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 inband 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.

View Answer

Answer: D