ACCESS Product Manual
47
Retransmit Squelch Trigger
– Determines the amount of time the
decoder must experience 100% packet loss before the
Retransmit
Squelch
function is triggered. Default is one second.
Retransmit Squelch Max
– The longest period of data loss during which
the squelch function is active — the default is two seconds. During the
squelch period, the buffer manager ignored the relative jitter experienced
and does not adjust buffer size to compensate.
Jitter Window
– This parameter defines the amount of time (in minutes)
that historical network performance is analyzed in order to make the
rest of the calculations. As an example, if the
Jitter Window
is set to the
default of five minutes, and if a dramatic network event happens and the
buffer manager reacts (perhaps by increasing the buffer), the event will
be included in the manager’s calculations for the next five minutes. If the
network experiences improved performance over this period, the manager
may choose to wind the buffer back down after the five minutes has
passed.
Loss Cushion
– Packets may arrive at the decoder displaying a range of
statistical properties. They may arrive in reasonably good timing and in
order, or half may arrive quickly with the other half delayed significantly.
In some cases, most of the packets arrive in a timely manner, but a
small percentage of them may be extremely late. In this case, it’s usually
preferable to allow these late packets to be left out, and keep the delay
lower. The decoder error concealment does a very good job of hiding
these losses. The
Loss Cushion
parameter instructs the buffer manager to
ignore a certain percentage of late packets in its calculation. The default
value is 5%. Applications that are not at all delay sensitive may wish to
reduce this value to zero, while extremely delay sensitive applications may
prefer to have this closer to 25%.
Delay Cushion
– The jitter buffer manager usually works very hard to
keep absolute delay to a minimum. Some applications are not delay
sensitive and would rather not have the manager working that hard. The
Delay Cushion
setting is a way to instruct the manager not to attempt
to drive the delay below a certain value. E.g. if the delay cushion is set to
500mS, this amount of fixed delay will be added to the buffer. If the jitter
manager needs to increase the buffer it will do so, but will not fall below
the ½ second level.
