Distributed communication in Disruption Tolerant Network

With the widespread use of mobile wireless devices, a distributed network infrastructure without heavily relying on centralized servers becomes possible when nodes cooperate with each other. There are challenging issues that need to be addressed in this new direction, especially in Disruption (Delay) Tolerant Networks (DTN). We focus our work on three areas of problem study in DTN, including data storage, security and the use of directional antennae in improving DTN performance. In this thesis, we first describe a novel distributed storage protocol in DTN. We define local distributed location regions which are called cells to facilitate the data storage and lookup process. Our protocol resorts to storing data items in cells which have a hierarchical structure to reduce the storage space for mapping related information. A data item is mapped and stored in a node in the lowest level cell using Peer-to-Peer (P2P) techniques. We then describe a novel Distributed Key Establishment (DKE) protocol in Disruption (Delay) Tolerant Location Based Social Wireless Sensor and Actor Networks (DTLBS-WSAN). In DKE, we propose that sensor nodes use neighboring signatures to establish their keys. Pre-distributed keys are used by actor nodes to strengthen communication security. In DTLBS-WSANs, key (certificate) establishment, storage and lookup are performed in a distributed way. Multiple copies of a certificate can be stored at nodes to improve key security and counter network disruptions. After that, we address the neighbor discovery issue when directional antennae are available. We explore the neighbor discovery using only directional antennae first, propose deterministic and randomized algorithms for wireless networks. The deterministic algorithms use knowledge of the vertex coloring for efficient neighbor discovery while the randomized algorithms require knowledge only of an upper bound on the size of the network. Finally, we study the neighbor discovery issue using sensors having two antennae patterns and propose a cooperative approach to speed up neighbor discovery. Nodes use short range omnidirectional antennae to find nearby nodes and use long range directional antennae to find neighbors that can not be found otherwise. Neighboring nodes cooperate with each other to reduce delays and improve energy efficiency.