Monitoring mode
MonitoringMode is a per-item switch with three states. Disabled means the server does not sample the item at all. Sampling means it samples and queues but sends nothing. Reporting means it samples, queues and delivers. It is changed with SetMonitoringMode, without deleting and recreating the item.
What each state costs
Disabled costs nothing: no sampling load, no queue, no traffic. Sampling costs the server the same acquisition work as Reporting but produces no notifications - it exists mainly so that triggering links have something queued to release. Reporting is the normal state. Switching among them is cheap compared with CreateMonitoredItems, which is the point of the service.
The screen-switching pattern
An HMI or dashboard that shows a hundred tags per page can create all its items once and then use SetMonitoringMode to enable only the visible page, in one bulk call per page change. That avoids repeated create and delete churn, keeps subscription membership stable, and removes the item-creation value storm from every navigation. It also keeps the server's item count predictable for capacity planning.
Item mode versus subscription publishing
MonitoringMode is per item; PublishingEnabled, set by SetPublishingMode, is per subscription and stops delivery for all its items at once while keeping them alive. Use PublishingEnabled to pause a whole collection - a maintenance window, a client going idle - and MonitoringMode for selective control within an active subscription.
Example
The three states side by side
mode server samples? queue fills? notifications sent? typical use
Disabled no no no page not open, item retired
Sampling yes yes no target of a triggering link
Reporting yes yes yes normal operation
SetMonitoringMode(subscriptionId, Reporting, [handles...]) - one call, many items.
SetPublishingMode(false, [subscriptionId]) - pause the whole subscription.Defined in: Part 4 - Services, SetMonitoringMode and SetPublishingMode; the MonitoringMode enumeration.
Last verified 7 September 2026 against OPC UA 1.05.07. OPC UA Connect is an educational resource and is not affiliated with the OPC Foundation.