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Core Issue

The user makes a call and hears announcement messages (for example, "enter your account number..."), but cannot pass Dual Tone Multifrequency (DTMF) digits. This symptom applies for both VoIP toll bypass and IP phone calls to the Public Switched Telephone Network (PSTN) or PBX.

A Cisco IP phone (Cisco CallManager scenario) or Plain Old Telephone Service (POTS) phone (VoIP toll bypass scenario) call leaves through a Cisco IOS  Software gateway, where the called number is usually an Interactive Voice Response (IVR) system that sends back an ISDN progress message, but does not connect until some account information is entered. By default, the audio path is cut-through in the backward direction (toward the IP phone or originating gateway), but not in the forward direction, until the terminating gateway receives a connect message. Therefore, there is no voice path to transmit DTMF tones or speech toward the terminating switch.


To establish (cut-through) the audio path in both directions prior to receiving an ISDN connect message from the PSTN, issue the voice rtp send-recv global configuration command.

For more information on this command, refer to Cisco IOS Voice, Video, and Fax Commands: Si through Z.

For more information about resolving one-way voice problems, refer to the Additional Information: Verify One-Way Audio section of Troubleshooting One Way Voice Issues.

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