The Foreign Exchange Office (FXO) interface is an RJ-11 connector that allows an analog connection to be directed at the public switched telephone network's (PSTN's) central office or to a station interface on a private branch exchange (PBX). The FXO sits on the switch end of the connection. It plugs directly into the line side of the switch so the switch thinks the FXO interface is a telephone.

The Foreign Exchange Office (FXO) interface is an RJ-11 connector that allows an analog connection to be directed at the public switched telephone network's (PSTN's) central office or to a station interface on a private branch exchange (PBX). The FXO sits on the switch end of the connection. It plugs directly into the line side of the switch so the switch thinks the FXO interface is a telephone.