H3C Technologies H3C MSR 50 - Manual (Page 629)

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b. Select Out-of-band Transmission for DTMF Transmission Mode.
c. Click Apply.
Figure 629 Configure out-of-band DTMF transmission mode
Verifying the configuration
After a call connection is established, if one side presses the telephone keys, the DTMF digits are
transmitted to the other side using out of band signaling, and the other side hears short DTMF tones from
the handset.