Legible Consensus: Topology-Aware Quorum Geometry for Asymmetric Networks
This work addresses the challenge of improving fault tolerance and diagnostic clarity in consensus protocols for physically tiered networks, such as space-based systems, though it is incremental in its approach.
The paper tackled the problem of designing quorum systems for asymmetric networks by separating inter-tier obligations and intra-tier replication, resulting in a topology-aware quorum geometry that makes failure modes legible and confirms specific consensus latencies, such as 5.1 seconds for the Moon tier.
Quorum design over asymmetric topologies conflates two independent concerns: inter-tier obligation (which tiers must participate for cross-tier safety) and intra-tier replication (how each tier survives local failures). Flat quorums treat all nodes as interchangeable; when consensus fails, the structure does not reveal whether a tier was unreachable or a tier lost too many replicas. We show that mapping a crumbling-wall quorum construction to a physically tiered network separates these concerns and makes the protocol's failure modes legible: an operator can determine which tiers retain global consensus capability from the wall structure and connectivity state alone, without runtime probing. Using a 10-node Earth/LEO/Moon/Mars topology as a magnifying glass, we confirm that three of four tiers retain global liveness during Mars conjunction blackout; only the disconnected tier loses it. Consensus latency at each tier equals the speed-of-light round-trip to Earth: 183~ms (Earth), 131~ms (LEO), 5.1~s (Moon). The wall also imposes a leadership cost gradient on Multi-Paxos elections that symmetric grid quorums cannot express. A comparison between sparse and full-coverage topologies separates wall obligations from network reachability as independent liveness constraints. All results are design-level; quorum intersection is verified exhaustively in TLA+.