setting the weight of WRR. However, you cannot obtain the required bandwidth by setting
the weight of WRR when the average length of packets in each queue changes.
l
The packets of short-delay services such as voice services cannot be scheduled in time.
DRR Scheduling
The principle of Deficit Round Robin (DRR) is similar to the principle of WRR.
The difference is that WRR schedules packets according to the number of packets, but DRR
schedules packets according to the length of packets. If the packet length exceeds the scheduling
capability of a queue, DRR allows the deficit weight to ensure that packets of a long length are
scheduled. When packets are scheduled in a polling manner again, this queue is not scheduled
until the weight becomes positive. Then, this queue participates in DRR scheduling.
DRR scheduling offsets the disadvantage of PQ scheduling and one disadvantage of WRR
scheduling, that is, bandwidth cannot be obtained according to the proportion.
The packets of short-delay services such as voice services cannot be scheduled in time in DRR
mode.
PQ+WRR/PQ+DRR Scheduling
PQ scheduling, WRR scheduling, and DRR scheduling have the following advantages and
disadvantages:
l
If only PQ scheduling is used, packets of lower priorities cannot obtain the bandwidth for
a long time.
l
If only WRR or DRR scheduling is used, delay-sensitive services such as voice service
cannot be scheduled first.
l
PQ+WRR or PQ+DRR scheduling can use the advantages of both PQ and WRR or DRR
scheduling and offset their disadvantages.
Through PQ+WRR or PQ+DRR scheduling, important protocol packets and delay-sensitive
service packets are put in a PQ queue and specified bandwidth is allocated to this queue. Other
packets are put into a WRR or DRR queue according to their priorities and scheduled in a polling
manner according to the weight of the queue.
3.2 Configuring Congestion Avoidance on the S3700HI
After congestion avoidance is configured, the S3700 processes packets of different colors based
on the WRED configuration.
3.2.1 Establishing the Configuration Task
Before configuring congestion avoidance, familiarize yourself with the applicable environment,
complete the pre-configuration tasks, and obtain the required data. This will help you complete
the configuration task quickly and accurately.
Applicable Environment
To prevent congestion and solve the problem of global TCP synchronization, you can configure
WRED to adjust the traffic on a network and remove the overload of the traffic on a network.
S3700HI Ethernet Switches
Configuration Guide - QoS
3 Congestion Avoidance and Congestion Management
Configuration
Issue 01 (2012-03-15)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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