3com 5500-ei pwr Installation Instruction

 

1-14 

Figure 1-8 Diagram for WRR queuing 

 

 

WRR queue-scheduling algorithm schedules all the queues in turn and every queue can be 

assured of a certain service time.  

In a typical Switch 5500-EI there are eight output queues on each port. WRR configures a 

weight value for each queue, for example: w7, w6, w5, w4, w3, w2, w1, and w0 respectively 

for queue 7 through queue 0. A weight value indicates the proportion of resources available 

for a queue. On a 100-Mbps port, configure the weight value of WRR queue-scheduling 

algorithm to 5, 5, 3, 3, 1, 1, 1, and 1 (corresponding to w7, w6, w5, w4, w3, w2, w1, and w0 

in order). In this way, the queue with the lowest priority can get 5 Mbps (100 Mbps × 

1/(5+5+3+3+1+1+1+1)) bandwidth at least, and the disadvantage of SP queue-scheduling 

that the packets in queues with lower priority may not get service for a long time is avoided. 

Another advantage of WRR queue is that: though the queues are scheduled in order, the 

service time for each queue is not fixed; that is to say, if a queue is empty, the next queue 

will be scheduled. In this way, the bandwidth resources are made full use.  

Congestion may cause network resource unavailable and thus need to be prevented. As a 

type of flow control mechanism, congestion avoidance aims to relieve network load through 

traffic adjusting. With congestion avoidance configuration performed, packets are dropped 

in advance when the utilization of certain network resources (such as output queues or 

buffer created in the memory) reaches certain degree.  

Tail drop is adopted in traditional packet drop policies. It drops all the newly arrived packets 

when the current queue length reaches a specific value.  

Such a policy will result in global TCP connection synchronization. If a queue drops 

packets of multiple TCP connections simultaneously, the TCP connections will turn to the 

state of congestion avoidance and slow startup for the traffics to be regulated. The traffic