Stability properties of delay tolerant networks with buffered relay nodes

We study stability properties of single-source single-destination delay tolerant networks with random packet arrivals and buffered relay nodes, using source spray and wait routing. We derive the stability threshold, the supremum of arrival rates for which the source queue is stable, as a function of the buffer space at the relays. In particular, we show that the stability threshold only doubles as the relays' buffer size increases from one to infinity for a network without packet delivery feedback. For the system without packet delivery feedback, we propose lower bounds for the average queueing delay and average delivery delay for packets and compare with simulations. We also obtain the stability threshold numerically for a network with instantaneous packet delivery feedback.