3Com 10014299 manual Weighted Fair Queuing WFQ, Schematic diagram of weighted fair queuing

Operating Principle of the Congestion Management Policies 685

Weighted Fair Queuing (WFQ)

In the network shown in Figure 217, it is assumed that the server of LAN 1 transmits the data of the key service to the server of LAN 2, and the PC of LAN 1 transmits the data of the non-key service to PC of LAN 2. If the serial interface to be connected with the WAN is configured for congestion management with CQ, and the data flows of the key services between the servers are input to queue A, while the data flows of the non-key services are input to queue B, the proportional relationship of the occupied interface bandwidth between queue A and queue B is configured as 3:1 (for example, during dispatching, queue A may continuously transmit 6000 bytes of data packets every time, while queue B may continuously transmit 2000 bytes of data packets every time). Thus, CQ will treat the data packets of both different services differently. Each time queue A is dispatched, the data packets are continuously transmitted, before the transmitted bytes are not less than 6000 or queue A is empty, the next user queue will not be dispatched. When queue B is dispatched, the condition to stop dispatching is that the continuously transmitted bytes are not less than 2000 or queue B is empty. Therefore, when congestion occurs and there are data packets in queues A and B ready to be transmitted, in the view of the statistic results, the proportion between the bandwidths allocated to the key services and the bandwidths allocated to the non-key services is approximately 3:1.

Weighted fair queuing (WFQ), is based on the guarantee of fair bandwidth delay, and reflects the weighted value that is dependent on the PI priority carried in the IP packet header. As shown in Figure 221, weighted fair queuing classifies the packets based on the flows (identical source IP address, destination IP address, source port number, destination port number, protocol number, and ToS packets that belong to the same flow), with each flow allocated to one queue. When dequeuing, WFQ allocates the available bandwidth of the egress to each flow. The smaller the value of the priority is, the less the allocated bandwidth is. The larger the value of the priority is, the more the allocated bandwidth is.

Figure 221 Schematic diagram of weighted fair queuing

queue1 wei ght 1

i ncomi ng packet s queue2 wei ght 2

	¡- ¡-
cl assi f yi ng	queueN- 1 wei ght N- 1

out goi ng packet s

int er f ace

queuei ng

queueN wei ght N

The occupied bandwidth proportion of each flow is:

(its own priority level+1)/(the sum of all of them (the priority levels of the flows+1))

For example, there are 5 types of traffic on an interface, and their priority levels are 0,1,2,3 and 4 respectively, the total quota of the bandwidth is the sum of each priority plus 1, that is 1 + 2 + 3 + 4 + 5 = 15. The percentage of the bandwidth