OPC UA has been designed for scalability and supports a wide range of application domains, ranging from field level (e.g. devices for measurement or identification, PLCs), to enterprise management support. To achieve these design goals, the OPC UA standard provides a multi-layered architecture as shown in the following figure:
OPC UA is built on the following Infrastructure:
- Discovery which allows Clients to find OPC UA Servers, their supported protocols, security policies and other capabilities.
- Transport which defines protocol mappings that allow establishing a connection and exchanging well-formed messages between OPC UA Applications.
- Information Access which comprises the means to expose object-based Information Models in an Address Space and the Services to access this information.
- Security and Robustness, which are integrated into Transport and Information Access.
Information models are layered on top of this infrastructure. OPC UA specifies a number of base information models (DataAccess – DA, Alarms&Conditions – AC, and more) that define commonly used objects including both real-time and historical data variables and alarms. Industry standard models inherit from and further specialize the lower layer models they are based upon.
Following is the catalogue of OPC UA Capabilities structured according to the layers and subsystems of the UA Framework outlined before.