Specifications

Preferred Codec Reference Manual (MGCP/NCS Version)
Mediatrix 4100
135
G.729
Specified in ITU-T Recommendation G.729, coding of speech at 8 kbit/s using conjugate structure-algebraic
code excited linear prediction (CS-ACELP). For all data rates, the sampling frequency (and RTP timestamp
clock rate) is 8000 Hz.
A voice activity detector (VAD) and comfort noise generator (CNG) algorithm in Annex B of G.729 is
recommended for digital simultaneous voice and data applications; they 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 comfort
noise frame occupies 2 octets.
The Mediatrix 4100 supports G.729A and G.729AB for encoding and G.729, G.729A and G.729AB for
decoding.
Preferred Codec
The preferred codec is the codec you want to favour during negotiation.
 To set a preferred codec:
1. In the voiceIfMIB, locate the voiceIfCodecPreferred variable (voiceIfCodecTable).
This variable sets the preferred codec for this line.
2. Choose the codec you want to use from one of the available configurations:
• pcmu
• pcma
• g723
• g729
• g726-16kbps
• g726-24kbps
• g726-32kbps
• g726-40kbps
The default value is pcmu.
Table 98: G.729 Features
Feature Description
Packetization time Range of 10 ms to 100 ms with increment of 10 ms. See “
Packetization
Time” on page 137 for more details.
Voice Activity Detection (VAD) The Mediatrix 4100 supports the annex B. Annex B is the built-in support
of VAD in G.729. See “
G.729 VAD” on page 144 for more details.
Note: If the MGCP/NCS Call Agent provides a list of codecs (always in preference order), the preferred
codec does not apply. In this case, the preferred codec of the Call Agent is used instead.
In the Unit Manager Network Administration Manual, refer to chapter Ports Parameters, section Port
Configuration Window.