Grandstrean GWX4101 Cobfiguration Problem

[xylogistix]

Good Day Ladies & Gents

I have a problem getting my Grandstream FXO to work with the 3CX Phone System Version 10
Please see attached JPEG file for my setup diagram.

The Problem is,
When I make or receive a call using a 3CX Phone system extention to the PSTN line, I cannot hear anyting from the otherside.
The PSTN phone rings but I cannot hear it and when it is answered, they can hear but I cannot hear them.

When a call comes through from the PSTN line to the 3CX phone system, the designated extension to recieve call rings.
When I answer, agnain I cannot hear anything but the call can hear me.

I am using 3CX Phone System version
Extension to Extension calls are OK
I am located in Zambia

Were can I look for fix this problem?

regards

Chris (Xylogistix)

 

[mixig]

Double post...

 

[jpillow]

Whys is the gateway not onsite? are you using a vpn?

 

[xylogistix]

Good Day
The 3CX phone system is in remote location.
It is connected to the internet via a wireless link.
The quality of the internet at this remote site is very good, but they have no phyiscal to access to PSTN lines (i.e. no PSTN cables to the site). This is how we came up with the idea of accessing the PSTN lines via the internet.

The IP addresses I have used in the drawing are not real
The port fowarder on the router are as follow

Port range 5000 - 6000 UDP/TCP points to 192.168.80.190 (3CX Phone system server)
Port range 9000 -9050 UDP/TCP point to 192.168.80.190
Port range 7000 - 7500 UDP /TCP points to 192.168.80.190

I am using a linksys router WRT54GL

The setup is in port range forwading of the applications & gaming menu.

Regards