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/etc/dahdi/system.conf
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# Autogenerated by /usr/sbin/dahdi_genconf on Sun Sep 21 09:19:12 2014
# If you edit this file and execute /usr/sbin/dahdi_genconf again,
# your manual changes will be LOST.
# Dahdi Configuration File
#
# This file is parsed by the Dahdi Configurator, dahdi_cfg
#
# Global data

loadzone	= us
defaultzone	= us
fxsks		= 4
echocanceller = mg2,3-4



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/etc/asterisk/chan_dahdi.conf
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[trunkgroups]
[channels]

;#include /etc/asterisk/dahdi-channels.conf

usecallerid=no
hidecallerid=no
callwaiting=no
threewaycalling=no
transfer=yes
canpark=yes


group=1
context=from-pstn
signalling=fxs_ks
channel=>4



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Instructions:
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1. dahdi_genconf - run this to generate /etc/dahdi/system.conf
2. add the following lines:
   fxsks = 4                ; this specifies the actual analog channel on the FXO card
   echocanceller = mg2,3-4  ; always need to set echo cancellation
3. /etc/asterisk/chan_dahdi.conf
In the included file, the following lines mean:
group=1			; this is a magic number
context=from-pstn	; dialplan entry point incoming analog line into FXO card
signalling=fxs_ks	; very unlikely to be anything but this, we're only going to be dealing with a
			; single analog line into the pbx
channel=>4		; this matches up with the channel specified in the system.conf

Everything else in this config is basic and will probably stay the same irrespective of the actual card.
4. Then comment out all the hardware specific drivers in /etc/dahdi/modules that do not match the FXO card.
5. Stop service dahdi.
6. Stop service asterisk
7. Start service dahdi
8. Start service asterisk