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.
Weight (Own weight): The weight of transaction A is proportional to the effort put in by its issuer, which can be assumed to be 3^n.
Cumulative weight:Transaction A’s own weight + the sum of own weights of all the followed transactions that directly/indirectly approve transaction A.
(E.g. In figure 4, transaction D has own weight as 1, and cumulative
weight as 6 = D’s own weight + A’s own weight + B’ own weight + C’s own
weight = 1 + 1 + 3 + 1.)
Figure 4: Weights (from IOTA white paper). Own weights at right-bottom. Cumulative weights at left-top, as bold.
Score:Transaction A’s own weight + the sum of own weights of all previous transactions approved by transaction A.
(E.g. In figure 5, transaction A has score as 9 = A’s own weight + B’s
own weight + D’s own weight + F’s own weight + G’s own weight = 1 + 3 + 1
+ 3 + 1.)
Figure 5: Score (from IOTA white paper). Score at left-top, in the circle.
Height: The length of the longest oriented path to the genesis.
Depth: The length of the longest reverse-oriented oath to certain tips.
For instance, in figure 5, the height of D is 3 (D → F → G → genesis), and the depth of D is 2 (D ← B ← A).
