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DTMF issue with SIP Intercom

Hi there,


I got a strange DTMF issue with SIP intercom.


Intercom (SIP) > Cisco IP Phone SCCP (When someone press the Intercom, it calls a Cisco IP Phone. It rings, the user pickup phone and talk (audio) and then open the door using DTMF.


When the user is not at his desk, he put a Call Forward All on his Cisco IP Phone to his Mobile. 

Interncom (SIP) > Cisco IP Phone (SCCP) > Call Forward All To Mobile (through PSTN gateway the call is routed to GSM)


In the last mentioned situation, the user on his mobile do hear the person behind the Intercom but when he try to open the door  by pressing #, it doesn't open the door (DTMF is not working!).


I have tried a few things on dial-peer (dtmf-relay cisco-rtp, dtmf-relay rtp-nte, and dtmf-relay h245-alphanumeric) and I have also tried to use MTP but it didn't solve this issue.


I hope someone can point me in the right direction and all suggestions are welcome.



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