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interact between two chains using IScrollMessenger interface, the Scroll bridge utilizes the Gateway Router. This contract ensures the smooth passage of these assets between L1 and L2, allowing users to transfer their Ethereum-based tokens seamlessly. depositETH and depositERC20 are payable functions, the amount of ETH sent to these functions will be used to pay for L2 fees. If the amount is not enough, the transaction will not be sent.

simple stack for interacting these two contracts in remix.ide, learnt about the optimistic rollups implemented by scroll network and how bridges work in general.

L1GatewayRouter selects the appropriate gateway for ERC20 token bridging.
L1StandardERC20Gateway for ERC20 tokens without custom logic on L2.
L1CustomERC20Gateway for tokens with custom logic on L2.
To bridge a token, use the depositERC20 function on L1GatewayRouter.
All Gateways send messages to L1ScrollMessenger, which can transmit messages to L2.
Users can send messages to L1ScrollMessenger to execute functions on L2.
Gateways simplify transfers and calls for token contracts on the bridge.