Legible Consensus: Topology-Aware Quorum Geometry for Asymmetric Networks

TL;DR

This paper introduces a topology-aware quorum design for asymmetric networks that separates inter-tier safety from intra-tier replication, improving failure mode clarity and latency analysis.

Contribution

It maps crumbling-wall quorum construction to tiered networks, enabling operators to identify failure modes from topology alone and analyze latency and leadership costs.

Findings

Three of four tiers retain global liveness during Mars conjunction blackout.

Consensus latency matches speed-of-light round-trip times for each tier.

The wall topology imposes a leadership cost gradient affecting Multi-Paxos elections.

Abstract

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+.