DTMF problem using speaker phone with Cisco 7940 and SIP load.

Unanswered Question
Apr 15th, 2009

Hi There,

I have run into a problem with DTMF digits using Cisco 7940 in speaker mode running SIP load.

If I for example dial to a conferencing system that requires code 12345 from a 7940 phone using speaker phone some of the digits doubles 1223445.

With some tests I have found that the problem only occurs running speaker phone and the volume control pretty high. It looks like the phone picks up the local DTMF playback on the phone with the MIC and the remote system actually hears 2 tones.

according to 7940 spec. the phone should not do this "For added security, the audible dual-tone multifrequency (DTMF) tones are masked when the speakerphone mode is used."

Searching the net I only found one bug related to this problem using Linksys IP Phone: "CSCse49603: Wrong DTMF tone level using speaker phone.

Root Cause: When using speakerphone, the DTMF tone is mixed with

the local DTMF echo playback.

Fix: Not mixing in the microphone input under such situation."

I have tested 2 versions. 8.8 and the new 8.11 version both having the same problem.

So do anyone have any solution or workaround using SIP?

(I think Skinny load is not affected with this problem?)

Best Regards

/Andreas

I have this problem too.
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