87
CNM format
When a CP detects the congestion state by sampling frames, it sends CNMs to the RPs.
The CP constructs a CNM as follows:
•
Uses the source MAC address of the sampled frame as the destination MAC address.
•
Uses the MAC address of the CP as the source MAC address.
•
Copies the VLAN tag and CN tag of the sampled frame.
•
Places the data as shown in
{
PDU EtherType
—2 bytes in length. It indicates the Ethernet type of the PDU and has a
value of 0x22E7.
{
CNM PDU
—24 to 88 bytes of payload of the PDU.
Figure 32 CNM PDU format
As shown in
, a payload contains the following fields:
Field Length
Description
Version
4 bits
Its value is fixed at 0.
ReserverV
6 bits
Its value is fixed at 0.
Quantized Feedback
6 bits
Quantized value indicating the extent of congestion.
CPID
8 bytes
Identifies the CP where congestion occurs.
cnmQoffset 2
bytes
Indicates the difference between instantaneous queue
size at the sampling point and desired queue length.
cnmQdelta 2
bytes
Indicates the difference between instantaneous queue
sizes at the current sampling point and at the previous
sampling point.
Encapsulated priority
2 bytes
Priority of the sampled frame that triggered the CNM.
Encapsulated destination MAC
address
6 bytes
Destination MAC address of the sampled frame that
triggered the CNM.
Encapsulated MSDU length
2 bytes
Number of bytes in the Encapsulated MSDU field of the
sampled frame that triggered the CNM.
Encapsulated MSDU
0 to 64 bytes
Initial bytes of the Encapsulated MSDU field of the
sampled frame that triggered the CNM.
Summary of Contents for FlexFabric 5940 Series
Page 23: ...17 Figure 3 QoS processing flow ...
Page 84: ...78 Figure 26 MPLS label structure ...
Page 91: ...85 Switch burst mode enable ...
