Tiers - Alcatel-Lucent 7450 Quality Of Service Manual

QoS Policies

Tiers

In single tier scheduling, queues are scheduled based on the forwarding class of the queue and
the operational state of the queue relative to the queue's CIR and PIR. Queues operating
within their CIR values are serviced before queues operating above their CIR values with
"high-priority" forwarding class queues given preference over "low-priority" forwarding
class queues. In single tier scheduling, all queues are treated as if they are at the same "level"
and the queue's parameters and operational state directly dictate the queue's scheduling.
Single tier scheduling is the system default scheduling policy for all the queues and
destinations listed above and has no configurable parameters.
Hierarchical scheduler policies are an alternate way to schedule queues that 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.
To illustrate the difference between single tier scheduling and hierarchical scheduling
policies, consider a simple case where, on service ingress, three queues are created for gold,
silver and bronze service and are configured as follows:
In the router, the CIR is used for profiling of traffic (in-profile or out-of-profile), and the PIR
is the rate at which traffic is shaped out of the queue. In single tier scheduling, each queue can
burst up to its defined PIR, which means up to 150 Mbps (10 Mbps + 40 Mbps + 100 Mbps)
can enter the service.
In a simple example of a hierarchical scheduling policy, a superior (or parent) scheduler can
be created for the gold, silver and bronze queues which limits the overall rate for all queues
to 100 Mbps. In this hierarchical scheduling policy, the customer can send in any combination
of gold, silver and bronze traffic conforming to the defined PIR values and not to exceed 100
Mbps.
Single Tier Scheduling
Single-tier scheduling is the default method of scheduling queues in the router. Queues are
scheduled with single-tier scheduling if no explicit hierarchical scheduler policy is defined or
applied. There are no configurable parameters for single-tier scheduling.
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• Gold: CIR = 10 Mbps, PIR = 10 Mbps
• Silver: CIR = 20 Mbps, PIR = 40 Mbps
• Bronze: CIR = 0 Mbps, PIR = 100 Mbps
Quality of Service Guide