Jitter Buffer Parameters (Voice Playout Delay); Silence Suppression Parameters (Voice Activity Detection) - Nortel 1000 Description, Installation And Operation Manual

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Jitter buffer parameters (voice playout delay)

Silence Suppression parameters (Voice Activity Detection)

553-3001-363 Standard 2.00
ITG engineering guidelines
There are three parameters that control the size of the jitter buffer in the
destination IP Trunk 3.01 (and later) node.
1 Voice playout nominal delay. This can range from twice the payload size
to 10 times, subject to a maximum of 320 ms.
2 Voice playout maximum delay.
3 Fax playout nominal delay. This can range from 0 to 300 ms, with 100
ms as the default size.
As discussed in "Adjust jitter buffer size" on
buffer size decreases the one-way delay of voice packets; however, setting the
jitter buffer size too small causes unnecessary packet discard.
If it is necessary to discard to downsize the jitter buffer, first check the delay
variation statistics. Obtain the one-way delay distributions originating from
all source IP Trunk 3.01 (and later) sites, using the measurements outlined in
"Measure intranet QoS" on
measurements" on page
delay for every flow. Some traffic sources with few hop counts yield small
delay variations, but it is the flows that produce great delay variations that
should be used to determine if it is acceptable to resize the jitter buffer.
Compute the standard deviation (σ) of one-way delay for that flow. It is
recommended that the jitter buffer size should not be set smaller than 2σ.
Silence Suppression, also known as Voice Activity Detection (VAD), is
enabled by default on a new IP Trunk 3.01 (and later) node. Enable/disable
VAD using the Enable voice activity detection checkbox on the OTM ITG
Node Properties -- DSP Profile codec Options tab. See Figure 55 on
page 327. To change the current DSP VAD state to match the current VAD
configuration, re-transmit card properties from OTM.
When silence is detected, the IP Trunk 3.01 (and later) node sends a flag to
the destination IP Trunk 3.01 (and later) node that denotes start of silence. No
September 2004
page 187 or "Post-installation network
222. Compute the standard deviation of one-way
page 183, lowering the jitter