Ullrich,
the picture in the documentation is a bit misleading. The GLS server is indeed outside of our corporate network, but the Unibox is within it. And that's the server we are trying to communicate with.
Both servers, however, do not support websocket communication.
Attaching page 6 won't do you no good. Paragraph 5 (starting at the top of page 6) is about 'Label dimensions and templates (Unibox returns information about the label we have to print in our warehouse).
Like I said, documentation is not quite comprehensive / elaborate.
Regards,
Micky.