A Deep Dive into Ethereum's Rollup Economics: Rollup Economics 2.0

简介：

In February 2022, Barnabé introduced a framework for Rollup economics centered around resource pricing and value flow. This was constructed for examining MEV in L1 dependent economies, interactions between L1 and L2 fees, and essential concepts like operator revenue and costs. It’s a straightforward framework, apt for a simple world: a centralized Rollup on an independently operated auxiliary cycle. Much has evolved over the past 18 months: shared sequencing, decentralization, proof/data aggregation, Rollup coalitions, governance. We’re introducing a new framework, shedding light on a Rollup world gearing up for expansion. There’s still a plethora of experiments underway, but several patterns have emerged. We will dissect these key patterns, hoping to offer tools to grasp the potential direction of developments and address existing open-ended questions.

Revisiting Rollup Economics 1.0

The initial Rollup economics framework included three entities: the user, the Rollup operator, and the foundational layer. It also offered a simplified view regarding value flow, involving L2 fees and MEV, operator costs, and data publishing expenses. This was a rudimentary framework, but a useful starting point because things soon become much more intricate.

From these basic flows, we can gauge the Rollup protocol’s surplus and derive associated ideas. Topics like MEV extraction and distribution, L2 issuance, allocation of L2 congestion fees, and the timeframe for Rollup to maintain a balanced budget or achieve a surplus (considering the L2 ecosystem is a continually growing economy, finding operational surpluses beneficial for community public goods funding, development, and expansion).

Rollup Protocol Surplus = L2 fees - Operating Costs - Data Costs

The Rollup protocol has control over its L2 fees (which includes congestion pricing and MEV) and its operating costs (covering issuance and operator rewards). Regardless of whether the protocol chooses to pursue a balance or surplus goal, L2 operations require coordination for:

（1）Optimally setting L2 congestion fees,

（2）Extracting and reallocating MEV,

（3）Reducing data costs through optimization and strategic publishing.

These represent the primary economic design choices that different L2 ecosystems are currently exploring. In the future, protocols might look towards using block space derivatives to mitigate the unpredictability of data costs.

Over the past 18 months, there’s been a significant shift. Much like L1 block construction, we’ve observed Rollup operators fragmenting into more specialized roles. As the economy grows, specialization naturally arises, which is positive since a separation of concerns can lead to more resilient systems if addressed properly in design. But now, with a broader design space, we need a fresh roadmap to guide our journey.

Rollup Comes of Age

As Rollup technologies mature, their complexities are also increasing, leading to what we dub the “Rollup Federation.” Rollup structures shared among the same type of Rollups are designed to bolster security (through shared governance and community coordination), efficiency (through shared features and economies of scale), and user experience (by enhancing interoperability and reducing fragmentation). Concurrently, independent providers are developing infrastructures to offer one or more of the aforementioned benefits to any Rollup that decides to utilize their services. We’ll delve deeper into these models below.

Independent Rollup

Individual Rollups are moving away from auxiliary wheels, amplifying their security and decentralization. From an operational/economic standpoint, the major cost areas include:

• Ordering: This incurs operational and incentive costs to motivate sorters.
• Data Availability (DA): Rollups must publish data at the base layer, hence incurring data costs, a major expense discussed in the original framework.
• State Verification (SV): This directly boosts the operational costs of zkRollup.

Within all these cost areas, individual Rollups face a pivotal trade-off between security and efficiency. For instance, they might opt for a less secure but cheaper data availability layer. The costs of data publication (which we simply term “data costs”, even though it encompasses some L1 computation costs related to publication) historically stood as the priciest item. With Ethereum’s swift implementation of EIP-4844, followed by the full-fledged Danksharding, this will significantly drop, granting Rollups the desired cost advantages to scale and support novel use cases. In the long run, efficiencies in data costs and related services may be realized through off-chain innovation aggregates, unleashing economies of scale.

Specific examples of aggregation include shared ordering services. For Optimistic Rollups, an intriguing idea is batch publishing, which accelerates the benefits of batch compression, especially for smaller participants, by offering reduced costs and enhanced security through faster data publication. For zkRollups, shared provers are among the most thrilling Rollup solutions, especially since they can recursively aggregate, reaping immense benefits in terms of efficient utilization of L1 data markets, albeit at the cost of more off-chain computation. It’s evident that Rollups will eventually opt for shared services, whether as part of a Rollup Federation or an economic alliance.

One potential direction the Rollup ecosystem might take is to have more independent Rollups closely aligned with L1. While we haven’t seen many implementations, at least two intriguing architectures emerge. One entails delegating its block ordering to the L1 Rollup, leveraging the L1 transaction supply network for MEV extraction but retaining the authority to set L2 congestion fees. An even more radical approach is the establishment of Rollups within Ethereum itself. We’ll explore the economics of these models more profoundly when discussing the MEV resilience and decentralization of Rollups.

Rollup Cooperatives

The first type of integration between two Rollups is purely economic cooperation, akin to economic cooperatives.

“A cooperative is an entity made up of people or groups that share or collaborate to achieve common objectives, such as economic benefits or savings.” — Wikipedia

In its simplest form, there exists a joint procurement agreement for some service between Rollups. Imagine a shared batch publishing service that Rollups can subscribe to, achieving lower data posting costs. Further economic integration, such as shared sequencing services, can offer cost benefits and make transactions between Rollups settle atomically, thus reducing trade barriers between them. This thinking is reminiscent of the European Economic Community or other similar common market associations.

A more complex model of standalone Rollup economics can be built by introducing intermediary service providers. Here, two new economic effects arise for the Rollup ecosystem:

• Rollup Cost Structure: The costs for a Rollup operator now encompass operational costs, service costs, and data publishing costs.
• Shared Service Economics: The new entity must achieve budget equilibrium.

Examples of such services include the Espresso sequencer, a shared service for ordering and publishing, limited to shared batch publication, or shared proof. In all these cases, shared services face two major economic challenges:

• Cost-sharing of L2 services: Dividing the total service cost among Rollups using the shared service in an economically fair manner.
• Decentralization of shared services: Achieving some level of decentralization, depending on the service type, striking a balance between performance and robustness. This standard is lower than the base layer but involves management incentives and MEV.

Rollup Federations

Rollup federations differ from economic cooperatives as they involve both economic integration and some form of political integration, analogous to a federal state.

Technically, political integration is achieved through a shared cross-chain bridge, but it also demands a shared governance system. Setting aside political and governance considerations, we’ll assume the existence of a shared cross-chain bridge and focus on the implied economic relations. This Rollup federation architecture is emerging across all major Rollup systems, becoming platforms for interoperable peer Rollups.

For instance, Optimism Superchain, Polygon 2.0, StarkWare SHARP, zkSync Hyperchains, and other related projects all share a similar pattern in their architectures. The diagram below outlines this (Note: for illustration purposes, we assume Rollup federations automatically opt for shared services and do not incur direct data publishing costs).

The presence of shared cross-chain bridges introduces additional economic variables. Notably, native L2 tokens, like the OP token in the Optimism ecosystem, offer vital decision-making power through governance, serving to allocate resources, roles, and economic flows within the ecosystem. As the Rollups tech stack matures and primary security issues are addressed, the next focus becomes robustness, possibly involving some level of decentralization.

When Rollups contemplate establishing decentralized services (for sequencing, proving, or verifying), they will need to operate consensus protocols. This is when sufficiently large ecosystems see the opportunity to “upgrade” their native tokens to productive assets (as Polygon 2.0 intends with POL). While this isn’t the only way to decentralize L2 services (since Ethereum L1 can leverage its superior security properties), for larger ecosystems wanting to retain more internal control/governance and associated rewards/incentive mechanisms, employing native tokens might be a compelling direction.

Native tokens play a crucial role in bootstrapping the L2 ecosystem/economy. Issuance can reward service operators, fund ecosystem support initiatives, or public goods. However, when native tokens are used to back decentralization via some native proof-of-stake protocol, their security might decrease with more dilution. Even if tokens are solely used for governance, excessive dilution might result in more budget-constrained holders selling, potentially leading to ownership concentration. It seems vital to have a token issuance plan aligned with demand growth. Lastly, making the L2 economy more reliant on native tokens (instead of ETH) also reduces its resilience against certain failure modes, as moving to L1 might not be an option. In extreme cases, while L2 remains secured by Ethereum, it loses the security provided by Ethereum acting as an external currency.

Layered Development Grows

Another rapidly evolving sector focuses on the development of specific applications or customized execution environments. These eventually settle on the foundational layer, even if not done directly. Typically, they cater to applications that require low execution costs and straightforward deployment, willing to trade off some security measures. This includes applications like games, social media, and NFT products that don’t need to initiate their own service economy or attract/secure a large amount of liquidity.

These encompass various types like L3, Validium, and Rollup as a Service (RaaS) platforms. For instance, Arbitrum Orbit is a platform that supports the deployment of L3 chains on Arbitrum L2 (One or Nova). It offers some configurability, such as opting for Arbitrum-sanctioned Data Availability Committees (DAC) or Ethereum L1 as the data availability layer. StarkNet and other zk rollups projects have been actively exploring L3 implementations. An extreme example in deployment simplicity is AltLayer or Caldera, offering no-code solutions to deploy “customizable” Rollups, empowering users to balance security with efficiency.

We are focused on the L3 system. Essentially, this is a layer added on top of L2. From the perspective of L2 Rollups, it represents another source of L2 fees. For the Rollup ecosystem, L3 is a novel entity with its own budgetary constraints:

• Revenue for L3 might come from fees, subscriptions (as in games), or other mechanisms, like revenue-sharing (as seen with NFTs).
• Costs for L3 include the operational costs of the system as well as the computational/data fees from L2. These expenses can be borne directly by L3 or, in the case of hosted services, paid by the RaaS platform. This is yet another service provider that requires budget balancing.

This is another instance of economic specialization within the Rollup ecosystem.

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