Communication in disruption tolerant networks: models, analyses and routing
Many scenarios for mobile and wireless networks demonstrate disruptions in communications where connections may not be available from time to time, examples include wireless sensor networks, tactical mobile ad hoc networks, planetary networks and vehicular networks. The intermittent connection could be a result of the mobility of wireless nodes, the limited transmission range, communication jamming or the low nodal density. To deal with the problems, Disruption Tolerant Networking (DTN) has been proposed to handle the disconnection based on a store-carry-forward paradigm. Among the approaches for reducing the communication latency in DTN, introducing the relay nodes called throw-box has been proved to be an effective one. However few studies have provided sufficient analysis and routing solutions for throw-box based network paradigm. This dissertation addresses several challenging issues relating to wireless networks, and specifically, DTN. Firstly, we study the issue of connectivity by focusing on the transition phase of wireless network from a state of partition to a state of connection according to the growth of node density. A percolation theory based model is proposed to derive the lower bound and the upper bound of critical density and further find the critical time points that mark the network transformation from partition to connected state. The second work is to analyze the latency of message dissemination in the throw-box assisted DTNs. In this network architecture, static wireless devices called throw-boxes are deployed to increase message delivery probability and to reduce transmission latency. The research works include modeling the message delivering process among throw-boxes and modeling the latency distribution for message collection. Finally, we propose efficient routing strategies for the throw-box assisted DTNs. In such a network, the mobile nodes traveling between the throw-boxes form time-dependent network links which carry the temporally stored messages from one box to another. Our protocol is designed to consider jointly the capacity of mobile nodes and the time-dependent delay. A Markov model is proposed to describe the evolution of the real-time link, and to help derive the forwarding decision and routing policy. Our trace based simulation validates the advantages of the proposed routing strategy.