DTMF Detection and Relay in RTP Changes

Each RTP channel provides a DTMF detection and relay feature. In-band DTMF tones may be detected at incoming TDM side and may be relayed to packet side in one of three ways:

Transparent, DTMF tones are passed as tone in the codec. This option is only useful when codec is G.711.
As named telephone events (NTE) according to RFC 2833 / RFC 4733. In this mode in-band DTMF tones are removed from the TDM side and converted to events at the IP side (see also note below).
Not relayed at all. Detected DTMF tones will be removed from the TDM side (see also note below).

The selection of detection and relay mode is made by MX-ONE Service Node based on e.g. SIP/H.323 negotiation with remote end-point/gateway or use-case. Note that DTMF detection can be enabled or disabled by MX-ONE Service Node, regardless of relay mode selected.

Note:

When the RTP channel removes a DTMF tone there might be a leakage of less than 20 ms, i.e. may be audible but not detectable by any standard compliant DTMF receiver. By configuration it is possible to enable "complete removal" at the expense of longer channel latency (see chapter 4, Configuration). Complete removal is however only able to completely remove qualified DTMF digits.

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