Authority Group Technical Reference - ZyXEL Communications X6004 User Manual

13.4 Authority Group Technical Reference

This section contains technical background information about the Authority
Group screens.
Voice Codecs
A codec (coder/decoder) codes analog voice signals into digital signals and
decodes the digital signals back into voice signals. The following table describes
the codecs supported on the X6004
Table 68 Voice Codecs Supported
CODEC
G.711
G.722
(pass-
through)
G.722
AMR-WB
(pass-
through)
(also
referred to
G.722.2)
G.723.1
X6004 User's Guide
DESCRIPTION
This is a Pulse Code Modulation (PCM) waveform codec. PCM measures
analog signal amplitudes at regular time intervals (sampling) and converts
them into digital bits (quantization). Quantization "reads" the analog signal
and then "writes" it to the nearest digital value. For this reason, a digital
sample is usually slightly different from its analog original (this difference is
known as "quantization noise").
G.711 provides excellent sound quality but requires 64kbps of bandwidth.
There are two main algorithms defined in the G.711 standard, the µ-law
algorithm (used in North America & Japan) and a-law algorithm (used in
Europe and the rest of the world).
G.722 is an ADPCM codec (see G.726) working at 48 ~ 64 Kbps, with an
audio sample rate of 16 KHz. G.722 provides excellent sound quality.
Note: The X6004 supports G.722 pass-through, meaning that devices
communicating via the X6004 must support this codec.
G.722.2 is similar to G.722, but with a lower compression rate that can vary
according to the amount of available bandwidth. When there is plenty of
bandwidth, the compression ratio decreases, and when there is network
congestion the compression ratio increases. This is also known as Adaptive
Multi Rate - WideBand (AMR-WB).
Note: The X6004 supports G.722.2 pass-through, meaning that devices
communicating via the X6004 must support this codec.
This is an ITU (International Telecommunication Union) standard for voice
coding. The G.723.1 codec compresses voice audio in 30 ms frames. The
G.723.1 operates at two bitrates: 6.3 kbps when sampling at 24 bytes or 5.3
kbps when sampling at 20 bytes per 30 ms frame.
Chapter 13 Authority Group
227