Name

Type

Description

MonitoringParameters

structure

Parameters that define the monitoring characteristics of a MonitoredItem.

clientHandle

IntegerId

Client-supplied id of the MonitoredItem. This id is used in Notifications generated for the list Node. The IntegerId type is defined in 7.19.

samplingInterval

Duration

The interval that defines the fastest rate at which the MonitoredItem(s) should be accessed and evaluated. This interval is defined in milliseconds.

The value 0 indicates that the Server should use the fastest practical rate.

The value -1 indicates that the default sampling interval defined by the publishing interval of the Subscription is requested. A different sampling interval is used if the publishing interval is not a supported sampling interval. Any negative number is interpreted as -1. The sampling interval is not changed if the publishing interval is changed by a subsequent call to the ModifySubscription Service.

The Server uses this parameter to assign the MonitoredItems to a sampling interval that it supports.

The assigned interval is provided in the revisedSamplingInterval parameter. The Server shall always return a revisedSamplingInterval that is equal or higher than the requested samplingInterval unless the requested samplingInterval is higher than the maximum sampling interval supported by the Server, in which case the maximum sampling interval shall be returned.

filter

Extensible Parameter

MonitoringFilter

A filter used by the Server to determine if the MonitoredItem should generate a Notification. If not used, this parameter is null. The MonitoringFilter parameter type is an extensible parameter type specified in 7.22. It specifies the types of filters that can be used.

queueSize

Counter

The requested size of the MonitoredItem queue.

The following values have special meaning for data monitored items:

ValueMeaning

0 or 1the Server returns the default queue size which shall be 1 as revisedQueueSize for data monitored items. The queue has a single entry, effectively disabling queuing.

For values larger than one a first-in-first-out queue is to be used. The Server may limit the size in revisedQueueSize. In the case of a queue overflow, the Overflow bit (flag) in the InfoBits portion of the DataValue statusCode is set in the new value.

The following values have special meaning for event monitored items:

ValueMeaning

0the Server returns the default queue size for Event Notifications as revisedQueueSize for event monitored items.

1the Server returns the minimum queue size the Server requires for Event Notifications as revisedQueueSize.

MaxUInt32the Server returns the maximum queue size that the Server can support for Event Notifications as revisedQueueSize.

If a Client chooses a value between the minimum and maximum settings of the Server the value shall be returned in the revisedQueueSize. If the requested queueSize is outside the minimum or maximum, the Server shall return the corresponding bounding value.

In the case of a queue overflow, an Event of the type EventQueueOverflowEventType is generated.

discardOldest

Boolean

Specifies the discard policy when the queue is full and a new Notification is to be queued. It has the following values:

TRUEthe oldest (first) Notification in the queue is discarded. The new Notification is added to the end of the queue.

FALSEthe last Notification added to the queue gets replaced with the new Notification.