Data communication over intermittently connected mobile ad hoc networks (ICMANs) can be carried out by opportunistically employment of mobility nature of nodes and the storage space of all nodes. In order to overcome mobility randomness and subsequently uncertainty of future network state, multi-copy-based routing approaches are widely considered. However, scalability is still an issue, even extra routing information such as mobility statistics and context is employed to control the number of message copies. This is because communicating overhead to exchange all such information still exponentially increases as network size increases. Therefore, this paper introduces an opportunistic virtual backbone (VBB) constructing algorithm to form a hierarchical architecture over ICMANs. Once VBB is formed, all routing information and multiple message copies are limited among the VBB members, and thereby routing overhead can be reduced dramatically. Different from the conventional unit disk graph (UDG) based solutions for MANETs, the proposed algorithm utilizes a weighted graph derived from mobility statistics to model underlying long-term stable topology of ICMANs. To reduce constructing overhead, only partial two-hop mobility statistics are collected by each node. Moreover, intermittent connectivity and delayed message transmission are also addressed in the paper. The simulation results indicate that the proposed algorithm is highly scalable as network size increases and the existing SCF routing protocols can work well over ICMANs where VBBs are formed.
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