Integer Programming Formulation for Grouping Clusters in Ferry-assisted DTNs

Communication among isolated networks (clusters) in delay tolerant networks (DTNs) can be supported by a message ferry, which collects bundles from clusters and delivers them to a sink node. When there are lots of distant static clusters, multiple message ferries and sink nodes will be required. In this paper, we aim to make groups each of which consists of physically close clusters, a sink node, and a message ferry. Our main objective is minimizing the overall mean delivery delay of bundles in consideration of both offered load of clusters and distance between clusters and their sink nodes. We first model this problem as a nonlinear integer programming, based on the knowledge obtained in our previous work. Because it might be hard to solve this problem directly, we take two-step optimization approach based on linear integer programming, which yields an approximate solution of the problem. Through numerical results, we show the two-step optimization approach works well.