Modbus RTU
Modbus RTU is an open, serial communications protocol based on the master/slave architecture. Since it is extremely easy to implement on all kinds of serial interfaces, it has gained wide acceptance.
Modbus TCP
Due to its open standards Modbus TCP is common for the use of Ethernet in the fields of automation. Modbus TCP has a so called “Well known port (Port 502)”, which makes it routable via the Internet.