What are FXO and FXS port?

Posted on 2009-04-25
Medium Priority
Last Modified: 2013-12-27
What are FXO and FXS port?
Question by:davidlu766

Accepted Solution

numero_uno earned 2000 total points
ID: 24234714
FXS and FXO are the name of ports used by Ananlog phones.FXS (Foreign eXchange Subscriber interface) is the basic connection port that you see at your home for connecting the RJ11 Jack of the phone. This port provides the dialtone, small current and voltage to the phone line.

FXO (Foreign eXchange Office) is that port that you see on the telephonic devices like the Phone, Fax etc. from where a cable is plgged in and the other end is plugged into the FXS jack on the wall.
So in short you can say that FXS is the the plug on the wall where as FXO is the plug on the phone.

Author Comment

ID: 24234722
So, both uses RJ11 ports?

Expert Comment

ID: 24234734
Yes, definately.
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Expert Comment

ID: 24235822
FXO = Office you connect your line on it
FXS = Station you connect a phone set on it

Generally FXS board need a power supply (same as for internal disk drive) because ring need a burst of power to make your phone ringing. While FXO do not need to be powered.

SR20 Service / France
LVL 32

Expert Comment

ID: 24236109

FXO is the outside line, the outside POTS line,

FXS is the port that connects your phones.

harbor235 ;}
LVL 79

Expert Comment

ID: 24246631
I like to think of it as where the dialtone comes from
FXO port - gets dialtone from the analog phone jack on the wall. FXO ports take incomming and make outgoing calls to outside lines possible.
FXS port - provides dialtone and ring voltage from the router to the phone device - fax machine, analog phone

If you plug an analog phone into a FXO port, you will not get dialtone or be able to make a call
If you plug a cable between a FXS port and the jack on the wall, you will not be able to make any calls

Yes, they both use standard telephone Rj11 jacks

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