Routing in hybrid Delay Tolerant Networks

Delay Tolerant Networks (DTNs) have emerged as communication paradigm for providing endto-end routing based on opportunistic forwarding, without the need for costly infrastructure. Nevertheless, empirical studies have shown that opportunistically integrating encountered infrastructure—e. g. Internet access via WiFi—into hybrid DTNs can significantly boost routing performance. However, designing hybrid DTNs is both complex and poorly understood. In this paper, we present the overlay-based Hybrid Routing System (HRS) which is—to the best of our knowledge—the first decentralized and collaborative routing approach for hybrid DTNs that does not rely on central servers. With HRS, a large class of existing DTN protocols can now benefit from nondeterministic infrastructure encounters. We characterize this class in an extensive analysis of existing DTN protocols, and exemplarily integrate three prominent representatives (Prophet, MaxProp, and Spray&Focus) into HRS. In an extensive simulation study we show that (1) routing towards the infrastructure in a first step is the dominating strategy for these protocols, and (2) HRS effectively bridges geographic distances via the Internet without heavy message replication. In summary, hybrid routing significantly boosts DTN performance as, e. g., only 30% of nodes with Internet access increase delivery probability by 250% for MaxProp in the considered setting.