Messages are transmitted in a fair order Highvolume conversations share the link

© 2004 Cisco Systems, Inc. All rights re bcran v2.1—10-5

The flow-based WFQ algorithm places packets of the various conversations in the fair queue before transmission. The order of removal from the fair queue is determined by the virtual delivery time of the last bit of each arriving packet.

WFQ assigns a weight to each flow, which determines the transmit order for queued packets. In this scheme, lower weights are served first. Small, low-volume packets are given priority over large, high-volume conversation packets.

After low-volume conversations have been serviced, high-volume conversations share the remaining link capacity and interleave or alternate transmission timeslots. In this figure, highvolume conversation packets are queued in order of arrival after the low-volume packet.

The queuing algorithm ensures the proper amount of bandwidth for each datagram. With flow-based WFQ, two equal-size file transfers get equal bandwidth, rather than the first file transfer using most of the bandwidth. Although the flow-based WFQ algorithm allocates a separate queue for each conversation, each queue can belong to one of only seven priority classifications, based on the IP precedence.

In the example, packet 3 is queued before packets 1 or 2 because packet 3 is a small packet in a low-volume conversation.

The result of the queuing order and the transmission order is that short messages that do not require much bandwidth are given priority and transmitted on the link first. For example, packet 3 before packets 1 and 2.

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