In this paper, we focus on the efficient routing of data among different areas in Delay Tolerant Networks (DTNs). In current algorithms, packets are forwarded gradually through nodes with higher probability of visiting the destination node or area. However, the number of such nodes usually is limited, leading to insufficient throughput performance. To solve this problem, we propose an inter-landmark data routing algorithm, namely DTN-FLOW. It selects popular places that nodes visit frequently as landmarks and divides the entire DTN area into sub-areas represented by landmarks. Nodes transiting between landmarks relay packets among landmarks, even though they rarely visit the destinations of these packets. Specifically, the number of node transits between two landmarks is measured tore present the forwarding capacity between them, based on which routing tables are built on each landmark to guide packet routing. Each node predicts its transits based on its previous landmark visiting records using the order-k Markov predictor. In a packet routing, a landmark determines the next hop landmark based on its routing table, and forwards the packet to the node with the highest probability of transiting to the selected landmark. Thus, DTN-FLOW fully utilizes all node movements to route packets along landmark paths to their destinations. We analyzed two real DTN traces to support the design of DTN-FLOW. We also deployed a small DTN-FLOW system in our campus for performance evaluation. This deployment and trace-driven simulation demonstrate the high efficiency of DTN-FLOW in comparison with state-of-the-art DTN routing algorithms.
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