Session isolationΒΆ
Situation
With Windows Server 2003, Windows Server 2008, Windows 7 services are alone in session 0. User applications run in session 1 (2 and so on).
Services:
A Windows service is a computer program that operates in the background.
Windows services can be configured to start when the operating system is started or can be started manually and run in the background as long as Windows is running. They can operate when a user is not logged on.
Services are:
Windows operating systems include numerous services. OPC client like S+ OPC scanner PGIM, Aspen CIM-IO Manager, ICONICS, .. can also installed as service.
User applications are:
Microsoft Word, Notepad, MatrikonExplorer, ControlBuilderPlus.exe and Codesys.exe
Problem
Service and user application are isolated in their session. They can not communicate with each other directly.
OPC Server uses, like the CBP and IEC 61131-3 editor, the gateway server from IEC 61131-3 editor (gateway.exe) for the communication with the AC500 and starts the gateway in their session. That creates undefined behavior, if the OPC Server runs as a service. The gateway server is not able to run in multi sessions.
Resolutions
- Install all OPC clients and OPC Server, which use the gateway server, in the same session.
- The OPC Server as a service (session 0) may not be connected at the same time (in parallel) with an OPC server as a user application or CBP or IEC 61131-3 editor (all in session 1) with the AC500. If this function is necessary, different PC or virtual machines must be used.
- Use tools like OPC tunnel. In a DigiVis 500 setup context the OPC server must not be registered as service. The OPC tunnel itself starts the OPC server within its service.