When two analog PBX or PABX are in two different offices, we hope all the extension of them can call each other for free, and two offices are in the same VPN or two offices are using the static public IP, but how will we connect them? and which device do we need?
You can refer to the below suggestions:
1. how will we connect them?
Because PABX does not have any port to connect the network, we just can connect them by the FXS port or FXO port, so we can use one VOIP device which have the FXS or FXO to do the connection firstly, after that, the VOIP device will transfer the call to network.
As usual, we connect the voip device with PABX like this:
PABX FXS—> FXO voip device
PABX FXO—> FXS voip device
2. which device do we need?
we had better use one VOIP gateway to do the connection, because it is easy to set it in the gateway.
but how many FXS or FXO do the gateway need? please refer to the below suggestions:
1. how many available FXS and FXO do the PABX have?
2. what are the concurrent calls you need? because one FXS or FXO will occupy one concurrent call, it means one FXS or FXO will just can go through one call at the same time.
In order to dial the number conveniently, as usual, different connections will have the different call direction.
When you do the connection like this: FXS of PABX —> FXO of gateway, the call will go from the gateway to the PABX;
When you do the connection like this:FXO of PABX —> FXS of gateway, the call will go from the PABX to the gateway.