Rollups

Arc deploys and maintains multiple rollups in its network. These are L2s settling on Ethereum or L3s settling on different L2s, bringing interoperability between all with its Shared Sequencer Network.

What is a rollup?

Rollups are scaling solutions that allow off-chain systems with self-custodiality of the underlying settlement layer. Rollups perform transaction execution outside the settlement layer and then the data is posted to the settlement layer where consensus is reached. As transaction data is included in layer 1 blocks, this allows rollups to be secured by native Ethereum security.

From the perspective of the settlement layer, rollups are off-chain systems that have a:

  1. State transition function (VM) which defines how state progresses.

  2. State and settlement smart contract on the settlement layer, which defines the canonical state of the rollup. This contract typically holds a state root that represents the state of the rollup accepting new updated state roots, and the necessary logic to validate its updates:

    1. In the case of a ZK rollup the logic refers to verifying a validity proof, and settlement is considered instantaneous once the proof is verified;

    2. In the case of an OP rollup, the logic refers to the possibility of opening a fraud proof dispute, and settlement takes a period of time (typically 7 days);

(Check Trust Assumptions and Settlement & Finality for further security details of the rollups used in Arc)

Arc uses and adds functionality to different stacks. Arc combines and exposes the most advantageous features of each tech stack.

Rollup Stacks differ with regards to many characteristics, providing Arc with plenty features, customization, and interoperability:

More about rollups:

In order for the rollups to function the following processes must be done off-chain:

  1. Inclusion is the process by which a transaction is accepted into the rollup.

  2. Ordering is the process of arranging transactions in a specific sequence in the rollup.

  3. Aggregation is the process of batching transactions into one batch. A batch of transactions consists of one or more transactions.

  4. Execution is the process by which the transactions in the blockchain are processed, and their effects are applied to the state of the rollup.

  5. Header production is the process of creating the rollup header backed by specific security properties.

  6. Proving is the process of creating the validity proof of the state update. (In case of a ZK rollup).

  7. Submission:

    1. submit to the Data Availability layer the transactions’ data (input/outputs);

    2. submit to the Settlement & Finality layer the new state update (also validity proof in case of a ZK rollup);

The majority of these processes are done by Arc’s Shared Sequencer Network.

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