DTMF Indication

There are three ways to convey DTMF information for packet-based communications:

• DTMF audio tones: DTMF digit waveforms are encoded inline with voice packets. This method only works with uncompressed audio codecs like G.711. Compressed audio codecs like G.729 and G.723 are incompatible with DTMF audio. DTMF audio is also referred to as in-band tones.
• Out-of-band signaling events:

  SIP INFO messages with Content-Type: application/dtmf-relay define out-of-band signaling events for transmitting DTMF information. SIP INFO messages separate DTMF digits from the voice stream and send them in their own signaling message.

• RTP named telephony events (NTE): RFC 2833 telephone-events are a standard that describes how to transport DTMF tones in RTP packets according to section 3 of RFC 2833. Of the three RTP payload formats available, the Oracle® Enterprise Session Border Controller supports RTP NTE.