Modbus RTU is a serial protocol and requires communication over a serial port. Modbus RTU over TCP provides Modbus serial packets that are encapsulated within a TCP/IP message.
Modbus RTU over TCP allows you to use an Ethernet port to communicate with the serial Modbus devices by adding a terminal server box at each remote device.
Modbus RTU over TCP has a different packet structure than Modbus TCP. They should be considered two entirely different protocols as they are not interchangeable.
Sinolta supports all three.