H3C LS-3100-52P-OVS-H3 Operation Manual page 1284

A port of the switch supports eight outbound queues. The WRR queue-scheduling algorithm schedules
all the queues in turn to ensure that every queue can be assigned a certain service time. Assume there
are eight output queues on the port. The eight weight values (namely, w 7, w 6, w 5, w 4, w 3, w 2, w 1,
and w 0) indicating the proportion of assigned resources are assigned to the eight queues respectively.
On a 100M port, you can configure the weight values of WRR queue-scheduling algorithm to 50, 30, 10,
10, 50, 30, 10, and 10 (corresponding to w7, w6, w5, w4, w3, w2, w1, and w0 respectively). In this way,
the queue with the lowest priority can be assured of 5 Mbps of bandwidth at least, thus avoiding the
disadvantage of SP queue-scheduling algorithm that packets in low-priority queues are possibly not to
be served for a long time. Another advantage of WRR queue-scheduling algorithm is that though the
queues are scheduled in turn, the service time for each queue is not fixed, that is to say, if a queue is
empty, the next queue will be scheduled immediately. In this way, the bandwidth resources are fully
utilized.
3) WFQ queue-scheduling algorithm
Figure 5-3 Diagram for WFQ queuing
Packets to be sent through
this port
Packet
classification
Before WFQ is introduced, you need to understand fair queuing (FQ). FQ is designed for fairly sharing
network resources, reducing the delay and jitter of all traffic. FQ takes all the aspects into consideration:
Different queues have fair dispatching opportunities for delay balancing among streams.
Short packets and long packets are fairly scheduled: if there are long packets and short packets in
queues, statistically the short packets should be scheduled preferentially to reduce the jitter
between packets on the whole.
Compared with FQ, WFQ takes weights into account when determining the queue scheduling order.
Statistically, WFQ gives high priority traffic more scheduling opportunities than low priority traffic. WFQ
can automatically classify traffic according to the "session" information of traffic (protocol type, TCP or
UDP source/destination port numbers, source/destination IP addresses, IP precedence bits in the ToS
field, etc), and try to provide as many queues as possible so that each traffic flow can be put into these
queues to balance the delay of every traffic flow on a whole. When dequeuing packets, WFQ assigns
the outgoing interface bandwidth to each traffic flow by the precedence. The higher precedence value a
traffic flow has, the more bandwidth it gets.
The S5500-EI series switches introduce the minimum guaranteed bandwidth mechanism, and use it in
conjunction with WFQ as follows:
The minimum guaranteed bandwidth configuration guarantees a certain amount of bandwidth for
each WFQ queue.
Queue 1 Band width 1
Queue 2 Band width 2
......
Queue N-1 Band width N-1
Queue N Band width N
5-3
Sent packets
Interface
Sending queue
Queue
scheduling