A DTN Routing and Buffer Management Strategy for Message Delivery Delay Optimization

Delay Tolerant Networks (DTNs) are sparse mobile ad-hoc networks in which there is typically no complete path between the source and destination. To increase the reliability of message delivery, multi-copy routing is often used at the expense of high buffer and bandwidth overhead. While much work has been done in the design of forwarding algorithms, little work has focused on studying forwarding under the presence of resource constraints such as short contact durations and small buffers. In this paper, we investigate a multi-copy routing strategy and a buffer management policy that minimize the average message delivery delay in DTN networks with resource constraints. We focus on three key issues: (1) to which next hop relay node should messages be replicated, (2) in which order should messages be replicated when contact duration and forwarding bandwidth are limited, and (3) which messages should be dropped first when the buffer is full. We propose to forward a message to a neighboring node with the least expected minimum delay among all possible routes to the message´s destination. For the second and third issue, we develop a utility function using global network information to compute per-packet average delay utility. Messages are then scheduled and dropped according to their utility values. Extensive simulation results based on the real-world San Francisco cab trace show that our proposed scheme can deliver messages in up to 30% less time than existing schemes, while still achieving a high delivery ratio.