Benefits of Network Coding in Disruption Tolerant Networks
Résumé
In this report, we investigate the benefits of applying a form of network coding known as Random Linear Coding (RLC) to unicast communications in mobile Disruption Tolerant Networks (DTNs). Under RLC, DTN nodes store and forward random linear combinations of packets as they encounter other DTN nodes. We first consider RLC applied to a single block of K packets where (a) all K packets have the same source and destination, (b) the K packets have different sources but a common destination and (c) the K packets each have a different source/destination pair; we also consider the case where blocks of K packets arrive according to a Poisson bulk arrival process. The 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 to deliver the block of data. We find through simulation that the benefit over non-network-coded packet forwarding 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 benefits when both bandwidth and buffers are constrained. We remark that when the network is relatively loaded, the RLC scheme achieves improvements over non-coded schemes only if the spreading of the information is appropriately controlled.
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