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Packets arriving untagged are assigned a default VPT value, which is set on a per port basis. The
assigned VPT is used to map the packet to the egress queue.
DSCP values can be mapped to priority queues. DSCP mapping is enabled on a per-system basis.
The following table contains the default DSCP mapping to egress queue values:
Table 7-2. DSCP Mapping to Egress Queue Default Values
CoS Services
After packets are assigned to a specific egress queue, CoS services can be assigned to the queue(s).
Egress queues are configured with a scheduling scheme by one of the following methods:
•
Strict Priority
— Strict Priority (SP) allows the prioritization of mission-critical and time-
sensitive traffic over less time-sensitive applications. Thus, ensuring that time-sensitive
applications are always forwarded before traffic with lower priority. For example, under Strict
Priority, voice over IP traffic is forwarded before FTP or e-mail (SMTP) traffic.
•
Weighted Round Robin
— Ensures that a single application does not dominate the Ethernet
switch forwarding capacity. Weighted Round Robin (WRR) forwards entire queues in a
Round Robin order. All queues can participate in WRR.
DSCP Value Forwarding Queue Values
0-15 q1 (Lowest Priority)
16-31 q2
32-47 q3
48-63 q4 (Highest Priority)
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