The Services defined for OPC UA are described in clause 6, and specified in OPC 10000-4.

Request/response Services are Services invoked by the Client through the OPC UA Service Interface to perform a specific task on one or more Nodes in the AddressSpace and to return a response.

The Publish Service is invoked through the OPC UA Service Interface for the purpose of periodically sending Notifications to Clients. Notifications include Events, Alarms, data changes and Program outputs.