Qos Scheduling Mechanism Settings - D-Link DGS-3427 - xStack Switch - Stackable Product Manual

x Stack
NOTE: Entering a 0 for the Max Packets field in the QoS Output Scheduling 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 window shown above, the xStack
for forwarding packets. This combination queue allows for a combination of strict and weight-fair (weighted round-robin, or
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 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 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 the maximum number of
packets a given priority class of service can transmit per WRR scheduling cycle to be selected. 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.

QoS Scheduling Mechanism Settings

Changing the output scheduling used for the hardware queues in the Switch can customize QoS. As with any changes to QoS
implementation, careful consideration should be given to how network traffic in lower priority queues is affected. Changes in
scheduling may result in unacceptable levels of packet loss or significant transmission delay. If the user chooses 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.
To view the following window, click QoS > Schedule Settings > QoS Scheduling Mechanism Settings, as shown below.
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DGS-3400 Series Layer 2 Gigabit Ethernet M anaged Sw itch
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DGS-3400 Series can implement a combination queue
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