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Seven dominant narratives of modular blockchain (I)
Seven dominant narratives of modular blockchain (Part 2)
Seven Dominant Narratives of Modular Blockchain (Part 3)
Seven Dominant Narratives of Modular Blockchain (Part 4)
Narrative 2: Data Availability Layer
2.1 Celestia: From modularization advocate to DA layer
Celestia first came into people's attention when Ethereum Rollup emerged. On the one hand, it advocates modular blockchain narrative, that is, a single chain can be split into several functional modules. On the other hand, it provides a new idea for Rollup, that is, data and consensus can be stored outside Ethereum (*Celestia's two pictures were widely circulated at the time. One is to split the single chain into: execution, liquidation, consensus + data, and the other is a picture called "Modular Stack" cited by Messari and Delphi Digital, which is actually a Rollup classification. Link: https://members.delphidigital.io/reports/the-complete-guide-to-rollups).
At that time, two pictures related to Celestia were widely circulated. One was the splitting of the single chain into: execution, settlement, consensus + data; the other was a picture called Modular Stack, which was actually a Rollup classification and had been cited by institutions including Messari and Delphi Digital. See the left and right pictures in the figure below.
Now, Celestia is generally seen as a network focused on providing a data availability layer. Of course, it is still advocating unique technical narratives such as the so-called "sovereign Rollup" (Soevereign Rollup, that is, settlement does not occur on L1 such as Ethereum).
It is particularly noteworthy that there is a big conflict of opinion between the Ethereum community and Celestia. According to the classification and annotation of the industry website L2beat, L2 that uses Ethereum itself as a DA is called Optimistic Rollup or ZK Rollup, while those that use external DA layers such as Celestia are called Optimium and Validium.
The subtext is that the latter is not pure L2. This naming will have a great psychological impact on developers and end users, who will tend to choose infrastructure that is accepted by the so-called mainstream.
Now, it is necessary to revisit Celestia's version of modular narrative. It is quite different from the currently accepted version, but it is still widely circulated, so we need to clarify our understanding through comparison.
Let us explain it in the form of three questions and one answer.
First question: Is the consensus layer together with data availability (DA)?
In Celestia's modular blockchain diagram, it combines the consensus layer and DA into one. From its current practice, as a DA layer, it provides DA for Ethereum L2 and Bitcoin L2. It can be seen that its DA is completely separated from the consensus of Ethereum and Bitcoin. In addition, from the practice of Ethereum, its EIP-4844 (proto-danksharding) upgrade also separates DA from consensus. In general, the consensus layer and DA should be separated logically.
Second question: Where does settlement take place?
In the early modular stack diagram, the settlement layer was largely underestimated. At the same time, it is believed that what happens in Rollup can also be called settlement. We believe that the core function of blockchain is settlement. We can extend an L1 chain (such as Ethereum) in the form of Rollup, but the final settlement still occurs on Ethereum. From the practical results, the so-called "smart contract Rollup" in the third column of the right figure is now widely accepted. In short, we believe that the four layers of modularization from bottom to top are: consensus, settlement, data availability, and execution.
Question 3: How important is the Data Availability Layer (DA)?
The two early diagrams also overemphasized the importance of DA. In layman's terms, data availability means publishing the data of a batch of transactions so that others can obtain and verify it when needed. This is why some people also call this layer the "data publishing layer". Verifiable data is the basis for the current blockchain to be trusted. Figuratively speaking, DA is an archive, which is important, but it is slightly controversial to say that it is the most important.
Of course, DA is important as a middleware service, which is beyond doubt. Now there are multiple providers in the DA layer. In addition to Celestia and Ethereum itself (EIP-4844), there are Near DA (converted from the public chain), EigenDA (using re-staking to ensure security), Avail (spun off from the Polygon ecosystem), Nubit (focusing on the Bitcoin ecosystem), 0g.ai (focusing on AI), Covalent (focusing on optimizing the development experience), etc.
We will not discuss the performance comparison of these DAs in detail here, but focus on the role of the DA layer in a modular blockchain.
