Users report that when they dial to Cisco Unity Connection from an external network, they cannot enter any digits. Assuming only in-band DTMF is supported, what is a reason for this malfunction?

Refer to the exhibit.

Users report that when they dial to Cisco Unity Connection from an external network, they cannot enter any digits. Assuming only in-band DTMF is supported, what is a reason for this malfunction?
A . The negotiated RTP port is outside of the range described by RFC, so in band DTMFs do not work.
B . There is SIP Delayed Offer. DTMF is supported only in Early Offer.
C . The rtpmap:0 value for the negotiated codec is marking DTMF as inactive.
D . No DTMF is negotiated.

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Answer: D