Nullspace-based stopping conditions for network-coded transmissions in DTNs

Abstract

In a challenged network environment, where end-to-end connectivity may be a rare occurrence, delay-tolerant routing protocols must strike a balance between the increased robustness and reliability that comes with message replication and the resulting high bandwidth and storage overhead. Network coded routing, in which a node combines messages from different sources, has been shown to increase reliability in the presence of link failures with small additional overhead. A drawback of network coded routing is the lack of a natural stopping condition to control the dissemination of data. We describe an enhanced coding router that uses the mathematical structure of the orthogonal complement, or nullspace, as an improved stopping condition to eliminate redundant transmissions, and an additional technique to balance multiple coded data flows. These changes are incorporated into the DTN2 Reference Implementation and evaluated in two types of experiments. In a simple data-mule scenario, our EBR router comes very close to perfect efficiency. In a more complicated scenario with segmented communities and occasional nodes moving between them, our solutions show a drastic improvement in delivery rates.