PolkadotConnected consensus

What is Polkadot?

What does it provide?

Pooled securityall constituent chains of our community guaranteed

Trust-free transactionsconstituent chains can send transactions to each other

How does it work?

Relay-chainthe top-level which coordinates consensus and

transaction delivery between constituents

Parachainsconstituent chains which gather and process

transactions

Basics of the Relay-chain

No functionalityno external transactions, no smart contracts

Fees leviedfees paid for voting/movement of tokens between

parachains

Governance of the Relay-chain

TBDno big decisions made yet, but likely to take much from

present political structures; bi-cameral, multi-role governance

Stakeholders hold final sayreferendum mechanism built-in

Polkadot’s Relay-chain ensures that transactions between the constituent parachains get delivered and that they are all operating correctly.

Parachains can take any form of globally-coherent consensus system; potentially even another relay-chain. Enterprise-friendly encrypted, private, proof-of-authority chains are supported.

Bridges can exist to ferry transactions between the relay chain and existing, independent chains like Ethereum.

Extensible, Scalable and Flexible

Who maintains it?

Validators/nominatorsverify and finalise parachain candidates into blocks

Collatorsgather parachain transactions into PoV candidates

Fishermenmonitor the network for misbehaviour

Polkadot’s mechanics work by incentivising three kinds of activity.

Collators work independently on each parachain collecting and executing transactions. They provide blocks of transactions to validators.

Validators route transactions between parachains. They take turns vetting blocks supplied by collators and finally sign off to commit one to finality.

Fishermen receive a reward for reporting misbehaving validators.

Validators, Collators and Fishermen

Why do they bother?

Validators/nominatorsrewarded via staking-token expansion

Collatorsparachain-specific transaction fees

Fishermengifted proportion of the bond of identified culprit

Forming Consensus

Relay-chain Proof-of-stakeguarantees shared canonicality of parachains

Structured state-machinenot yet finalised; PBFT-derivative likely

Parallel validation groupsvalidators partitioned to allow scaling

Validators & Nominators

Approval votingall nominate acceptable validators, minimum reward

Constraint optimiserprovides configuration of validators/nominators for maximum lowest-bonded, minimum total inflation

Adaptive rewardsrewards alter to target % of capital bonded

Validating parachains

Collator candidatescome with proof-of-validity, external data

Availability & validityvoted on to ensure external data real

Relaying Transactions

Peer-to-peervalidators & collators self-organise to arrange delivery

of data

Tries & proofstries used to encode ingress/egress queues, allowing

compact proofs of misbehaviour

Ensuring Availability

Validatorsconsensus includes giving availability guarantees

Proof-of-Collatorregistered collators can challenge data availability

Mild punishmentvalidators given slight reward reductions on complaints

Ensuring Fairness

important that collator set contains some good guys

Golden ticketrandomly selected address

Mild rewardfor validators backing blocks whose collator’s address

is close to ticket

Open parachains can be tightly integrated into Polkadot, using Polkadot’s validators to ensure their correct operation. They are the easiest and cheapest form of integration.

Closed parachains can be weakly integrated into Polkadot, giving them the freedom to manage validation internally e.g. using a set of recognised authorities.

Bridged chains can be integrated into Polkadot too. Bridges add complexity and cost to integration, but allow the chain to exercise its own means of consensus.

Polkadot network

Internal/consortium parachain

Authorities manage parachain validation, access controls &c.

Transactions andinter-chain consensus

PolkadotConnected consensus

@gavofyork @polkadotproject @polkadotnetworkgithub.com/polkadot-io gitter.im/polkadot-io/Lobby