FXO (Foreign Exchange Office)

When a customer receives phone service from a central office other than the one that would normally serve them, the line between the customer and the "Foreign" office is called a "Foreign Exchange" line.

FXO (Foreign eXchange Office) is the office end of the line, and FXS (Foreign eXchange Station) is the station end.

FXO and FXS are also used to refer to the type of interface on phone equipment.

• An FXS interface provides power (battery) and generates ring signals.
• An FXO interface receives power (battery) and receives ring signals.

If you want to connect an ordinary telephone to a computer, you need a card in the computer with an FXS interface.

If you want to connect a line to your computer so that it can make and answer calls on your analog PSTN telephone line, you need to add an FXO interface to your computer.

Always check the sense of the device whether it is labeled FXS or FXO, as some vendors get it backwards and your device will provide power when you expect it to behave as a station and receive power. Be careful!

See also

• FXS
• PSTN