The components of this parameter are defined in Table 144.

Table 144– MonitoringParameters

Name

Type

Description

MonitoringParameters

structure

Parametersthat define the monitoring characteristics of a MonitoredItem.

clientHandle

IntegerId

Client-supplied id of the MonitoredItem. This id is used in Notificationsgenerated for the list Node. The IntegerIdtype 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 Servershould use the fastest practical rate.

The value -1 indicates that the default sampling interval defined by the publishing interval of the Subscriptionis 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 Serveruses this parameter to assign the MonitoredItemsto a sampling interval that it supports.

The assigned interval is provided in the revisedSamplingIntervalparameter. The Servershall always return a revisedSamplingIntervalthat is equal or higher than the requestedsamplingIntervalunless the requested samplingIntervalis 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 Serverto determine if the MonitoredItemshould generate a Notification. If not used, this parameter is null. The MonitoringFilterparameter 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 MonitoredItemqueue.

The following values have special meaning for data monitored items:

ValueMeaning

0 or 1the Serverreturns the default queue size which shall be 1 as revisedQueueSizefor 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 Servermay limit the size in revisedQueueSize. In the case of a queue overflow, the Overflowbit (flag) in the InfoBitsportion of the DataValue statusCodeis set in the new value.

The following values have special meaning for event monitored items:

ValueMeaning

0the Serverreturns the default queue size for Event Notificationsas revisedQueueSizefor event monitored items.

1the Serverreturns the minimum queue size the Serverrequires for Event Notificationsas revisedQueueSize.

MaxUInt32the Serverreturns the maximum queue size that the Servercan support for Event Notificationsas revisedQueueSize.

If a Clientchooses a value between the minimum and maximum settings of the Serverthe value shall be returned in the revisedQueueSize. If the requested queueSizeis outside the minimum or maximum, the Servershall return the corresponding bounding value.

In the case of a queue overflow, an Eventof the type EventQueueOverflowEventTypeis generated.

discardOldest

Boolean

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

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

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