(1) request: the client sends a request to the master node.
(2) pre-prepared: The master node receives the request from the client and needs to verify whether the signature of the client request message is correct. If correct, a pre-prepare message is broadcast to other replica nodes.
(3) prepared: the replica node receives the pre-prepare message from the master node and carries out verification. If correct, the replica node sends a prepare message to other nodes, including the primary.