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The subrate capabilities and per-service scheduling control are required to make multiple services
per physical port possible. Without egress shaping, it is impossible to support more than one
service per port. There is no way to prevent service traffic from bursting to the available port
bandwidth and starving other services.
For accounting purposes, per-service statistics can be logged. When statistics from service ingress
queues are compared with service egress queues, the ability to conform to per-service QoS
requirements within the service core can be measured. The service core statistics are a major asset
to core provisioning tools.
Service egress QoS policies define egress queues and map forwarding class flows to queues. In the
simplest service egress QoS policy, all forwarding classes are treated like a single flow and
mapped to a single queue. To define a basic egress QoS policy, the following are required:
•
•
•
Optional service egress QoS policy elements include:
•
•
•
Each queue in a policy is associated with one of the forwarding classes. Each queue can have its
individual queue parameters allowing individual rate shaping of the forwarding class(es) mapped
to the queue. More complex service queuing models are supported in the router where each
forwarding class is associated with a dedicated queue. The forwarding class determination per
service egress packet is determined at ingress. If the packet ingressed the service on the same
router, the service ingress classification rules determine the forwarding class of the packet. If the
packet is received, the forwarding class is marked in the tunnel transport encapsulation (for
example: QinQ encapsulated packet).
Service egress QoS policy ID 1 is reserved as the default service egress policy. The default policy
cannot be deleted or changed. The default access egress policy is applied to all SAPs service
egress policy explicitly assigned. The characteristics of the default policy are listed in the
following
7210 SAS D, E, K OS Quality of Service Guide
A unique service egress QoS policy ID.
A QoS policy scope of template or exclusive.
At least one defined default queue.
Additional queues up to a total of 8 separate queues. A forwarding class queue is shared
by unicast and multipoint (BUM) traffic type mapped to that forwarding class.
IEEE 802.1p priority value remarking based on forwarding class.
Option to use IP DSCP values for marking based on FC.
Table
23.
QoS Policies
Page 59
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