Confuse which PBX port connect to router's VIC port

In the attached file I got confused to what I have found : is two different figures from two different sites

From the top in the first figure FXS for SmartNode 2300 ( I guess it is a voice gateway ) is connected to FXO for PBX.

While in second Figure FXO for Cisco router (it is a voice gateway ) is connected to FXS for PBX.
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grbladesConnect With a Mentor Commented:
The port provided by the telco is a FXS port and supplies the ringing voltage and caller id etc...
A FXO port is like a telephone.

So on the PBX you would use a FXO port to connect to the telco.

It is not always as straight forward as that though since if the PBX is using a FXO port it can dial any number it wants to BUT when accepting a call it can only see callerID and not any information regarding what number was dialed. This means either each line has to be dedicated to a single phone or group of phones or each call is sent to a voice menu.
For this reason often both FXO and FXS ports are used for connectivity between systems. FXO is used for outgoing calls while all incoming calls come in over a FXS port so that the destination number can be obtained.
zillahAuthor Commented:
That means (correct me if I am wrong) If I have got a router with two voice interface cards, one of them is FXS and other is FXO.

With PBX, I can have one of these scenario :

1- Router's FXS port to be connected to a PBX's FXO.

2- Router's FXO port can be connected to a PBX's FXS.

But with modem, telephone, fax, in all scenario these devices should be connected to a router's FXS.
No you can just buy a router with a FXS interface. That way you will be able to dial out to any number.
The limitation you will have is that any incoming calls will effectivly just ring whatever is connected to the port. If you have multiple telephone numbers assigned to the port then you wont be able to distinguish between them.

Perhaps it would be a good idea if you could describe what you wish to do.
logicomusaConnect With a Mentor Commented:
Follow this link, it will give you a basic understanding of FXS and FXO, it will than explain what the terms mean with regards to VoIP

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