The S110M FXS module allows 400 Series or 800 Series analog cards to terminate a single analog station per module.
The X100M FXO module allows 400 Series or 800 Series analog cards to terminate a single analog line per module.
Because of the modular design, you can activate additional ports at any time with more S110M or X100M daughter cards. The X100M module passes all the call features any standard analog telephone line will support.
FXS (Foreign Exchange Station)
FXS is an interface that connects to a station, such as an analog telephone or the FXO interface of another PBX. It provides ringing voltage and battery to the FXO devices. FXS interfaces are used on the inside of your PBX, they do not connect directly to the PSTN. One FXS channel is required for each telephone that you wish to connect to your Asterisk system.
FXO (Foreign Exchange Office)
FXO is an interface that connects to a trunk line, like the one from your service provider. It receives ringing voltage and battery from FXS devices. FXO interfaces are used to connect your PBX to the PSTN. One FXO channel is required for each line your receive from your telco.