both users behind firewalls

[nike66]

hi, for some time I have a problem that prevents me from exchanging with a user I care about in particular. I press that before when I had the ADSL we exchanged files quietly. but since I switched to a connection with the mobile phone via usb tethering, it was no longer possible to exchange. in fact the message appears to both me and him "both users behind firewalls". i also tried to temporarily disable windows firewall and avira antivirus. but it didn't help. I ask someone more experienced than me how I could solve this annoying problem that has been tormenting me for years.
thanks to those who will help me.

[White Stripes]

you will need to forward ports in the phone the same as you did with your DSL router...
if you cant, see what your friend can do with their connection. one of you will need open ports to transfer.

another option depending on your budget would be a dedicated cell modem, a device that is designed for constant internet use... phones should only really be used temporarily

[nike66]

ok thanks for the advice now I think about what I can do