Source: Thor Hartvigsen

Compiled by: Leo, BlockBeats

Scalability has always been the focus of the industry. Blockchain is currently facing the problem of "scalability triple dilemma". Modular blockchain, which started with Celestia, is proposing solutions around its scalability, high-level security and decentralization. Modular blockchain is becoming a mainstream narrative. Crypto Kol Hor Hartvigsen wrote an article on "Modular Blockchain and Its Intrinsic Value", which BlockBeats compiled as follows:

PART 1: Starting from the basic concepts

Today's issues needing improvement:

- Trustless cross-chain communication

-Rollup scalability when the number of transactions grows large enough

- Maintaining high levels of security and decentralization while aiming for increased throughput (the blockchain trilemma)

First, to ensure that we fully understand these concepts, we need to establish some terminology, as shown below:

Block

Blocks are the components of the blockchain. A single block consists of two components: block header and block body. The header contains the hash, timestamp and other data of the previous block, and the body contains all the transactions in the block.

A popular scaling strategy is to have bigger blocks (Solana).

Bigger blocks = increased throughput, but with some issues at the decentralization level.

Bigger blocks = more data required for nodes, and few people can afford more expensive hardware that can handle that much data.

Node

A full node needs to store the entire blockchain and all transactions since the first block. In order to trade on the blockchain, it is necessary to ensure consensus, ensure that data is available and blocks are valid.

Light Node (Light Client)

Light nodes are used for Rollup and outsource most of the work to full nodes. They do not verify transactions, but check whether each block has consensus and whether the block data is available to the network. Most light nodes rely on the "majority honesty assumption", assuming that most participants (such as validators) are honest. Light nodes require less hardware, more nodes, but the overall security is weaker (sometimes).

Rollup (on Ethereum)

Rollup/L 2 is a chain built on top of Ethereum, using the Ethereum mainnet as the settlement layer. Rollup can be considered as a separate execution layer and returns transaction packages to the mainnet for verification.

There are currently two types of Rollup: Optimistic Rollup and ZK Rollup.

Blockchain layer:

Blockchain can be divided into 4 layers: -Execution layer, which provides the environment for Dapps and processes transactions in it;

-Data availability layer: Nodes receive blocks from block generators and check if the data (transactions) are publicly available

-Consensus layer: Determine the order of transactions

- Settlement layer: determines the actual state of the blockchain (finally)

Monolithic vs. Modular

A monolithic blockchain is a chain that consists of all the above 4 layers, so the monolith needs to handle all of the above parts, which is the case with Ethereum and most other blockchains you know.

A modular blockchain is one that outsources one or more of these 4 layers to an external chain, allowing new levels of scalability to be achieved because modular blockchains can focus on specific elements.

The above explains some basic concepts, which are summarized in the following table:

The current Rollups on Ethereum (such as Arbitrum and Optimism) act as the execution layer and implement the data availability layer, consensus layer, and settlement layer through the Ethereum mainnet. These Rollups will use "on-chain data availability" to publish data to the designated L 1 (Ethereum).

On the contrary: a Rollup with "off-chain data availability" publishes its data to a location other than the designated L1. The Rollup can still use Ethereum as a settlement layer, but Celestia acts as a data availability layer by publishing data in this way (off-chain data availability).

The following are different types of Rollup structures on Ethereum:

-Monolith = Ethereum Mainnet

-Rollup = e.g. Arbitrum, Optimism (acts as execution layer and uses Ethereum for other things)

-Validium = "Off-chain data availability Rollup", such as Celestia

Part 2: Learn more about Celestia

Celestia is a modular blockchain network. Blockchains and all VM rollups (not just EVM) can use Celestia as the data availability layer and consensus layer. As shown in the figure below, Celestia provides different solutions for modular expansion, such as "Sovereign rollups, Celestium, etc."

First, you need to have a deep understanding of the "Data Availability Layer"

Data availability: As a node, you receive a block from a block generator and need to verify that the data is public (published) in order to add it as the next link in the blockchain.

Data availability issues: occur when data is retained.

Specifically, the block generator does not reveal the data of the new block (data hiding attack), and the node suddenly cannot approve the block because it cannot read the data, which is a common problem in Rollup.

Introduction to Data Availability Sampling (DAS):

Light clients (which I introduced earlier) can verify data availability without downloading all the data. Light clients run small samples of the data and each time get 50% certainty that the data was actually published.

In many cases, light nodes only need to download less than 1% of the data to ensure that 99% of the data has been published, which is a big improvement!

Learn more

Coming back to light clients, I said before that light nodes are much cheaper in terms of hardware requirements, but because they rely on the "majority honesty assumption", they are less secure.

So, what about light clients with the “honest minority assumption”?

For example, Celestia's light nodes use data availability sampling by downloading a small portion of the data. They rely on the "minority honesty assumption" (assuming that a minority of blockchain transactors are honest and abide by the protocol rules), which greatly improves security.

The following figure shows the comparison of different nodes and clients.

Now let’s look at Celestia’s different solutions:

-Sovereign Rollup

-Sovereign Rollup handles the execution and settlement layers itself, instead of using Ethereum as the settlement layer like Arbitrum and Optimism.

Advantages of Sovereign Rollup:

- Greater freedom over the execution environment

- No sharing of computing resources

-Hard fork can be performed if problems arise

Sovereign Rollup is more similar to L1 and can be bridged to other Sovereign Rollups and settlement layers.

Cluster

A blockchain Cluster is a group of blockchains and Rollups that can communicate with each other in a "trust-minimized manner". A trust-minimized bridge is a bridge between two chains that does not require a middleman or majority honest assumption to ensure the security of funds.

An example of a Cluster is Ethereum and its Rollup (L2) or different chains in the Cosmos ecosystem that are able to have intra-Cluster communication (trust-minimized bridge instead of trusted bridge).

Here are all the things that combine with Celestia:

Trust-minimized communication (intra-Cluster communication) requires "a few honest assumptions", which is what Celestia exploits, and light nodes can use data availability sampling. Trust-minimized bridges are much more secure, forming the "Cluster" and "intra-Cluster communication" of the chain. Therefore, Celestia provides a key part for Rollup to form a Cluster and communicate in a trustless manner.

Celestia Quantum Gravity Bridge 和 Celestium

Celestia Quantum Gravity Bridge is a data availability bridge between Ethereum and Celestia, which allows "off-chain data availability" for L2 on Ethereum (Ethereum Rollup using Celestia as the data availability layer).

Celestium is an L2 Rollup built on Ethereum, using Celestia instead of Ethereum as the data availability layer, and still using the Ethereum mainnet for settlement and consensus. Other L2s can also follow suit to improve their scalability.

Summarize:

Celestia serves as an independent data availability layer and can also be a consensus layer in some cases. Rollup can use Celestia to improve scalability due to the inherent technology of data availability sampling and "minority honest" light nodes.

Part 3: End at Fuel Labs

Let’s end this topic by talking about Fuel Labs, who are building an execution layer that can be implemented with Ethereum and Celestia, maintaining high security and decentralization to scale throughput.

Learn more about Fuel Labs:

-One of Fuel Labs’ products is their Optimistic Rollup built to scale Ethereum. It includes:

-Trust-minimized bridge between Fuel and Ethereum

-FuelVM — Parallel verification by running smart contracts using “UTXO” (Unspent Transaction Output)

-Sway programming language

In short, FuelVM can run multiple processes at the same time (parallel validation) and because Celestia works with all VMs, Fuel can also launch Rollups using Celestia as a data availability layer and/or consensus layer.