19.2.2.2. Feature activation while DMC is active 
When a DMC is active for a two party call and a feature is being activated
the DMC is released and the call is switched back to the master connection.
This applies for features that are activated by one of the involved
parties and also for features activated by a third party (e.g. campon,
override).
When the feature is finished and the call returns to the normal two
party talk state the DMC is not reactivated except for the features that
are listed in the chapter above.
Feature response in exception situations:
- DTMF Handling
-
A DMC is released if the endpoint requests the sending of DTMF via SIU (signaling unit). E.g. a HFA phone requests the sending of DTMF via access code.
- DTMF transmission over DMC
-
DTMF tones are recognized in DMCs and transmitted, e.g. if the tone is received by the OpenScape 4000 system at a CO interface or a DTMF enabled anate sends DTMF by itself.