ISAAC+: Compared with classic PBFT

Basically the well-known principles of PBFT are,

  • Consensus tries to reach the majority by voting.
  • Each view has a leader and it proposes the next block.
  • Each node validates and votes the next block of leader.

ISAAC+ is also based these rules and has some additional rules,

  • Each round has a proposer(leader) and it proposes proposal, which is the contents of next block.

  • Each acting suffrage group member validates the proposal and votes the established result of proposal.

    • If acting round is failed to get agreement, all the suffrage group members move to next round.

  • To start new round, all the nodes in acting suffrage group must agree at the next INIT stage.

    • If network is failed to agree at INIT stage, suffrage group members try to get agreement of INIT stage.

Like PBFT, the recommended agreement threshold within acting suffrage group is at least 67% and to keep consensus going in the network level, the recommended number of nodes should be greater than 4. 4 nodes means the consensus will be going if 1 node fails at most. To make network to be more sustainable against the failed nodes, the number of nodes should be increased by the rule, 3F+1 (F is the number of failed node)

Phases and Stages

Traditionally PBFT has 4 phases, each phase represents how the incoming request from client reaches to the consensus.

  1. Request
  2. Pre-Prepare
  3. Prepare
  4. Commit

ISAAC+ has also similar 3 phases(in ISAAC+, it is called voting stage),

  1. INIT
  2. SIGN
  3. ACCPET

Each stage does have similar meaning.

INIT
  • All the node of suffrage group members participate.
  • At this stage, suffrage group members will get agreement on the new block and it’s round, which is voted at the previous ACCEPT stage.
  • When the agreement is reached, the next block will be established and start new round for next block
SIGN
  • Only members of acting suffrage group participate.
  • Similar to the Pre-Prepare, the selected proposer(leader in PBFT) broadcasts its proposal to the network
  • Similar to the Prepare, each node will validate the proposal
ACCEPT
  • Only members of acting suffrage group participate.
  • Similar to the Prepare, when ACCEPT stage gets agreement, the new block is ready to established and ready to move next block.

Unlike the classic PBFT, ISAAC+ will establish the new block at the INIT stage by all the member of suffrage group, this means all the members of suffrage group should agree the new block for establishing it.