Classification - Cisco IE 3000 Software Configuration Manual
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Understanding QoS
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Figure 32-2
Basic QoS Model
Classification
Classification is the process of distinguishing one kind of traffic from another by examining the fields
in the packet. Classification is enabled only if QoS is globally enabled on the switch. By default, QoS is
globally disabled, so no classification occurs.
During classification, the switch performs a lookup and assigns a QoS label to the packet. The QoS label
identifies all QoS actions to be performed on the packet and from which queue the packet is sent.
The QoS label is based on the DSCP or the CoS value in the packet and decides the queueing and
scheduling actions to perform on the packet. The label is mapped according to the trust setting and the
packet type as shown in
You specify which fields in the frame or packet that you want to use to classify incoming traffic. For
non-IP traffic, you have these classification options as shown in
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Cisco IE 3000 Switch Software Configuration Guide
32-4
packets to different thresholds based on the QoS label. If the threshold is exceeded, the packet is
dropped. For more information, see the
page
32-11.
Scheduling services the four egress queues based on their configured SRR shared or shaped weights.
One of the queues (queue 1) can be the expedited queue, which is serviced until empty before the
other queues are serviced.
Figure 32-3 on page
Trust the CoS value in the incoming frame (configure the port to trust CoS). Then use the
configurable CoS-to-DSCP map to generate a DSCP value for the packet. Layer 2 ISL frame headers
carry the CoS value in the 3 least-significant bits of the 1-byte User field. Layer 2 IEEE 802.1Q
frame headers carry the CoS value in the 3 most-significant bits of the Tag Control Information field.
CoS values range from 0 for low priority to 7 for high priority.
Trust the DSCP or trust IP precedence value in the incoming frame. These configurations are
meaningless for non-IP traffic. If you configure a port with either of these options and non-IP traffic
is received, the switch assigns a CoS value and generates an internal DSCP value from the
CoS-to-DSCP map. The switch uses the internal DSCP value to generate a CoS value representing
the priority of the traffic.
"Queueing and Scheduling Overview" section on
32-6.
Figure
Chapter 32
Configuring QoS
32-3:
OL-13018-01
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