  With the current trend towards low Earth orbit mega-constellations with
inter-satellite links, efficient routing in such highly dynamic space-borne
networks is becoming increasingly important. Due to the distinct network
topology, specifically tailored solutions are required. Firstly, the relative
movement of the constellation causes frequent handover events between the
satellites and the terminals on ground. Furthermore, unevenly distributed
traffic demands lead to geographical hot spots. The physical size of the
network also implies significant propagation delays. Therefore, monitoring the
dynamic topology changes and link loads on a network-wide basis for routing
purposes is typically impractical with massive signaling overhead. To address
these issues, we propose a distributed load-balanced routing scheme based on
Software Defined Networking. The approach divides the large-scale network into
sub-sections, called clusters. In order to minimize signaling overhead, packets
are forwarded between these clusters according to geographical heuristics.
Within each cluster active Quality of Service-aware load-balancing is applied.
The responsible on-board network controller forwards routing instructions based
on the network state information in its cluster. We also analyze specific
design choices for the clusters and the interfaces between them. The protocol
has been implemented in a system-level simulator and compared to a
source-routed benchmark solution.
