Istanbul BFT

Istanbul BFT inherits from the original PBFT by using 3-phase consensus, PRE-PREPARE, PREPARE, and COMMIT. The system can tolerate at most of F faulty nodes in a N validator nodes network, where N = 3F + 1. Before each round, the validators will pick one of them as the proposer, by default, in a round robin fashion.

The proposer will then propose a new block proposal and broadcast it along with the PRE-PREPARE message.

Upon receiving the PRE-PREPARE message from the proposer, validators enter the state of PRE-PREPARED and then broadcast PREPARE message. This step is to make sure all validators are working on the same sequence and the same round.

While receiving 2F + 1 of PREPARE messages, the validator enters the state of PREPARED and then broadcasts COMMIT message. This step is to inform its peers that it accepts the proposed block and is going to insert the block to the chain.

Lastly, validators wait for 2F + 1 of COMMIT messages to enter COMMITTED state and then insert the block to the chain.