Differentiated QCN

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Differentiated QCN

• Marina Lipshteyn

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Typical Use Case
There are two flows of traffic to
storage. Both flows are mapped to the same CoS /
Traffic Priority in the egress. For example the
mapping is done by VLAN tag priority.
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Flows QoS profiles

• Flow 1 has QoS profile
• CIR 100Mb/s
• PIR 1Gb/s
• Flow 2 has QoS profile
• CIR 500Mb/s
• PIR 1Gb/s
• Both flows are injecting 1Gb/s

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Policing
Assume some of flow1 packets are colored yellow
by a policer Flow2 packets are colored green by
a policer
Possibly only Reaction Point2 will get a CNM !
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Differentiated QCN at the Congestion Point

• At the Congestion Point define two thresholds for
  the queue
• The first threshold
• When number of bytes in the queue exceeds it,
• send CNM ONLY IF the probed packet is YELLOW.
• The second threshold
• When number of bytes in the queue exceeds it,
• send CNM for any probed probed packet

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How to configure such a threshold?

• Option 1
• Classify through VLAN tag
• Option 2
• Use DSCP marking
• Option 3
• Change flow id ( for example one bit can
  represent the color)

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My thoughts and questions

• Does that work? Will QCN algorithm converge?
• Is this behavior according to the standard?
• Does it violate the standard?