FXO interface

A foreign exchange office (FXO) interface, that is, a two-port loop trunk interface, uses an RJ-11 connector and a telephone cable to connect local calls to a PSTN or PBX. Like an FXS interface, an FXO interface accomplishes signaling exchange based on the level changes on the Tip/Ring line. An FXO interface can be connected only to an FXS interface.