Cisco 400-051 Exam

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.
Answer: Option A. 

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.

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