May I say, “ModbusTCP over Serial Gateway” is a bit confusing wording.
The aim is not to send ModbusTCP frames over serial interface as the wording suggests. The aim is to convert between ModbusTCP to ModbusRTU frames, the latter tied to the serial interface.
A better wording would be just “ModbusTCP/RTU Gateway” or “ModbusTCP to ModbusRTU (serial) Gateway”.