Dissertation (Ph.D.)--Auburn University,2009. / Abstract. Includes bibliographic references (p.107-112).

Increasing capacity in wireless mesh networks can be achieved by using multiple channels and radios. By using different channels, two nodes can send packets at the same time without interfering with each other. To utilize diversity of available frequency, a channel assignment scheme is required. Hybrid channel assignment is an interesting approach where at least one radio is tuned to a fixed channel for receiving and the remaining interfaces switch their channels dynamically in order to match the receiving channel at the receiving node. This provides full connectivity, but at the expense of introduced switching costs. Due to hardware limitations it is too costly to switch channels on a per packet basis. Instead, this thesis proposes an anypath routing and forwarding mechanism in order to allow each node along the route to select the best next hop neighbor on a per packet basis. The routing algorithm finds for each destination a set of next hop candidates and the forwarding algorithm considers the state of the channel switch operation when selecting a next hop candidate. Also, in order to allow latency-sensitive packets to be transmitted before other packets, latency-awareness has been introduced to distinguish e.g. VoIP flows from FTP traffic. The ideas have been implemented and tested using real-world experiments, and the results show a significant reduction in latency.

Tato práce zkoumá vhodnost a požadavky návrhu simulací pro simulátor NS-3 pro případ bezdrátových sítí používaných v měřící infrastruktuře společnosti Kamstrup. V práci je popsán simulátor NS-3 a je vytvořena základní implementace dvou protokolů. Wireless M-Bus jako příklad jednosměrného protokolu pro zařízení napájené z baterií. Simulace Wireless M-Bus je porovnána s daty naměřenými v reálném systému. NS-3 poskytuje flexibilní prostředí pro vývoj simulací různých síťových protokolů, včetně těch určených pro sítě inteligentních měřidel.

Due to the high availability of cheap hardware, wireless multi-hop networks and in particular Wireless Mesh Networks (WMNs) are becoming popular in more and more contexts. For instance, IEEE 802.11 based WMNs have already started to be deployed as means to provide Internet access to rural areas in the developing world. To lower the cost and increase the coverage in such deployments, the wired network is extended with a wireless backbone of fixed mesh routers. With advances in technology and reduction in price comes also the possibility for more powerful wireless nodes, having multiple radios that allow transmitting on different channels in parallel. To be a successful platform for providing general Internet access, wireless multi-hop networks must provide support for common Internet applications. As most of the applications in the Internet today use the Transmission Control Protocol (TCP), TCP performance is crucial. Unfortunately, the design of TCP’s congestion control that made it successful in today’s Internet makes it perform less than optimal in wireless multi-hop networks. This is due to, among others, TCP’s inability to distinguish wireless losses from congestion losses. The current trend for operating system designers is also to focus TCP development on high-speed fixed networks, rather than on wireless multi-hop networks. To enable wireless multi hop networks as a successful platform there is therefore a need to provide good performance using TCP variants commonly deployed in the Internet. In this thesis, we develop novel proposals for the network layer in wireless multi-hop networks to support TCP traffic more efficiently. As an initial study, we experimentally evaluate different TCP variants, with and without mobile nodes, in a MANET context. Our results show that TCP Vegas, which does not provoke packet loss to determine available bandwidth, reduces the stress on the network while still providing the same or slightly increased performance, compared to TCP Newreno. We further propose and evaluate packet aggregation combined with aggregation aware multi-path forwarding to better utilize the available bandwidth. IP layer packet aggregation, where small packets are combined to larger ones before sent to the link layer, has been shown to improve the performance in wireless multi-hop networks for UDP and small packet transfers. Only few studies have been made on the impact of packet aggregation on TCP traffic, despite the fact that TCP traffic constitutes the majority of the Internet traffic. We propose a novel aggregation algorithm that is specifically addressing TCP relevant issues like packet reordering, fairness and TCP timeouts. In a typical WMN scenario, the aggregation algorithm increases TCP performance by up to 70 % and decreases round trip time (RTT) by up to 40 %. A detailed evaluation of packet aggregation in a multi radio setting has shown that a naive combination of multi path routing and packet aggregation can cause valuable aggregation opportunities to be lost. Therefore, we propose a novel combined packet aggregation and aggregation aware forwarding strategy that can reduce delay, packet loss and increase TCP performance by around 30 %.

Orientador: Edmundo Roberto Mauro Madeira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Computação / Made available in DSpace on 2018-08-11T08:18:18Z (GMT). No. of bitstreams: 1 Paschoalino_RacheldeCarvalho_M.pdf: 2064052 bytes, checksum: e9b127c3cba93b04b66044600728e3a9 (MD5) Previous issue date: 2008 / Resumo: Devido à facilidade de implantação e gerência, as redes mesh sem fio constituem uma escolha natural para atender a crescente demanda por acesso sem fio com cobertura em larga escala. Formadas por roteadores mesh interligados através de enlaces sem fio, as WMNs (Wireless Mesh Networks) fornecem um backbone flexível para diversas aplicações e serviços. Entretanto, os protocolos de roteamento existentes aplicados às WMNs não provêem escalabilidade, reduzindo a vazão conforme o tamanho da rede aumenta. Esta dissertação apresenta um protocolo de roteamento escalável com QoS para WMNs multirádio. Incorporamos uma métrica local de qualidade do enlace e suporte a múltiplos rádios ao protocolo OLSR (Optimized Link State Routing). A métrica de qualidade é usada na seleção de nós especiais de relay, que irão compor as rotas. Variações na métrica de qualidade são tratadas na vizinhança de 1 salto, preservando estabilidade no roteamento. Por sua vez, o uso de múltiplos rádios por nó provê um melhor aproveitamento do espectro sem fio, minimizando a contenção. Essa abordagem simples e escalável permite distribuir o tráfego na rede por caminhos com enlaces de melhor qualidade. Através das simulações realizadas, demonstramos que o protocolo proposto, chamado LQ-OLSR (Link Quality OLSR), traz melhorias expressivas na vazão, atraso e perda de pacotes em relação ao OLSR original, com um aumento mínimo do overhead / Abstract: Due to their deployment and management simplicity, Wireless Mesh Networks (WMNs) have become a natural way to fulfill the increasing demand for large area wireless coverage. Formed by mesh routers connected by wireless links, WMNs provide a flexible backbone for various applications and services. Nevertheless, the available routing protocols applied to WMNs suffer from scalability, where throughput decreases as the number of nodes grows. In this thesis, a scalable QoS routing protocol for multi-radio WMNs is proposed. We incorporate a locallink quality metric and multi-radio support in the OLSR (Optimized Link State Routing) protocol. The quality metric is used in the selection of relay nodes which will form the routes. Significant changes to link quality metric are treated in l-hop neighborhood, preserving route stability. Using multiple radios in each node allows a better utilization of the wireless spectrum, minimizing contention. This simple and scalable approach permits traffic distribution among better quality links. Simulations were conducted and the results showed expressive performance improvements .concerning throughput, delay and packet loss of the proposed protocol LQ-OLSR (Link Quality OLSR) over the original OLSR, with a minimum overhead increase / Mestrado / Redes de Computadores / Mestre em Ciência da Computação

Wireless mesh networks are communication networks possessing radio nodes with mesh organization structure. They are expected to be widely employed by personal, local, campus and metropolitan area applications. Most of the needed components for the deployment of WMNs; such as ad-hoc network routing protocols, wireless security protocols, IEEE 802.11 MAC protocol are already available, while there are problems sourced from various protocol layers. These problems restrict WMNs from serving their potential. The purpose of this work is to evaluate the WMN routing mechanisms with respect to several performance indicators and to determine the routing protocols, which maintain scalable, robust and efficient operation. The performance of B.A.T.M.A.N (Better Approach to Mobile Ad-hoc Networking) protocol is compared to conventional AODV and OLSR protocols in addition to an experimental wireless MPLS routing mechanism (LWMPLS). The OMNeT++ simulation environment helps to determine the performance of routing mechanisms throughout our tests. The simulation results point out that B.A.T.M.A.N protocol performs stable routing in networks with varying link qualities or failing nodes. It has low packet loss rate even when it is employed in environments with extremely high thermal noise, therefore B.A.T.M.A.N is foreseen to become one of the most popular routing mechanisms of WMNs. / +46 (0)739554313

Autonomous Mesh Networks potentially allows for cheaper networks, of use for impoverished areas with poor infrastructure and little interest from service providers for expansion. The subject of wireless mesh networks is interesting for several reasons. Non-reliance, or at the very least reduced reliance on existing infrastructure and service providers gives more control of a network to the users and their communities. These kinds of networks are however conceived to be quite complex to set up, manage and maintain. The goal of this paper was to create an autonomous network without any need for infrastructure, that was relatively easy to configure, use, and performs well. The implementation technique used succeeds at reaching these goals. The script and environment that was constructed makes it easy to set up and join nodes into the network, and the network can increase and decrease in size without affecting the core functionality of the network. The implementation for automatic host discovery makes it simple for anyone with a small amount of knowledge to find and communicate with other hosts, and the network has proven to be resilient to some common ways of tampering.

Multi-radio multi-channel wireless mesh networks (WMNs) have been the focus of numerous research efforts during the past few years. These efforts aimed at extending the utilization of technologies based on the IEEE 802.11 standard in large-scale communities and even for city wide networking. However, mesh nodes in these networks are typically limited in their resources (e.g., bandwidth, power and radio interfaces). Such a limitation has led to an unsatisfactory network performance as well as users dissatisfaction. This dissertation addresses three important performance issues related to WMNs, namely, network performance enhancement, network survivability and green communications. To address the first issue, a novel quality of service (QoS) aware joint channel assignment (CA) and routing algorithm is developed. The proposed algorithm employs both dynamic and static CA techniques and corresponding link schedules that maximize the network throughput and minimize the delay and packet loss ratio. Next, the thesis addresses the problem of network survivability and theoretically analyzes the effects of node failure probabilities on the ability of the remaining network nodes to maintain their connectivity. A tight upper bound on the node failure probabilities needed to maintain full network connectivity on the one hand is first developed. On the other hand, a lower bound, at which the system loses connectivity, is also derived. We show that these bounds are dependent only on the nodes' geometric distribution and density. Based on the premise that failure of nodes in a small area may lead to failure of dependent nodes in other areas due to the quick divergence of traffic in these areas, an efficient node failure backup scheme is presented. The scheme relies on the capacity of the surviving network components in order to find new paths that do not overload the neighbours of the failed node which reduces the probability of generating congestion. Finally, the thesis addresses the problem of realizing energy-efficient WMNs that can operate using renewable energy sources. In these systems, batteries are often used to store and regulate the use of the supplied green energy to transmit the received data at each network router in order to overcome the problem of supply fluctuating of various energy sources. To realize these networks, the behaviour of the residual energy of the battery at a heavily loaded green wireless mesh node with a general traffic arrival and energy charging functions is first analyzed. Based on obtained theoretical results, both an online and an offline QoS aware packet scheduling schemes are proposed to minimize the probability of depleting the battery. Each of the aforementioned contributions is supported with various experimental evaluations to demonstrate the achieved performance enhancements.

Ce travail de thèse présente trois contributions qui portent sur le routage et la fourniture de qualité de service dans les réseaux maillés sans fil basés sur IEEE 802.11. La première contribution définit une métrique de routage qui permet de sélectionner les chemins empruntant des liens avec de bonnes performances exprimées en termes d’interférences physiques (qui causent des pertes), d’interférences logiques (qui causent des délais) et de capacité. L’évaluation de cette métrique par rapport aux principales métriques de la littérature scientifique montre une amélioration des performances du réseau. La deuxième contribution concerne l’amélioration du mécanisme de maintenance de route le plus souvent utilisé par les protocoles de routage réactifs. Ce mécanisme considère qu'une route est coupée si l'un de ses liens observe plusieurs échecs successifs de retransmission. Nos études montrent que ces échecs sont assez souvent dûs à de problèmes transitoires sur les liens (bruit, interférence etc.). Nous avons donc proposé des algorithmes de maintenance de route qui appréhendent mieux les problèmes ponctuels ou soutenus sur les liens ce qui permet de prendre une décision cohérente et réfléchie quant à la coupure d’un lien (et donc d'une route). Les études de performances montrent une amélioration conséquente des performances globales du réseau. La dernière contribution propose un cadre pour la fourniture de la Qualité de Service (garantie de bande passante) dans les réseaux maillés multi-interfaces, multi-canaux. Ce cadre intègre un protocole de routage réactif couplé à un mécanisme de contrôle d'admission et de partage de charge. Ces derniers exploitent la diversité des liens entre nœuds voisins afin d’améliorer le taux d’admission des flux avec garantie de bande passante / This thesis presents three contributions in the area of routing and Quality of Service for IEEE 802.11-based Wireless Mesh Networks. The first contribution defines a routing metric for the selection of route by taking into consideration the performance of wireless links in terms of physical interference (which causes packet losses), logical interference (which causes delay) and the capacity of the links. The performance evaluation of the proposed metric compared to the popular existing metrics shows an improvement in the performance of the network. The second contribution improves the route maintenance mechanism most often used by reactive routing protocols. The existing mechanism considers a route as broken if any of the links in the route experiences multiple successive transmission failures. Our study shows that the transmission failures are often caused by transient problems on the wireless link (noise, interference etc). We propose a novel mechanism of route maintenance which distinguishes between links with temporary or transient transmission problems compared to those with sustained problems in order to make a coherent decision about link breakage (and consequently route breakage). The performance evaluation shows a substantial improvement in the performance of the network. The final contribution proposes a framework for providing Quality of Service (bandwidth guarantee) in multi-radio multi-channel wireless mesh networks. The framework integrates a reactive routing protocol coupled with an admission control mechanism and load balancing. The framework exploits link diversity between neighboring nodes to improve the flow admission ratio with bandwidth guarantees

Thesis (MSc.) -- University of Limpopo, 2017 / The notion of ubiquitous computing, Internet of things (IoT), big data, cloud computing and other emerging technologies has brougt forward the innovative paradigms and incredible developments in wireless communication technologies. The Wireless Mesh Networks (WMNs) technology has recently emerged as the promising high speed wireless technology to provide the last mile broadband Internet access and deliver flexible and integrated wireless communication solutions. The WMNs has the potential to enable people living in rural, peri-urban areas and small businesses to interconnect their networks and share the affordable Internet connectivity. The recent multimedia applications developed, such as voice over Internet protocol (VoIP), online gaming, cloud storage, instant messaging applications, and video sharing applications require high speed communication media and networks. These applications have witnessed enormous growth in the recent decade and continue to enhance communication amongst the users. Hence, the WMNs must have adequate capacity to support high bandwidth and real-time and multimedia applications. While the wireless communications networks are dependent on the radio frequency (RF) spectrum, the traditional wireless technologies utilise the RF spectrum bands inefficiently, resulting in sporadic and underutilisation of the RF spectrum. This inefficient usage of RF spectrum calls for novel techniques to leverage the available RF spectrum amongst different players in the wireless communication arena. There have been developments on integration of the WMNs with cognitive ratios to allow unlicensed users of RF spectrum to operate in the licensed portions of spectrum bands. This integration will provide the required bandwidth to support the required high speed broadband communication infrastructure. In this dissertation, we focus our research on the routing layer in a multi-hop wireless network environment. We addressed the routing challenges in both the WMNs and the cognitive radio based wireless mesh networks (CR-WMNs). The primary focus was to identify the routing protocols most suitable for the dynamic WMN environment. Once identified, the routing protocol was then ported to the CR-WMN environment to evaluate its performance given all the dynamics of cognitive radio environment. vi We further proposed the routing protocol called the extended weighted cumulative expected transmission time (xWCETT) routing protocol for the CR-WMNs. The design of our proposed xWCETT routing protocol is based on the multi-radio multi-channel architecture as it gives the base framework matching the cognitive radio environment. The xWCETT integrates features from the Ad-hoc On-demand Distance Vector (AODV) routing protocol and the weighted cumulative expected transmission time (WCETT) routing metric. The xWCETT was implemented using the Cognitive Radio Cognitive Network (CRCN) patch ported in network simulator (NS2) to incorporate the shared and dynamic spectrum access features. We compared the performance of our proposed xWCETT routing protocol with the AODV, dynamic source routing (DSR), the optimised link source routing (OLSR), Destination Sequences Distance Vector (DSDV), and the CRCN-WCETT routing protocols. The extensive simulation and numerical results show that the proposed xWCETT protocol obtained on average, around 10% better performance results in the CR-WNNs as compared to its routing counterparts. The comparative analysis and evaluation was performed in terms of the average end-to-end latency, throughput, jitter, packet delivery ratio, as well as the normalised routing load. The performance results obtained indicates that the proposed xWCETT routing protocol is a promising routing solution for dynamic CR-WMNs environment. / National Research Foundation (NRF)