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Also abbreviated as FEX circuit. A dedicated circuit that draws dial tone from a foreign exchange, i.e., a central office exchange (COE) other than the one in which the system resides. An FX line (KTS) or trunk (PBX) allows a user organization to avoid toll charges for long distance calls, as the leased line or trunk is billed on a flat rate basis, sensitive to bandwidth and distance, rather than a usage sensitive basis. If the user organization places a great many calls to a foreign exchange area, the costs savings can be considerable, particularly if the foreign exchange is in reasonable proximity and the FX circuit, therefore, is a relatively short haul.The interface typically found at each end of the FX circuit is of two types. FXO faces the office or switch, receives battery and ringing, and seizes the line by closing the loop. FXS faces the subscriber, gives battery and ringing voltage, and responds to a phone going off hook.