DNP3 communication can be set up in two alternative modes.
- Polled mode, also called “polled report by exception”. In this mode the DNP3 client always initiates the transaction with a read or write request to the DNP3 server. The server must reply with a response message.
- Unsolicited mode, called also “Unsolicited reporting mode”. In this mode the DNP3 server may spontaneously send changed class events to the client. The client can yet make additional read or write requests to the server.
By default, DNP3 operates in polled mode. Unsolicited reporting mode can be activated with the UR mode parameter.