SAP Ingress and SAP Egress QoS Policies
784 Quality of Service Guide
Egress Queue CIR Based Dot1P Remarking
The HSMDA adds the capability to perform remarking of one dot1p value within a dot1q or
qinq- tagged packet based on the dynamic CIR state of the egress queue at the time the packet
is scheduled out the egress port. This allows downstream aggregation Layer 2 aggregation
devices to manage congestion based on the dot1p field (including the DEI bit). This feature
is not supported on IOM-1.
SAP Ingress and SAP Egress QoS Policies
The queue definition and scheduling behavior for HSMDA queues require different
provisioning behavior from the standard QChip based service level queuing.
SAP Ingress QoS Policy
The SAP Ingress QoS policy performs three distinct functions:
• Service queue definitions
• FC and sub-class queue mappings and ingress attributes
• Definition of hierarchical packet classification rules
For standard queuing, the application of the SAP ingress QoS policy to a SAP results in a set
of hardware queues being dynamically assigned to the SAP representing the service queues
defined in the policy.
The remaining sections of the policy affect resources within the hardware forwarding plane.
Each ingress policy within the ingress forwarding plane consists of a set of classification rules
consisting of dot1p, IP Precedence and IP DSCP tables used to match packets that ingress the
SAP. Each table entry maps the packet to a forwarding class (each sub-class is contained with
a forwarding class, so sub-classes indirectly map to a forwarding class). The section of the
policy that represents the forwarding class to queue mappings is also represented by a table
which allows the forwarding plane to take the forwarding class and determine which service
queue (and the resulting hardware queue) that will handle the packet.
The SAP ingress policy has been expanded so a single ingress policy contains queue
definitions for both standard service queues and for HSMDA service queues. This provides
a policy assignment model that does not need to know the difference between a SAP using
standard service queues and another SAP using HSMDA service queues.
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