Xblue Networks X-2020 - Manual (Page 92)

Web Programming
92 XBLUE Networks
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Once the codec is determined, it is important to know how often to send or what size the payload of information
should be before it is considered the right size to send. G.711 uses a timer, how often should the information be
sent. Therefore, both devices know how often to look for more information but neither device knows how much
information will be contained in the packet. All four G.726 protocols use the packet size rather than the time to
transmit. Therefore, both devices know how much information will be coming, but neither knows when to expect
the packets.
Codec G.711 u-law
•
Pronounced “Mu-Law” (like new with an M) and generally written µ-law is the algorithm used by
telephone communications products in the United States. This algorithm allows us to send
communications signals down long expanses of wires with very little distortion.
Codec G7.11 a-law
•
The a-law algorithm is used in many European telecommunications products. This algorithm also allows
communication signals to be send down long expanses wires with very little distortion but a-law does
not have as many different frequency ranges that
µ-law , so the signal decreases faster over a shorter
distance.
Codec G.726-xx
•
G.726 is an Adaptive Differential Pulse-code Modulation (ADPCM) protocol that reduces the amount of
bandwidth needed by over 50 percent, with minimal loss of voice quality. This protocol can be used
with both
µ-law and a-law devices.
•
There are four G.726 protocol or compression rates; G.726-40, G.726-32, G.726-24 and G.726-16. The
lower the number, (40, 32, 24, 16) the higher the compression. Thus, the lower the bandwidth require-
ments. Therefore, G.726-16 has the most compression and G.726-40 has the least.