Specifications

Chapter 10 - Voice Transmissions Voice Activity Detection
144
Mediatrix 4100
 To enable G.711 and G.726 VAD:
1. In the voiceIfMIB, locate the voiceIfTable group.
2. Define the sensitivity of the VAD algorithm to silence periods in the
voiceIfG711VoiceActivityDetectionEnable variable.
The following settings are available:
The difference between transparent and conservative is how “aggressive” the algorithm considers
something as an inactive voice and how “fast” it stops the voice stream. A setting of conservative is
a little bit more aggressive to react to silence compared to a setting of transparent.
The default value is conservative.
3. Restart the Mediatrix 4100 so that the changes may take effect.
G.729 VAD
G.729 has a built-in VAD in its Annex B version. It is recommended for digital simultaneous voice and data
applications and can be used in conjunction with G.729 or G.729 Annex A. A G.729 or G.729 Annex A frame
contains 10 octets, while the G.729 Annex B frame occupies 2 octets. The CN packets are sent in accordance
with annex B of G.729.
 To enable G.729 VAD:
1. In the voiceIfMIB, locate the voiceIfTable group.
2. Define the voiceIfG729VoiceActivityDetectionEnable variable.
The following settings are available:
See “
Enabling Individual Codecs” on page 136 for more details.
G.729 Annex B Negotiation
You can indicate whether the G.729 Annex B is negotiated through the Session Description Protocol (SDP) or
not.
RFC 3555 (MIME Type Registration of RTP Payload Formats), July 2003 explains how the Annex B can be
negotiated by using the SDP.
The Annex B indicates that Annex B, voice activity detection, is used or preferred. Permissible values are 'yes'
and 'no' (without the quotes); 'yes' is implied if this parameter is omitted.
m=audio 5004 RTP/AVP 0 18 13
a=fmtp:18 annexb=yes
Table 105: G.711/G.726 VAD Settings
Setting Description
Disable VAD is not used.
Transparent VAD is enabled. It has low sensitivity to silence periods.
Conservative VAD is enabled. It has normal sensitivity to silence periods.
Table 106: G.729 VAD Settings
Setting Description
disable G.729 uses annex A only. The Mediatrix 4100 does not send G.729 Annex B
comfort noise frames.
enable G.729 annex A is used with annex B. The Mediatrix 4100 sends G.729 Annex
B comfort noise frames during silence periods.