FXO and FXS cards can be used to interface to PBX's, but they are not the recommended way of doing this. This is what E&M interfaces were designed for - and E&M gives you answer and disconnect supervision, which is often not available on PBX ports.
A FXS port provides line power (-48VDC) and ringing singal to the attached device , which is normally a telephone handset. It is similar to a extension port on a PBX.
A FXO port is passive, meaning it expects to see the -48VDC line power coming from an external source. It senses the ring signal and goes off hook and plays a secondary dial tone. It can be compared to a PBC trunk port that interfaces to an exchange line.
You will have to tell us what a "Dot Line" is so we can confirm if FXO or FXS ports will work with one.
