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7975 SIP Not Sending DTMF


  I am having problems getting 7975's to send DTMF across a SIP trunk.  Other phones such as my 8865 can complete this with out issue.  The SIP trunk in question is linked to another vendor PBX. 

I have attempted to use a MTP, but no change in symptoms occurred.

I have tried with the trunk DTMF Signaling Method set at no preference, RFC2833, and OOB + RFC2833.  No option provided a resolution.

CUCM 10.5.2

7975 SIP 9-4-2SR2-2S

Any suggestions is greatly appreciated.


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