Digium, Inc.
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Chapter 3: Telephone System Configuration
FXS and FXO ports provide the ability to receive and send calls through
the traditional telephone network, or POTS (Plain Old Telephone
System). FXS modules provide both dial tone and ringing voltage to an
analog phone. FXO modules accept dial tone and provide an interface to
the traditional phone lines. You plug a telephone line into an FXO port,
and an analog telphone into an FXS port.
On this page you can specify the signalling type for your FXS and FXO
ports. You have two choices; either Kewl Start or Loop Start. The Loop
Start method uses a short to request a dial tone. All North American home
phone lines use loop start signalling. Kewl Start is the same as Loop Start,
but is better able to detect disconnects. Select either Kewl Start or Loop
Start for each FXS and FXO module. Kewl Start is the default and is
preferred for analog circuits in Asterisk.
Note: Ground Start signalling is not supported.
You also need to select a tone region, which defines the set of tones (dial
tones, ringing tone, busy tone, etc) used in your region. Select your
country, or the nearest neighboring country, from the Tone Region drop-
down list. The default setting is North America (United States/Canada).
