Siemens S223, S323 Scheduling Algorithm, Weighted Round Robin WRR, Weighted Fair Queuing WFQ

User Manual	UMN:CLI
SURPASS hiD 6615 S223/S323 R1.5

7.6.3.1Scheduling Algorithm

To process incoming packets by the queue scheduler, the hiD 6615 S223/S323 provides the scheduling algorithm as Strict Priority Queuing (SP), Weighted Round Robin (WRR) and Weighted Fair Queuing (WFQ).

Weighted Round Robin (WRR)

WRR processes packets as much as weight. Processing the packets that have higher priority is the same way as strict priority queuing. However, it passes to next stage after processing as configured weight so that it is possible to configure for packet process not to be partial to the packets having higher priority. However, there is a limitation of provid- ing differentiated service from those existing service.

The process in WRR when packets having the Queue numbers

Lowest priority highest priority

1

3

3

3

4

4

6

7

7

7

7

Weight = 1 Weight = 1 Weight = 1 Weight = 1 Weight = 2

Weighted, Round-Robin Scheduler

3 3 4 7 7 1 3 4 6 7 7

Fig. 7.1 Weighted Round Robin

Weighted Fair Queuing (WFQ)

Weighted fair queuing (WFQ) provides automatically sorts among individual traffic streams without requiring that you first define access lists. It can manage one way or two way streams of data: traffic between pairs of applications or voice and video.

In WFQ, packets are sorted in weighted order of arrival of the last bit, to determine trans- mission order. Using order of arrival of last bit emulates the behavior of Time Division Multiplexing (TDM), hence "fair"

From one point of view, the effect of this is that WFQ classifies sessions as high- or low- bandwidth. Low-bandwidth traffic gets priority, with high-bandwidth traffic sharing what's left over. If the traffic is bursting ahead of the rate at which the interface can transmit, new high-bandwidth traffic gets discarded after the configured or default congestive-messages threshold has been reached. However, low-bandwidth conversations, which include con- trol-message conversations, continue to enquire data.

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