QoS Policies
54 Quality of Service Guide
The buffering, queuing, policing and remarking operation at the ingress and egress remain
unchanged. Egress reclassification is possible. The profile processing is completely
unaffected by overriding the forwarding class.
When used in conjunction with QPPB (QoS Policy Propagation Using BGP), a QPPB
assigned forwarding class takes precedence over both the normal ingress forwarding class
classification rules and any egress forwarding class overrides.
Figure 6: Egress Forwarding Class Override
Figure 6 shows the ingress service 1 using forwarding classes AF and L1 that are overridden
to L1 for the network egress, while it also shows ingress service 2 using forwarding classes
L1, AF, and L2 that are overridden to AF for the network egress.
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:
• 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
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.
al_0187
FC EF
These 2 AF classes are
combined and use FC
L1 across the core
These 3 CP classes are
combined and use FC
L1 across the core
FC AF
FC L1
FC BE
FC EF
FC L1
FC AF
FC BE
EF
FC EFEF
FC L2
FC AFCP2
FC L1CP1
FC BE
AF21
CP3
Classification
Ingress (Service 2):
Ingress (Service 1):
Egress (Network):
AF11
BE
BE
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