Transaction batching#

Rollup or Validium mode#

The trusted sequencer must batch the transactions using the following BatchData struct specified in the ZkEVM.sol contract:

struct BatchData {
        bytes transactions;
        bytes32 transactionsHash;
        bytes32 globalExitRoot;
        uint64 timestamp;
        uint64 minForcedTimestamp;
}

The trusted sequencer can choose Rollup or Validium mode when invoking the sequenceBatches method.

function sequenceBatches(
        BatchData[] calldata batches,
        address l2Coinbase,
        bytes calldata signaturesAndAddrs
)

• Rollup: BatchData.transactions data is set using the data from transactions, while the signaturesAndAddrs field is empty.
• Validium: The hash calculated based on the transactions is set as BatchData.transactionsHash. Transactions data is signed using the DAC private key from DataCommittee.sol, and the resulting signatures are set in the signaturesAndAddrs field.

Batch data parameters#

Transactions#

These are byte arrays containing the concatenated batch transactions for rollup mode. Each transaction is encoded according to the Ethereum pre-EIP-155 or EIP-155 formats using the Recursive-Length Prefix (RLP) standard, but the signature values, v, r, and s, are concatenated as shown below:

1. EIP-155: rlp(nonce, gasprice, gasLimit, to, value, data, chainid, 0, 0,)
2. pre-EIP-155: rlp(nonce,gasprice,gasLimit,to,value,data)

GlobalExitRoot#

This is the root of the bridge’s Global Exit Merkle Tree, which will be synchronized in the layer 2 State at the start of batch execution. The bridge moves assets back and forth between layer 1 and layer 2. To access the assets on the destination network, you need to complete a claiming transaction.

Timestamp#

As Ethereum blocks have timestamps, each batch also has its own timestamp. To make sure batches are arranged in chronological order and align with layer 1 blocks, two conditions must be met:

1. The timestamp of a batch must be equal to or later than the timestamp of the last batch that was sequenced.
2. A trusted sequencer can’t assign a batch with a timestamp greater than the timestamp of the layer 1 block, where the sequencing transaction is processed.

MinForcedTimestamp#

If a batch is a so-called forced batch, this parameter must be greater than zero. Censorship is countered by using forced batches. You can learn more about this in the next section - Batch Sequencing.