Alcatel-Lucent 7950 Quality Of Service Manual page 31

Committed Information Rate
The committed information rate (CIR) for a queue performs two distinct functions:
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 oper-
ating below their CIR are always served before those queues operating at or above their CIR.
Queue scheduling is discussed in
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.
1. When defining the CIR for a queue, the value specified is the administrative CIR for the
queue.The router has a number of native rates in hardware that it uses to determine the oper-
ational CIR for the queue. The user has some control over how the administrative CIR is con-
verted to an operational CIR should the hardware not support the exact CIR and PIR
combination specified. The interpretation of the administrative CIR is discussed below in
Adaptation Rule on page 33
Although the router is flexible in how the CIR can be configured, there are conventional ranges for
the CIR based on the forwarding class of a queue. A service ingress queue associated with the
high-priority class normally has the CIR threshold equal to the PIR rate although the router allows
the CIR to be provisioned to any rate below the PIR should this behavior be required. If the service
egress queue is associated with a best-effort class, the CIR threshold is normally set to zero; again
the setting of this parameter is flexible.
The CIR for a service queue is provisioned on ingress and egress service queues within service
ingress QoS policies and service egress QoS policies, respectively.
The CIR for network queues are defined within network queue policies based on the forwarding
class. The CIR for the queues for the forwarding class are defined as a percentage of the network
interface bandwidth.
7950 XRS Quality of Service Guide
Virtual Hierarchical Scheduling on page
QoS Policies
56.
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