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Table 9-86. CoS to Queue Mapping Table Default values
CoS Value
7
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. The following table contains the default DSCP
mapping to egress queue values:
Table 9-87. DSCP to Queue Mapping Table Default Values
D S C P Va l u e
0-15
16-31
32-47
48-63
DSCP mapping is enabled on a per-system basis.
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 — Ensures that time-sensitive applications are always forwarded. Strict Priority
(SP) allows the prioritization of mission-critical, time-sensitive traffic over less time-sensitive
applications.
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 Module forwarding capacity. Weighted Round Robin (WRR) forwards entire queues
in a Round Robin order. All queues can participate in WRR, with expect SP queues.
SP queues are serviced before WRR queues. If the traffic flow is minimal, and SP queues do
not occupy the whole bandwidth allocated to a port, the WRR queues can share the
bandwidth with the SP queues. Ensuring the remaining bandwidth is distributed according to
the weight ratio.
Defining CoS Global Parameters
Class of Service global parameters are set from the CoS Global Parameter pages.
290
Configuring Quality of Service
Forwarding Queue Values
q4 (Highest Priority)
Fo r w a r d i n g Q u e u e Va l u e s
q1 (Lowest Priority)
q2
q3
q4 (Highest Priority)
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