Arris NVG599, Administrator'S Handbook

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Figure 4. Illustration of weighted fair queue scheduling
Figure 5. Illustration of a hybrid queue that is both priority and WFQ, to both constrain bandwidth usage and expedite one of
the queues.
After the packet has been classified, it can be put in the proper queue. Queues are assigned to interfaces and
can be constructed of several queue components to deliver the desired behavior. The components of an
interface queue are these building blocks:
‹
basic queues: a 1 input 1 output packet list with a length of 64 packets by default. Packets will tail-drop
when the enqueued to a full basic queue.
‹
priority queue: 2 or more input, 1 output. Schedules the packets from the various inputs strictly according to
input's priority.
‹
weighted fair queue: 1 or more input, 1 output. Schedules the packets according to bandwidth constraints
Packets are enqueued to basic queues, and only to basic queues. Basic queues are output to priority queues
and weighted fair queues, which act as “plumbing” elements that alter the dequeuing order and rate,
respectively. Priority queues and weighted fair queues can contain one another.
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.