1. Introduction

Ethereum has limited resources, these being:

• Bandwidth

• Computation (bottleneck)

• Storage (bottleneck)

 

Optimistic Rollups → Submit transaction data on-chain, but execute transactions off-chain.

• If an error occurs in off-chain execution → Fault proofs can be submitted on-chain.
You only execute transactions on-chain if their is a ‘fault’.

 

EVM Equivalence

This describes a complete compliance with the state transition function described by the Ethereum specification.

 

Protocol Guarantees

1. Liveness
Anyone can update the rollup chain.
• By submitting to sequencer (low latency, cheaper).
• By submitting directly to L1 (censorship-resistant).

2. Availability
Anyone is able to download and reconstruct the rollup chain.
• Data required to derive the chain is available on L1.

3. Validity
All transactions are executed correctly and withdrawals are processed correctly.
• Rollup state and withdrawals are managed by the L2 State Oracle contract.
This contract only finalises valid rollup block hashes (under single honest verifier assumption).
If an invalid block hash is asserted on L1, an honest verifier will prove it is invalid and win a bond.
 

 

Users

• Can deposit/withdraw on L2 by interacting with an L1 contract.

• Use L2 contracts by submitting transactions to sequencers.

• Check transaction status by communicating with a verifier. Verifiers can power services such as block explorers.

 

Sequencers (primary block producer)

1. Accepts off-chain transactions (L2 transactions).

2. Observes on-chain transactions (deposit events coming from L1).

3. Consolidates both off and on-chain transactions into L2 blocks (ordering them as well).

4. Propagates L2 blocks to L1 (by submitting calldata to L1), this involves including:
• Pending off-chain transactions
• Information about the ordering of on-chain transactions to construct L2 blocks.
 

💡

Sequencer also gossips the L2 blocks that it creates (for the use of soft finality).

 

Verifiers

Have 2 purposes:

1. Serving rollup data to users.

2. Verifying rollup integrity and disputing invalid assertions.

 

 

Important components

• Rollup Node

• Execution Engine

• L2 Output Oracle

• L2 Output Submitter

 

Withdrawals

Withdrawals are initiated by L2 transactions and then completed by L1 transaction after dispute period has elapsed.