Also I’ll post some of the settings I had to setup on the NAT Phones in order to work properly in my case, so if anyone has similar issues can test their networks with these settings:
- Use of STUN is mandatory. Go to Settings > General Settings and input there a STUN server. Here is a list of them
- On Account > SIP Settings > Custom SIP Headers, option “Use X-Grandstream-PBX Header”, set it to NO.
- On Account > Network Settings > NAT Traversal, set it to STUN, and on Proxy-Require, input the extension number. Also if you want, set DNS Mode to “Use Configured IP” and setup the fields with your preferred DNS servers.
- On Account > SIP Settings > Basic Settings, set Register expiration and Subscribe expiration to 10, and set “Enable OPTIONS Keep Alive” to YES.
- Setup different SIP ports and RTP Ports for each phone.
- On your router, opening those ports, help, if you don’t want the fuss of it, you can check UPnP and check if the combination of that works fine with STUN, if not, you need to open those ports.
Hope this helps