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Service Egress QoS Policies
Service egress queues are implemented at the transition from the service core network to the
service access network. The advantages of per-service queuing before transmission into the access
network are:
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The sub-rate 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. The
system allocates 8 queues to service egress by default. To define a basic egress QoS policy, the
following are required:
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•
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Optional service egress QoS policy elements include:
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In 7210 SAS-X, the 'sap-qos-marking' command is provided that allows option for the user to
configure SAP-based marking and port-based marking. In SAP-based marking, the remark policy
defined in the SAP egress policy associated with each SAP is used to mark the packets egressing
out of SAP if marking is enabled. In port-based marking, the remark policy defined in the access-
egress policy associated with the access port determines the marking values to use for all the SAPs
defined on that port. More information is available in the section on Access Egress policies in this
guide.
In 7210 SAS-R6, the user has an option to use SAP-based marking. With SAP based marking the
remark policy defined in the SAP egress policy associated with each SAP is used to mark the
packets egressing out of SAP if marking is enabled. The user also has an option to enable port-
7210 SAS-X and 7210 SAS-R6 OS Quality of Service Guide
Per-service egress subrate capabilities especially for multipoint services.
More granular, fairer scheduling per-service into the access network.
Per-service statistics for forwarded and discarded service packets.
A unique service egress QoS policy ID.
A QoS policy scope of template or exclusive.
The parameters that can be configured for a queue are discussed in
page
38.
Specify remark policy that defines IEEE 802.1p priority value remarking based on
forwarding class.
QoS Policies
Queue Parameters on
Page 51
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