Contact Graph Routing enhancements for delay tolerant space communications

In this paper we present two enhancements to Contact Graph Routing (CGR), a Delay-/ Disruption- Tolerant Networking routing algorithm developed by NASA JPL for space environments with predetermined connectivity schedules, such as Interplanetary communications and LEO satellite systems. The first enhancement, CGR-ETO, aims to improve the accuracy of predicted bundle delivery time by considering the available information on queueing delay. The second, the Overbooking Management, aims to proactively handle contact oversubscription, which occurs when high priority bundles are forwarded for transmission on a contact that is already fully subscribed by lower priority bundles. Both enhancements have been inserted as optional features in the Interplanetary Overlay Network CGR implementation in order to comparatively evaluate their performance on a GNU/Linux testbed running the full protocol stack. The results show that the two enhancements are complementary and can significantly improve routing decisions compared to standard CGR.