What is FXS and FXO?

What do the terms FXS and FXO mean?

In telecommunication, a foreign exchange service (FX) is a network-provided service in which a telephone in a given local area is connected, via a private line, to a central office in another, i.e., “foreign”, exchange, rather than the local exchange area’s central office.

In telecommunications, a Foreign Exchange Office, or FXO, is a telephone signaling interface that receives POTS, or “plain old telephone service”. It generates the on-hook and off-hook indicators used to signal a loop closure at the FXS’s end of the circuit. Analog telephone handsets, fax machines and (analogue) modems are FXO devices, though the term is rarely used except in connection with Foreign exchange service (FX).

FXO interfaces are also available for computers and networking equipment, to allow these to interact directly with POTS systems. These are commonly found in devices acting as gateways between Voice over Internet Protocol (VoIP) systems and the public switched telephone network (PSTN).

A Foreign eXchange Station, or FXS, is a telephone interface which supplies battery power, provides dialtone, and generates ringing voltage. A device that connects to such an interface contains an Foreign exchange office (FXO) interface and could be a standard analog telephone or a private branch exchange (PBX) to receive telephone service.

So to break this all down for you in even simpler terms, an FXS interface/port would connect to an analog phone, or analog device. The FXO interface/port would connect to a telephony PSTN line from a analog service provider.

In todays world FXS and FXO work hand in hand with VoIP Telephony Systems. The main use of this cooperation is so current and next-gen VoIP Systems can use older analog telephony. A benefit of this is that analog PSTN lines are still highly reliable forms of communication, and by using VoIP and analog you truely have a redundant feature rich phone system.

Tags: FAX, Networking, Ports, VoIP