Symmetry-Driven Asynchronous Forwarding with Fast Reroute for LEO Satellite Networks (SDAF)

Interior Gateway Protocols (IGPs) such as OSPF are commonly employed in satellite networks to address topology awareness and autonomous routing in response to link interruptions, link/node failures, and subsequent repairs. However, IGP-based approaches suffer from inherent limitations. Synchronization delays between the control plane and the forwarding plane can cause routing black holes, while asynchronous convergence across nodes may induce micro-loops (as described in prior work), leading to packet loss and congestion. These issues are particularly exacerbated in satellite networks characterized by highly dynamic topologies, long inter-satellite propagation delays, and constrained on-board computing resources. This document describes the Symmetry-Driven Asynchronous Forwarding (SDAF) mechanism, which leverages the intrinsic symmetry of toroidal topologies in satellite networks. Low Earth Orbit (LEO) satellite constellations are typically composed of multiple circular orbital planes, forming a toroidal topology by inter-satellite links. SDAF autonomously triggers and processes reverse flows based solely on local link-state information, without requiring control-plane convergence, protocol extensions, or packet header modifications. SDAF is fully compatible with existing protocols and technologies such as OSPFv3, IS-IS, and MPLS, and is specifically tailored to the resource-constrained nature of satellite systems. It achieves microsecond-scale convergence and low packet loss under failure conditions. Simulation results and tests conducted on actual satellite routers demonstrate that the SDAF mechanism significantly suppresses packet loss caused by routing black holes and micro-loops, while also alleviating link congestion and packet reordering issues.