  Fueled by the growing popularity of proof-of-stake blockchains, there has
been increasing interest and progress in permissioned consensus protocols,
which could provide a simpler alternative to existing protocols, such as Paxos
and PBFT. In particular, the recently proposed Streamlet protocol provides a
surprisingly simple and streamlined consensus approach, which crystallizes
years of research in simplifying and improving classical consensus protocols.
While the simplicity of Streamlet is a major accomplishment, the protocol lacks
certain practical features, such as supporting a stable block proposer, and it
makes strong assumptions, such as synchronized clocks and the implicit echoing
of all messages. Most importantly, it requires sending $O(N^3)$ messages per
block in a network of $N$ nodes, which poses a significant challenge to its
application in larger networks. To address these limitations, we introduce
Pipelet, a practical streamlined consensus protocol. Pipelet employs the same
block-finalization rule as Streamlet, but attains state-of-the-art performance
in terms of communication complexity and provides features that are crucial for
practical applications, such as clock synchronization and stable block
proposers. At the same time, Pipelet retains the simplicity of Streamlet, which
presents significant practical advantages, such as ease of implementation and
verification.
