Schulte, Stefan

Interoperability is crucial for advancing blockchain technology, as many networks operate in isolation. Existing solutions are often inefficient or tailored to specific blockchains. This thesis introduces novel solutions for cross-blockchain communication with oracles utilizing threshold signatures and Zero-Knowledge Succinct Non-interactive Arguments of Knowledge (zk-SNARKs). Additionally, we integrate blockchain technology into Distributed Key Generation (DKG) protocols and present new protocols for cross-blockchain token transfers and smart contract calls, bridging the gaps between different blockchain networks.

The Internet of Things (IoT) leads to an ever-growing presence of ubiquitous networked IoT devices. The computational resources of these devices, which can be used not only for collecting data but also for data processing, are often neglected. Being located at the network edge, these resources can be exploited to execute IoT applications in a distributed manner. The combination of the IoT devices at the edge and resources in the cloud opens doors to novel IoT scenarios and use cases, for example, smart cities. This new paradigm, which seamlessly considers technology, infrastructure, and computations from the edge to the cloud, is known as fog computing. While the theoretical foundations of fog computing have been already established, there is a lack of concrete approaches to enable the efficient exploitation of fog-based computational resources. Particular challenges of adopting these resources in the fog are the adherence to the geography of data sources, the reliability and fault tolerance of computational resources of IoT devices, and the delay-sensitivity of IoT applications. In order to enable the efficient exploitation of fog-based computational resources, this thesis introduces fog colonies, which resemble mini data centers consisting of devices at the edge of the network and in the cloud. A multitude of fog colonies forms a fog landscape, where we aim to enable IoT application execution. For that, we introduce a conceptual architecture and novel approaches for resource provisioning and service placement in the fog. We model resources and applications in the fog and formulate and solve the Fog Service Placement Problem to efficiently distribute IoT applications over fog resources. This thesis addresses the fundamental and critical issues that come along with the adoption of fog computing. The conceptual architecture for fog computing becomes the foundation for the fog computing framework FogFrame – a system able to manage and monitor edge and cloud resources in a fog landscape, and to execute IoT applications. We enable communication and interaction within the fog as well as provide application management, namely decentralized service placement, deployment, and execution. We show, through experiments in FogFrame, the performance of different resource provisioning approaches in a real-world fog as well as adaptations to volatile changes in the fog, balancing the workload, and recovering from failures.

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