[channels] ;omit this line if you are including these lines in zapata_additional.conf
        context = from-pstn
         switchtype = national
         usecallerid = yes
         callerid=asreceived
         echocancel = yes
         echocancelwhenbridged = yes
         ;add the is option if you are problems with DTMF detection
         relaxdtmf = yes 
         rxgain = 0.0
         txgain = 0.0

        signalling = fxs_ks
        group = 1
        channel => 1-2
 
        signalling = fxo_ks
        group = 2
        channel => 3-4