Medias Mediatrix 1204, Справочное руководство

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Adaptative Jitter Buffer Reference Manual (SIP Version)
Mediatrix 1204 209
Adaptative Jitter Buffer
The jitter buffer allows better protection against packet loss, but increases the voice delay. If the network to
which the Mediatrix 1204 is connected suffers from a high level of congestion, the jitter buffer protection level
should be higher. If the network to which the Mediatrix 1204 is connected suffers from a low level of
congestion, the jitter buffer protection level should be lower.
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To set Jitter Buffer variables:
1. In the voiceIfMIB , locate the voiceIfTable group.
2. Define the jitter buffer length in the voiceIfTargetJitterBufferLength variable.
The adaptive jitter buffer attempts to hold packets to the target holding time. This is the minimum
delay the jitter buffer adds to the system. The target jitter buffer length is in ms and must be equal
to or smaller than the maximum jitter buffer.
Values range from 0 ms to 300 ms. The default value is 30 ms. You can change values by
increments of 1 ms, but Mediatrix recommends to use multiple of 5 ms.
It is best not to set target jitter values below the default value. Setting a target jitter buffer below 5 ms
could cause an error. Jitter buffer adaptation behaviour varies from one codec to another. See
“About Changing Jitter Buffer Values” on page 209 for more details.
3. Define the maximum jitter buffer length in the voiceIfMaxJitterBufferLength variable.
This is the maximum jitter the adaptive jitter buffer can handle. The jitter buffer length is in ms and
must be equal to or greater than the target jitter buffer.
Values range from 0 ms to 300 ms. The default value is 125 ms. You can change values by
increments of 1 ms, but Mediatrix recommends to use multiple of 5 ms.
See “About Changing Jitter Buffer Values” on page 209 for more details.
4. Enable the jitter buffer protection by setting the voiceIfAdaptativeJitterBufferEnable variable to
enable .
5. Restart the Mediatrix 1204 so that the changes may take effect.
About Changing Jitter Buffer Values
Mediatrix recommends to avoid changing the target and maximum jitter buffer values unless experiencing or
strongly expecting one of the following symptoms:
If the voice is scattered and a lot of jitter buffer events are received when the syslog is enabled,
try to increase the maximum jitter buffer value.
If the delay in the voice path (end to end) is too long, you can lower the target jitter value, but
ONLY if the end-to-end delay measured matches the target jitter value.
For instance, if the target jitter value is 50 ms, the maximum jitter is 300 ms and the delay measured
is 260 ms, it would serve nothing to reduce the target jitter. However, if the target jitter value is
100 ms and the measured delay is between 100 ms and 110 ms, then you can lower the target jitter
from 50 ms to 30 ms.
Note:
You cannot disable the adaptative jitter buffer on the Mediatrix 1204. However, if you set the
voiceIfTargetJitterBufferLength and voiceIfMaxJitterBufferLength variables to the same value, you will have
a non-adaptative jitter buffer.