  Dynamic replication is a wide-spread multi-copy routing approach for
efficiently coping with the intermittent connectivity in mobile opportunistic
networks. According to it, a node forwards a message replica to an encountered
node based on a utility value that captures the latter's fitness for delivering
the message to the destination. The popularity of the approach stems from its
flexibility to effectively operate in networks with diverse characteristics
without requiring special customization. Nonetheless, its drawback is the
tendency to produce a high number of replicas that consume limited resources
such as energy and storage. To tackle the problem we make the observation that
network nodes can be grouped, based on their utility values, into clusters that
portray different delivery capabilities. We exploit this finding to transform
the basic forwarding strategy, which is to move a packet using nodes of
increasing utility, and actually forward it through clusters of increasing
delivery capability. The new strategy works in synergy with the basic dynamic
replication algorithms and is fully configurable, in the sense that it can be
used with virtually any utility function. We also extend our approach to work
with two utility functions at the same time, a feature that is especially
efficient in mobile networks that exhibit social characteristics. By conducting
experiments in a wide set of real-life networks, we empirically show that our
method is robust in reducing the overall number of replicas in networks with
diverse connectivity characteristics without at the same time hindering
delivery efficiency.
