How the field instruments communicate with DCS and How far DCS communicates with SCADA?

there are three main communication protocol between instraument tranmiter and the control system (DCS)

HART,  Profibus and Fieldbus

communication from system to system or controller to control and sharing information as between PLC and SCADA by

Modbus 

OPC

the distance does not matter if they are linked together in some how. Even if they are in differed countries. 

Hope i understand the question "How far DCS ...." correctly