Routing in future space-terrestrial integrated networks with SATNET-OSPF

Abstract

Connectivity in satellite networks is governed by the spacecraft nodes' orbital dynamics together with the planet's continuous rotation where ground nodes are located. The resulting time-dynamic but predictable topology demands the design of specific distributed routing schemes. However, terrestrial Internet routing schemes' maturity, proven scalability, and efficiency shall be leveraged whenever possible to facilitate space-terrestrial integration while reducing risk and costs. In line with this reflection, we introduce SATNET-OSPF: a backward-compatible satellite extension for the widely used Open Shortest Path First routing protocol. The key features of SATNET-OSPF are (a) accurate routing interface mapping to inter-satellite links and ground-to-satellite links, (b) accelerated link-up/link-down event detection adapted to space-specific wireless technologies, (c) proactive routing and forwarding mechanism to take advantage of predicted link-down events, and (d) low memory footprint topology model to efficiently propagate the forthcoming space connectivity events via constrained telecommand links. Leveraging existing IPv6 and OSPFv3 open-source stacks, we implemented SATNET-OSPF in an actual space router comprising a space-grade SPARC V8 CPU and a radiation-hardened FPGA. Furthermore, we present the details of an emulation test bench supporting various configurations with COTS terrestrial OSPF routers that enabled a realistic performance evaluation of the SATNET-OSPF. Results show that SATNET-OSPF reduced OSPFv3 routing protocol overhead by up to 31%; shortened the link event detection delay by four orders of magnitude; decreased the routing outage by a factor of 22; and ensured flooding control message generation and forwarding times, as well as routing computing time, satisfy the original requirements (192, 37, and 17 ms, respectively).