# FXO

> FXO (Foreign Exchange Office) is the interface that connects to a telephone line and consumes dial tone — the side of the connection that behaves like a telephone.

- Also known as: Foreign Exchange Office, FXO port
- Last reviewed: July 29, 2026

## How it works

An FXO port draws loop current from the line, closes the loop to go off-hook, sends DTMF digits, and detects ring voltage. It is the counterpart to FXS: whatever supplies the line is FXS, and whatever attaches to it is FXO.

## Why it matters

Understanding the pairing prevents a common wiring error. When integrating a replacement appliance with an existing phone system, you have to know which side of each connection supplies dial tone and which consumes it, or the link will not come up.

## Common use cases

- Connecting a PBX trunk port to an existing analog line
- Integrating legacy phone systems during a phased migration

The rule of thumb: dial tone flows from FXS to FXO. If you can identify which device is
expected to supply it, the wiring follows.

## Common misconceptions

**Claim:** An FXO port can power a telephone.

**Correction:** FXO draws power from the line rather than supplying it. Powering a telephone requires an FXS port.

## Frequently asked questions

**Is FXO or FXS what I need for POTS replacement?**

FXS. Your analog equipment expects to be fed dial tone, so the replacement appliance must present FXS ports to it.

## Sources

- [Copper Retirement](https://www.fcc.gov/general/copper-retirement) — Federal Communications Commission


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Canonical page: https://dataremote.com/newsroom/definitions/fxo
Organization: DataRemote, Inc. — POTS line replacement, cellular failover, and fixed wireless access solutions. https://dataremote.com