3Com 3C13636 Configuration Manual page 1310

3Com Router 3000 Ethernet Family
Configuration Guide
IV. WFQ (Weighted Fair Queuing)
incoming packets
Figure 3-4 WFQ diagram
Before further to Weighted Fair Queuing, FQ (Fair Queue) is to be introduced first. FQ
is designed for fairly sharing network resources, which will try to reduce the delay and
jitter of all traffics to their optimum levels. It has taken all the aspects into consideration,
which has the following features:
Different queues have fair opportunity of dispatching to equilibrate the delay of
each stream on the whole.
Short packets and long packets are treated fairly while dequeuing: if there are long
packets in a queue and short packets in another queue waiting simultaneously to
be send out, the short packets should also be cared, and statistically the short
packets should be treated preferentially, and the jitter between packets of every
traffic will be reduced on the whole.
Compared with FQ, WFQ considers priority in addition when calculating the dispatching
sequence of packets. Statistically, with WFQ, high priority traffic takes priority over low
priority packets in dispatching. WFQ can automatically classify traffic according to the
"session" information of traffic (protocol type, source/destination TCP or UDP port
number, source/destination IP address, preference bits of ToS field, etc), and try to
provide more queues so that each traffic will be equably put into different queues and
equilibrate the delay of every traffic on a whole. While dequeuing, WFQ can assign the
bandwidth of egress interfaces occupied by each flow according to IP precedence or
DSCP. The bigger the numerical value of the precedence is, the more bandwidth can
be obtained. At last, when sending packets, WFQ polls each queue and picks out
packets based on bandwidth ratio.
For example: Now if there are five traffics on the interface, and their precedence levels
are 0, 1, 2, 3, 4, respectively, then the total bandwidth quota will be: the sum of total
(precedence of traffic +1), i.e.
1+2+3+4+5=15
queue1 weight1
queue2 weight2
......
queueN-1 weightN-1
classify
queueN weightN
3Com Corporation
Chapter 3 Congestion Management
transmit
scheduler queue
3-4
outgoing packets
interface