D-Link TM DES-6500, Руководство пользователя

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DES-6500 Chassis-based Layer 3 Ethernet Switch Manual
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QoS Output Scheduling
QoS can be customized by changing the output scheduling used for the hardware classes of service in the Switch. As with
any changes to QoS implementation, careful consideration should be given to how network traffic in lower priority classes
of service is affected. Changes in scheduling may result in unacceptable levels of packet loss or significant transmission
delay. If you choose to customize this setting, it is important to monitor network performance, especially during peak
demand, as bottlenecks can quickly develop if the QoS settings are not suitable. In the
Configuration folder open the QoS
folder and click QoS Output Scheduling, to view the screen shown below.
Figure 6- 44. QoS Output Scheduling Configuration window
You may assign the following values to the QoS classes to set the scheduling.
Parameter Description
Max. Packets Specifies the maximum number of packets the above specified hardware priority
class of service will be allowed to transmit before allowing the next lowest priority
queue to transmit its packets. A value between 0 and 15 can be specified.
Click Apply to implement changes made.
NOTE: Entering a 0 for the Max Packets field in the QoS Output
Scheduling Configuration window above will create a Combination
Queue. For more information on implementation of this feature, see the
next section,
Configuring the Combination Queue.
Configuring the Combination Queue
Utilizing the QoS Output Scheduling Configuration window shown above, the DES-6500 switch can implement a
combination queue for forwarding packets. This combination queue allows for a combination of strict and weight-fair
(weighted round-robin
“ WRR ” ) scheduling for emptying given classes of service. To set the combination queue, enter a 0
for the Max Packets entry of the corresponding priority classes of service listed in the window above. Priority classes of
service that have a
0 in the Max Packet field will forward packets with strict priority scheduling. The remaining classes of
service, that do not have a 0 in their Max Packet field, will follow a weighted round-robin ( WRR ) method of forwarding
packets — as long as the priority classes of service with a 0 in their Max Packet field are empty. When a packet arrives in
a priority class with a 0 in its Max Packet field, this class of service will automatically begin forwarding packets until it is
empty. Once a priority class of service with a 0 in its Max Packet field is empty, the remaining priority classes of service
will reset the weighted round-robin ( WRR ) cycle of forwarding packets, starting with the highest available priority class of
service. Priority classes of service with an equal level of priority and equal entries in their Max Packet field will empty
their fields based on hardware priority scheduling. The Max Packet parameter allows you to specify the maximum number
of packets a given priority class of service can transmit per weighted round-robin ( WRR ) scheduling cycle. This provides
for a controllable CoS behavior while allowing other classes to empty as well. A value between 0 and 15 packets can be
specified per priority class of service to create the combination queue.