What’s the difference in design of Classical Rainbow Bridge and Fast Rainbow Bridge?

In order to enable fast transfers and overcome the limitations of the Classical Rainbow Bridge, the team introduced the three additional components:

LP-Relayer (Liquidity provider relayer): An off-chain service with accounts on both Ethereum and NEAR, the relayer holds liquidity in tokens on the Ethereum side and facilitates token transfers between NEAR and Ethereum. Upon receiving the tokens back on the NEAR side, the relayer transfers his funds back to Ethereum to replenish its liquidity using the classical Rainbow Bridge.

NearFastBridge: A contract on NEAR that locks tokens and transfers them to the relayer upon providing proof of the finalized transaction on the Ethereum side.

EthereumFastBridge: A contract on Ethereum used by the relayer to transfer tokens to users. This contract generates events of token transfers on the Ethereum side.

With the introduction of these new elements, the Rainbow Bridge is now able to perform transfers of ERC-20 tokens from the NEAR to the Ethereum ecosystem within a few minutes and with an additional relay fee.