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.
An Analog Telephone Adataper (ATA)
For VoIP service, this HT813 analog telephone adapter connects an analog telephone to a router (LAN) or the Internet (WAN). For backup, it includes an FXO port that connects to a traditional PBX or telephone company. See central office
. (Image courtesy of Grandstream Networks, Inc., www.grandstream.com)