The Servicesdefined for OPC UA are described in 7, and specified in OPC 10000-4.

Request/response Servicesare Servicesinvoked by the Clientthrough the OPC UA ServiceInterface to perform a specific task on one or more Nodes in the AddressSpaceand to return a response.

The Publish Serviceis invoked through the OPC UA ServiceInterface for the purpose of periodically sending Notificationsto Clients. Notifications include Events, Alarms, data changes and Programoutputs.