What Is FXO?

Q: Easy way to remember FXO

FXO = the side connecting to the Office (carrier). It receives analog trunks, the side that consumes power.

Q: Does FXO support caller ID

Yes, all modern FXO gateways receive caller ID from the carrier and forward it to the IP PBX.

Q: Is FXO better than SIP Trunk

Not in terms of quality. FXO is a temporary migration bridge, long-term the goal should be SIP Trunks.

2026-05-07 2 min readSIPPER Team

An FXO port acts as a phone endpoint, receiving power and ring from a carrier. Used to bring legacy analog trunks from NT or True into an IP PBX.

Definition

FXO (Foreign Exchange Office) means "the side that connects to the office (carrier)." The gateway emulates a subscriber phone, receiving dial tone and ring.

Usage

Plug analog trunks from the carrier into FXO ports. The gateway converts to SIP for the IP PBX. Useful for organizations with legacy analog lines not yet migrated to SIP Trunks.

Related Concepts

Opposite of FXS, which supplies power to phones. Easy mnemonic: FXO = phone side, FXS = carrier side.

Frequently Asked Questions

Easy way to remember FXO

Does FXO support caller ID

Is FXO better than SIP Trunk

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