An Foreign eXchange Office (FXO) card is a card that connects to a central office. A modem is a classic example of an FXO card (in fact, if you have one of Digium’s old FXO cards, the X100P, it is in actual fact a modem). An FXO device must be able to:

• Generate DTMF (touch tones)
• Detect dial tone
• Detect ringing
• Detect message waiting
• Interpret Caller ID
• Signal On Hook/Off Hook condition to the far end, as well as Flash

The main difference in the settings that are provided above when configuring an FXO channel instead of an FXS channel is signalling.

In your /etc/asterisk/zapata.conf file we will want to add the following:

So your the whole file should now look like this:

In the first example we listed channel 1 as an FXS channel. To create an FXO channel on the same TDM400P card, we list all the settings for the channel and then define the channel number. Instead of only having signalling be fxo_ks though we want the signalling to be fxs_ks. Because the other settings haven’t been changed (signalling=fxs_ks replaces the previous value of signalling), they stay the same. Which means that while channel 1 takes on the values language=en, context=default, switchtype=national, and signalling=fxo_ks; channel 4 takes on the values language=en, context=default, switchtype=national, and signalling=fxs_ks.