For one of my PBXAct (FreePBX) setups there are two internet connections;
One is the main connection - a fast cable connection with static IP.
Sometimes this cable connection goes out, so that is why this setup has a backup SIM (LTE) internet connection which auto failovers in case the cable connection goes out.
The problem is that the LTE connection doesn’t have it’s own public IP address (no dynamic and no static IP address); the way it works is that the SIM card is under the ISP’s network and it’s sort of like a “node” on their network and they assign it a private IP address from their subnet. So this means that I cannot do any port forwarding for the LTE connection (since it’s as a private IP on the ISP’s network and doesn’t have a public IP of any kind) which means in the event the main cable connection goes out, remote extensions cannot register to the PBX (since no port forwarding works on the SIM card connection due to ISP restriction!).
So I was thinking - is there any way to have a sort of “proxy” where the remote phones “register to”, and the PBX “sends/funnels” the traffic to/from these remote extensions in a way where no port forwarding is required? Like a SBC or something that links the connection from the PBX to the remote phones, so that it works without need for port forwarding. Like how TeamViewer works - when the client computer you’re connecting to has TeamViewer application open, you can enter the ID/password and connect without need for port forwarding since the application opened the port (it reached out to TeamViewer’s proxy/server). Also for those who want to host a website but don’t have their own public IP (it’s more common for ISPs to limit handing out of public IPs so their users get a ‘private IP’ on the ISP’s subnet instead of their own public IP), there are “proxy” services like cloudflared where you install it on the machine and it funnels out/sends out the traffic to the server thus eliminating need for port forwarding… I am looking for this type of solution but for SIP + RTP ports on the PBX. Like a service you can install which “connects” the requests.
Keep in mind that DDNS is irrelevant in this scenario since the backup SIM connection doesn’t have it’s own public IP so even if you try to connect to the PBX with DDNS, it’s useless since no ports are/can be forwarded through the SIM connection.
I’m sure someone has thought of something like this!!