I have a fritzbox with 2 phones connected to a RUTX11. When the fritzbox is booted the phones are connected to my remote pabx. Phone calls can be made, and audio is of good quality. But after about 30 minutes of inactivity (no phone calls) both phones get unregistered. The only solution to get the phones registered again is to reboot the fritzbox. I also tried to add a port forward rule to the fritzbox but that doesn't solve the problem. Any help will be much appreciated.