Grandstream Networks GXV3140 Application Manual page 46

Preferred Video Codec
H.264Payload type
H.263+ Payload type
L16-256 Payload type
H.263 Encoder
Resolution
Silence Suppression
Voice Frame per TX
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When this has been configured, the system will select the preferred vocoder
from the list and the same order is sent with the SDP messages.
The user can change the preferred vocoder priority order by toggling with the up
and down buttons. It is recommended to use the default setting "PCMU"; if other
vocoders are chosen, there could be an audio transmission error.
Selects the preferred video codec from the available list. It is recommended to
use H.264.
Selects the dynamic H.264 codec payload type (ranges from 96-127). The
default setting is 99.
Selects the H.263+ codec payload type (ranges from 96-127). The default
setting is 103
Selects the L16-256 codec payload type (ranges from 96-127). The default
setting is 103
Selects the resolution (CIF/QCIF) used for H.263 codec. The default resolution is
CIF.
This controls the G723/G729 silence suppression/VAD. If set to YES, when no
audio is detected, the phone will send a small number of VAD packets (instead of
audio packets). If Set to NO, this feature is disabled. The default setting is NO.
This configures the number of voice frames transmitted per packet. (It is
recommended to set this based on the Ethernet IS packet limitation – 1500 Byte
or 120kb/s)
When configuring this, it should be noted that the "ptime" value for the SDP will
change with different configurations here. This value is related to the codec used
and the actual frames transmitted during the in payload call.
For example: if the codec is configured to be G.723 and "Voice Frames per TX" is
set to 2. Then in the INVITE request, the "ptime" value for SDP will be 60 ms.
This is because the G723 voice frame is 30 ms. Similarly, if the setting is 2 and
the codec is G729 or G711 or G726, the "ptime" value for SDP in the INVITE
request will be 20 ms.
If the voice frames per TX configuration exceeds the maximum value allowed,
the phone will choose the preferred codec and use the maximum value allowed.
The maximum value is 64 frames.
Adjusting these values will also change the jitter buffer. The phone has an
algorithm for setting the jitter buffer and the jitter buffer rate is around 20-200ms.
For end-users, it is recommended to use the default setting, as incorrect settings
GXV3140 USER MANUAL
FIRMWARE VERSION 1.0.3.10
Page 46 of 117
Updated : 12/2009