This section describes the differences between depositing and withdrawing assets on Thanos' L2 Native Token Bridge compared to Optimism's bridge design. L2 Native Token Bridge supports deposits and withdrawals of ETH, L2 native tokens, and ERC20 assets that are not L2 native tokens. Understanding these processes is essential for smooth operations within the L2 environment, as they are the foundation for cross-layer interoperability.

L1StandardBridge and L2StandardBridge are smart contracts used for depositing and withdrawing tokens. They're responsible for initiating and finalizing the bridge process and can be modified based on specific functionality requirements. The following section details the flow of function calls and token movements when users deposit or withdraw tokens using the L1StandardBridge and L2StandardBridge contracts.

Deposit flows

The process begins with a deposit request on L1, which the bridge processes to ensure a secure and synchronized asset transfer to L2. Understanding each step of this deposit process is crucial for enhancing user experience and maintaining network security.

<aside> 📌

In the finalization process with L1StandardBridge, the op-node takes on the role of delivering messages from L1 to L2, acting on behalf of L1CrossDomainMessenger. Actions by services or users that are not calls between contracts are shown with a dotted line.

</aside>

Deposit ETH

The deposit flow of ETH differs from Optimism's depositETH where:

• ETH is locked in the L1StandardBridge instead of OptimismPortal.
• On the Thanos, users receive ERC20 token that represents ETH instead of native ETH as in Optimism.

Deposit ERC20 (not L2 native token)

The flow is the same as Optimism’s depositERC20, except it does not allow using L2 Native Token.

Deposit L2 native token

The L2 native token must be locked in OptimismPortal. And the flow of deposit L2 native token is almost the same as Optimism’s depositETH except using some other function interfaces (but provides the same logic) and an ERC20 is used instead of ETH. Transferring token by using the function transferFrom **in the destination contracts/EOAs.

Withdraw flows

This flow outlines the process of transferring assets from Layer 2 (L2) back to Layer 1 (L1). It provides a step-by-step breakdown, from initiating the withdrawal on L2 to finalizing it on L1, offering users a comprehensive understanding of the cross-layer asset return process.