With the maturity of Ethereum’s layer-2 networks and the significant reduction in Gas fees, these networks are experiencing rapid growth. However, issues such as fees and speed can affect user experience negatively. In this context, the importance of transaction sequencing becomes increasingly prominent, as it is key to resolving transaction bottlenecks and optimizing user experience.

In April this year, Astria, a modular blockchain focusing on shared sequencers, completed a $5.5 million seed round of financing, led by Maven 11, with participation from 1kx, Delphi Ventures, and Robot Ventures. Just three months later, Astria raised an additional $12.5 million, led by dba and Placeholder VC, with participation from Hasu and others.

What is Astria?

Astria is developing a decentralized shared sequencer network aimed at providing Rollups with fast finality, censorship resistance, composability, and decentralization.

Currently, it is more convenient, cheaper, and user-friendly for L2s to run a centralized sequencer, which is why most mainstream L2s are managed by their teams. Although L2 users can bypass sequencers by directly submitting transactions to L1, they must pay L1 transaction Gas fees, and the transactions may take longer to finalize.

Sequencers control the order of transactions and theoretically have the power to exclude user transactions. Sequencers can also extract MEV (Miner Extractable Value) from transaction groups. If there is only one sequencer, the risk of centralization increases. Therefore, a decentralized shared sequencer still holds significance.

How Astria Works

Astria’s decentralized sequencer network consists of multiple sequencer nodes, enabling the ordering of Rollup transactions. In Astria’s operational model, users submit transactions to Rollups, and the transactions automatically enter their respective Rollup node memory pools. Combiners collect the transactions and send them to the sequencers. Finally, the sequencers aggregate the transactions into a shared block and send pre-acknowledgment to the users.

Currently, sequencers are implemented based on specific Rollups. Astria, however, processes blocks for multiple Rollups in batches. Through data compression, it can save more costs when publishing data to L1. The decentralized shared sequencer network incentivizes participants from multiple Rollup ecosystems to act as validators on the network.

Astria Stack

The main components of Astria include five parts: combiner, sequencing layer, relay, DA (Data Availability), and conductor.

Combiner

Technically skilled professionals might be able to use the sequencing layer directly for better transaction ordering, but this increases the difficulty for most ordinary users. Interacting directly with the sequencing layer requires users to hold sequencer tokens and maintain a sequencer wallet, both of which negatively impact user experience. Astria provides combiners as tools to abstract this complexity for users. Combiners act like gas stations, bearing the cost of transaction sequencing for users. They also provide unordered guarantees, bundling transactions in the order they are received.

Sequencing Layer

The Astria sequencing layer uses CometBFT as its consensus algorithm. Chains that support CometBFT can support IBC (Inter-Blockchain Communication), meaning it can operate across many other chains. The unique feature of Astria’s sequencer is that the transactions it contains are not executed (delayed sequencing) but are assigned to another execution engine, Rollup. Sequencer nodes can choose to act as “validators,” actively participating in the production and finalization of new blocks.

Astria’s sequencer application logic allows for three main functions:

1. Ordering of Rollup data
2. Value transfer
3. Changes to the validator set

Relayer

The relayer’s function is to take verified blocks from the sequencer and pass them to the DA (Data Availability) layer. Since the sequencer’s block time is faster than the DA, the relay first batches the ordered data from multiple sequencer blocks, then compresses it and submits it to the DA.

Individual sequencer blocks can also be retrieved by the conductor before the relayer submits them to the DA. This allows for fast finality, improving the user experience by acting as a soft commit to the execution layer. The data set sent by the relayer to the DA layer is used as the source of truth and is ultimately extracted from the DA to be used as a confirmation of finality in the Rollup.

DA

Astria uses Celestia as its data availability layer, which is the final destination for all data sequenced by the sequencer network. Once data is written to Celestia, the transaction order is considered final, and when new Rollup nodes are launched, all data will be extracted from here.

Conductor

The conductor can be seen as the consensus implementation of a Rollup full node, similar to the operation nodes in the OP Stack. The conductor is the counterpart to the execution engine, together forming a complete Rollup node. Its role is to connect the sequencer and DA layer to the Rollup execution layer by extracting transactions belonging to the Rollup node from each sequencer block and forwarding them to the execution layer.

For each sequencer block, the required relevant Rollup data is extracted. After verifying the batch of Rollup data and waiting for the verification to be completed, it converts the data into a list of transactions and passes it to the execution engine.

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