VOIP with SMARTY and CGNAT

If you are using Smarty in say a 4g/5g router, it is well known that VOIP and CGNAT don't go together well. It's not uncommon to get problems such as unreliable connections or registration failures. If you are experiencing problems, there are a few settings that might help.

Firstly turn off SIP ALG setting in your 4/5g router, ALG  can corrupt VOIP packets

Next settings in your VIOP hardware, move away from standard registration ports like 5060  and use say 8060 and then if your setup allows use a random port range such as SIP port range 8061 to 8068  and RTP port range 9004 to 9020 (you might even try port ranges outside standard such as  SIP 49152 to 49200 but your hardware might not allow it)

Reduce the registration refresh time right down to say 60 sec

Finally, and this is probably the clincher, in your VOIP settings, configure a  STUN server with a low STUN refresh rate (30sec) and a low NAT refresh rate (say 20 sec). Ideally use the STUN server from your VOIP provider in my case I'm with soho66 and their stun server is stun.soho66.com 

If your VOIP provider doesn't have a stun server there are public ones available,an internet search shows many available such as stun.1.google.com (not that i've tested it)

Hopefully this might help