FXO and FXS gateway for PBX
Since modern telephone exchanges still function via IP protocols, FXO and FXS gateways are needed to connect analog devices. The acronyms FXS and FXO are general terms when it becomes necessary to purchase equipment for automatic telephone exchanges, which allows connecting analog telephone lines to IP-PBX or classical analog mini-PBXs to an Internet telephony provider or to connect such equipment via Internet channels.
FXO vs FXS Gateway
Used to connect analog telephones to IP-PBX system, or operator of IP-Telephony or connect a VoIP operator to an analog mini-PBX.
Used to connect analog city lines to IP-PBX, or internal ports of analog mini-PBX to IP-PBX.
In simple words, FXO gateway is an analog signal to digital. And FXS does the reverse conversion, that is, digital to analog.