It is working now and the reason is the listen() was in the wrong position and you need an additional Signal/Slot connection from main program to the network extension as following:

the main program gets changed like this:
Qt Code: 
  1. wifi= new WirelessNet(0);
  2. QThread *thread = new QThread;
  3. wifi->moveToThread(thread);
  4. connect(thread,SIGNAL(started()), wifi,SLOT(initWifi()));
  5. thread->start();
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the constructor of WirelessNet is now empty, therefore it gets a new public slot function:

Qt Code: 
  1. void WirelessNet::initWifi()
  2. {
  3.     listen(QHostAddress::Any, 5220);
  4. }
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And that's the trick.

If one is creating a WirelessNet-Instance, starts listenting inside the constructor but first then uses the movetoThread(), the connection is lost.

Concluding in one sentence: First move to the right thread and afterwards start listening

Thanks for your help. Let me tell you I hate the official Qt-""Tutorials""