Hello,

You have understood correctly that in order to make a subscription, you need to know the NodeId of the node. The NodeId uniquely identifies a Node in an OPC UA server. It’s used to address the Node in OPC UA services. When you’re connecting to an unknown OPC UA server for the first time, you do need to find out the NodeIds by some mechanism. The mechanism can be OPC UA browse service calls, or alternatively it can be a configuration file supplied by the administrator of the application.

There’s no mechanism to automatically find out a NodeId corresponding to a given BrowseName. So, you have understood correctly that you need to browse through the AddressSpace in order to find out the NodeIds. However, it’s good to note that typically OPC UA servers do not dynamically change NodeIds between restarts. In the normal situation the client application can safely cache the NodeIds and use the same NodeIds everytime.

I would also like to mention that there’s a service called TranslateBrowsePathsToNodeIds which can be used to find out the NodeId of a Node in certain BrowsePath. In certains situations, this can function as a “more convenient browse”. The original use case of TranslateBrowsePathsToNodeId service is that client application can be programmed by using TypeDefinitions.

In the end, it’s also good to note that there may be some caveats when using BrowseNames. The main point is that there’s no guarantee that BrowseNames are unique like NodeIds. For example, it’s possible that TranslateBrowsePathsToNodeId service may return an array of NodeIds. Then you need to be able to decide which one of the NodeIds is the correct one.