>Magister Scientiae - MSc / Wi-Fi authentication mechanisms include central authentication, dynamic and distributed authentication and some encryption methods. Most of the existing authentication methods were designed for single-hop networks, as opposed to multihop Wi-Fi mesh networks. This research endeavors to characterize and compare existing Wi-Fi authentication mechanisms to find the best secure connection mechanism associated with Wi-Fi mesh network fragmentation and distributed authentication. The methodology is experimental and empirical, based on actual network testing. This thesis characterizes five different types of Wrt54gl firmware, three types of Wi-Fi routing protocols, and besides the eight Wi-Fi mesh network authentication protocols related to this research, it also characterizes and compares 14 existing authentication protocols. Most existing authentication protocols are not applicable to Wi-Fi mesh networks since they are based on Layer 2 of the OSI model and are not designed for Wi-Fi mesh networks. We propose using TincVPN which provides distributed authentication, fragmentation, and can provide secure connections for backbone Wi-Fi mesh networks.

A thesis submitted to the Faculty of Science and Agriculture in fulfilment of the Degree of Doctor of Philosophy in the Department of Computer Science at the University of Zululand, 2017 / InfrastructureWireless Mesh Networks (I-WMNs) are increasingly used to provide network connectivity and Internet access to previously under-served areas in the developing world. It is common for some of these deployments to be battery-powered due to a lack of electrical infrastructure in the targeted areas. Thus, the energy-efficiency of these networks gains additional importance. Topology Control (TC) has been previously reported to improve the energy-efficiency and network performance of wireless ad-hoc networks, including I-WMNs. However,simulation-based studies have been relied upon to reach these conclusions and the study of TC prototypes applicable to I-WMNs has largely been limited to design issues. Thus, the study of the efficacy of TC prototypes as a mechanism for improving energy-fficiency and network performance remains an open issue. The thesis addresses this knowledge gap by studying the dynamic, run-time behaviours and the network topologies created by two standards-compatible TC prototypes. This study provides unique insight into how the prototypes consume computational resources, maintain network connectivity, produce cumulative transceiver power savings and affect the workings of the routing protocol being employed. This study also documents the topology instability caused by transceiver power oscillations produced by the PlainTC prototype. A context-based solution to reduce transceiver power oscillations and the subsequent topology instability is proposed. This solution applies the Principal Component Analysis statistical method to historical network data in order to derive the weights associated with each of the identified context variables. A threshold value is defined that only permits a node to adjust its transceiver power output if the observed change in a node’s context exceeds the threshold. The threshold mechanism is incorporated into the PlainTC+ prototype and is shown to reduce topology instability whilst improving network performance when compared to PlainTC.The results obtained in this study suggest that I-WMN topologies formed by TC are able to closely match the performance of networks that do not employ TC. However, this study shows that TC negatively affects the energy efficiency of the network despite achieving cumulative transceiver power savings.

Internet rate control protocols, such as TCP, encounter severe performance problems in wireless mesh networks. Because wireless networks use shared communication channels, contention and interference can significantly degrade flow throughput and fairness. Existing research takes either an engineering-based or optimization-based approach to solve the performance problems. The engineering-based approach usually solves a specific observed problem, but does not necessarily optimize the overall performance. The optimization-based approach mathematically models the network to find the optimal resource allocation among competing flows. The model can lead to a distributed rate control algorithm with performance guarantees, but relatively little work has been done to verify that the algorithm leads to good performance in real networks. This dissertation develops a more accurate network optimization model, implements the derived distributed rate control algorithm in a mesh testbed, and discusses observations in the extensive experiments. We first synthesize models used for optimizing fair rate control for wireless mesh networks, and discuss their tradeoffs. We then propose a partial interference model which uses more accurate objective functions and constraints as compared to the binary interference model. Numerical results show that the partial interference model outperforms the binary interference model in all scenarios tested, and the results also suggest that partial interference should be modeled separately from contention. Our experimental results confirm the prevalence of partial interference in our mesh testbed, and show that the partial interference model results in significantly improved performance in a typical interference topology. We also observe a significant deviation between theory and practice, whereby, the assumption of a linear relationship between interfering links breaks in our experiments. We discuss several directions to further investigate this issue.

<p> Wireless mesh networks are now being used to deploy radio coverage in a large variety of outdoor applications. One of the major obstacles that these networks face is that of providing the nodes with electrical power and wired network connections. Solar powered mesh nodes are increasingly used to eliminate the need for these types of connections, making the nodes truly tether-less. In these types of networks however, the cost of the energy collection and storage components can be a significant fraction of the total node cost, which motivates a careful selection of these resources.</p> <p> This thesis focusses on key issues relating to the deployment and operation of solar powered wireless mesh networks. First, the problem of provisioning the mesh nodes with a suitable solar panel and battery configuration is considered. This is done by assuming a bandwidth usage profile and using historical solar insolation data for the desired deployment location. A resource provisioning algorithm is proposed based on the use of temporal shortest-path routing and taking into account the node energy-flow for the target deployment time period. A methodology is introduced which uses a genetic algorithm (GA) to incorporate energy-aware routing into the resource assignment procedure. Results show that the proposed resource provisioning algorithm can achieve large cost savings when compared to conventional provisioning methods.</p> <p> During post-deployment network operation, the actual bandwidth profile and solar insolation may be different than that for which the nodes were originally provisioned. To prevent node outage, the network must reduce its workload by flow controlling its input traffic. The problem of admitting network bandwidth flows in a fair manner is also studied. A bound is first formulated which achieves the best max/min fair flow control subject to eliminating node outage. The bound motivates a proposed causal flow control algorithm whose operation uses prediction based on access to on-line historical weather data. The results show that the proposed algorithm performs well when compared to the analytic bound that is derived for this problem.</p> <p> Finally, as user traffic evolves, the network resources need to be updated. This problem is considered using a minimum cost upgrade objective. A mixed integer linear programming (MILP) formulation is derived to obtain a lower bound on the network update cost. A genetic algorithm is used to determine practical cost-effective network resource upgrading. The results show that the proposed methodology can obtain significant cost savings.</p> / Thesis / Doctor of Philosophy (PhD)

The rapid advances in networking technology have enabled large-scale deployments of online video streaming services in today's Internet. In particular, wireless Internet access technology has been one of the most transforming and empowering technologies in recent years. We have witnessed a dramatic increase in the number of mobile users who access online video services through wireless access networks, such as wireless mesh networks and 3G cellular networks. Unlike in wired environment, using a dedicated stream for each video service request is very expensive for wireless networks. This simple strategy also has limited scalability when popular content is demanded by a large number of users. It is desirable to have a robust wireless access environment that can sustain a sudden spurt of interest for certain videos due to, say a current event. Moreover, due to the mobility of the video users, smooth streaming performance during the handoff is a key requirement to the robustness of the wireless access networks for mobile video users. In this dissertation, the author focuses on the robustness of the wireless mesh access (WMA) environment for mobile video users. Novel video sharing techniques are proposed to reduce the burden of video streaming in different WMA environments. The author proposes a cross-layer framework for scalable Video-on-Demand (VOD) service in multi-hop WiMax mesh networks. The author also studies the optimization problems for video multicast in a general wireless mesh networks. The WMA environment is modeled as a connected graph with a video source in one of the nodes and the video requests randomly generated from other nodes in the graph. The optimal video multicast problem in such environment is formulated as two sub-problems. The proposed solutions of the sub-problems are justified using simulation and numerical study. In the case of online video streaming, online video server does not cooperate with the access networks. In this case, the centralized data sharing technique fails since they assume the cooperation between the video server and the network. To tackle this problem, a novel distributed video sharing technique called Dynamic Stream Merging (DSM) is proposed. DSM improves the robustness of the WMA environment without the cooperation from the online video server. It optimizes the per link sharing performance with small time complexity and message complexity. The performance of DSM has been studied using simulations in Network Simulator 2 (NS2) as well as real experiments in a wireless mesh testbed. The Mobile YouTube website (http://m.youtube.com) is used as the online video website in the experiment. Last but not the least; a cross-layer scheme is proposed to avoid the degradation on the video quality during the handoff in the WMA environment. Novel video quality related triggers and the routing metrics at the mesh routers are utilized in the handoff decision making process. A redirection scheme is also proposed to eliminate packet loss caused by the handoff.

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This thesis studies multicasting high bandwidth media traffic in wireless mesh networks (WMNs). Traditional multicast methods use a single multicast tree to reach all destinations, and adapt the multicast rate to the destination with the worst path quality. This approach does not fully utilize the network resources nor distinguish the quality of service (QoS) requirements of different users. It also penalizes the users having better path quality and requiring higher QoS. In multi-hop transmissions, the end-to-end transmission rate is limited by the link with the worst transmission conditions. This makes it difficult to multicast high-bandwidth media traffic with good quality. Using multiple description coding (MDC), the source traffic can be split into multiple sub-streams, referred to as descriptions, each of which requires a much lower bandwidth and can be transmitted along separate paths. In this thesis, we study routing and QoS provisioning jointly for multicasting multiple description (MD) encoded media traffic in WMNs. Routing for the multiple descriptions is jointly studied, while considering the channel quality of different links in the network and QoS at individual destinations. The work in this thesis is divided into two parts. The first part (Chapters 3 and 4) considers balanced descriptions, each of which contributes equally to the quality of the recovered media at a destination, and we study the problem of power efficient multicasting for the MD-encoded media traffic in WMNs. In Chapter 3, single-hop transmissions are considered. That is, the access points (APs) that store the source traffic communicate with the destination nodes directly. We study two problems jointly, description assignments and power allocations. The former is to assign a description for each AP to transmit, and the latter is to allocate the transmission power for the APs. Different power efficiency objectives are considered, subject to satisfying the QoS requirements of the destination nodes. For each objective, an optimization problem is formulated and heuristic solutions are proposed. Chapter 4 extends the work to multi-hop transmissions, where relay stations (RSs) are available to forward the traffic from the APs to the destinations. We consider two different routing structures based on whether an RS is allowed to forward more than one description. The objective is to minimize the total transmission power of the APs and the RSs in the network, subject to the QoS requirements of the destinations. An optimum problem is formulated and then translated to an integer and linear programming problem, and a centralized scheme with much lower complexity is proposed. Following that, a distributed scheme, referred to as minimum weight k-path scheme, is proposed, which builds one multicast tree for each description. By permitting only neighboring nodes to exchange related information, the scheme allows each node to find its best parent node based on the additional transmission power needed to establish the link. The second part (Chapter 5) of the thesis considers unbalanced descriptions. Routing for the multiple descriptions is jointly considered with application layer performance, so that the maximum distortion of recovered media at the destinations is minimized. An optimization problem is first formulated, and a centralized scheme with lower complexity is proposed. The centralized scheme first finds a set of candidate paths for each destination based on a predefined set of criteria, then it iteratively expands the multicast trees by only merging the paths that minimize the maximum distortion for all destinations. A distributed scheme is also proposed by modifying the minimum weight k-path scheme. In the modified scheme, each RS makes a local decision to join different multicast trees based on the expected distortion among its connected downstream nodes. The proposed multicasting schemes require much lower implementation complexity, compared to the optimum solutions. The centralized scheme is more suitable for small size networks, and achieves close-to-optimum performance for a wide range of parameter settings. The distributed scheme only requires neighboring nodes to exchange information, and can be implemented to networks with a relatively large number of APs, RSs, and destination nodes. / Thesis / Doctor of Philosophy (PhD)