Problem sending DTMF tones from FXS module.

Hi,
I have a A400P card with two FXO and one FXS modules. I'm running Elastix and everything looks ok except that when I send DTMF tones from an analogue phone to FXS module the tones quality both in sip phones and the called PSTN phone number (Analogue Telephone->FXS ->Asterisk->FXO->PSTN->FarEnd PBX->IVR) is very bad and the remote IVR (DIGITAL RECEPTIONIST) makes wrong selection.
Any help please?
Thanks in advance,
Dimos

can you supply ssh to me , i will help you to check it
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Chunlei.yi thank you very much for the response.
Unfortunately, the whole system is running in a LAN and I have not the rights to open/forward ports throw firewall. Can you please guide/advice me what is wrong? Do you like I to post any conf file?

please send the chan_dahdi.conf file to me
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