  The state-of-the-art HotStuff operates an efficient pipeline in which a
stable leader drives decisions with linear communication and two round-trips of
message. However, the unifying proposing-voting pattern is not sufficient to
improve the bandwidth and concurrency performance of the modern system. In
addition, the delay corresponding to two rounds of message to produce a
certified proposal in that scheme is a significant performance bottleneck.
Thus, this study developed a new consensus protocol, Multi-pipeline HotStuff,
for permissioned blockchain. To the best of the authors' knowledge, this is the
first protocol that combines multiple HotStuff instances to propose batches in
order without a concurrent proposal, such that proposals are made
optimistically when a correct replica realizes that the current proposal is
valid and will be certified by quorum votes in the near future. Because
simultaneous proposing and voting are allowed by the proposed protocol without
transaction duplication, it produced more proposals in every two rounds of
messages. In addition, it further boosted the throughput at a comparable
latency with that of HotStuff. The evaluation experiment conducted confirmed
that the throughput of Multi-pipeline HotStuff outperformed that of the
state-of-the-art protocols by approximately 60\% without significantly
increasing end-to-end latency under varying system sizes. Moreover, the
proposed optimization also performed better when it suffers a bad network
condition.
