Exchange can be on-chain and cross-chain, e.g.:
On-chain (from POL to USDT-POL, from USDC-ETH to USDT-ETH)
Cross-chain (from POL to USDT-ETH, from USDC-ETH to USDT-SOL)
On-chain exchange requires paying only the network fee, while cross-chain exchange also requires the protocol fee.
Protocol fee is the fee which is paid to the exchange 3rd party provider (deBridge). It consists of two parts: one part is paid in the "From" amount and the other - in the native coin. Example:
We exchange USDT-POL to BNB. The network fee is paid in POL, the protocol fee is paid in USDT-POL and POL.
Here is the table which shows what fees you should pay using different types of exchange:
Exchange type | Network fee | Protocol fee |
On-chain | yes | no |
Cross-chain | yes | yes |