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

Shenshen Luan (Beihang University), Wenting Wei, Mingliang Ke (Xidian University), Dongxu Hou, Min Xiao (ZTE)

• Why: Not the PM's domain — but a fresh routing idea: instead of fighting topology churn in LEO constellations, exploit the toroidal symmetry of Walker-Delta constellations to get microsecond convergence with almost no state. It's a reminder that geometric structure can replace protocol machinery.
• What: SDAF performs failure-driven reverse-flow forwarding using only local link-state detection and a static Interface Symmetry Mapping Table — no control-plane convergence, no protocol extensions, no header changes. Compatible as-is with OSPFv3, IS-IS, MPLS.
• How: On detecting a failed egress, a node tags packets by ingress port; when egress matches ingress (packet returning to its origin arc), it reverse-forwards along the ring's major arc to a Phase Transition Point, then resumes forward flow. Two policies — RF-CF (counter-facing detour first, best for intra-orbit failures) and RF-LF (lateral-facing first, best for inter-orbit) — scale from ring to torus. Simulation on a 16×16 torus: up to 17.5% packet-loss reduction vs. normal forwarding under link faults, RF-LF best. Real 5-router ring experiments with OSPFv3: total packet loss drops by ~3 orders of magnitude (e.g., 310 vs. 432,485 packets), microloop loss eliminated, black-hole loss near zero, latency/jitter comparable, peak congestion reduced from 3,000 to 2,000 Mbps.
• Where applicable: LEO constellations with torus-like topology only, and only while the topology remains connected — a partitioned network needs higher-layer recovery. Individual draft (-00) seeking RTGWG feedback on whether the problem is even in scope. The evaluation is simulation plus a small physical testbed, not a production constellation.