Nortel Meridian 1 Description, Installation And Operation page 74

Page 74 of 262 IP Telecommuter Engineering Guidelines
$GMXVWLQJ#MLWWHU#EXIIHU#VL]H
,PSOHPHQWLQJ#4R6#LQ#,3#QHWZRUNV
553-3001-119 Standard 2.00 April 2000
The jitter buffer parameters directly affect the end-to-end delay. Lowering the
voice playout settings decreases one-way delay, but this comes at the expense
of giving less waiting time for voice packets that arrive late.
The jitter buffer size is adjustable through the MAT input. It is not applicable
to a client (optimized built-in value cannot be changed).
The following parameters control the size of the jitter buffer in the destination
IP Line card node.
• Voice playout nominal delay. This can range from twice the payload
size to 10 times. The MAT default value is 60.
• Voice playout maximum delay is 120.
Lowering the jitter buffer size decreases the one-way delay of voice packets;
however setting the jitter buffer size too small will cause unnecessary packet
discard.
If the technician wishes to discard to downsize the jitter buffer, he should first
check the delay variation statistics. First obtain the one-way delay
distributions originating from all source ITG sites. Compute the standard
deviation of one-way 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 whether 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.
Today's corporate intranets evolved primarily because of the need to support
data services, services which for the most part a "best effort" IP delivery
mechanism suffices. Thus it is not surprising that traditionally intranets are
designed to support a set of QoS objectives dictated by these data services.