secondlayer

Second-layer, or second-layer solutions, are protocols built on top of a blockchain's base layer (layer 1) to improve scalability, throughput, and user experience. They move most transactions off the main chain while periodically anchoring data or proofs to layer 1 to preserve security and finality.

Common approaches include state channels, sidechains, and rollups. State channels enable participants to transact off-chain with on-chain settlement at closure. Sidechains are separate blockchains connected to the main chain via a two-way peg, maintaining their own security model. Rollups bundle or compress a large number of transactions off-chain and post proofs or transaction data back to layer 1 for settlement. Optimistic rollups assume correctness and use fraud proofs to challenge misbehavior; zk-rollups use zero-knowledge proofs to validate batches of transactions.

Notable implementations include the Lightning Network for Bitcoin as a payment-focused second layer; on Ethereum, optimistic rollups projects such as Optimism and Arbitrum, and zk-rollups such as zkSync and StarkNet. Polygon provides a range of layer-2 solutions and interoperability within the Ethereum ecosystem. These technologies are designed to preserve the security guarantees of the base chain while increasing throughput.

Advantages include higher transaction throughput, lower fees, and faster finality for user-facing operations. Limitations and trade-offs involve differing security assumptions, data availability considerations, and the complexity of asset bridging between layers. User experience and custody models can be affected, and there is ongoing work to standards and interoperability.

Second-layer solutions are widely used for payments and DeFi use cases, and they continue to evolve as scaling challenges and regulatory considerations influence deployment and governance. They are intended to complement layer 1 rather than replace it.