Quality of Service Guide QoS and QoS Policies
Edition: 01 3HE 11014 AAAC TQZZA 31
Traffic is discarded in the following order: low-priority out-of-profile user traffic is
discarded first, followed by high-priority out-of-profile user traffic, then low-priority
in-profile user traffic, high priority in-profile user traffic, and lastly control plane traffic.
In the ingress direction, intelligent discards is applied to traffic entering the card from
the physical ports. Traffic is discarded in the following order: low-priority user traffic
is always discarded first, followed by high-priority user traffic. This order ensures that
low-priority user traffic is always the most susceptible to discards.
In the egress direction, the system differentiates between high-priority and
low-priority user traffic based on the internal forwarding class and queue-type fabric
header markers. In the ingress direction, the system differentiates between
high-priority and low-priority user traffic based on packet header bits. Table 3 details
the classification of user traffic in the ingress direction.
Intelligent discards during overload ensures priority-based handling of traffic and
helps existing traffic management implementations. It does not change how
QoS-based classification, buffer management, or scheduling operates on the 7705
SAR. If the node or card is not in overload operation mode, there is no change to the
way packets are handled by the network processor.
There are no commands to configure intelligent discards during overload; the feature
is automatically enabled on the following cards, modules, and ports:
• 10-port 1GigE/1-port 10GigE X-Adapter card
• 2-port 10GigE (Ethernet) Adapter card (only on the 2.5 Gb/s v-port)
• 2-port 10GigE (Ethernet) module (only on the v-port)
• 8-port Gigabit Ethernet Adapter card
• 6-port Ethernet 10Gbps Adapter card
• Packet Microwave Adapter card
• 4-port SAR-H Fast Ethernet module
• 6-port SAR-M Ethernet module
• 7705 SAR-A Ethernet ports
• 7705 SAR-Ax Ethernet ports
Table 3 Ingress Packet Priority During Overload
Fabric Header Marker High-priority Values Low-priority Values
MPLS TC 7 to 4 3 to 0
IP DSCP 63 to 32 31 to 0
Eth Dot1p 7 to 4 3 to 0
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