🧻
Rollup Economics Research (ROP-3)
/
OP Stack codebase V1 - Bedrock

OP Stack codebase V1 - Bedrock

💡
Bedrock = the first release of the OP stack codebase.
 
Components
Rollup Protocol
Bedrock (Q1 2023)
1. Block storage
2. Block production
  • Sequencer has a mempool (but it is private to mitigate MEV opportunities).
  • Blocks produced every 2 seconds (regardless of whether no transactions, filled to gas limits, or anything in between).
 
Transaction can get to sequencer in 2 ways:
  1. Transactions submitted on L1
      • these are called deposits whether they have assets attached or not → they are included in the chain in the appropriate L2 block.
      • L2 blocks are identified by an epoch (the L1 block which it corresponds to).
      • 1st block of an epoch includes all the deposits that happened in the L1 block to which it corresponds.
      • If the sequencer attempts to ignore a legitimate L1 transaction, it ends up with a state that is inconsistent with the verifiers.
  1. Transactions submitted directly to the sequencer
      • Cheaper to submit.
3. Block execution
Execution Engine (op-geth component) receives blocks using 2 mechanisms:
  • Execution Engine updates itself using P2P networking with other execution engines.
  • Rollup node (op-node component) derives L2 blocks from L1 (slow mechanism, but censorship resistant).
4. Bridging assets between layers
Deposits (L1 → L2):
  • You use L1CrossDomainMessenger or L1StandardBridge.
  • Deposit transactions become part of the canonical blockchain in the first L2 block of the “epoch” corresponding to the L1 block where the deposits were made.
Withdrawals (L2 → L1):
  1. Initiate withdrawal with an L2 transaction.
  1. Wait for next output root to be submitted to L1 (use SDK).
  1. Submit the withdrawal proof using proveWithdrawalTransaction.
      • This enables off-chain monitoring of the withdrawals, making it easier to identify incorrect withdrawals or output roots.
  1. After the fault challenge period ends (week on mainnet), finalise the withdrawal.
5. Fault proofs
If a proposed state commitment goes unchallenged for the duration of the challenge window (7 days), then it is considered final.
  • Once a commitment is considered final, smart contracts on Ethereum can safely accept withdrawal proofs about the state of Optimism based on that commitment.
  • When a state commitment is challenged, it can be invalidated through a fault proof.
  • If the commitment is successfully challenged then it is removed from the StateCommitmentChain to eventually be replaced by another proposed commitment.
  • NB! A successful challenge does not roll back Optimism itself, only the published commitments about the state of the chain.
💡
The ordering of transactions and state of Optimism is unchanged by a fault proof challenge.tw
🧻
Rollup Economics Research (ROP-3)
/
OP Stack codebase V1 - Bedrock

OP Stack codebase V1 - Bedrock

💡
Bedrock = the first release of the OP stack codebase.
 
Components
Rollup Protocol
Bedrock (Q1 2023)
1. Block storage
2. Block production
  • Sequencer has a mempool (but it is private to mitigate MEV opportunities).
  • Blocks produced every 2 seconds (regardless of whether no transactions, filled to gas limits, or anything in between).
 
Transaction can get to sequencer in 2 ways:
  1. Transactions submitted on L1
      • these are called deposits whether they have assets attached or not → they are included in the chain in the appropriate L2 block.
      • L2 blocks are identified by an epoch (the L1 block which it corresponds to).
      • 1st block of an epoch includes all the deposits that happened in the L1 block to which it corresponds.
      • If the sequencer attempts to ignore a legitimate L1 transaction, it ends up with a state that is inconsistent with the verifiers.
  1. Transactions submitted directly to the sequencer
      • Cheaper to submit.
3. Block execution
Execution Engine (op-geth component) receives blocks using 2 mechanisms:
  • Execution Engine updates itself using P2P networking with other execution engines.
  • Rollup node (op-node component) derives L2 blocks from L1 (slow mechanism, but censorship resistant).
4. Bridging assets between layers
Deposits (L1 → L2):
  • You use L1CrossDomainMessenger or L1StandardBridge.
  • Deposit transactions become part of the canonical blockchain in the first L2 block of the “epoch” corresponding to the L1 block where the deposits were made.
Withdrawals (L2 → L1):
  1. Initiate withdrawal with an L2 transaction.
  1. Wait for next output root to be submitted to L1 (use SDK).
  1. Submit the withdrawal proof using proveWithdrawalTransaction.
      • This enables off-chain monitoring of the withdrawals, making it easier to identify incorrect withdrawals or output roots.
  1. After the fault challenge period ends (week on mainnet), finalise the withdrawal.
5. Fault proofs
If a proposed state commitment goes unchallenged for the duration of the challenge window (7 days), then it is considered final.
  • Once a commitment is considered final, smart contracts on Ethereum can safely accept withdrawal proofs about the state of Optimism based on that commitment.
  • When a state commitment is challenged, it can be invalidated through a fault proof.
  • If the commitment is successfully challenged then it is removed from the StateCommitmentChain to eventually be replaced by another proposed commitment.
  • NB! A successful challenge does not roll back Optimism itself, only the published commitments about the state of the chain.
💡
The ordering of transactions and state of Optimism is unchanged by a fault proof challenge.tw