Asterisk: The Future of Telephony

Configuring an FXO Channel

We’ll start by configuring an FXO channel. First we’ll configure the Zaptel hardware , and then the Zapata hardware. We’ll set up a very basic dialplan, and we’ll show you how to test the channel.

Zaptel Hardware Configuration

The zaptel.conf file located in /etc/ is used to configure your hardware. The following minimal configuration defines an FXO port with FXS signaling:

    fxsks=2
    loadzone=us
    defaultzone=us

In the first line, in addition to indicating whether we are using FXO or FXS signaling, we specify one of the following protocols for channel 2:

• Loop start (ls)

• Ground start (gs)

• Kewlstart (ks)

The difference between loop start and ground start has to do with how the equipment requests a dial tone: a ground start circuit signals the far end that it wants a dial tone by momentarily grounding one of the leads; a loop start circuit uses a short to request a dial tone. Though not common for new installations, analog ground start lines still exist in many areas of the country.^[29] For example, ground start lines are predominately used to reduce a condition known as “glare "^[30] that is associated with loop start lines and PBXs with high call volumes. All home lines (and analog telephones/modems/faxes) in North America use loop start signaling. Kewlstart is in fact the same as loop start, except that it has greater intelligence and is thus better able to detect far-end disconnects .^[31] Kewlstart is the preferred signaling protocol for analog circuits in Asterisk. ...