Finding Nemo-Nemo: CFT DAG-based Consensus in the WAN

2026-04-10

AI Summary

This work addresses the throughput degradation of crash-fault tolerant (CFT) consensus protocols in wide-area networks caused by single-leader bottlenecks and network latency. The authors propose a novel multi-leader CFT consensus protocol based on a causally ordered directed acyclic graph (DAG), which, for the first time, decouples command dissemination from consensus logic. By integrating a multi-leader architecture with a deterministic delayed execution mechanism, the protocol enables automatic command scheduling and achieves commitment within two communication hops. Experimental results demonstrate that the proposed approach significantly improves throughput in wide-area deployments while maintaining low commit latency, offering a practical solution that combines high performance, strong resilience, and deployment feasibility.

Technology Category

• Search and Optimization: Distributed Search
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems

Application Category

• Security and Privacy: Large-scale security measurements
• Responsible Web: Human-perceived consequences of algorithmic deployment on the web
• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization

Abstract

This paper introduces Nemo-Nemo, a practical crash-fault tolerant (CFT) consensus protocol designed to outperform existing protocols in wide-area networks by bridging design principles from the CFT and Byzantine-fault tolerant (BFT) worlds. By structuring command propagation through a causally ordered DAG, Nemo-Nemo allows all consensus replicas to propose commands with a naturally self-regulating communication regime. By exploiting multi-leader architecture, Nemo-Nemo avoids the performance bottleneck inherent to single-leader protocols. By separating command dissemination from consensus logic, Nemo-Nemo handles challenging network conditions even when consensus commits are stalled. Moreover, leader proposals that miss a deadline are never dropped, but deterministically deferred and executed later, preserving throughput under transient network delays. And by enabling Nemo-Nemo to commit on a DAG in just two network hops, it matches the latency of existing CFT systems, while achieving significantly higher throughput. The result is a robust, deployable system: the first DAG-based CFT consensus protocol proven to exceed state-of-the-art wide-area network performance in both speed and resilience.

Problem

• crash-fault tolerant
• consensus protocol
• wide-area network
• throughput
• latency

Innovation

• DAG-based consensus
• crash-fault tolerance
• multi-leader architecture
• command dissemination decoupling
• two-hop commit