3Com Switch 8800 Family Configuration Guide

QoS Configuration 197
Different outbound queues at the port may use different algorithms. The switch
supports three scheduling modes:
1 All-SP scheduling mode
2 All-WRR mode: A queue is selected from each of the two WRR groups during
scheduling, and then the two queues are compared for priority. The queue with
higher priority will be scheduled. After scheduling, another queue is selected from
the WRR group containing the queue with higher priority, and the newly selected
queue will be compared with the previously selected queue that has lower priority.
3 SP plus WRR mode: The outbound queues are put into different scheduling
groups. SP group uses SP algorithm, WRR groups use WRR algorithm. The select
one queue respectively from SP group, WRR group 1 and WRR group 2 and
schedule them using SP algorithm.
Perform the following configurations in Ethernet port view.
By default, the switch uses all-SP mode, so those queues not configured with WRR
algorithm are SP mode.
See the corresponding Command Manual for details of the commands.
Configuring WRED
Parameters
In the case of network congestion, the switch drops packets to release system
resources. And then no packets are put into long-delay queues.
The switch allocates drop precedence for it when receiving a packet (also called
coloring the packet). The drop precedence values range from 0 to 2, with 2 for
red, 1 for yellow and 0 for green. In congestion, red packets will be first dropped,
and green packets last.
You can configure drop parameters and thresholds by queue or drop precedence.
The following two drop modes are available:
1 Tail drop mode: Different queues (red, yellow and red) are allocated with different
drop thresholds. When these thresholds are exceeded respectively, excessive
packets will be dropped.
2 WRED drop mode: Drop precedence is taken into account in drop action. When
only min-thresholds of red, yellow and green packets are exceeded, excessive
packets are dropped randomly at given probability. But when max-thresholds of
red, yellow and green packets are exceeded, all excessive packets will be dropped.
You must first configure WRED parameters for every outbound queue in defining
drop precedence.
Tab le 171 Configure queue scheduling
Operation Command
Configuring queue scheduling
queue-scheduler wrr { group1 { queue-id
queue-weight } &<1-8> | group2 { queue-id
queue-weight } &<1-8> }*
Restore the default setting undo queue-scheduler [ queue-id ] &<1-8>