On the Benefits of Random Linear Coding for Unicast Applications in Disruption Tolerant Networks

In this paper, we investigate the benefits of using a form of network coding known as Random Linear Coding (RLC) for unicast communications in a mobile Disruption Tolerant Network (DTN) under epidemic routing. Under RLC, DTN nodes store and then forward random linear combinations of packets as they encounter other DTN nodes. We first consider the case where there is a single block of packets propagating in the network and then consider the case where blocks of K packets arrive according to a Poisson arrival process. Our performance metric of interest is the delay until the last packet in a block is delivered. We show that for the single block case, when bandwidth is constrained, applying RLC over packets destined to the same node achieves (with high probability) the minimum delay needed to deliver the block of data. We find through simulation that RLC achieves smaller block delivery delay than non-network-coded packet forwarding under bandwidth constraint, and the relative benefit increases further when buffer space within DTN nodes is limited. For the case of multiple blocks, our simulations show that RLC offers only slight improvement over the non-coded scenario when only bandwidth is constrained, but more significant improvement when both bandwidth and buffers are constrained. We remark that when the network is relatively loaded, RLC achieves improvements over non-coding scheme only if the spreading of the information is appropriately controlled.