What is the cause of the issue?

Refer to the exhibit.

The SDP offer/answer has been completed successfully but there is no DTMF when users press keys.

What is the cause of the issue?
A . Payload type 110 was negotiated rather than type 101.
B . DTMF was negotiated properly in these messages.
D . 729 rather than
E . 711ulaw was negotiated.
F . DTMF was not negotiated on the call.

Answer: A