Considering Multi-Contact Encounters in Opportunistic Networks.

Opportunistic networks, often characterized by their intermittent connectivity and sparsity of nodes, has sparked routing in these networks to focus on isolated contact opportunities. Routing has predominantly been viewed as an exchange of messages between a pair of nodes. In this paper, we take a new look at contact opportunities, specifically focusing on the occurrence of having multiple simultaneous node contacts. Multi-contact encounters warrants a more holistic view of routing decisions, where more factors than just the features of a message-node tuple can be considered. We discuss these aspects and propose a protocol addition to leverage multi-contact opportunities with the notion of heterogeneous link quality, in order to limit energy consumption. The approach, implemented for the Epidemic, Spray-and-Wait and PRoPHETv2 protocols, re-evaluates routing decisions, weighting the routing metrics value against the estimated cost of the relay. Results indicate a two to three fold decrease in the number of messages lost, as well as a reduction in message relays, while maintaining a high delivery ratio for all three protocols.