  In this paper we propose a novel architecture, CARD, for resource discovery
in large scale Mobile Ad hoc Networks (MANets) which, may scale up to thousands
of nodes and may span wide geographical regions. Unlike previously proposed
schemes, our architecture avoids expensive mechanisms such as global flooding
as well as complex coordination between nodes to form a hierarchy. CARD is also
independent of any external source of information such as GPS. In our
architecture nodes within a limited number of hops from each node form the
neighborhood of that node. Resources within the neighborhood can be readily
accessed with the help of a proactive scheme within the neighborhood. For
accessing resources beyond the neighborhood, each node also maintains a few
distant nodes called contacts. Contacts help in creating a small world in the
network and provide an efficient way to query for resources beyond the
neighborhood. As the number of contacts of a node increases, the network view
(reachability) of the node increases. Paths to contacts are validated
periodically to adapt to mobility. We present mechanisms for contact selection
and maintenance that attempt to increase reachability while minimizing
overhead. Our simulation results show a clear trade-off between increase in
reachability on one hand, and contact selection and maintenance overhead on the
other. Our results suggest that CARD can be configured to provide a desirable
reachability distribution for different network sizes. Comparisons with other
schemes for resource discovery, such as flooding and bordercasting, show our
architecture to be much more efficient and scalable.
