QoS Policies
Quality of Service Guide 69
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 Committed Information Rate
(CIR) and Peak Information Rate (PIR). Queue’s operating within their CIR values are
serviced before queue’s 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.
A pair of schedulers, a high-priority and low-priority scheduler, transmits to a single
destination switch fabric port, access port, or network interface. Table 17 below lists how the
forwarding class queues are mapped to the high and low scheduler:
By using the default QoS profile, all ingress traffic is treated as best effort (be) (mapped to
FC be and to low priority scheduler). For an egress SAP using the default QoS profile, all
egress traffic will use the same queue.
While competing for bandwidth to the destination, each scheduler determines which queue
will be serviced next. During congestion (packets existing on multiple queues), queues are
serviced in the following order:
Queues associated with the high-priority scheduler operating within their CIR
• Queues associated with the low-priority scheduler operating within their CIR
• All queues with traffic above CIR and within PIR will be serviced by a biased round
robin
Table 17: Forwarding Class Scheduler Mapping
Scheduler Forwarding Class
High Network Control
Expedited
High-2
High 1
Low Low-1
Assured
Low-2
Best-Effort
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