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Cisco H.323 Gateway and DTMF Tones Not Passed to Lync

I was recently at a client configuring Lync Dial-In Conferencing. All functionality worked within the Lync environment as well as between the internal Cisco phones.
When testing external PSTN access to the Lync Dial-In Conferencing bridge, I noticed that the call would connect with two-way audio but DTMF signaling was not being accepted. Below is a breakdown of the environment.

My first thought was to add the “dtmf-relay rtp-nte” command to the voip dial peer on the voice router. When we took a look at the voip dial peer, we noticed that “dtmf-relay rtp-nte” had already been added. After further research and investigation, we determined that the H.323 gateway required its own DTMF relay command to pass DTMF tones out-of-band. We replaced the dtmf-relay command with “dtmf-relay h245-alphanumeric” and DTMF tones were accepted!

VOIP Dial Peer Before

dial-peer voice 100 voip
preference 2
destination-pattern 555555….
progress_ind setup enable 3
voice-class codec 1
voice-class h323 1
session target ipv4:X.X.X.X
incoming called-number .
dtmf-relay rtp-nte
fax rate disable
no vad
!

VOIP Dial Peer After

dial-peer voice 100 voip
preference 2
destination-pattern 555555….
progress_ind setup enable 3
voice-class codec 1
voice-class h323 1
session target ipv4:X.X.X.X
incoming called-number .
dtmf-relay h245-alphanumeric
fax rate disable
no vad
!

Further information regarding H.323 and DTMF frequency can be found below:

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