Need some Understanding

Hello everyone,

I am having a hard time wrapping my head around something simple but hey I can admit that it is not sinking with me.

The difference in the FXO and FXS.

If I understand correctly the FXO port is the line coming in from POTS. And the FXS port is for like hooking up a fax machine or analog phone that can by pass the system.

Or do I have this backwards or all wrong together?

Digium uses FXO to refer to the local module that connects to the central office, and FXS to refer to the local module that connects to the station. FXO modules expect to see ringing current on an incoming call. FXS modules generate ringing current on an outgoing call, and detect incoming ones by DC changes in the loop.

So to simplify that. FXO from Phone COmpany and FXS to Analog phone (Device)? Correct?

That’s the most common case, but you could have another PABX taking the central Office role, or another PABX taking the Station role. The end that has the battery is generally the end to which an FXO module connects.

Foreign Exchange Office = what it looks like coming out of the Central Office. Has dialtone, usually, and listens for touchtone digits typically. Has -48VDC to ground in an Idle state. Signalling = FXS.

Foreign Exchange Station = what it looks like coming out of your phone. No Voltage, 600-ohm impedance {off-hook} Produces DTMF onto a powered loop. Signalling = FXO

Clear as mud?