Messari: Disassemble the modular blockchain to understand the functional layers

By Stephanie Dunbar, Analyst, Messari

Compilation: Luffy, Foresight News

In response to the limitations of traditional monolithic architectures, including slow innovation, scalability limitations, and lack of development flexibility at the application layer, modular blockchains emerged, which split blockchains into distinct, interchangeable components .

Splitting components can be customized and optimized at each layer of the blockchain technology stack, and professional providers will appear in each functional component field.

The most prominent current modular systems include the Ethereum ecosystem and the upcoming Celestia.

Rollup is the most secure form of modular blockchain.

Rollups thrive, ranging from general-purpose execution environments (e.g., OP Mainnet and zkSync Era) to specific Rollups hosting individual applications.

Most Ethereum-centric Rollups are general-purpose L2, and an important narrative in the Celestia ecosystem is application specificity.

Rollups can be stacked to scale with requirements and tailor application-specific use cases while becoming part of a composable Rollup bridging ecosystem.

Developers can join the ecosystem they agree with, or choose the execution environment, sorting scheme, verification system, consensus and DA layer that best suit their needs, and even mix and match between different ecosystems.

The success of any Rollup ecosystem or application will depend on the competitive advantage that their chosen configuration brings.

Execution layer

This layer is where new transactions are processed. It takes the current state of the blockchain, applies these new transactions, and calculates the resulting state. The function that controls the state change rules is called a state transition function (STF).

Most of the projects built on the execution layer are generic Ethereum-centric Rollups, such as Scroll, Taiko, and Linea.

Their goal is to maintain compatibility with the EVM, provide users with a familiar cryptographic experience, and provide developers with reusable tools.

alt-VMs (Alternative Virtual Machines) are optimized for specific use cases, such as Fuel Network for parallel transaction processing and Aztec Network for privacy applications.

Arbitrum and Fluent will use Wasm's traditional programming language to introduce smart contracts, while Cartesi will allow Rollup to run on Linux.

Settlement Layer

The settlement layer is an optional layer of the modular stack. The shared settlement layer is used for verification and dispute resolution of various rollups, and can serve as a liquidity center to help bridge the gap between different rollups.

Sort

Transactions are submitted to the network by users, and the orderer accepts them, determines their order (in most cases) and publishes the transaction data to components of the consensus layer and DA layer.

All major rollups currently use centralized sorters. Decentralizing the sorter will enhance liveness and censorship resistance. Shared sequencer networks between multiple Rollups, such as Espresso and Astria, provide composability advantages close to atomicity.

Validation layer

This layer ensures correct execution and state transitions. There are currently 2 main systems under development:

• Optimistic: Fraud proofs prevent fraudulent activity *ZK: Validity proof cryptographically confirms the correctness of all transactions

Arbitrum and Optimism are leaders in optimistic rollups, proving market efficiency through @RiscZero and @nil_foundation outsourced proofs. Like shared ordering, outsourcing proofs can bring interoperability benefits, such as aggregated proofs across chain bridges.

Consensus and DA (data availability)

At the consensus layer, nodes agree on the final order of transactions, providing a unified view of rollup history.

The DA layer further guarantees that all necessary data is available to reconstruct the Rollup state. The DA layer acts as an immutable bulletin board where transaction data and proofs are posted. Without DA, Rollup cannot guarantee liveness. Using the transaction data provided by the DA layer, anyone can continue calculating the next block from where the previous person left off.

The DA layer is also the final determinant of Rollup throughput.

Ethereum is developing a dedicated fee market and "blob" space for rollups, and projects such as Celestia and Avail focus on lightweight performance with dedicated DA layers.

A DAC like EigenDA that separates consensus and DA offers low, predictable fees and the ability to reserve DA bandwidth.

Although these functions can be separated, only working together can provide the complete security guarantee of the blockchain network.

The most critical aspect of consensus and DA layer adoption is the trust-minimization composability advantage they bring

The cost of changing the consensus and DA layers will be high because the rollup will lose composability with other previously shared rollups.