Alcatel-Lucent 7450 Quality Of Service Manual page 194

Service Egress QoS Policy
When any of the queue parameters are reduced, packets that are already in the queue will not
be affected and will be forwarded. Reducing these parameters will constrain the latency for
newly arriving packets, but those packets already in the queue before the new parameter
values were set will be forwarded with the delay associated with the actual queue depth when
the packet was enqueued (based on the previous parameter values).
The configured CBS is used as a minimum operational MBS. The maximum MBS is capped
by the maximum administrative MBS (1 GB).
If the operational MBS changes such that its value is similar or equal to the configured CBS,
the system increases the CBS to ensure that buffers can be requested from the correct portion
of the buffer pool (shared or reserved); this operation is automatic and the CBS reverts to its
configured value if the MBS is increased sufficiently. The automatic increase in the CBS
could, however, cause the resv-cbs red or amber alarms to be raised if the increase in the
related queues' CBS results in the total CBS assigned (but not necessarily used) matching or
exceeding the resv-cbs red and amber thresholds.
If a LAG is used together with pool-per-queue, the related hardware queues exist in their
own pool in the egress WRED megapool on a given FP and the operational MBS is used to
size the shared part of the pool with the sum of the CBS defining the reserved part of the pool.
Dynamic MBS is supported for both native FP and pool-per-queue queues within an egress
queue group template, which can be applied to access or network Ethernet ports and used for
egress network interface traffic, egress SAP traffic, and subscriber egress policed traffic.
The configuration of dynamic MBS and queue depth monitoring are mutually exclusive.
Dynamic MBS is configured as follows:
The operational MBS can be shown using the show pools and show qos scheduler-
hierarchy commands.
The following example shows the use of dynamic MBS. A queue group template is applied
to port 5/1/1 configured with multiple queues using HQoS, one of which has the following
parameters:
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configure
qos
queue-group-templates
egress
queue-group <queue-group-name> create
queue-group "qg1" create
queue 1 best-effort create
parent "s1" cir-level 1
rate 50000
queue <queue-id>
Quality of Service Guide