Consensus

The Zilliqa network is composed of one DS Committee (a special type of shard), and n normal shards. Each shard has a number of nodes, with one node being a leader and k number of backups.

Broadly, each shard runs an algorithm called practical Byzantine fault tolerance (pBFT) to achieve consensus on the state of the blockchain at any point. A rough outline is as follows:

  1. Pre-prepare: the leader announces the state of the blockchain it has to all backup nodes in the shard as a pre-prepare message.
  2. Prepare: each node receives and validates the state received from the leader in the pre-prepare phase, and multicasts its decision as a prepare message to the rest of the nodes in the shard.
  3. Commit: upon receiving a valid prepare message from a super majority (⅔) of nodes, it multicasts a commit message to all other nodes. Once a commit message is recieved from a super majority, the node records the new state.