Author: YBB Capital Researcher Ac-Core
The working principle of Ethereum is that each node will store and execute every transaction submitted by the user. In order to expand the entire network, Ethereum adopts the Rollup solution. Simply put, it moves most of the transaction processing off-chain (L2), thereby reducing the burden on the Ethereum main network (L1) and reducing transaction fees, that is, Rollup = a set of smart contracts of L1 + network nodes of L2, that is, on-chain Smart contracts and off-chain aggregators, which rely on Ethereum itself for its own settlement, consensus and data availability, are only responsible for executing transactions. The L2 network node consists of multiple parts, the most important of which is the sequencer, but currently Rollup's sequencers are facing centralization problems.
Rollup is a scaling solution for Ethereum (L1) that executes transactions off-chain, packaging transactions in blocks. For each block, Rollup publishes the data needed to reconstruct the chain state (as a source of data availability) to the data availability layer, and publishes proof of the correctness of the off-chain execution to the settlement layer (there are two types of Rollup, in In the case of ZK-rollup, zero-knowledge proofs are issued for each block; in the case of Optimistic rollup, fraud proofs are only issued when a dispute occurs). After EIP-4844, when data publishing switches to blobs, This layer might be called the "data publishing layer". Among them, Rollup's smart contract verifies the issued proof on L1, and each Rollup will have one or more bridges to realize data transmission between chains as well as deposits and withdrawals.
In the implementation logic of Rollup, the sequencer is a key component. It is mainly responsible for receiving transaction requests on L2, determining their execution order, and packaging the transactions into batches (Batch) and finally transmitting them to L1. Rollup smart contracts play an important role in improving transaction processing efficiency and reducing costs.
The function and working principle of the sorter mainly include four parts.
1. Receive transactions: The sequencer receives transaction requests from users or applications. These transactions are first processed on L2 instead of directly on the Ethereum mainnet;
2 Sorting transactions: The sequencer is responsible for sorting the received transactions and determining their execution order. This process is similar to what Ethereum miners do before packaging transactions into blocks;
3 Packed Transactions: The sorter packs sorted transactions into batches, which contain aggregate information from multiple transactions ;
4 Submit to L1: Finally, the sequencer submits the packaged transaction batch to the Ethereum mainnet (L1), where settlement and data storage are performed. This way, L1 can verify and store state updates on L2.
Although Rollup technology provides an effective scaling solution, there are still some problems in the design and implementation of sequencers. The first one is the centralization problem. Most Rollup projects currently rely on centralized sequencers, usually managed by a single entity. Or controlled by a few entities, the intuitive risks are a lack of transparency and single points of failure.
Putting aside the above rigid explanation, the discussion on the L2 decentralized sorter solution, mentioned in YBB Capital’s previous articles, is whether it is the L2 solution of sorting pool node staking that Metis directly opens to the market, or the L2 solution The Espresso plan, a newly launched independent project, is essentially about the distribution of the "profit cake" and the space expectations for future market speculation, so correctness of interests and legitimacy is the key that cannot be avoided.
图源：@drakefjustin
The Rollup concept was first proposed by Vitalik Buterin, the founder of Ethereum. Its original idea was to achieve a completely unconstrained "Total Anarchy" state to allow any Unlimited transaction expansion for people. Combining the above-mentioned problems with the current sorter, in 2023 Ethereum Researcher: Justin Drake proposed a solution called Based Rollups in which the sorter is managed by Ethereum L1 itself. The content is as follows (see extended link 1 for the source):
“When the ordering of aggregations is driven by the base layer (L1), we call it L1-based or L1-ordered aggregation. Specifically, L1-based aggregation means that the next L1 proposer can match the L1 searcher and Builders cooperate to include the next Rollup block in the next L1 block without permission. ”
Liveness: Based Rollup enjoys the same liveness guarantee as L1. Please note that the activity of non-Based Rollup with Escape Hatches will be reduced (Escape Hatches is a safety mechanism in Rollup that allows users to safely extract assets from L2 back to the L1 master when there is a problem with the Rollup system. chain. It is similar to an emergency exit);
Weaker settlement guarantee: Escape pod transactions must wait for a timeout period before settlement is guaranteed;
Censorship-based MEV: Rollups with escape hatches are vulnerable to adverse MEV effects from short-term sequencer censorship during timeouts;
At risk for network effects: mass exits triggered by sequencer liveness failures (e.g. for 51% attack on the decentralized PoS sorting mechanism) will destroy Rollup's network effect. Note that unlike L1, Rollup cannot use social consensus to recover gracefully from sequencer liveness failures. In all known non-Based Rollup designs, mass exit is the Sword of Damocles;
Gas Penalty: Transactions settled via escape pods often incur Gas penalties for their users (e.g. due to transactions not being batch-packed) sub-optimal data compression).
Decentralization: Based Rollup inherits the decentralization of L1 and naturally reuses the L1 searcher-builder-proposer infrastructure. L1 seekers and builders are incentivized to include rollup blocks in their L1 blocks to extract the rollup's MEV. This then incentivizes L1 block proposers to package rollup blocks on L1.
Simplicity: Based Rollup sorting is the simplest, even much simpler than centralized sorting. Based Rollup requires no orderer signature verification, no escape hatches, and no external PoS consensus.
Historical Note: In January 2021, Vitalik called the solution based on L1 sorting "complete anarchy", which has the risk of submitting multiple rollup blocks at the same time, resulting in a waste of Gas and workload. The current block proposer-builder separation (PBS) scheme can strictly control L1 ordering, with at most one rollup block per L1 block, and no gas waste. This avoids wasting the proof work of a ZK-rollup when block n+1 of the rollup (or n+k for k >= 1) contains a SNARK proof of block n.
Cost: Based Rollup has zero gas overhead - there is no need to even verify signatures from decentralized or centralized orderers. The simplicity of Based Rollup reduces development costs, shortens release time, and reduces the exposure area for code vulnerabilities. Based Rollup sorting is also token-free, avoiding the regulatory burden of token-based sorters.
Consistent with L1 economic alignment: MEV originating from Based Rollup naturally flows to the L1 it is based on. This flow strengthens L1 economic security and, in the event of MEV destruction, increases the economic scarcity of L1’s native tokens. This strong economic integration with L1 may help build the legitimacy of Based Rollup. Importantly, despite sacrificing MEV revenue, Based Rollup retains the option to generate revenue from L2 congestion charges (such as L2 base charges in the form of EIP-1559).
Sovereignty: Although sorting is delegated to L1, Based Rollup retains sovereignty. Based Rollup can have a governance token, charge a base fee, and the proceeds from these base fees can be used when appropriate (e.g. Optimism funds public goods).
No MEV income: Based Rollup hands off MEV to L1, limiting its income to base fees. Counter-intuitively, this may increase the total revenue of Based Rollup. The reason is that the rollup landscape appears to be winner-take-all, with the winning rollup likely to leverage the security, decentralization, simplicity, and consistency of Based Rollup to achieve dominance and ultimately maximize revenue.
Constrained sorting: Delegating sorting to L1 reduces sorting flexibility. This makes certain ordering services more difficult and possibly impossible to achieve:
Pre-confirmation: Fast pre-confirmation is not a problem for centralized ordering and can be achieved through external PoS consensus. Fast prevalidation using L1 sorting is an open problem with many promising research directions, including EigenL, Inclusion Lists, and Builder Bonds.
First come first served (FCFS): Arbitrum-style FCFS sorting is not sure whether it can be implemented on Based Rollup. EigenL may provide an overlay of FCFS for L1 sorted Based Rollup.
"Based Rollup" The name comes from the proximity to the base chain (Base L1). This conflicts with Coinbase’s recently announced Base chain, which is a wonderful coincidence. In fact, Coinbase shared two design goals in their Base announcement:
Tokenlessness: “We have no plans to issue new network tokens.”
去中心化 (decentralisation)：「 我们 [...] 计划随着时间的推移逐步去中心化区块链。」
Base 可以通过成为 Based Rollup 来实现无代币的去中心化。
图源：@jchaskin22
综上理论，Based Rollup可让任何人都可扩展到Rollup区块，把排序后的交易状态变化发布到L1即可从L2中提取MEV，让所有的排序和安全性均由以太坊L1提供。这样可以规避外部权益证明共识和特定的Rollup的Token需求，同时相比于其他Rollup为保住资产安全必不可少的”紧急逃生舱“功能相比，在Based Rollup的愿景中可以去除，其过程只需在保住以太坊安全运行的前提下，在Rollup上的交易既可顺利完成。
图源：Taiko官网
Taiko Labs是开发和推广Based Rollup的主要团队，而Based Rollup是Taiko Labs在以太坊第二层扩展解决方案方面的项目。其愿景是通过Based Rollup等创新技术，解决以太坊主网的扩展性问题。其主要有三个特点：
1.完全等同于以太坊的EVM(Type 1) ZK-EVM：使用的（Type1) zkEVM具备完全的以太坊兼容性，开发者可以无缝地在以太坊和Taiko之间迁移去中心化应用（dApps），而无需担心智能合约执行失败的风险；
2.开源：Taiko的所有源代码都公开在GitHub上，任何人都可以查看、构建或修改。这种开源模式确保了区块链技术的发展不仅局限于一个小团队的努力，还涵盖了全球范围内的社区和开发者；
3.完全去中心化：除了确保与EVM的高度兼容性，Taiko还致力于实现协议的完全去中心化。Taiko计划通过去中心化的提议者和验证者来提交区块和生成zkPs，从而保障系统的去中心化特性。
Taiko致力构建类型1完全等效于以太坊(fully Ethereum-equivalent)
的ZK-EVM，即Vitalik Buterin 在《The different types of ZK-EVMs》（见扩展链接2），中提到的追求完全且毫无妥协地与以太坊等效。其目的是与以太坊完全兼容来验证以太坊区块（至少可验证执行层，不包括信标链共识但包括所有的交易，智能合约和账户逻辑，且不会取代哈希，状态/事务树和其他共识逻辑），所以相比于其他类型，为接近原生解决方案，Type 1 是最具复杂性和挑战性的一种。
图源：Vitalik Buterin：《The different types of ZK-EVMs》
可竞争的Rollup(BCR - Base Competitive Rollup)
是Taiko Labs开发的一种创新型区块链扩展解决方案。BCR旨在通过竞争机制提高Rollup的效率和安全性，使得不同的参与者可以自由竞争提交区块和生成证明，从而提升整个网络的性能和去中心化程度，综合来看总结如下。
特点
开放竞争：允许任何符合条件的参与者竞争提交区块和生成证明，这种开放机制减少了中心化控制，提高了网络的去中心化程度。竞争者通过提供更优质的服务来赢得奖励和交易费用；
高效扩展：可以有效提升区块生成和验证的效率。多个竞争者可以并行工作，避免了单点瓶颈，提升了交易处理的速度和网络的扩展能力；
安全性：通过多方参与的竞争机制，提高了系统的抗攻击能力。多方竞争生成的区块和证明，增加了系统的透明度和安全性，难以被单一实体控制或攻击。
优势
EVM兼容：BCR与以太坊虚拟机（EVM）完全兼容，使得现有的以太坊智能合约和去中心化应用（DApps）可以轻松迁移到BCR上运行，而无需进行重大修改；
高吞吐量：由于BCR可以并行处理交易和生成区块，网络的吞吐量显著提高，能够处理更高的交易量，降低了交易成本和延迟；
去中心化：通过去中心化的区块生成和证明机制，确保了网络的去中心化特性，降低了被中心化实体控制的风险。
劣势
复杂性增加：系统复杂性需要复杂的算法和协议来协调多个竞争者之间的区块生成和验证，智能合约复杂性让智能合约可能需要额外的逻辑来处理竞争结果；
潜在问题：在BCR的竞争机制下，多个竞争者同时计算和提交区块时，可能导致的费用上升，用户在使用BCR进行交易时可能面临较高的交易费用，尤其是在网络繁忙或竞争激烈的情况下。同时资源丰富的大节点可能在竞争中占据优势，造成中心化的集中。
基于助推器的Rollup(BBR-Based Booster Rollup)
助推器（Booster）在BBR中是一个特殊的参与者，它负责优化交易批次，对交易数据进行压缩和并行处理多个交易批次的作用，实际作用是将执行和存储进行分离，保持L2执行的同时L1保持去中心化，并且让智能合约在L1和所有BBR上的地址保持一致。
与此同时，它也面临系统复杂性增加、资源消耗、潜在中心化等问题的挑战。未来，BBR仍需要进一步优化和扩展，以满足区块链技术不断发展的需求。
图源：Taiko Labs
当下整体观察来看，Based Rollup算得上以太坊二层扩展方式的巨大转变，将Rollup的排序直接委托在一层提议者，利用提议者与构建者的分离设计， 让一层为 Rollup 执行所有的排序者角色。同时也让MEV得到扩展，这样 L2 搜索者可将交易捆绑发送给 L2 构建者，同样后者也是 L1 的搜索者，而这些完整的 L2 区块随后成为 L1 区块的一部分，最终由 L1 构建者和以太坊主网处理。
能否将Based Rollup假设为Rollup的最终解我们还有待考证，但不可否认的是它在现阶段是以太坊二层扩展的一次重大创新，为扩展提供了更安全，去中心化解决方案。如果将同等思维带入比特币生态，与有强可扩展性的以太坊实现原生且去中心化的VM相比，其实现难度都无可厚非，所以目前整个行业在解决真正去中心化扩展的问题上仍有很长一段路要走。
扩展链接：
【1】 Based rollups—superpowers from L1 sequencing https://ethresear.ch/t/based-rollups-superpowers-from-l1-sequencing/15016/1
【2】The different types of ZK-EVMs https://vitalik.eth.limo/general/2022/08/04/zkevm.html
参考文章：
【1】信用的游戏：被多签和委员会操控的Rollup们 https://mp.weixin.qq.com/s?__biz=Mzk0OTYwMDM1Mg==&mid=2247486544&idx=1&sn=7a0ee8eb1d32e6ef0bd08354986c0a1f&source=41#wechat_redirect
【2】Taiko研报：实现无缝扩展与完全兼容的以太坊Layer 2解决方案 https://www.panewslab.com/zh/articledetails/id09jfto.html
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