Queue Hardware Scheduler; Committed Information Rate - Alcatel-Lucent 7450 Quality Of Service Manual

Queue Parameters

Queue Hardware Scheduler

The hardware scheduler for a queue dictates how it will be scheduled relative to other queues
at the hardware level. When a queue is defined in a service ingress or service egress QoS
policy, it is possible to explicitly define the hardware scheduler to use for the queue when it
is applied to a SAP.
Being able to define a hardware scheduler is important as a single queue allows support for
multiple forwarding classes. The default behavior is to automatically choose the expedited or
non-expedited nature of the queue based on the forwarding classes mapped to it. As long as
all forwarding classes mapped to the queue are expedited (nc, ef, h1 or h2), the queue will be
treated as an expedited queue by the hardware schedulers. When any non-expedited
forwarding classes are mapped to the queue (be, af, l1 or l2), the queue will be treated as best
effort by the hardware schedulers.
The expedited hardware schedulers are used to enforce expedited access to internal switch
fabric destinations.

Committed Information Rate

The committed information rate (CIR) for a queue performs two distinct functions:
All router queues support the concept of in-profile and out-of-profile. The network QoS
policy applied at network egress determines how or if the profile state is marked in packets
transmitted into the service core network. If the profile state is marked in the service core
packets, out-of-profile packets are preferentially dropped over in-profile packets at
congestion points in the core.
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1. Profile marking service ingress queues — Service ingress queues mark packets in-
profile or out-of-profile based on the queue's CIR. For each packet in a service
ingress queue, the CIR is checked with the current transmission rate of the queue. If
the current rate is at or below the CIR threshold, the transmitted packet is internally
marked in-profile. If the current rate is above the threshold, the transmitted packet is
internally marked out-of-profile.
2. Scheduler queue priority metric — The scheduler serving a group of service ingress
or egress queues prioritizes individual queues based on their current CIR and PIR
states. Queues operating below their CIR are always served before those queues
operating at or above their CIR. Queue scheduling is discussed in
Hierarchical Scheduling.
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