I've just installed Softswitch and have added two users: 2 mobiles with MizuDroid.

I'm running on Windows10 using a Draytek Router. I have a spare static IP so I've opened Port 5060 on that IP, pointing to the server. Both mobiles register and they can both call each other but there is no audio in either direction. I'm guessing this is an RTP issue (well, it's probably me that's the issue lol) and have tried various things including setting the RTP base to 5000 and opening 5000-5100 on the Draytek to point to the server.

I can't work out what actually sets the RTP ports in order to tell the router which ports to open. Help would be very appreciated because this software looks exacltly what I need.