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DTMF Problem Noted 7945G on Speaker

I had an intermittent problem reported from our Operations Center.   When they call a particular IVR at one of our providers the DTMF entry for the pass code is often not recognized if the call was placed with speaker on.  If the call is made instead with the hand set held to the head then it seems that the DTMF codes are more likely to be recognized and processed correctly.  Is this a known issue?  Any advice on how to go about trouble shooting something like this?  Thank you.

The setup..

7945G  CUCM 7.1   --[SIP Trunk]--  [Cisco 3845 ISR]  -[SIP Trunk]- {PSTN} [IVR SP]

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VIP Super Bronze

DTMF Problem Noted 7945G on Speaker

It's not a known issue. Remember that while DTMF events are an out-of-band (or NTE) event on the VoIP side, once the PSTN turns the call into traditional TDM the DTMF events return to an in-band audio signal. At that point anything that can interfere with the call audio (e.g. voltage impeedence mismatch, incorrect input/output attenuation levels, excessive background noise, etc) will also impact the DTMF events.

It's probably a combination of factors such as background noise in the Ops Center as well as something on that particular far-end since this only happen to one dialed number.

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