| Traditional ad hoc routing protocols do not work in intermittently connected networks since end-to-end paths may not exist in such networks. Hence, routing mechanisms that can withstand disruptions need to be designed. A store-and-forward approach has been proposed for disruption tolerant networks. Recently, several approaches have been proposed for unicast routing in disruption-prone networks e.g. the 2-hop relay approach, delivery probability based routing, and message ferrying. In our earlier paper, we have evaluated a combined multihop and message ferrying approach in disruption tolerant networks. In that paper, we assume that a special node is designated to be a message ferry. A more flexible approach is to let regular nodes volunteer to be message ferries when network dynamics mandate the presence of such ferries to ensure communications. Thus, in this paper, we design a node-density based adaptive routing (NDBAR) scheme that allows regular nodes to volunteer to be message ferries when there are very few nodes around them to ensure the feasibility of continued communications. Our simulation results indicate that NDBAR scheme can achieve high delivery ratio in very sparse networks that are prone to frequent disruptions. |