Alcatel-Lucent 7950, Quality Of Service Manual, Page: 58 / 612

QoS Policies
Page 58 7950 XRS Quality of Service Guide
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 16 below lists how the forwarding class
queues are mapped to the high and low scheduler:
Note, that 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:
1. Queues associated with the high-priority scheduler operating within their CIR.
2. Queues associated with the low-priority scheduler operating within their CIR.
3. All queues with traffic above CIR and within PIR will be serviced by a biased round robin.
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.
Table 16: Forwarding Class Scheduler Mapping
Scheduler Forwarding Class
High Network Control
Expedited
High-2
High 1
Low Low-1
Assured
Low-2
Best-Effort