Opportunities and limits of moderate source routing in delay-/disruption-tolerant networking space networks

This paper aims to investigate the potential advantages and also the limits of source routing when applied to delay-/disruption-tolerant networking (DTN) space networks. To this end, it uses a variant of contact graph routing (CGR) called moderate source routing (MSR), recently proposed by the authors and fully compatible with interplanetary overlay network (ION), the DTN suite developed by NASA-JPL. MSR differs from standard CGR as the route to destination is not recalculated from scratch at each node, but possibly reused, if still valid, by next nodes. For this purpose, the route is saved in a dedicated extension block of the forwarded bundle (the data unit of the bundle protocol, used in DTN). Performance of MSR versus CGR is assessed by considering a simple but very challenging space layout. Numerical results, obtained on a GNU/Linux testbed, show that MSR is effective at reducing the chances of loops, in particular when the source has full knowledge of the state of the network; otherwise, network instabilities are still possible. In this case, they can be neutralized by means of the combined use of source routing and anti-loop tools, as shown in the paper. A further advantage of MSR is that it is compatible with standard CGR, which would facilitate a gradual or partial deployment.