  In this paper, we present BunchBFT Byzantine fault-tolerant state-machine
replication for high performance and scalability. At the heart of BunchBFT is a
novel design called the cluster-based approach that divides the replicas into
clusters of replicas. By combining this cluster-based approach with
hierarchical communications across clusters, piggybacking techniques for
sending messages across clusters, and decentralized leader election for each
cluster, BunchBFT achieves high performance and scalability.
  We also prove that BunchBFT satisfies the basic safety and liveness
properties of Byzantine consensus. We implemented a prototype of BunchBFT in
our PaxiBFT framework to show that the BunchBFT can improve the MirBFT's
throughput by 10x, depending on the available bandwidth on wide-area links.
