Which protocol has a communication method where the slave can report without being requested by the master?

DNP3 (Distributed Network Protocol) is a protocol commonly used in the automation of electric and water utilities. One of its key features is the ability for slave devices to report status and events without needing a request from the master device. This functionality allows for more efficient communication since devices can send important alerts or changes in state immediately as they occur, rather than waiting for the master to poll them. This capability is particularly useful in critical infrastructure settings, where timely information can significantly impact operations and response times.

In contrast, protocols such as Modbus require the master to initiate communication for data exchange, which means slaves cannot send information until prompted. Others, like Ethernet/IP, may also rely on request-response mechanisms for data transactions, limiting their ability to report information autonomously. OPC, primarily used for data access and integration in industrial settings, generally does not facilitate unsolicited communications between devices.

The design of DNP3 emphasizes reliability and real-time reporting, which are essential in scenarios where monitoring and response to changing conditions are critical.