coordination Function), contrairement au mécanisme DCF l'accès au canal se fait à l'aide d'une unité centrale. Le mécanisme le plus utilise par la norme 802.11 est DCF vu qu'il ne nécessite pas d'infrastructure au déploiement. Pour améliorer la qualité de service dans les réseaux sans multi- sauts, cette thèse aborde cette problématique dans deux couches de la pile protocolaire, à savoir la couche routage et la couches MAC. Elle améliore le routage a QoS en utilisant le protocole de routage a état de lien optimisé (OLSR) et améliore aussi l'efficacité de l'accès au médium sans fil lors du fonctionnement de la couche MAC en mode le plus courant DCF. Pour l'amélioration de routage, nous proposons une approche basée sur le graphe de conflit pour l'estimation de la bande passante partagée entre les nœuds adjacents. Pour la couche MAC, nous proposons un nouveau schéma de Backoff nomme l'algorithme Backoff de Padovane (PBA), pour améliorer l'efficacité de l'accès au médium sans fil dans les réseaux sans fil mobiles Ad Hoc (MANETs). / IEEE 802.11 based wireless networks are considered the cornerstone of autonomous communication systems. These networks allow users to communicate with each others via base stations deployed in specic locations through a set of dedicated communication protocols like Ad Hoc routing protocols. The IEEE 802.11 standard proposes specications for both physical and MAC layers of the OSI model. MAC layer denes dierent types of access to the wireless medium as explained below. The DCF (Distributed Coordination Function) mechanism, in which the access to the medium is executed localy in each station. The PCF (Point Coordination Function) method, unlike DCF mechanism the access the medium is managed by a central unit. The most widespread mechanism among them is the DCF mode as it does not require any infrastructure deployment. To improve the Quality of Service (QoS) oered to the dierent applications in multihop wireless networks, this thesis proposes original solutions to enhance the eciency of certain protocols in two dierent layers of OSI, i.e., routing and MAC layers. More specically, our proposed solutions enable higher eciency of OLSR protocol and ensure more ecient usage of the available bandwidth through the designed Padovan based medium access scheme operating in DCF mode. The routing approach used in OLSR is improved by applying the conict graphs to acquire more accurate estimation of the bandwidth shared with the adjacent nodes. At MAC layer, the number of collisions in dense networks is signicantly reduced by designing new backo scheme dubbed Padovan Backo Algorithm (BEB).

Broadcasting is used in on-demand routing protocols to discover routes in Mobile Ad-hoc Networks (MANETs). On-demand routing protocols, such as Ad-hoc On-demand Distance Vector (AODV) commonly employ pure flooding based broadcasting to discover new routes. In pure flooding, a route request (RREQ) packet is broadcast by the source node and each receiving node rebroadcasts it. This continues until the RREQ packet arrives at the destination node. Pure flooding generates excessive redundant routing traffic that may lead to the broadcast storm problem (BSP) and deteriorate the performance of MANETs significantly. A number of probabilistic broadcasting schemes have been proposed in the literature to address BSP. However, these schemes do not consider thermal noise and interference which exist in real life MANETs, and therefore, do not perform well in real life MANETs. Real life MANETs are noisy and the communication is not error free. This research argues that a broadcast scheme that considers the effects of thermal noise, co-channel interference, and node density in the neighbourhood simultaneously can reduce the broadcast storm problem and enhance the MANET performance. To achieve this, three investigations have been carried out: First, the effect of carrier sensing ranges on on-demand routing protocol such as AODV and their impact on interference; second, effects of thermal noise on on-demand routing protocols and third, evaluation of pure flooding and probabilistic broadcasting schemes under noisy and noiseless conditions. The findings of these investigations are exploited to propose a Channel Adaptive Probabilistic Broadcast (CAPB) scheme to disseminate RREQ packets efficiently. The proposed CAPB scheme determines the probability of rebroadcasting RREQ packets on the fly according to the current Signal to Interference plus Noise Ratio (SINR) and node density in the neighbourhood. The proposed scheme and two related state of the art (SoA) schemes from the literature are implemented in the standard AODV to replace the pure flooding based broadcast scheme. Ns-2 simulation results show that the proposed CAPB scheme outperforms the other schemes in terms of routing overhead, average end-to-end delay, throughput and energy consumption.

Mobile Ad hoc Networks (MANETs) can be deployed instantaneously and adaptively, making them highly suitable to military, medical and disaster-response scenarios. Using real-time applications for provision of instantaneous and dependable communications, media streaming, and device control in these scenarios is a growing research field. Realising timing requirements in packet delivery is essential to safety-critical real-time applications that are both delay- and loss-sensitive. Safety of these applications is compromised by packet loss, both on the network and by the applications themselves that will drop packets exceeding delay bounds. However, the provision of this required Quality of Service (QoS) must overcome issues relating to the lack of reliable existing infrastructure, conservation of safety-certified functionality. It must also overcome issues relating to the layer-2 dynamics with causal factors including hidden transmitters and fading channels. This thesis proposes that bounded maximum delay and safety-critical application support can be achieved by using cross-layer middleware. Such an approach benefits from the use of established protocols without requiring modifications to safety-certified ones. This research proposes ROAM: a novel, adaptive and scalable cross-layer Real-time Optimising Ad hoc Middleware framework for the provision and maintenance of performance guarantees in self-configuring MANETs. The ROAM framework is designed to be scalable to new optimisers and MANET protocols and requires no modifications of protocol functionality. Four original contributions are proposed: (1) ROAM, a middleware entity abstracts information from the protocol stack using application programming interfaces (APIs) and that implements optimisers to monitor and autonomously tune conditions at protocol layers in response to dynamic network conditions. The cross-layer approach is MANET protocol generic, using minimal imposition on the protocol stack, without protocol modification requirements. (2) A horizontal handoff optimiser that responds to time-varying link quality to ensure optimal and most robust channel usage. (3) A distributed contention reduction optimiser that reduces channel contention and related delay, in response to detection of the presence of a hidden transmitter. (4) A feasibility evaluation of the ROAM architecture to bound maximum delay and jitter in a comprehensive range of ns2-MIRACLE simulation scenarios that demonstrate independence from the key causes of network dynamics: application setting and MANET configuration; including mobility or topology. Experimental results show that ROAM can constrain end-to-end delay, jitter and packet loss, to support real-time applications with critical timing requirements.