tation) The analog interface provided by a telephone company (PSTN) to its customers, which includes dial tone, power and ring voltage. The telephone jack on the wall is a foreign exchange station (FXS) interface. See foreign exchange service
.FXS and FXO
The plug on an analog telephone is a foreign exchange office (FXO) interface, which provides on-hook/off-hook loop closure to the telephone company. Thus, an FXO phone plugs into an FXS jack. A PBX's FXO interface is connected to the FXS interface, and all analog phones (FXO) connect to the FXS interface on the PBX.