Alcatel-Lucent 7450 Quality Of Service Manual page 70

QoS Policies
Queues associated with a single scheduler are serviced in a round robin method. If a queue
reaches the configured PIR, the scheduler will not serve the queue until the transmission rate
drops below the PIR.
The router QoS features are flexible and allow modifications to the forwarding class
characteristics and the CIR and PIR queue parameters. The only fundamental QoS
mechanisms enforced within the hardware are the association of the forwarding classes with
the high priority or low priority scheduler and the scheduling algorithm. Other parameters can
be modified to configure the appropriate QoS behavior.
Hierarchical Scheduler Policies
Hierarchical scheduler policies are an alternate way of scheduling queues which can be used
on service ingress and service egress queues. Hierarchical scheduler policies allow the
creation of a hierarchy of schedulers where queues and/or other schedulers are scheduled by
superior schedulers.
The use of the hierarchical scheduler policies is often referred to as hierarchical QoS or H-
QoS on the SR OS.
Hierarchical Virtual Schedulers
Virtual schedulers are created within the context of a hierarchical scheduler policy. A
hierarchical scheduler policy defines the hierarchy and parameters for each scheduler. A
scheduler is defined in the context of a tier (Tier 1, Tier 2, Tier 3). The tier level determines
the scheduler's position within the hierarchy. Three tiers of virtual schedulers are supported
(Figure
scheduler. It is not necessary for Tier 1 schedulers to obtain bandwidth from a higher tier
scheduler. A scheduler can enforce a maximum rate of operation for all child queues and
associated schedulers.
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10). Tier 1 schedulers (also called root schedulers) are defined without a parent
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