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Introduction to DRO-250i
Random Early Detection (RED):
Random Early Detection is a classless qdisc which limits its queue size
smartly. Regular queues simply drop packets from the tail when they are
full which may not be the optimal behaviour. RED also performs tail drop
but does so in a more gradual way.
The RED gateway calculates the average queue size using a low pass filter
with an exponential weighted moving average. The average queue size is
compared to two thresholds, a minimum threshold and a maximum
threshold. When the average queue size is less than the minimum
threshold, no packets are marked. When the average queue size is greater
than the maximum threshold every arriving packet is marked
When the average queue size is between the minimum and the maximum
threshold, each arriving packet is marked with probability p, where p is a
function of the average queue size. Each time that a packet is marked, the
probability that a packet is marked from a particular connection is roughly
proportional
to
that
connection's
share
of
the
bandwidth
at the gateway.
Handle:
Queues are identified by a handle <major number, minor number>, where
the minor number is zero for queues. Major number uniquely identifies the
queue.
Parent:
Parent does not apply for root qdisc. Major number represents the parent
of the sub-queue or child queue. This will be equal to the handle major
number of parent queue. Parent minor number will be minor number of
the class to whom it (red) belongs.
Min:
Average queue size at which marking becomes a possibility.
Recommended (<Max> - (3 * <Min>)).
DRO-250i User Manual
97
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