# AggLayer + Shared sequencers

By [chandan](https://paragraph.com/@iamchandan) · 2024-03-31

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On Mar 30 sassal.eth tweeted that _“AggLayer + shared sequencers If you're not paying attention to these things, you should be - this tech will further supercharge the already dominant Ethereum layer 2 ecosystem”_

In this article, let's look at what _AggLayer and shared sequencers are individually, and then let's explore what we can achieve if we combine them._

**what is a Sequencer:**

![](https://storage.googleapis.com/papyrus_images/c2985ed2e07c4b330bcb89eb562f4cf0a53db6260ee4a9b65eeb83397fda7719.png)

*   Read transactions from the Layer 2 mempool and execute them
    
*   Batch transactions together and send the batches to Layer 1
    

Today, all sequencers are isolated and run by the Layer 2 team, as shown in the image below.

![](https://storage.googleapis.com/papyrus_images/24c6dc24adf32ef0e2cd3080fda59d7104308e9c5d88d3a8553488eac2e1fc55.png)

We need to strive for decentralized sequencers, but they still don't solve the interoperability between Layer 2s.

**Enter Shared Sequencers:** Shared sequencers operate a separate blockchain to perform the role of a decentralized sequencer for multiple rollups, introducing interoperability advantages.

*   Decentralized sequencers = serve one chain
    
*   Shared sequencers = serve multiple chains
    

![](https://storage.googleapis.com/papyrus_images/cb89ddf9b583bd0f17b6c08a8c816d311e748a71e7afacd482d8cd92b82cd2ab.png)

**Benefits of Shared Sequencers (SS):**

*   Performing cross-chain transfers
    
*   Performing cross-chain DEX arbitrage
    
*   Censorship resistance
    
*   Economies of scale
    

**Cons for Developers:**

*   Not as performant as centralized sequencers
    
*   Loss of sovereignty (Layer 2 developers give up control of their sequencer)
    

**AggLayer:**

![](https://storage.googleapis.com/papyrus_images/5ca4d84535fcbef2ab00da3a2621e06e1f0610ad58aa02dae0a253f3130bc89b.png)

**How it Works:**

*   Each chain's sequencers execute transactions as usual (centralized or decentralized)
    
*   Each chain's sequencer generates a ZK proof of its updated state
    
*   Each chain sends the proof to the AggLayer rather than the Ethereum
    
*   The AggLayer aggregates all the proofs and generates a single, aggregated ZK proof, guaranteeing the validity of proofs for all chains
    
*   The AggLayer posts that aggregated proof to Ethereum
    

The AggLayer (aggregation layer) enables the same atomic transactions and cross-rollup interoperability as shared sequencers without forcing rollup developers to give up control of their sequencers and sovereignty.

**Now, the most important part: let's see how AggLayer and shared sequencers can help each other?**

Currently, building a shared sequencer with cross-chain transactions is complex. However, even without cross-chain transactions, shared sequencers make sense because they bring censorship resistance and economies of scale to the rollup. Additionally, shared sequencers can let the AggLayer solve the cross-chain transaction problem, decreasing the time to market for shared sequencers.

**Most of the info is taken from:**

[![]({{DOMAIN}}/editor/youtube/play.png)](https://www.youtube.com/watch?v=57mhX-5LMDE)

[https://gateway.pinata.cloud/ipfs/QmbvZY784N8fBcQz9NAC1STB2AUvpaQuHPMzR7e6nN24p3](https://gateway.pinata.cloud/ipfs/QmbvZY784N8fBcQz9NAC1STB2AUvpaQuHPMzR7e6nN24p3)

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*Originally published on [chandan](https://paragraph.com/@iamchandan/agglayer-shared-sequencers)*