Applied Formal Methods in Wireless Sensor Networks

This work covers the application of formal methods to the world of wireless sensor networks. Mainly two different perspectives are analyzed through mathematical models which can be distinct for example into qualitative statements like "Is the system error free?" From the perspective of quantitative propositions we investigate protocol optimal parameter settings for an energy efficient operation

Evaluierung der Energie-Effizienz von Sicherheitsmechanismen in drahtlosen Sensornetzen

Im Rahmen dieser Arbeit wurde der Einfluss verschiedener Faktoren auf den Energiebedarf von Sicherheitsmechanismen in drahtlosen Sensornetzen evaluiert. Im Mittelpunkt der Untersuchungen stand insbesondere der Einfluss des Medienzugriffsverfahrens auf den Energiebedarf von (hardwarebasierten) Sicherheitsmechanismen. Als Evaluierungswerkzeuge kam dabei neben dem Testbed SANDBed auch der Simulator AVRORA+ zum Einsatz, dessen Energiemodell im Rahmen dieser Dissertation entstand

Self-Organizing Directional Wireless Backbone Networks

Directional wireless communications is emerging as a viable, cost-effective technology for rapidly deployable broadband wireless communication infrastructures. This technology provides extremely high data rates through the use of narrow-beam free space optical (FSO) and/or radio-frequency (RF) point-to-point links. The use of directional wireless communications to form flexible backbone networks, which provide broadband connectivity to capacity-limited wireless networks or hosts, promises to circumvent the scalability limitations of traditional wireless networks. The main challenge in the design of directional wireless backbone (DWB) networks is to assure robustness and survivability in a dynamic wireless environment. DWB networks must assure highly available broadband connectivity and be able to regain connectivity in the face of loss or degradation. This dissertation considers the use of topology control to provide assured connectivity in dynamic environments. Topology control is defined as the autonomous network capability to dynamically reconfigure its physical topology. In the case of DWB networks, the physical topology can be reconfigured through 1) redirection of point-to-point links and/or 2) reposition of backbone nodes. Coverage and connectivity are presented as the two most important issues in DWB-based networks. The aim of this dissertation is to provide initial designs for scalable self-organized DWB networks, which could autonomously adapt their physical topology to maximize coverage to terminals or hosts while maintaining robust backbone connectivity. This dissertation provides a novel approach to the topology control problem by modeling communication networks as physical systems where network robustness is characterized in terms of the system's potential energy. In our model, communication links define physical interactions between network nodes. Topology control mechanisms are designed to mimic physical systems' natural reaction to external excitations which drive the network topology to energy minimizing configurations based on local forces exerted on network nodes. The potential energy of a communications network is defined as the total communications energy usage for a given target performance. Accurate link physics models that take into account the variation of the wireless channel due to atmospheric attenuation, turbulence-induced fading, node mobility, and different antenna patterns have been developed in order to characterize the behavior of the potential energy stored at each wireless link in the network. The net force at each backbone node is computed as the negative gradient of the potential energy function at the node's location. Mobility control algorithms are designed to reposition backbone nodes in the direction of the net force. The algorithms developed are completely distributed, show constant time complexity and produce optimal solutions from local interactions, thus proving the system's self-organizing capability

Anycast services and its applications

Anycast in next generation Internet Protocol is a hot topic in the research of computer networks. It has promising potentials and also many challenges, such as architecture, routing, Quality-of-Service, anycast in ad hoc networks, application-layer anycast, etc. In this thesis, we tackle some important topics among them. The thesis at first presents an introduction about anycast, followed by the related work. Then, as our major contributions, a number of challenging issues are addressed in the following chapters. We tackled the anycast routing problem by proposing a requirement based probing algorithm at application layer for anycast routing. Compared with the existing periodical based probing routing algorithm, the proposed routing algorithm improves the performance in terms of delay. We addressed the reliable service problem by the design of a twin server model for the anycast servers, providing a transparent and reliable service for all anycast queries. We addressed the load balance problem of anycast servers by proposing new job deviation strategies, to provide a similar Quality-of-Service to all clients of anycast servers. We applied the mesh routing methodology in the anycast routing in ad hoc networking environment, which provides a reliable routing service and uses much less network resources. We combined the anycast protocol and the multicast protocol to provide a bidirectional service, and applied the service to Web-based database applications, achieving a better query efficiency and data synchronization. Finally, we proposed a new Internet based service, minicast, as the combination of the anycast and multicast protocols. Such a service has potential applications in information retrieval, parallel computing, cache queries, etc. We show that the minicast service consumes less network resources while providing the same services. The last chapter of the thesis presents the conclusions and discusses the future work

Link Delay Inference in ANA Network

Estimating quality of service (QoS) parameters such as link delay distribution from the end-to-end delay of a multicast tree topology in network tomography cannot be achieved without multicast probing techniques or designing unicast probing packets that mimic the characteristics of multicast probing packets. Active probing is gradually giving way to passive measurement techniques. With the emergence of next generation networks such as Autonomic Network Architecture (ANA) network, which do not support active probing, a new way of thinking is required to provide network tomography support for such networks. This thesis is about investigating the possible solution to such problem in network tomography. Two approaches, queue model and adaptive learning model were implemented to minimized the uncertainty in the end-to-end delay measurements from passive data source so that we could obtain end-toend delay measurements that exhibit the characteristics of unicast or multicast probing packets. The result shows that the adaptive learning model performs better than the queue model. In spite of its good performance against the queue model, it fails to outperform the unicast model. Overall, the correlation between the adaptive learning model and multicast probing model is quite weak when the traffic intensity is low and strong when the traffic intensity is high. The adaptive model may be susceptible to low traffic. In general, this thesis is a paradigm shift from the investigation of ”deconvolution” algorithms that uncover link delay distributions to how to estimate link delay distributions without active probing.Master i nettverks- og systemadministrasjo

Model Checking and Model-Based Testing : Improving Their Feasibility by Lazy Techniques, Parallelization, and Other Optimizations

This thesis focuses on the lightweight formal method of model-based testing for checking safety properties, and derives a new and more feasible approach. For liveness properties, dynamic testing is impossible, so feasibility is increased by specializing on an important class of properties, livelock freedom, and deriving a more feasible model checking algorithm for it. All mentioned improvements are substantiated by experiments

Opportunistische Weiterleitung von netzwerkcodierten Multicast-Übertragungen in drahtlosen Sensornetzen

In dieser Dissertation wird ein Kommunikationsschema für drahtlose Sensornetze entwickelt, welches die Multicast-Kommunikation unterschiedlicher Anwendungen mittels Netzwerkcodierung überlagert. Eine besondere Herausforderungen stellen hierbei die Eigenschaften drahtloser Sensornetze dar. Die eingeschränkte Netzwerkkapazität beschränkt zugleich das erreichbare Maximum der handhabbaren Datenmenge