How to properly set up sip calls through mikrotik?

Question

SIP

Good day!
Please help with setting up Mikrotik. The bottom line is this: there is a GSM gateway with which I call various subscribers. To do this, I use either a program for sip calls (for example, PhonerLite) or the built-in android tools. To work in PhonerLite, I simply specify the IP address of the gateway as a proxy for outgoing calls and calmly call. But everything works only in the local network of the enterprise. There is an urgent need to use this GSM gateway, being in any other place, having only access to the Internet. If you connect via vpn to Mikrotik, everything works. And how to do it without a vpn tunnel. To register the external IP Mikrotik as a proxy and, if necessary, the port, and call.
Thanks in advance for your time. Sorry if the question is stupid.

Answer 1

You can try forwarding ports from the GSM gateway using NAT (this is easy to google), but I'm afraid SIP will not survive if it finds itself in a double NAT situation (one on the gateway side, the second on the subscriber side). Therefore, it seems that the most correct solution would be to receive another white IP address from the provider and assign it directly to the gateway.
In general, start with NAT, test it, if there are problems, buy an address.
And do not forget about the protection of this device, otherwise evil hackers will quickly scam you for calls to Australia.

Answer 2

Thanks for the answer. Indeed, NAT does not help. I started with this. Forwarded ports - did not help. The second IP from the provider, you mean, on the side of Mikrotik with a gateway? That is, do without Mikrotik at all? Give an Internet directly to the gateway? Did I understand correctly?