User Manual - Configuration Guide (Volume 3)
Versatile Routing Platform Chapter 3
Congestion Management
3-7
IV. WFQ
queue 1
queue 2
queue N
...
Classification
Dequeuing dispatch
Packets leaving the interface
Queue
Packets sent from
this interface
Figure QC-3-5 Schematic diagram of weighted fair queuing
WFQ embodies the weight on the basis of ensuring fairness, and t he amount of the
weight depends on the IP Precedence brought in the IP packet head ers. As s hown in
the figure above, WFQ classifies the packets according to the flow (pack ets with the
same source IP address, destination IP address, source port num ber, destination por t
number, protocol number and TOS), and each flow is allocated with to one queue.
When outgoing from the queue, WFQ allocates the bandwidth t o be occupied at the exit
by each flow according to the precedence of the flow. The smaller number of the
precedence, the less bandwidth of the flow. The bigger number of the precedence, the
more bandwidth of the flow.
For example, there are currently 8 flows at the interface, with priority of 0, 1, 2, 3, 4, 5, 6
and 7.So, the total bandwidth allocated is the sum of all priorities (flow prior ity + 1).
That is, 1+2+3+4+5+6+7+8=36
The proportion of bandwidth occupied by each flow is: (priority number +1) / (all
priorities (flow priority + 1)) That is, each flow can acquire th e bandwidth as fo llows:
1/36, 2/36, 3/36, 4/36, 5/36, 6/36, 7/36, 8/36.
Another example: there are 4 flows currently, the priority of three flows is 4, and the
priority of one flow is 5, then the total bandwidth allocated is:
(4 + 1) * 3 + (5 + 1) = 21
Therefore, the bandwidth for the three flows with priority 4 is 5/21, and the band width
for the flow with priority 5 is 6/21.
3.2 Configuration of Congestion Management3.2.1 Configuring PQ
I. PQ Configuration task list
Configuration task list of priority queue is as follows:
z Configure the priority queue
z Apply priority queue at the interface
z Maintain and monitor the priority queue