FXS
From PhonePower Knowledge Base
In telephony, a Foreign Exchange Station, or FXS, is a telephone interface which supplies battery power, provides dialtone, and generates ringing voltage. An FXS interface utilizes an FXO protocol to detect when the terminating device (telephone) goes on-hook or off-hook, and can send and receive voice signals. An FXS interface provides service at the "station" end of a foreign exchange line.
