Delay Analysis of the BFT Blockchain Data Dissemination: Case of Narwhal Protocol

This article investigates data dissemination delays in a Directed Acyclic Graph (DAG)-based Byzantine Fault Tolerant (BFT) blockchain. We focus particularly on the Narwhal protocol, a mempool-based approach for efficiently disseminating transactions and constructing a DAG. Narwhal is designed to work alongside a BFT consensus protocol like Tusk. Tusk then orders the transaction metadata based on the DAG information. Through an in-depth analysis of the protocol messages, we establish a mathematical model for message propagation delays. We start by considering a specific probability distribution for data network propagation delays: Gaussian Distribution. Then, we consider a general propagation delay distribution. Also, we assume large networks and apply some approximations, i.e., the Central Limit Theorem (CLT). Finally, we develop the Narwhal protocol and demonstrate that the simulated delays <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">are</sup> compatible with the theoretical ones.