3Com Switch 4800G PWR 24-Port, Руководство по настройке

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1-12
WRR queuing schedules all the queues in turn and ensure that all of them can be served for a certain
time by assigning each queue a weight representing a certain amount of resources. Assume there are
eight output queues on the port. WRR assigns queues 7 through 0 the weights w7, w6, w5, w4, w3, w2,
w1, and w0.
For example, on a 100 Mbps port, you can configure the weights for WRR queuing to 50, 50, 30, 30, 10,
10, 10, and 10 (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,
thus avoiding the disadvantage of SP queuing that the packets in low-priority queues may failed to be
served for a long time.
Another advantage of WRR queuing is that though the queues are scheduled in order, the service time
for each queue is not fixed. With WRR, if a queue is empty, the next queue will be scheduled
immediately. In this way, the bandwidth resources are fully utilized.
3) SDWRR
Compared with WRR, SDWRR reduces scheduling delay and smoothes jitter for lower priority queues.
For example, set the weight values of queue 0 and queue 1 to 5 and 3 respectively. WRR and SDWRR
schedule the queues as follows:
z
WRR: dequeues the number of packets identical to weight 3 from queue 1 only after the number of
packets identical to weight 5 are dequeued from queue 0. If there is a wide difference between the
weight values of two queues, great delay and jitter will result for the lower-weight queue.
z
SDWRR: schedules the two queues in turn in such a way that packets identical to one weight are
dequeued from queue 0 first and then from queue 1. The procedure is repeated until the scheduling
for one queue is over. Then, SDWRR schedules the queue with remaining weights to dequeue the
number of packets identical to the remaining weights. The detailed scheduling sequence is
described in the Table 1-8 .
Table 1-8 Queue-scheduling sequence of SDWRR
Queue scheduling
algorithm
Queue scheduling sequence Remarks
WRR 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1
SDWRR 0, 1, 0, 1, 0, 1, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0
0 indicates packets
identical to one weight
in queue 0.
1 indicates packets
identical to one weight
in queue 1.
Flow-Based Traffic Accounting
Flow-based traffic accounting uses ACL rules for traffic classification and collects statistics about ACL
matching packets. With this function, you can collect statistics about the packets you are interested in.
Burst
The burst function improves packet buffering and forwarding performance in the following scenarios:
z
Dense broadcast or multicast traffic and massive burst traffic are present.
z
High-speed traffic is forwarded over a low-speed link or traffic received from multiple interfaces at
the same speed is forwarded through an interface at the same speed.