How Are Traffic Queues Defined; Which Queue Management Methods Are Supported - Dell PowerConnect 8024 User Configuration Manual

How Are Traffic Queues Defined?

For each queue, you can specify:
• Minimum bandwidth guarantee—A percentage of the port's maximum
negotiated bandwidth reserved for the queue. Unused reserved bandwidth
can be utilized by lower-priority queues.
• Scheduler type—strict/weighted:
– Strict priority scheduling gives an absolute priority based on CoS
queue number, with traffic in the highest numbered queue sent first,
then the next lowest numbered queue, and so on. Weighted queues
are serviced after all strict priority queues have been serviced.
– Weighted scheduling selects packets for transmission with a fixed
weighting equal to the CoS queue number plus one. For example, if
CoS queues 0, 1, and 2 have an equal offered load toward a congested
output port, CoS queue 2 will receive 3/6 of the bandwidth, CoS
queue 1 will receive 2/6 of the bandwidth, and CoS queue 0 will
receive 1/6 of the bandwidth.
The minimum bandwidth setting can be used to override the strict priority
and weighted settings. The highest numbered strict priority queue will
receive no more bandwidth than 100 percent minus the sum of the minimum
bandwidths percentages assigned to the other queues. If used, it is
recommended that minimum bandwidth percentages only be high enough to
ensure a minimum level of service for any queue; i.e., the sum of the
minimum bandwidth percentages is a fraction of 100%. This ensures that the
system can respond to bursts in traffic. Setting the minimum bandwidth
percentages such that they sum to 100% effectively sets the scheduler such
that no queue can exceed its minimum bandwidth percentage when
congestion occurs.

Which Queue Management Methods Are Supported?

The switch supports the following methods, configurable per-interface-
queue, for determining which packets are dropped when the queue is full:
• Taildrop—Any packet forwarded to a full queue is dropped regardless of its
importance.
Configuring Class-of-Service
1135