---
id: basics-zil-consensus
title: Consensus Mechanism
keywords:
  - consensus
  - ds committee
  - pbft
  - zilliqa
description: Zilliqa 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)](http://pmg.csail.mit.edu/papers/osdi99.pdf)
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.
1. 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.
1. Commit: upon receiving a valid **prepare** message from a super majority
   (2/3) 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.