A joint relay selection and buffer management scheme for delivery rate optimization in DTNs

Abstract

Due to the unstable network topology of Delay Tolerant Networks (DTNs), multi-copy routing is often used to increase the reliability of message delivery. However, this routing approach suffers from 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 maximize the delivery rate in DTNs. We consider a realistic DTN environment with resource constraints, heterogeneous node mobility, and varied message sizes. There are three key issues in DTN routing: (1) to which next hop relay node should messages be replicated, (2) in which order should messages be replicated, and (3) which messages should be dropped first when the buffer is full. We propose to forward a message to a neighboring node that has both a stronger social tie with the destination and a smaller or similar queue length. This aims to reduce traffic at highly connected network nodes, avoiding frequent message drops which compromise the delivery ratio. For the second and third issue, we develop a utility function using global network information to compute per-packet delivery rate 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 achieve a delivery rate of up to 22% higher than existing schemes, while still maintaining a comparable average delivery delay. Furthermore, our scheme distributes the network loads more evenly, with the top 10% of network nodes handling only 24% of the forwardings.