The default change rate for the variables in the Simulation Server is 1 s. In order to get more samples, you need to change that in the server, under the Simulation tab.

Hi,

Could it be possible to explain your use-case? Also is this “100ms” a real-time requirement or an informative/approximate value?

OPC UA Subscriptions by their definition are what you are calling asynchronous. There is no such thing as a “synchronous Subscription” in OPC UA (sort-of-except if you instead mean the Part 14 PubSub thing; see P.S. part).

The “OPC UA way” to do what you say synchronous would be to do a periodic Read operation from a client. Though, in most cases a Subscription should be used instead of doing this. Also, note that it is quite hard to get the timing to be exact.

This might not be what you would be looking for, but the Subscriptions with their MonitoredItems are quite configurable in OPC UA: https://reference.opcfoundation.org/Core/docs/Part4/7.17.2/ you could set a DataChangeTrigger so that a timestamp change in the server would also trigger a datachange (i.e. not just the value itself changing). It would still require that at least the timestamp would change.

P.S.
Depending on things, the Part 14 “PubSub” added in OPC UA 1.04 could be what you are looking for: https://reference.opcfoundation.org/Core/docs/Part14/, though none of our apps include it yet. SDK has some support (server-to-server or server-to-cloud/mqtt+json). Howerver it should be noted that this is sort of, well, “completely different” from the “normal” client-server OPC UA. And most likely if you have an “OPC UA Server”, it wont support PubSub yet.

At least based on that description I would just make a Subscription with MonitoredItems per node in your list and cache the values in the client side. That way you will know the latest value for all “synchronous” operations (I’m assuming something polls you application for these) and can use the DataChangeNotifications i.e. updating of the cache as a trigger to send notifications to your “asynchronous” ones.

P.S.
Note that I did mention PubSub only because it sort of “fit” the description (only cyclic data sending server-wise; plus in the future with https://en.wikipedia.org/wiki/Time-Sensitive_Networking it could be deterministic real-time) , but in practice it most likely is not what you would want here (like 99% likelihood that the server you have doesn’t support it). It can be quite complicated, since it sort of builds on top of everything in the traditional client-server OPC UA and is basically sort of a completely new protocol.