Ethereum Layer2: The Evolution and Competition of Rollup Technology

Layer 2 is one of the key solutions to address Ethereum's scalability issues. By building an additional network layer on top of the main chain, it can handle more transactions while maintaining the security and decentralization of the main chain.

Rollup is currently the most mainstream Layer 2 scaling solution. It achieves scaling by processing transactions off-chain and then "packing" the data onto the main chain. Compared to other off-chain solutions, Rollup has three characteristics:

1. Layer2 is a relatively independent platform where users can trade directly on Layer2, but interactions with Layer1 must go through smart contracts.

2. All transaction information is fully recorded on the main chain, solving the data availability issue.

3. Transactions are executed on Layer 2, but the state summary is published to Layer 1 and verified.

According to the different data verification methods, Rollup can be divided into two categories: Optimistic Rollup and ZK Rollup.

The Development History of Rollups

The earliest Layer 2 solution is sidechains, which are independent blockchains linked to the main chain, allowing for asset transfers between the two chains.

In 2017, Joseph Poon and Vitalik Buterin proposed the Plasma solution, which is an evolution of sidechains. Plasma chains are child chains built outside of Ethereum, forming a tree-like network that can decompose large computational tasks to be handled by each child chain.

However, Plasma has issues such as data availability attacks, exit delays, and high monitoring costs. In 2019, John Adler proposed the Optimistic Rollup solution to address some of Plasma's problems.

On the other hand, Vitalik introduced zero-knowledge proof technology to verify state changes in 2018, laying the foundation for ZK Rollup. The introduction of the Plonk algorithm in 2019 solved the trusted setup problem of ZK-SNARK, accelerating the development of ZK Rollup.

Comparison of Mainstream Rollup Projects

Currently, Optimistic Rollup accounts for the majority of TVL, but ZK Rollup is developing rapidly.

Optimistic Rollup

Representative projects include Arbitrum and Optimism.

Arbitrum launched its mainnet in September 2021 and is the Layer 2 with the highest TVL. The ecosystem includes three networks: Arbitrum One, Nova, and Orbit.

Optimism launched in August 2021, with a TVL second only to Arbitrum. It achieves EVM equivalence and has launched the OP Stack open-source toolkit, supporting the construction of superchain networks.

ZK Rollup

Representative projects include zkSync, StarkNet, Polygon zkEVM, and Scroll.

zkSync is the first zkEVM project to go live, using technologies such as optimistic transfers to improve performance.

StarkNet uses zkSTARK and sharding technology to provide higher privacy and throughput.

Polygon zkEVM achieves EVM compatibility at the bytecode level.

Scroll is an EVM-compatible ZK Rollup that supports the same development environment as Ethereum.

Summary

Rollup technology is expected to solve the performance bottleneck of blockchain. In the short term, Optimistic Rollup has more advantages in general EVM computations, while ZK Rollup is suitable for simple payment scenarios. However, in the long run, with technological advancements, ZK Rollup may become the ultimate solution for Ethereum scalability.