The OPC UA Stack implements the serialization, security and transport of messages exchanged between different UA Applications. The stack does not contain any application layer functionality. The OPC Foundation is providing different implementations of the stack. The ANSI C version has a platform layer that contains the platform specific code separated from the platform independent functionality.
The SDK/Toolkit simplifies the UA stack APIs, implements common UA functionality needed in most or all UA applications, provides base functionality and helper functions, implements the security handling and provides samples for common use cases.
ANSI C SDK Provider Architecture
The application provides or consumes information via OPC UA. This layer contains the application specific logic and a mapping to OPC UA using the OPC SDKs.
The ANSI C OPC UA Server SDK provides an ANSI C library used to develop OPC UA Servers providing a standard interface to vendor specific systems. The OPC UA Server is normally used to describe the available information from a vendor system and to provide access to the data for external systems in a standard way.
The ANSI C OPC UA SDK is a compact OPC UA SDK designed for embedded devices which provides the basic infrastructure to create an OPC UA Server.