It seems I a had to be not sure. I never saw the 8000 in the Telnet initiator. So I tried port 23 since this ist the normal telnet port. On port 8000 it responded normally. Sorry for my dumbness.
But I found some missbehaviour: I tried to check what happens if I type more than the buffer can hold. The answer is bad: it crashes. Several red flashes and the a reboot.
I tried to find the error handling routine, but all that class syntax is too complicated for me as an old fashioned C programmer.
The next problem is how to adopt the telnet server so that I can use the input routine also on serial port. I mean, I want to use both, serial and the telnet server to enter commands. But I don’t know how to build a “stream” class for the serial port which fetches character by character, allowing some simple line editing (backspace) and then supply it to the command parser as an output stream.