As the upgrade of Cancun is completed and the reduction of L2 Gas fees, the market's focus has once again turned to L2. There are currently two main types of solutions for Rollup L2: Optimistic Rollup and ZK Rollup. Due to its mature market application, Optimistic Rollup occupies the majority of the market share. However, both Optimistic Rollup and ZK Rollup have some issues. In order to address these limitations, and further optimize efficiency and decentralization, Based Rollup has emerged. It not only simplifies technical complexity and reduces transaction latency, but is also the only solution that fully inherits Ethereum's liveness. Among all known projects, only the ZK Rollup team Taiko is currently developing a Based Rollup solution.

Issues with Existing Rollup

Optimistic Rollup requires a long challenge window, usually 7 days, to correct potential fraudulent behavior when confirming transactions. This design results in a long wait for funds to be withdrawn, slowing down the overall transaction process. Additionally, during peak periods on the Ethereum network, Optimistic Rollup incurs high Gas fees when processing fraud proofs. While ZK Rollup can provide faster transaction confirmation times and reduce on-chain data storage to save costs, it consumes a significant amount of computing resources and time in generating zero-knowledge proofs, affecting costs and transaction processing speed (TPS).

In summary, the technical complexity of Optimistic Rollup and ZK Rollup requires them to maintain a complex infrastructure and security mechanisms to handle and verify L2 transactions, negatively impacting transaction costs and network efficiency.

Based Rollup Solution

In March 2023, Ethereum Foundation researcher Justin Drake proposed Based Rollup to effectively overcome these issues. Based Rollup, also known as L1-sequenced Rollup, is a Rollup whose sequencing is entirely driven by the underlying L1. This design allows L1 proposers to collaborate with L2 searchers and builders without permission, directly including Rollup blocks in L1 blocks, thereby outsourcing the sequencing rights to L1 validators. Based Rollup's consensus layer, data availability layer, and settlement layer are all on Ethereum, with only the execution layer built on the Rollup network, responsible for transaction execution and state updates. It is worth noting that Based Rollup addresses the efficiency issues from a sequencing perspective, which differs from the verification perspective of Optimistic Rollup and ZK Rollup. Because of this difference in dimension, the classification of Based Rollup does not conflict with that of OP and ZK, meaning that if Optimistic Rollup or ZK Rollup outsources sequencing rights to L1 validators, it can be called Based Rollup.

Based Rollup inherits its security and liveness from L1 by transferring the responsibility of transaction sequencing to L1, while optimizing the performance of L2. It is the only Rollup solution that fully inherits 100% of Ethereum's liveness. This design brings the following advantages:

• Full inheritance of liveness: Based Rollup's security and decentralization are consistent with Ethereum, without the need for additional security mechanisms or consensus algorithms to ensure the validity and sequence of transactions. Compared to Rollups with escape hatches, it is safer, faster, and more convenient. In Rollups with escape hatches, if the Rollup fails or is attacked, users can safely withdraw their funds back to L1 through the escape hatch, but must wait for a period to ensure settlement.

• Simplified technical complexity: When L2 needs to handle transaction sequencing and data availability issues on its own, it introduces additional complexity and potential security risks. Transferring the responsibility of sequencing to L1 can simplify the structure of L2, eliminating the need for sequencer signature verification, escape hatches, and external PoS consensus.

• Reduced latency: Using L1 to sequence transactions can quickly confirm the validity and sequence of transactions, reducing confirmation time and improving the overall network's responsiveness and efficiency.

• Reduced operating costs: Since L1 has already handled transaction sequencing, L2 can more efficiently batch and confirm transactions, reducing the verification complexity of L2 and the resources and costs required specifically for sequencing. This cost efficiency is more pronounced with high transaction volumes.

• Consistency in economic incentives: L1 miners can earn additional fees and incentives by participating in L2 transaction sequencing, increasing their motivation to maintain the overall health of the network. This design also helps maintain consistency in incentives between different layers of the network, enhancing the overall economic security of the ecosystem.

Challenges Faced by Based Rollup

Although Based Rollup can address some of the current shortcomings of Rollup solutions, this technology also faces some challenges:

• Income limitations: Relying on L1 for sequencing limits the opportunity to capture MEV, with most Based Rollup MEV flowing to L1 validators. Based Rollup itself cannot directly benefit from this.

• Sequencing flexibility: Delegating sequencing tasks to L1 may reduce the flexibility of sequencing, affecting specific transaction sequencing strategies and the implementation of fast transaction confirmation. For example, L1's sequencing decisions may involve miners choosing to prioritize processing certain transactions to maximize their own interests, so implementing a FCFS (First-Come First-Served) sequencing mechanism similar to Arbitrum in Based Rollup would require additional technical support (such as EigenLayer).

Projects Building Based Rollup

Since the concept of Based Rollup was proposed only a year ago, it is a relatively new concept, and its theory and implementation details are still in the exploration and improvement stage. Therefore, there are few projects currently building Based Rollup, and the most well-known project is Taiko. Taiko is an L2 that uses ZK Rollup technology and has developed Type-1 zkEVM, providing the same opcodes and functionality as Ethereum, ensuring high compatibility with the existing Ethereum ecosystem. Shortly after the concept of Based Rollup was proposed, Taiko began to build Based Rollup by outsourcing transaction sequencing to Ethereum validators and using Ethereum as the settlement and data availability layer and consensus mechanism to simplify the structure of Rollup. On January 15, 2024, Taiko launched the Katla testnet, implementing Based Contestable Rollup (BCR), a Based Rollup that incorporates the dispute resolution process (similar to a fraud proof system) into the transaction verification workflow.

Future Outlook

Although the development of Based Rollup may require more time and resources, as well as dual validation from the market and technology, in the long run, Based Rollup is expected to gain an advantage in the market competition due to its enhanced security, decentralization, simplified structure, and consistent goals. Especially in the DeFi field, Based Rollup demonstrates significantly faster transaction confirmation speeds and lower transaction costs, showing significant potential advantages. It is believed that with continuous technological improvements and gradual market acceptance, Based Rollup is expected to gain a strong position in the market for Rollup L2 solutions.

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