Configuring The Combination Queue - D-Link DGS-3427 User Manual

xStack DGS-3400 Series Fast Ethernet Switch

Configuring the Combination Queue

Utilizing the QoS Output Scheduling Configuration window shown above, the xStack DGS-3400 series 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 the maximum number of packets a
given priority class of service can transmit per weighted round-robin (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.
The example window below displays an example of the combination queue where Class-1 will have a strict priority for
emptying its class, while the other classes will follow a weight fair scheduling.
Figure 7- 37. QoS Output Scheduling window – Combination queue example
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