Message Size Matters: AlterBFT's Approach to Practical Synchronous BFT in Public Clouds

2025-03-13

AI Summary

Synchronous Byzantine Fault Tolerant (BFT) consensus in public clouds suffers from high latency due to stringent timing assumptions. Method: This paper proposes a hybrid-synchronous system model—first distinguishing “timely small messages” from “eventually timely large messages” based on message size—and designs AlterBFT, a lightweight, communication-driven protocol integrating hierarchical message scheduling, an optimized three-phase consensus mechanism, and empirically calibrated adaptive parameters for cloud networks. Contribution/Results: Without compromising safety or the standard $f < n/3$ fault tolerance, AlterBFT breaks the latency bottleneck of synchronous BFT: it achieves up to 15× lower end-to-end latency than state-of-the-art synchronous BFT protocols while maintaining comparable throughput; against typical partially synchronous protocols, it offers superior fault tolerance, higher throughput, and competitive latency.

Technology Category

• Machine Learning: Scalability of ML Systems
• Data Mining & Knowledge Management: Scalability, Parallel & Distributed Systems
• Search and Optimization: Distributed Search

Application Category

• Security and Privacy: Large-scale security measurements
• Responsible Web: Algorithmic accountability and transparency on the web
• Systems and Infrastructure for Web, Mobile and WoT: Cloud, edge and content delivery systems for the Web

Abstract

Synchronous consensus protocols offer a significant advantage over their asynchronous and partially synchronous counterparts by providing higher fault tolerance -- an essential benefit in distributed systems, like blockchains, where participants may have incentives to act maliciously. However, despite this advantage, synchronous protocols are often met with skepticism due to concerns about their performance, as the latency of synchronous protocols is tightly linked to a conservative time bound for message delivery. This paper introduces AlterBFT, a new Byzantine fault-tolerant consensus protocol. The key idea behind AlterBFT lies in the new model we propose, called hybrid synchronous system model. The new model is inspired by empirical observations about network behavior in the public cloud environment and combines elements from the synchronous and partially synchronous models. Namely, it distinguishes between small messages that respect time bounds and large messages that may violate bounds but are eventually timely. Leveraging this observation, AlterBFT achieves up to 15$ imes$ lower latency than state-of-the-art synchronous protocols while maintaining similar throughput and the same fault tolerance. Compared to partially synchronous protocols, AlterBFT provides higher fault tolerance, higher throughput, and comparable latency.

Problem

• Improves latency in synchronous BFT protocols
• Introduces hybrid synchronous system model
• Enhances fault tolerance and throughput

Innovation

• Hybrid synchronous system model introduced
• Distinguishes small and large message timings
• Achieves lower latency with high fault tolerance