HUBCODE: hub-based forwarding using network coding in delay tolerant networks

Most people-centric delay tolerant networks have been shown to exhibit power-law behavior. Analysis of the temporal connectivity graph of such networks reveals the existence of hubs, a fraction of the nodes, which are collectively connected to the rest of the nodes. In this paper, we propose a novel forwarding strategy called HubCode, which seeks to use the hubs as message relays. The hubs employ random linear network coding to encode multiple messages addressed to the same destination, thus reducing the forwarding overheads. Further, the use of the hubs as relays ensures that most messages are delivered to the destinations. Two versions of HubCode are presented, with each scheme exhibiting contrasting behavior in terms of the computational costs and routing overheads. We formulate a mathematical model for message delivery delay and present a closed-form expression for the same. We validate our model and demonstrate the efficacy of our solutions in comparison with other forwarding schemes by simulating a large-scale vehicular delay tolerant network using empirically collected movement traces of a city-wide public transport network. Under pragmatic assumptions, which account for short contact durations between nodes, our schemes outperform comparable strategies by more than 20%. Copyright © 2011 John Wiley & Sons, Ltd.