Use of contact duration for message forwarding in intermittently connected mobile networks

Several routing schemes have been proposed for intermittently connected mobile networks. In these schemes, a node carries a message and forwards the message to another node when they meet. To increase the delivery success rate and reduce the message delivery delay, the node to forward the message is selected based on such criteria as the probability that the node is likely to meet the destination. However, even if a node is suitable under such criteria, the contact duration may be too short to complete the message forwarding, which is called 'forwarding failure' in this paper. The risk of forwarding failure due to link disconnection during transmission has been mostly ignored in the existing routing schemes. In this paper we focus on avoiding forwarding failure. To this end, a large message is divided into smaller fragments, and we present a mathematical model to derive the optimal fragment size that minimizes message delivery delay. We then present a run-time algorithm which determines whether a current message fragment should be forwarded to a node encountered. Contact duration with the candidate node is estimated for this decision. Delayed forwarding and transmission power adjustment is incorporated into this algorithm to enhance energy efficiency of message forwarding. The benefits and feasibility of the proposed scheme are extensively evaluated by simulations and experiments.