|Title:||Reliable service discovery and access in pervasive computing environments|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Service-oriented architecture (Computer science)
Wireless communication systems -- Quality control
|Department:||Department of Computing|
|Pages:||xix, 180 p. : ill. ; 31 cm.|
|Abstract:||Service discovery is one of the fundamental services in pervasive computing. Different services are provided by various portable devices which are interconnected in an ad hoc manner. However ensuring reliable service discovery and seamless service access is a desirable as well as challenging task in highly dynamic pervasive environments. Given the mobility and resource-constraints of pervasive devices and the unreliability of wireless connection, service unavailability can frequently occur in pervasive environments due to service provider failure, network partitioning, or service scope outage by service provider or user mobility. Due to the resource limitation of mobile nodes service discovery protocols must be message efficient which implies consumption of less bandwidth as well as lower processing overhead. Moreover, devices can suddenly fail, get disconnected or depart the network in which case, the services may become unavailable. Existing service discovery protocols did not adequately address the issues in providing users with continuous service access at all the times in an autonomous and proactive manner. In this research we address the challenging issues and make the following original contributions in this field. Firstly, we propose a directory community framework which works as the basis of our research in reliable service discovery and access in ad hoc networks. The directory community framework consists of a set of directory nodes along with a suite of protocols and algorithms to collaboratively provide reliable service discovery and seamless service access supports for mobile users in ad hoc networks. The directory community is constructed by dynamically electing a set of devices as directory nodes. Because of the resource constraints of mobile nodes, we choose to elect resource-rich nodes with higher energy or computational capabilities as directories. We model the directory community formation problem as top-K weighted leader election in mobile ad hoc networks and develop a distributed algorithm to achieve the objective. Here, the weight indicates available node resources in terms of memory, processing power or energy. Our proposed directory election algorithm is scalable, reliable, message-efficient, and can handle dynamic topological changes in an efficient manner. Secondly, using afore-mentioned directory community, we propose a quorum-based fault-tolerant service discovery protocol. The elected directory nodes are divided into multiple quorums. Services registered with a directory are replicated among its quorum members, so that, upon the failure of a directory, services can still be available. This approach guarantees network-wide service availability using the quorum intersection property and reduces replication and update costs by minimizing the quorum size. Finally, based on the directory community, we develop a reliable and continuous service access mechanism for mobile users which works using service handoff. Service handoff provides mobile users seamless service access by proactively finding new matching services once the original service becomes unavailable. The proposed service handoff mechanism has two steps handoff initiation and new service provider selection. Three different service handoff protocols have been designed for different situations. Our handoff protocols can reduce handoff message cost and time delay while achieving a load balance on service providers.|
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