In most legacy SCADA the host does all the talking - it polls and devices answer. Unsolicited reporting breaks that pattern: it lets a field device speak first, pushing important data to the host the instant an event occurs rather than waiting to be asked. It is a defining feature of telemetry protocols like DNP3 and a key reason they suit remote, event-driven operations. This guide explains what unsolicited reporting is and how it works.
What Is Unsolicited Reporting? in one line: Unsolicited reporting is when a field device sends data to the SCADA master on its own initiative, without being polled first. Instead of waiting for the host to request a value, the device pushes an event report as soon as it happens - most commonly implemented in the DNP3 protocol.
Normally a SCADA master is the only device allowed to start a conversation: it polls, and the outstation (RTU) responds - a solicited response. Unsolicited reporting reverses the initiative for events. Once enabled, the outstation is authorized to transmit a report the moment a monitored point changes state or crosses a threshold, without waiting for its turn in the poll cycle. The master acknowledges the message so the outstation knows it was received.
In DNP3, where this is most standardized, points are grouped into classes (Class 1, 2, and 3) by priority, and the outstation can be configured to send unsolicited responses for changes in specific classes. A critical alarm - a high-high tank level, an ESD trip - propagates immediately, while routine background data can still be gathered by ordinary polling. The master typically performs an integrity poll after establishing communications to synchronize its full picture, then relies on unsolicited events between polls.
A solicited response is data returned because the master asked; an unsolicited response is data the outstation sent without being asked. The two coexist: a well-configured DNP3 link uses periodic integrity polls to stay synchronized and unsolicited responses to deliver events with minimal latency in between.
Unsolicited reporting and report by exception are related but not identical. Report by exception describes the criterion - only report on meaningful change. Unsolicited reporting describes the mechanism - the outstation initiates the transmission rather than answering a poll. In practice DNP3 outstations combine both: they detect exception-worthy changes and report them unsolicited. The payoff is low-latency alarms and efficient use of marginal links, since the device transmits only when it has something to say.
For upstream and pipeline operators, unsolicited reporting means a safety-critical event at a remote wellsite reaches the control room in seconds rather than at the next scheduled poll, which could be minutes away. On a large poll list over slow comms, waiting for a device's turn to be asked is exactly the latency you cannot afford for a leak or a shutdown.
It also lightens the comms load: routine values move on a relaxed poll while only events trigger immediate traffic. A SCADA host must support unsolicited responses, acknowledge them promptly, and still run integrity polls for consistency. Merobix reads DNP3 outstations including their unsolicited responses, so event-driven alarms from RTUs arrive with minimal delay while routine data is polled at a sensible cadence.
It is a DNP3 feature that lets an outstation (RTU) transmit event data to the master on its own initiative, without being polled. When a monitored point changes, the outstation sends an unsolicited response immediately, so critical events reach the SCADA host with very low latency.
A solicited response is data an outstation sends because the master polled it. An unsolicited response is data the outstation sends without being asked, triggered by an event. A typical DNP3 link uses both - periodic integrity polls to stay in sync and unsolicited responses for immediate event delivery.
They overlap but describe different things. Report by exception is the rule - only send data on meaningful change. Unsolicited reporting is the mechanism - the device initiates the message instead of answering a poll. DNP3 outstations typically combine both: they detect exception changes and report them unsolicited.
This page references the protocol specifications published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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