6F2T0207 (0.01)GRE200 (5,6)- 947 -11.5.4 InteroperabilityThe IEC 60870-5-103 protocol provides a physical layer and an application layer for thecommunication to secure the interoperability.(i) Physical layerEither an electrical or optical interface† is defined in the IEC 60870-5-103 standard.Electrical interface of RS-485When a RS485 module is selected for the IEC 60870-5-103 serial, 32 IEDs are possibleto connect in.Optic interfaceFiber optic module is available for the IEC 60870-5-103 serial.†Note:Either interface is provided and that specification is discussed separately. SeechapterTechnical description: Signal processing and communication module(→page 645).(ii) Application LayerThe following layers are provided on the application layer:COMMON ADDRESS of ASDUOne COMMON ADDRESS OF ASDU (identical with station address)