Upstream Qos: Priority And Shaping - Motorola nvg589 Administrator's Hanbook

Weighted fair queues are used to constrain bandwidth. For example, consider a weighted fair queue
with three basic queues as inputs, EF, AF and BE:
WFQ
Input 1: EF
Input 2: AF
Input 3: BE
Each input entry is configured with a weight value, which is the rate at which to limit the traffic. This
weight can be either absolute (bps) or a relative percentage of the interface's data-rate. This allows
dedicating a split amount of bandwidth to each queue. A special value for the weight parameter is zero,
which will use the remainder of unclaimed bandwidth.
There is an option to enable bandwidth sharing, so that unused bandwidth in idle queues can be
shared to other queues. When the traffic resumes in the previously idle queue, the previously shared-
out bandwidth is taken back.
When bandwidth sharing is enabled, a secondary rate configuration appears on each input entry, the
peak parameter. This is a hard limit on the amount of bandwidth that the particular input entry can use.
This rate will not be exceeded, even if there is an excess pool of idle bandwidth that could otherwise
be shared.

Upstream QoS: Priority and shaping

The Gateway uses the DSL sync rate to determine traffic shaping requirements for WAN traffic. In this
case there are 6 basic queues, and a hierarchy of both priority queue and weighted fair queue with
bandwidth sharing and dual rate shaping. First the packets are classified via the filterset, to set the
QoS-marker with the name of the desired basic queues. The queues are shown here, with packets
traveling from left to right. Each basic queue feeds into a WFQ entry, and is shaped between the mini-
mum bandwidth defined by "weight", and the maximum rate defined by "peak". If there is sufficient
bandwidth, the WFQ entry shapes at the peak rate. If there is no spare bandwidth available for shar-
ing, then the queue is shaped at the "weight" rate. The weight" rate is defined either as a bps value, or
as a percentage of line-rate that is determined once the upstream WAN data-rate is acquired. This
"weight" value behaves as a Committed Information Rate (CIR), and the "peak" value behaves as a
Peak Information Rate (PIR.)
Figure 6. Illustration of default queues used for AT&T
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