Rollups
Rollups process transactions outside the Layer 1 and only post aggregated data to the Layer 1. Because all transaction data is included on a Layer 1, rollups benefit from the inherent security of it, most notably of Ethereum.
There are two main categories of rollups, each with its own security approach:
- Optimistic rollups operate under the assumption that transactions are valid by default and only execute a verification as a response to a dispute (Arbitrum, Optimism, Base).
- Zero-knowledge rollups execute computation off-chain and provide validity proofs to the blockchain (zkSync, zkEVM).
Rollups are the most prevalent type of modular scaling, with 8/10 biggest scaling solutions relying on this technology.
Sidechains
Sidechains are independent blockchains that run alongside the Layer 1. They connect to the Layer 1 through bi-directional bridges and operate under their own consensus rules and block parameters.
Sidechains allow for more experimental or application-specific environments while staying linked to the Layer 1.
The most popular examples are Lisk, Cosmos, and Polygon with its PoS Ethereum sidechain.
State channels
State channels use multi-signature contracts, allowing participants to conduct transactions off-chain swiftly and without restrictions, settling the final state on the Layer 1. This approach reduces network congestion, fees, and delays.
This concept allows multiple transactions to occur in a private channel located off-chain. Only the initial and final states are recorded onchain. This is ideal for applications requiring high transaction throughput, like gaming or microtransactions.
State channels are a complex solution that still suffers from many flaws. After years of development the technology is still in the testing phase. In addition, the UX leaves much to be desired for.
Plasma chains
Plasma chains are distinct blockchains tethered to the main Ethereum blockchain, utilizing fraud proofs (similar to optimistic rollups) for resolving disputes.
The created child-blockchains are anchored to the main Ethereum blockchain. Each child-chain can have its own rules and operate independently, which is beneficial for creating scalable decentralized applications (dApps).