3Com MSR 50 Series, Руководство по настройке

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1652 C
HAPTER
86: C
ONGESTION
M
ANAGEMENT
WFQ (Weighted Fair Queuing)
Figure 467 WFQ diagram
Before further to Weighted Fair Queuing, Fair Queuing (FQ) 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 sent 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. The bigger the
numerical value of the precedence is, the more bandwidth can be obtained.
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 t1), i.e.
1 + 2 + 3 + 4 + 5 = 15