Polkadot is a blockchain network that connects multiple blockchains together through a relay chain that coordinates consensus and transaction delivery between connected blockchains called parachains. Parachains can take various forms from proof-of-stake systems to private or permissioned chains. Validators secure the relay chain through proof-of-stake voting and validate parachains proposed by collators who bundle transactions. Validators, collators, and fishermen who monitor for misbehavior are incentivized through staking rewards. The relay chain provides pooled security, trustless transactions between parachains, and scalability through parallel validation groups.

1. Polkadot
Connected consensus

2. What is Polkadot?

3. What does it provide?
Pooled security
all constituent chains of our community guaranteed
Trust-free transactions
constituent chains can send transactions to each other

4. How does it work?
Relay-chain
the top-level which coordinates consensus and
transaction delivery between constituents
Parachains
constituent chains which gather and process
transactions

5. Basics of the Relay-chain
No functionality
no external transactions, no smart contracts
Fees levied
fees paid for voting/movement of tokens between
parachains

6. Governance of the Relay-chain
TBD
no big decisions made yet, but likely to take much from
present political structures; bi-cameral, multi-role
governance
Stakeholders hold final say
referendum mechanism built-in

7. 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

8. Who maintains it?
Validators/nominators
verify and finalise parachain candidates into blocks
Collators
gather parachain transactions into PoV candidates
Fishermen
monitor the network for misbehaviour

9. 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

10. Why do they bother?
Validators/nominators
rewarded via staking-token expansion
Collators
parachain-specific transaction fees
Fishermen
gifted proportion of the bond of identified culprit

11. Forming Consensus
Relay-chain Proof-of-stake
guarantees shared canonicality of parachains
Structured state-machine
not yet finalised; PBFT-derivative likely
Parallel validation groups
validators partitioned to allow scaling

12. Validators & Nominators
Approval voting
all nominate acceptable validators, minimum reward
Constraint optimiser
provides configuration of validators/nominators for
maximum lowest-bonded, minimum total inflation
Adaptive rewards
rewards alter to target % of capital bonded

13. Validating parachains
Collator candidates
come with proof-of-validity, external data
Availability & validity
voted on to ensure external data real

14. Relaying Transactions
Peer-to-peer
validators & collators self-organise to arrange delivery
of data
Tries & proofs
tries used to encode ingress/egress queues, allowing
compact proofs of misbehaviour

15. Ensuring Availability
Validators
consensus includes giving availability guarantees
Proof-of-Collator
registered collators can challenge data availability
Mild punishment
validators given slight reward reductions on complaints

16. Ensuring Fairness
important that collator set contains some good guys
Golden ticket
randomly selected address
Mild reward
for validators backing blocks whose collator’s address
is close to ticket

17. 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 and
inter-chain consensus

18. Polkadot
Connected consensus
@gavofyork @polkadotproject @polkadotnetwork
github.com/polkadot-io gitter.im/polkadot-io/Lobby