> For the complete documentation index, see [llms.txt](https://bitcoin-layers.gitbook.io/bitcoin-layers/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://bitcoin-layers.gitbook.io/bitcoin-layers/types-of-protocols-that-may-support-bitcoin-scaling.md).

# Types of protocols that may support Bitcoin scaling

We have seen the following protocols being used to scale Bitcoin.

* Federations: Custodial protocols (e.g. Fedimint) or blockchains operated by permissioned federation members (e.g. Liquid)
* State channels: Multi-signature contracts where parties can perform transactions while the channel is open
* Sidechains: Permissionless consensus protocols (blockchains) that exist to provide more functionality to BTC the asset, or are merge-mined with Bitcoin, or do both.
  * Sidechain rollups: Rollups that use sidechains for DA and additionally receive settlement assurances from sidechain consensus
* Validiums or Optimiums: Blockchains that post DA somewhere but have a trustless BTC bridge.
  * This is not currently possible. Blockchains may be pseudo-validiums (or optimiums) if they have a BitVM bridge program, but no implementation of this is currently live.
* Rollups: Blockchains that post DA to Bitcoin (and have a trustless BTC bridge)
  * Rollups *can* have trust-minimized validating bridges (that may also validate ZK-proofs) with something like a BitVM bridge program. No implementations of this are currently live. The requirement for being a rollup is using Bitcoin as the DA layer.
* Other: Client side validation protocols, Taproot assets, L3s

### Notes

* We classify rollups that settle to other blockchains that are not merge-mined, or don't use Bitcoin for data availability, as sidechains.
* Alternative Layer 1 blockchains are not sidechains because they do not exist to scale Bitcoin.