Dmft tone probelm

Hi
i am newbie to Asterisk

i am unable to receive DMFT tone from the answered phone . i am using sip server to terminate the PSTN call .
sip server setting from asterisk side
was

[XX.XX.XX.XX]
type=friend
host=XX.XX.XX.XX
allow=g711
allow=alaw
allow=gsm
allow=ulaw
nat=no
canreinvite=no
context=check
insecure=port
dtmfmode=rfc2833