Multi-Round Visibility: A Post-Consensus Ordering Layer for DAG-Based BFT

2026-05-22

AI Summary

Existing DAG-based BFT protocols lack a verifiable, structured ordering mechanism under high concurrency, resulting in ambiguous execution order at decision boundaries. This work proposes a post-consensus ordering mechanism that decouples ordering logic from the critical consensus path. By leveraging authenticated metadata of DAG vertices—such as creator identity, round number, and ancestor relationships—it constructs multi-round visibility evidence. Priority is then derived through structural visibility within a bounded evidence horizon. Ambiguities are explicitly resolved via deterministic graph completion combined with Atomic Uniform Fairness (AUF) comparison techniques. Experimental evaluation based on the Narwhal/Tusk architecture demonstrates that the system achieves fair, verifiable, and structured ordering while maintaining high throughput across 5 to 50 replicas and under diverse fault scenarios.

Abstract

Directed acyclic graph (DAG)-based Byzantine Fault-Tolerant (BFT) protocols achieve high throughput by decoupling dissemination from agreement and allowing many vertices to be committed concurrently. This same concurrency, however, weakens ordering evidence at the execution boundary: once units are committed in a shared DAG frontier, their final linearization is driven by traversal or deterministic tie-breaking rather than verifiable structural precedence. Prior fair-ordering designs address ambiguity by collecting or reconstructing transaction-level ordering evidence within the consensus workflow. While effective, this couples ordering with agreement and places ordering logic on the critical path. This paper presents Multi-Round Visibility (MRV), a post-consensus structural ordering layer for DAG-based BFT that reinterprets the committed DAG as an ordering evidence substrate. Committed vertices inherently carry authenticated creator, round, and ancestry metadata, enabling replicas to derive multi-round structural visibility without extra consensus-path messages. MRV accumulates this visibility within a bounded evidence horizon, compares concurrently committed atomic units of fairness (AUFs) after they coexist in the DAG, and derives precedence constraints from Byzantine-robust visibility advantages. When the DAG lacks such constraints, MRV exposes and resolves the remaining ambiguity through deterministic graph completion rather than hiding it inside traversal rules. We implement MRV on a Narwhal/Tusk-based prototype. Evaluation across 5-50 replicas under various fault settings shows MRV preserves the high-throughput regime of the DAG-BFT stack, proving it provides post-consensus structural ordering without burdening the consensus-critical path.

Problem

• DAG-based BFT
• fair ordering
• structural precedence
• post-consensus ordering
• Byzantine Fault Tolerance

Innovation

• Multi-Round Visibility
• DAG-based BFT
• post-consensus ordering
• structural precedence
• atomic units of fairness