xStack
®
DGS-3600 Series Layer 3 Gigabit Ethernet Managed Switch
Figure 9- 4. QoS Output Scheduling window
The following values may be assigned 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.
Configuring the Combination Queue
Utilizing the
QoS Output Scheduling
window shown above, the 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 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.
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