TryLearn More

Use SIP trunks, WebRTC & Apps

Slash your Phone Bill by 80%

Redirect incoming PSTN calls to an FXS port

On this topic

Redirect incoming PSTN calls to a FXS port


Case 1: ISDN Inbound directly to fax device

Case 2: SIP Incompatible Devices



If your beroNet bero*fix gateway contains FXS ports the setup wizard will offer to register those ports to a (fax-) extension inside your 3CX. However there are cases where it’s better or needed to redirect incoming calls from the same gateway directly to the fax ports (bypass the 3CX).


  • The device must be local to 3CX, in the same subnet and/or locally routed subnet
    (including site to site VPN)

Case 1: ISDN Inbound directly to fax device

If you exclusively use the PSTN ports of your beroNet device (no other gateway or sip trunks are configured in 3CX) it is advisable to redirect calls directly to the FXS port. There is no need to send the call first to 3CX and then back to the gateway (PSTN ⇒ SIP ⇒ SIP ⇒ Analog).

Case 2: SIP Incompatible Devices

If you are using modes or postage meters this configuration is a must as those protocols (modem) can not be transported via SIP. The device must be connected to the beroNet gateway and from there routed in and out to the public PSTN network in order to work.


The configuration for an FXS or ISDN port redirection is the same. For ISDN the port must be changed from te → nt (internal isdn) from the “Hardware” node of the beronet web interface. Adapt the configuration accordingly.

  1. During the first time setup Wizard (Step 4 the FXS or ISDN port(s) must be excluded from the configration.
  2. Open the Web interface of your beroNet and navigate to “PSTN+ → Analog FXS”.
  3. Create a “Group” and place an available FXS port in the group. Give the group a use case reflecting name. Select the devices matching tone set (refer to the admin manual of the analog device).

  1. Navigate to the “Dialplan” and “Add” two entries on position 1 and 2 above the already created rules.

  1. First Rule “Inbound Redirect ISDN ⇒ Analog for DID” ending in 99.

  1. Second Rule (Optional) “Outbound Calls from the FXS ⇒ ISDN” directly.

  1. Save the changes be pressing “Activate”.

Free for up to 1 year! Select preferred deployment:


for Linux on a $200 appliance or as a VM

Get the ISO


for Windows as a VM

Download the setup file

On the cloud

In your Google, Amazon, Azure account

Take the PBX Express