Stability and average delay in delay tolerant networks with Poisson packet arrivals and buffered relay nodes

Abstract

We consider a single-source single-destination delay tolerant network (DTN) with Poisson packet arrivals. The source uses a store and forward protocol which makes multiple copies of a packet to relays which buffer them until delivery to the destination. We characterize the stability threshold, defined as the maximum value of arrival rate for which the source has finite average queue length, as a function of number of relays, relay contact rate, relay packet buffer capacity, and number of packet copies. We analyse DTNs without packet delivery feedback and with instantaneous feedback. For DTNs without packet delivery feedback, we obtain a non-asymptotic analytical stability threshold and show that it only doubles as the relay-buffer capacity increases from one to infinity. For DTNs with instantaneous packet delivery feedback, we characterize the stability threshold using simulations. We also present an analytical approximation for the stability threshold in the case of unit relay-buffer capacity, and show that it is approximately double of that without feedback for large number of packet copies and relays. For DTNs with and without feedback, we also study the average delay performance through simulations. We obtain analytical approximations for the average delays of the packets for DTNs without feedback. We observe that the last-in-first-out relay to destination packet transmission policy has the minimum delay.