Comtec CDM-840 Installation And Operation Manual page 306

CDM-840 Remote Router
Appendix J
J.2.2.3 QoS Group Pri-Weighted Control Mode
In Pri-Weighted Control Mode, you may enter the weight while configuring queues, similar to
configuring other parameters such as minimum or maximum bandwidth, priority, etc. In this
QoS Control Mode, the weight is considered only if multiple queues are configured with the
same priority, and at least one of the weights is different from others and the minimum
bandwidth has already been achieved. When valid weights are configured in this QoS Control
Mode, the weighted scheduling algorithm is applied. In all other cases, Strict Priority and Round-
robin scheduling will be applied.
J.2.2.3.1 Weight
Weight is a user-configurable parameter. The greater the weight, the higher the precedence will
be given to that queue when draining the packets. Weight values range from 1 to 9 and 0 is an
invalid value. The Scheduler will drain more bytes from weight 9 queues than weight 8 queues
under the same priority, and so on.
J.2.2.3.2 Weighted Scheduling
In weighted scheduling mode, the QoS Scheduler calculates each quantum based on available
bandwidth, total weights, and per-queue weights as follows:
Per queue quantum=available bandwidth*per queue weight/total weights)
There are some exceptions when assigning per-queue quantum to each queue, as represented
by three cases:
•
Case 1 – The per-queue quantum is greater than the configured maximum bandwidth.
When the LAN ingress data rate is greater than the maximum bandwidth, the Scheduler
drains packets only up to the maximum bandwidth, and then drops the remaining packets.
With Case 1, maximum bandwidth is the limiting factor, and weight is not applied.
•
Case 2 – The per-queue quantum is less than the configured maximum bandwidth but
more than the configured minimum bandwidth.
In this scenario, when the available bandwidth is greater than the total minimum bandwidth
but less than total maximum bandwidth, the QoS Scheduler first satisfies the minimum
bandwidth for all queues with the same priority, and then divides the remaining bandwidth
amongst the queues based on their weight value.
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MN-CDM840
Revision 3