Specifications

Mediatrix 4100 133
C HAPTER
10
Voice Transmissions
This chapter describes the various codecs the Mediatrix 4100 supports for transmitting audio signals.
Codec Descriptions
The lines of the Mediatrix 4100 can simultaneously use the same codec (for instance, G.711 PCMA), or a mix
of any of the supported codecs. Set and enable these codecs for each line.
G.711 PCMA and PCMU
Specified in ITU-T Recommendation G.711. The audio data is encoded as 8 bits per sample, after logarithmic
scaling. PCMU denotes µ-law scaling, PCMA A-law scaling.
Analog Modem
The Mediatrix 4100 can send modem transmissions in clear channel (G.711). If configured adequately,
modems with higher rate capabilities (for instance, V.90) will automatically fall back in the transmission range
supported.
Currently, the Mediatrix 4100 does not NACK the modem tone request, but the modem tone request is not yet
supported.
Quality of modem transmissions is dependent upon the system configuration, quality of the analog lines, as
well as the number of analog-to-digital and digital-to-analog conversions. Modem performance may therefore
be reduced below the optimum values stated above.
Table 94: Codecs Comparison
Compression Voice Quality
G.711 None Excellent
G.723.1 Highest Good
G.726 Medium Fair
G.729a/ab High Fair/Good
Table 95: G.711 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) Can be enabled or disabled. When enabled, two levels of detection are
available: transparent or conservative. See “
G.711 and G.726 VAD” on
page 143 for more details.
Comfort noise Supports white and custom comfort noise as defined in RFC 3389. See
“
Comfort Noise” on page 145 for more details.