A subscription consists of at least one monitored item, that has to be created within the context
of a session and can be transferred to another session. To create a session, a secure channel
between the client and the server has to be established.
There are two different types of “changes” a client can subscribe to when adding monitored
items to the subscription:
● subscribe to data changes of Variable Values (Value attribute of a Variable)
● subscribe to Events of Objects (EventNotifier attribute of an Object & EventFilter Set)
Publish interval
"Clients define MonitoredItems to subscribe to data and Events. Each MonitoredItem identifies
the item to be monitored and the Subscription to use to send Notifications. The item to be
monitored may be any Node Attribute.
Notifications are data structures that describe the occurrence of data changes and Events.
They are packaged into NotificationMessages for transfer to the Client. The Subscription
periodically sends NotificationMessages at a user-specified publishing interval, and the cycle
during which these messages are sent is called a publishing cycle." (see OPC UA Part 4 -
Services 1.03 Specification.pdf (https://opcfoundation.org/))
Sampling interval
"Each MonitoredItem created by the Client is assigned a sampling interval that is either
inherited from the publishing interval of the Subscription or that is defined specifically to
override that rate. [...] The sampling interval indicates the fastest rate at which the Server
should sample its underlying source for data changes." (see OPC UA Part 4 - Services 1.03
Specification.pdf (https://opcfoundation.org/))
See also
Technical data (Page 69)
Functionality
5.3 Variable access
SINUMERIK Integrate for Engineering Access MyMachine / OPC UA
46 Configuration Manual, 04/2018, 6FC5397-1DP41-0BA0
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