Table of Contents
Advertisement
Quality of Service Overview
Figure 2
Weighted Fair Queuing
With weighted fair queuing, queue access to bandwidth is divided up by percentages of the time
slices available. For example, if 100 percent is divided into 64 time slices, and each queue is
configured for 25 percent, each queue will get 16 time slices, after which the next lowest priority
queue will get the next 16, and so on. Should a queue empty before using its current share of time
slices, the next priority queue inherits the time slices that remain. Figure
fair queuing works. Inbound packets enter on the upper left of the box and proceed to the
appropriate priority queue. Outbound packets exit the queues on the lower right. Queue 3 has
access to its percentage of time slices so long as there are packets in the queue. Then queue 2 has
access to its percentage of time slices, and so on round robin. Weighted fair queueing assures that
each queue will get at least the configured percentage of bandwidth time slices. The value of
weighted fair queueing is in its assurance that no queue is starved for bandwidth. The downside
of weighted fair queueing is that packets in a high priority queue, with low tolerance for delay,
will wait until all other queues have used the time slices available to them before forwarding. So
weighted fair queuing would not be appropriate for applications with high sensitivity to delay or
jitter, such as VoIP.
February 22, 2008
Strict Priority Queuing Packet Behavior
3 depicts how weighted
Page 5 of 29
Advertisement
Table of Contents
