Delay Tolerant Networks (DTNs) are sparse mobile ad-hoc networks in which there is typically no complete path between the source and destination. Multicast is an important group communication paradigm that is required by many potential DTN applications, such as data dissemination during military and rescue operations. While multicasting has been studied extensively in the context of the Internet and Mobile Ad-Hoc Networks (MANETs), efficient multicasting in DTNs is a significantly different and challenging problem due to frequent partitions and intermittent connectivity among nodes. In this paper, we propose a two-level single-copy multicast routing strategy that optimizes both the computing resource usage and the delivery rate.

Furthermore, our scheme minimizes the transmission cost by bundling multiple multicast receivers into a single copy of the data packet, and forwarding it to an encounter node that has high delivery probabilities to those multicast receivers. This dynamic tree branching technique allows routing paths to be efficiently shared among multicast destinations. Lastly, we propose new methods to compute one-hop and multihop delivery probabilities that are used in forwarder selection. Through extensive simulation studies using a real-world mobility trace, we show that our scheme achieves a high delivery ratio, low delay, and low (or comparable) transmission cost compared to other multicast strategies.

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