Media5 Mediatrix 4104, Reference Manual, Page: 263 / 466

Adaptative Jitter Buffer Reference Manual (SIP Version)
Mediatrix 4104 241
Adaptative Jitter Buffer
The jitter buffer allows better protection against packet loss, but increases the voice delay. If the network to
which the Mediatrix 4104 is connected suffers from a high level of congestion, the jitter buffer protection level
should be higher. If the network to which the Mediatrix 4104 is connected suffers from a low level of
congestion, the jitter buffer protection level should be lower.

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 135 ms. The default value is 30 ms. You can change values by
increments of 1 ms, but Media5 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 241 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 135 ms. The default value is 125 ms. You can change values by
increments of 1 ms, but Media5 recommends to use multiple of 5 ms.
The maximum jitter buffer value should be equal to the minimum jitter buffer value + 4 times the
ptime value. Let’s say for instance that:
• Minimum jitter buffer value is 30 ms
• Ptime value is 20 ms
The maximum jitter buffer value should be: 30 + 4x20 = 110 ms
See “About Changing Jitter Buffer Values” on page 241 for more details.
4. Restart the Mediatrix 4104 so that the changes may take effect.
About Changing Jitter Buffer Values
Media5 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, 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 135 ms and the delay measured
is 130 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 100 ms to 30 ms.
Note:
Do not put 0 as values for the voiceIfTargetJitterBufferLength and voiceIfMaxJitterBufferLength
variables.