OPC UA defines a node type called a Method that allows a client application to synchronously execute a predefined function on the server. The client calls the OPC UA method with zero or more arguments and waits for it to complete. OPC UA servers may use methods as an alternative to executing their internal functions in response to a data value change.

OPC UA methods are synchronous, and normally cannot be executed through a DataHub tunnel, because data flow through a tunnel is always asynchronous. You can, however, use a DataHub script to convert an asynchronous data change into a synchronous OPC UA method call. Please see Calling OPC UA Methods from DataHub Scripts for details.