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-stampbase as the regular audio channel to
simplify the generation of audiowaveforms at a gateway. The default clock frequency is 8,000 Hz,
butthe clock frequency can be redefined when assigning the dynamicpayload type.