# Layer 2 Scaling Solution Overview - Scroll


>What is Layer 2 Scaling for Ethereum?
>What are enterprise use-cases?
>Multiple specialized rollups are emerging. What is slowing the rise of generalized rollups?
>Learn about cross-chain bridging and composability between different L2 solutions.
>An overview of the Ethereum layer 2 roadmap.
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### What is layer 2 and what are the different solutions that are available to scale Ethereum?

We define layer 2 as a chain that fully or partially derives its security from layer 1 Ethereum, so that users do not have to rely on the honesty of layer 2 validators for the security of their funds.

It’s a separate layer where you can move the on-chain transactions off-chain, while still enjoying the same security and decentralization as layer1. There are a few layer2 solutions, while popular, the security depends on a few relatively centralized nodes compared to Ethereum layer1.

### Are zk-rollups more secure/efficient than Optimistic ones?
Both zk-rollups and optimistic rollups share a similar security level. However, the security of a zk-Rollup could be considered slightly higher, since it only relies on math instead of the Economic hypothesis.  Also, the TPS upper bound of zk-rollups is higher than the optimistic ones.

### How do we see the vision for generalized rollups and specialized rollups?
Generalized rollups have better compatibility, where you can see defi projects interacting with each other more smoothly. With specialized rollups, you might need customized circuits, which is suitable for stand-alone products where you can optimise for efficiency. Business models such as derivative exchanges or some NFT use cases perhaps have less need for compatibility, as opposed to efficiency and higher frequency.

If we can reduce the overhead for generalized rollups, then all transactions can be moved there. One property of a zk-rollup is that if you have more transactions, you can amortize for cheaper transaction fees. And this is because one proof can be amortized over multiple transactions. Its assumption is still dependent on the performance, but that's our current prediction.

### Some believe that with multiple L2s launching, the liquidity will be split into different L2s. How we think about this assumption?

We don't believe this to be the case. When multiple Layer 2s are launching, there will be different use cases and different Dapps launching on different Layer 2s. Also, there will be bridges connecting them -- in fact, there's already ongoing work building bridges between different L2s. In the near future, we wouldn't be surpised to see 90% of ETH Layer 1 transactions moving to different Layer 2s.

### As Vitalik mentioned, rollup is the future of Ethereum scaling. How Rollup will integrate with ETH 2.0?

Data sharding and POS are two of the most important milestones in the ETH 2.0 upgrade. There will be multiple data shards that can store on-chain data. It can solve the most noticeable bottleneck for rollups -- the data availability issue. Once we upgrade to ETH 2.0 with data sharding, it can highly increase the throughput of rollups and thus can decrease the cost of storing data on-chain. Ultimately this would result in significantly decreased transaction fees and achieving a TPS even higher than 20k.

### There will be a few general purpose L2s to choose from in a year’s time, so what are the things developers should be deliberating when picking a L2 to use?

We're striving toward something called zkEVM: a general EVM-compatible solution, so developers won't need to make adjustments from their current layer 1 DApp building process or need adaptation during the transition. Devs care about whether it's easy to integrate, whether they'll need to modify their code, whether you are fully and partially compatible, or language compatible.

Overall, we're more focused on open integration rather than being the first.

### What will be the new breed of application that rollups will enable?

Right now, most of the applications that are popular on Ethereum Layer 1 are related to investments, lending, or value accrual. With the advent of rollups, gas fees will become such a small proportion of overall on-chain transactions, we're hoping to see the appearance of applications related to useful or fun use cases. There might also be enterprise-level specialised applications, where you can enjoy lower gas fees and you can run your own node for your own transactions. That may be the trend in the future.

### Scroll's Roadmap

Our nearest milestone will be a concept demo, where our user can try to input some opcodes, and our demo will generate some proof for execution related to some transaction. The next milestone will be in Q2 next year, when we plan to launch our native EVM compatible testnet with all opcodes. After auditing and testing of our testnet, we can then launch mainnet with the smoothest and improved integration in est Q3/Q4 of next year.