How are DTMF digits transported in RFC 2833?

A.
In the RTP stream with the named telephone events payload format.

B.
In the RTP stream with the regular audio payload format.

C.
In SIP NOTIFY messages.

D.
In SIP INFO messages.

E.
In SIP SUBSCRIBE messages.

Explanation:

DTMF digits and named telephone events are carried as part of the audio stream, and MUST use the
same sequence number and time-stamp base as the regular audio channel to simplify the generation
of audio waveforms at a gateway. The default clock frequency is 8,000 Hz, but the clock frequency
can be redefined when assigning the dynamic payload type.