BFT-Blocks: The Case for Analyzing Networking in Byzantine Fault Tolerant Consensus

Abstract

Byzantine fault tolerant (BFT) consensus allows the construction of robust, distributed systems via the state-machine replication (SMR) approach. Still, after more than 40 years of research, limitations on performance and scalability for practical systems remain. A large corpus of existing work improves on consensus complexity, performance and introduces a multitude of optimization techniques. The state-of-the-art is complex. On the other hand, many protocols designed for practical deployments are built on strong, common assumptions about underlying communication and authentication primitives. To fulfill these assumptions, often, commodity tools and libraries are employed without further analysis and caution for negative interplay.Instead of contributing to the existing complexity, we choose a different approach. In this paper, we outline the feasibility and potential impact of the optimization of common building blocks of BFT-SMR systems. We systemize existing work in terms of common model assumptions and identify optimization potential. Finally, we choose the building block of networking transport as a representative example and analyze its optimization space, both in context of general BFT-SMR systems and a case study of the HotStuff protocol. We describe behavior, challenges, and desired configuration of network transports for use in byzantine agreement, and identify lossy links as the main catalyst for significant performance differences between protocols and configurations.