Unsolicited Message Handling

A PLC typically registers a critical event before the OI Server has had a chance to poll for that data. To mitigate the potential information lag, the PLC should have the capability to inform the OI Server immediately, without having to wait for the OI Server to poll it.

This is the role of an unsolicited message. Once a PLC has determined that a critical condition (such as an alarm event) exists, it can generate a message that is immediately sent to the OI Server without a prior request from the OI Server. Compared to polling the PLC for an irregular event at fixed intervals, sending unsolicited messages from the PLC to the OI Server when the event occurs not only reduces network traffic, but may also get the data to the server more promptly.