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Voice
In this section, select the order and preferred CODEC's, plus
sent for each.
Also, select the options that effect the different codecs used and DTMF sending method and
payloads.
When selecting the codecs consider the data rate that will be required by your network. As a
guild the list here show the data bit rate required for each codec, if the network is via a low
speed ADSL then the PCMu/a may not be a suitable choice.
Table 1. Codec comparison
Codec
G.711(PCMu /a)
G726-32
GSM
iLBC 20ms
iLBC 30ms
Speex
G.729
If the iLBC or SPEEX codecs are used, then set the following for each,
a) iLBC codec, select the frame size your network requires to 20mS or 30mS.
b) SPEEX codec, select a suitable bit rate for best quality available, the range
is from 2.15kBits/s to 24.6kBits/s.
The Frames per TX selects how many blocks of data (10mS segments) are transmitted with
each packet sent over the network. (note the higher the number, the more the delay), 2 - 4 is
recommended.
The Send DTMF type selects how the unit will send DTMF digits over the network (only
required for unit fitted with a front panel keypad and if digits are dialled during a conversation).
The remaining options set the payload required for each protocol and it is recommend that
the default values be used.
Dallas Delta Corporation Pty.Ltd.
bit rate (kbit/s)
64
32
13.2
15.2
13.3
2.15 - 24.6
8
the amount of frames per packet to
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