Rock-Scissors-Paper cycle of cooperation strategies in Opportunistic Mobile Networks

Opportunistic Mobile Networks (OMNs) are characterized by intermittent connectivity among the nodes, which results in lack of end-to-end communication paths. The nodes depend upon the other nodes for forwarding their messages and, therefore, the intermediate nodes play the crucial role of cooperation in forwarding the messages of the others nodes. Many existing mechanisms - for example, incentive- and punishment-based schemes - are costlier in OMNs, since in both of these schemes it is required to trace the recipient nodes for providing credit/punishment. In this work, we study the problem of cooperation by considering three groups of nodes based on three strategies - cooperate, exploit, and isolate. The cooperators help the other nodes for forwarding their messages. The exploiters, on the other hand, use other nodes as free-riders without helping them in forwarding the messages. Finally, the isolators neither take help, nor provide so to the other nodes in forwarding the messages. We investigate the impact of such behaviors on the performance of message delivery using synthetic and real-life traces. The simulation results confirm the formation of a Rock-Scissors-Paper (RSP) cycle, when the sizes of the groups, and hence, the dominating strategy, varies. Further, the delivery ratio of the messages increases upto 20%-35%, when most of the nodes in the network choose to cooperate.