var identifier: String?
This field uniqly identifies physical connection to which control unit is connected. Only the format (not for simulation, but for real life) allowed at the moment is file://{filename}.
Under windows it is something like file://COM1 or file://COM11. Under linux it is file:///dev/path/to/comport.
For simulation of control unit it is sim://{controlUnitId}.
For proxy server it is proxy://{controlUnitId}@{hostname}:{port}. Example: proxy://PPLUS0001@localhost:43434