Quantized Congestion Notification
As discussed earlier, PFC enables you to throttle down transmission for no-drop traffic classes, such as FCoE, between two adjacent DCB-capable switches. As PFC is invoked, a back-pressure is applied from the point of congestion toward the source of transmission (FCoE initiator or target) in a hop-by-hop fashion. Quantized Congestion Notification mechanism, defined in the IEEE 802.1Qau standard, takes a different approach of applying back-pressure from the point of congestion directly toward the source of transmission without involving intermediate switches. This approach maintains feature isolation and affects only the parts of the network causing the congestion. Figure 11-4 demonstrates the principle behind ...
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