Optimal Joint Expected Delay Forwarding in Delay Tolerant Networks

Multicopy forwarding schemes have been employed in delay tolerant network (DTN) to improve the delivery delay and delivery rate. Much effort has been focused on reducing the routing cost while retaining high performance. This paper aims to provide an optimal joint expected delay forwarding (OJEDF) protocol which minimizes the expected delay while satisfying a certain constant on the number of forwardings per message. We propose a comprehensive forwarding metric called joint expected delay (JED) which is a function of remaining hop-count (or ticket) and residual lifetime. We use backward induction to calculate JED by modeling forwarding as an optimal stopping rule problem. We also present an extension to allow OJEDF to run in delay constrained scenarios. We implement OJEDF as well as several other protocols and perform trace-driven simulations. Simulation results confirm that OJEDF shows superiority in delay and cost with acceptable decrease of delivery rate.