Bandwidth - NEC Univerge SV9100 Manual

Issue 2.0
SV9100 Networking Manual
G.726

G.726 is an ITU-T ADPCM speech CODEC standard covering voice
transmission at rates of 16, 24, 32, and 40kbit/s. It was introduced to supersede
both G.721, which covered ADPCM at 32kbit/s, and G.723, which described
ADPCM for 24 and 40kbit/s. G.726 also introduced a new 16kbit/s rate. The four
bit rates associated with G.726 are often referred to by the bit size of a sample
as 2-bits, 3-bits, 4-bits, and 5-bits respectively.
G.729A

This ITU-T recommendation describes the algorithm for coding of speech
signals at 8kbps using CS-ACELP (conjugate-structure algebraic code-excited
linear prediction). This CODEC samples the analog signal at 8000Hz and uses
a frame size of 10ms. This CODEC has a MOS score of 4.0.
G.729 is the most commonly used CODEC for UNIVERGE SV9100 VoIP
installations. This is due to the fact that it offers high compression (and therefore
low bandwidth) while maintaining good speech quality.
G.723

This ITU-T recommendation describes a very low bit-rate compression
algorithm. The standard describes two versions 5.3Kbps and 6.4Kbps.
UNIVERGE SV9100 uses the higher bit rate. This CODEC offers low bandwidth
speech transmission, but has a lower MOS score of 3.9. This CODEC is not
commonly used on the UNIVERGE SV9100, but is particularly suited to low
bandwidth WAN connections.
iLBC

The iLBC CODEC is an algorithm that compresses each basic frame (20ms or
30ms) of 8000 Hz, 16-bit sampled input speech, into output frames with rate of
400 bits for 30ms basic frame size and 304 bits for 20ms basic frame size. This
CODEC is suitable for real-time communications such as, telephony and video
conferencing, streaming audio, archival and messaging.
Packet Size:
Each CODEC has a set frame length. This is the time that the frame
encapsulates. For G.729 and G.711 the frame length is 10ms and for G.723 the
frame length is 30ms. It is possible to configure the packet size in the UNIVERGE
SV9100 programming. To do this, we tell the UNIVERGE SV9100 how many
frames to encapsulate into each packet for transmission.
For example, the G.729 has a frame length of 10ms - the packet size is set to 3 (in
Program 84-11-01). This gives a 10ms x 3 = 30ms packet.
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