Time-constrained anycast routing under short contact duration in delay-tolerant networks

Delay-tolerant networks (DTNs) are sparse mobile ad hoc networks, in which there is typically no complete path between the source and destination. Anycast is an important group communication paradigm for numerous DTN applications such as resource discovery and information exchange in emergency or crisis situations. Unlike unicast and multicast, which have been studied extensively in DTNs, few prior works have addressed the DTN anycast routing problem. Furthermore, they often ignore the time constraint and assume long contact durations in formulating the relay selection strategy. In this paper, we study a single-copy time-constrained anycast (TCA) routing under short contact duration. We address two key issues: (1) to which next hop relay node should messages be forwarded and (2) in which order should messages be forwarded. To reduce the transmission cost, we select relay nodes from both current and past contacts based on the one-hop and two-hop delivery probabilities, respectively. We derive the delivery probability from the distribution of inter-contact time and contact duration time. We address the case of exponential and Pareto distribution, which are the most popular assumptions in literature. For the message scheduling, messages with the highest delivery probability are prioritized to be transmitted first. Extensive simulation results based on Cabspotting and MIT Reality traces show that our scheme can achieve up to 29% higher delivery rate, 24% lower delay, and 36% lower transmission cost compared to other anycast routing strategies.