[trunkgroups]

[channels]
switchtype=euroisdn
echocancel=yes ; You can set this to 32, 64, or 128, tweak to your needs.
echocancelwhenbridged=yes
echotraining=400 ; Asteris the beginning of the call, number is in milliseconds
callerid=asreceived
group=1
context=default ; Points to the default context of your extensions.conf
channel => 1-15,17-31

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/etc/zaptel.conf

span=1,1,1,CCS,HDB3,crc4
loadzone=za
defaultzone=za
bchan=1-15,17-31
dchan=16