Configuration - SIP session lost after time

Good day.

I’ve got some kind of problem with asterisk configuration - after a virtual device connects to asterisk, in approximately 3 minutes it loses its SIP session and can’t be dialed. After re-connecting, device is available and loses connection after the same period of time.

Problem exists only on public server, asterisk server with the same configuration on the local network works fine.

Could you please name some configuration properties that should be checked in this case?

Thanks for your time!

qualify in sip.conf

The firewall/NAT device.