Difference Between an FXO Adapter and an FXS Adapter

A guide on what they do and when each should be used.

FXO Adapters (VoIP to telephone line adapters)

An FXO adapter can be used to connect VoIP systems such as an IP-PBX in a LAN environment, to regular analog telephone lines (POTS PSTN lines). An FXO adapter from the point of view of a telephone exchange seems to be a regular telephone. As such, it is able to accept ring signals, go on-hook and off-hook, and send and receive voice signals. From the VoIP system it appears to be an external line.

When to Use an FXO adapter:

More Information: To purchase an FXO or for more information on features and specifications, please click here.

FXS Adapters (telephone to VoIP adapters)

An FXS adapter is used to connect a regular analog telephones to a VoIP system such as an IP-PBX in a LAN environment or a VoIP telephone service. An FXS adapter is a device that, from the point of view of a telephone, seems to be a telephone exchange but connects to a VoIP service instead.

When to Use an FXS adapter:

Technical Notes

FXO and FXS adapters ARE NOT interchangeable.
  1. You CAN NOT plug a phone into an FXO
  2. You CAN NOT plug and FXS into a telephone line