I am using 3CX v10 on a box with a private IP address, behind a Linksys router with a public address. CallCentric is my VOIP provider. I am able to send and receive phone calls without any port forwarding setup. How is this possible? I was under the impression from different blog posts and the user-manual that port-forwarding was a must. I'm not trying to "fix" anything, I'm just looking to better understand how this is functioning.