I would like to revive this thread.
I have studied and tested both: Basic networking guide by Kevin Summers from the documentation and AGK_Comms app posted by blink0k (thanks for it!).
That method with HostNetwork () and JoinNetwork () commands works perfectly over LAN. But when it comes to connecting devices over the Internet, you need to
"set up your router to forward the specified port to the machine running your server app".
I don't have a frigging idea on how to do that, but it doesn't even matter, because its obvious that I can not make all users of my hypothetic multiplayer app to go through this procedure.
So, the question is if there is any way to allow two devices, running AppGameKit apps, to exchange data over the Internet without any router setup and without the use of any 3rd party servers?