The IEC 60870-5-104 protocol is recommended by IEEE for communication among master stations, RTUs (Remote Terminal Units) and IEDs (Intelligent Electronic Devices).
The IEC 60870-5-104 applies to TCP/IP communication links. OPC servers are available in master or slave configurations. A master OPC server polls slave devices while a slave OPC server responds to requests sent by a master device.
IEC 60870-5-104 OPC Server Features