The HD2000IP supports up to 6 different Vocoder types including
G.711 A-/U-law，G.723.1, G.726, G.729A/B, G.722, iLBC, GSM_FR .
Depending on the product model, some of these Vocoders may not be
provided in standard release.
Users can configure Vocoders in a preference list that will be included
with the same preference order in SDP message. The first Vocoder in
this list can be entered by choosing the appropriate option in “Choice
1”. Similarly, the last Vocoder in this list can be entered by choosing the
appropriate option in “Choice 6”.
This field contains the number of voice frames to be transmitted in a
single packet. When setting this value, the user should be aware of the
requested packet time (used in SDP message) as a result of configuring
this parameter. This parameter is associated with the first vocoder in the
above vocoder Preference List or the actual used payload type
negotiated between the 2 conversation parties at run time. e.g., if the
first vocoder is configured as G723 and the “Voice Frames per TX” is
set to be 2, then the “ptime” value in the SDP message of an INVITE
request will be 60ms because each G723 voice frame contains 30ms of
audio. Similarly, if this field is set to be 2 and if the first vocoder chosen
is G729 or G711 or G726, then the “ptime” value in the SDP message
of an INVITE request will be 20ms. If the configured voice frames per
TX exceeds the maximum allowed value, the HD2000IP will use and
save the maximum allowed value for the corresponding first vocoder
choice. The maximum value for PCM is 10(x10ms) frames; for G726, it
is 20 (x10ms) frames; for G723, it is 32 (x30ms) frames; for
G729/G728, 64 (x10ms) and 64 (x2.5ms) frames respectively.
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