19.2.1.3.3. HFA 
optiPoint phones generate CN frames on the master connection once
DMC is established.
OpenStage phones do not generate CN on master connection once
DMC is established.
VAD setting in AMO SDAT controls the sending CN for normal connections
and DMC slave connections.
The phone’s DSP (Digital Signal Processor) will accept VAD for G711,
G729 or G723 regardless of the phone VAD SDAT setting. VAD is not defined
for G722.
Codecs and silent suppression
- G711 - High quality codec, capable of Voice Activity Detection (VAD) and Comfort Noise Generation (CN);
- G723.1 - Audio codec for voice that compresses voice audio in 30 ms frames; Capable of silent suppression (VAD) and comfort noise (CN); Not reliable for transporting music or tones such as DTMF or fax.
- G729 - Voice compression codec; Not capable of silent suppression (VAD) - implicitly silence suppression is off
- G729A - Voice compression codec; Not capable of silent suppression (VAD) - implicitly silence suppression is off
- G729B - Voice compression codec; Capable of silent suppression (VAD); not compatible with G729 or G729A
- G729AB - Voice compression codec; Capable of silent suppression (VAD); only compatible with G729B