Specifications

Echo Cancellation Reference Manual (MGCP/NCS Version)
Mediatrix 4100
145
 To define the G.729 Annex B negotiation:
1. In the mgcpncsExperimentalMIB, set the mgcpncsG729AnnexBNegotiation variable to the proper
value.
The following values are available:
Echo Cancellation
Echo cancellation eliminates the echo effect caused by signal reflections. An echo is a signal that has been
reflected or otherwise returned with enough magnitude and delay to be perceived. The echo cancellation is
usually an active process in which echo signals are measured and cancelled or eliminated by combining an
inverted signal with the echo signal.
Comfort Noise
Comfort Noise (CN) defines how the Mediatrix 4100 processes silence periods information it receives.
During silence periods, the Mediatrix 4100 may receive CN packets containing information about background
noise. When enabling Comfort Noise Generation (CNG), those packets are used to generate local comfort
noise.
Table 107: G.729 Annex B Negotiation Parameters
Parameter Description
disable The G.729 Annex B is NOT negotiated through the SDP. This is the default
value.
In that case, the G.729 Annex B is based on the MIB variable
voiceIfG729VoiceActivityDetectionEnable. When this variable is set to enable,
the G.729 codec negotiated as payload number 18 (G729) supports the Annex
B implicitly.
However, when the voiceIfG729VoiceActivityDetectionEnable variable is set to
disable, the G.729 codec negotiated as payload number 18 (G729) does NOT
support the Annex B implicitly.
enable The G.729 Annex B is negotiated through the SDP.
In that case, the G.729 Annex B is advertised in the offer. The value depends
on the MIB variable voiceIfG729VoiceActivityDetectionEnable. If this variable is
set to enable, then the Annex B is set to 'yes'; otherwise, the value 'no' is
advertised.
The answerer MAY not be able to support the Annex B. In that case, the
answer to the Annex B can be set to 'no'. This forces the offerer not to use the
Annex B in G.729. However, the opposite is not possible. The answerer can
NOT force the offerer to use the Annex B if this one does not bear such
capability.
Standards Supported • RFC 3389: Real-time Transport Protocol (RTP) Payload for
Comfort Noise (CN)
Note: Comfort noise only applies to the G.711 and G.726 codecs. G.723 and G.729 CNG is not
configurable because it is part of the codec.