How Qcn Works - HP FlexFabric 5700 series Configuration Manual

Figure 31 CNM PDU format
Quantized Feedback
Congestion Point Identifier (CPID)
Encapsulated priority
Encapsulated destination MAC address
Encapsulated MSDU length
Encapsulated MSDU

How QCN works

Figure 32 shows how QCN works.
The CP periodically samples frames from queues that are enabled with QCN and sends CNMs to
•
the RPs when congestion occurs.
The RPs reduce their transmission rates when receiving CNMs. The RPs also periodically probe the
•
bandwidth and increase their transmission rates if they fail to receive CNMs for a specific period of
time.
Figure 32 How QCN works
Version
ReservedV
cnmQOffset
cnmQDelta
Octet
Length
1 4 bits
1, 2 6 bits
2 6 bits
3 8
11 2
13 2
15 2
17 6
23 2
–
25
0 64
97