Ph.D. Thesis

Service Discovery and Compsition in Pervasive Environments

Service discovery and composition has been an active area of research in the domain of wired web-based environments as well as mobile and pervasive environments. The advent of mobile computing elements (handhelds) along with the concomitant development of wireless and ad-hoc networking technologies such as Bluetooth, 802.11, Infrared etc have recently led to the growth of infrastructure-less pervasive environments - environments that do not assume the existence of the umbilical cord: a stable network backbone. Examples of such environments range from war front activities, fire fighting, futuristic malls, and smart traffic scenarios to deep space exploration research. Services - resources, data as well as computation components are resident on heterogeneous devices and connected through heterogeneous networking technologies in such environments. These type of environments pose several interesting and challenging issues in the development of end applications that intend to utilize the resource-rich vicinity. Service discovery and composition are key technologies to enable end applications in such environments. Research in service discovery and composition has mostly focused on wired/web-based environments and infrastructure-based mobile and pervasive environments - environments where devices can connect to the stable network backbone and access services in the wired infrastructure. Understandably, architectures proposed for service discovery and composition are mostly centralized or semi-centralized and registry-based. However, such architectures are unsuitable for infrastructure-less pervasive environments. Current solutions for service discovery and composition in infrastructure-less environments are primarily broadcast-based and are inefficient in the utilization of networking and computing resources. Solutions focus on discovering services and composing them in a constrained network following a peer-to-peer model and do not address the issues of scalability and network-wide reachability. Moreover, issues of mobility and adaptability of protocols with respect to varying environments is also not addressed. This dissertation identifies key issues related to service discovery and composition in infrastructure-less pervasive environments. It proposes a conceptual architecture to enable integrated service discovery, servicecentric routing and service composition in infrastructure-less pervasive environments. We develop, implement and extensively evaluate distributed protocols at various layers of the conceptual architecture. The design of the architectures and the protocols use several cross-layer optimizations that improve the overall performance of the system. The primary contributions of this dissertation are the architecture and the novel and innovative protocols that enable distributed and integrated service discovery, service-centric routing and service composition in pervasive environments. Additionally, we also propose and evaluate a queuing theoretic formalism to model the service cache - the basic unit that affects discovery and composition protocols. We design an ontology grounded in Web Ontology Language (OWL), to describe services in pervasive environments in terms of its inputs and outputs, platform constraints and device capabilities. This information is used in various aspects of distributed discovery and composition in pervasive environments.

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University of Maryland, Baltimore County

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