Alcatel-Lucent 7950 Quality Of Service Manual page 387

wred-queue
Syntax wred-queue [policy slope-policy-name]
no wred-queue
Context config>qos>qgrps>egr>qgrp>queue>xp-specific
Description
This command alters the generic buffer pool association of the queue for the purpose of allowing queue-
specific WRED slopes with minimal provisioning. When the wred-queue command is defined and the
queue ID is created on an , a buffer pool is created specifically for the queue and the queue obtains all
buffers from that pool. The size of the pool is the same as the size of the queue. In this manner, the WRED
slopes that operate based on the pool's buffer utilization are also reacting to the congestion depth of the
queue.
The size of the buffer pool is dictated by the queue's mbs parameter. The size of the reserved CBS portion
of the buffer pool is dictated by the queue's cbs parameter. The provisioning characteristics of the mbs and
cbs commands have not been changed.
In the case where the QoS policy is applied to a SAP on an which has WRED queue support shut down
(config>card>fp>egress>wred-queue-control>shutdown) the WRED buffer pool is created, but the
queue will continue to map to either to its default pool or the pool defined in the pool command. If the no
shutdown command is executed, the queue will at that point be automatically moved to its own WRED
pool.
Each pool created for a queue using the wred-queue command shares buffers with all other wred-queue-
enabled queues on the same . The WRED pool buffer management behavior is defined within the
config>card>fp>egress>wred-queue-control context.
The WRED slopes within the pool are defined by the slope policy associated with the queue. When a policy
is not explicitly defined, the default slope policy is used. The slope policy enables, disables and defines the
relative geometry of the high and low WRED slopes in the pool. The policy also specifies the time average
factor (TAF) used by the pool when calculating the weighted average pool depth.
As packets attempt to enter the egress queue, they are associated with either the high or low WRED slope
based on the packets profile. If the packet is in-profile, the high slope is used. The low slope is used by out-
of-profile packets. Each WRED slope performs a probability discard based on the current weighted average
pool depth.
When wred-queue is enabled for a SAP egress queue on an , the queue's pool and hi-priority-only
commands are ignored.
The no form of the command restores the generic buffer pool behavior to the queue. The WRED pool is
removed from the system.
Parameters
slope-policy-name — Overrides the default WRED slope policy with an explicit slope policy. The defined
slope policy must exist or the command will fail.
7950 XRS Quality of Service Guide Page 387