Allied Telesis AT-S62 - Manual (Page 309)

AT-S62 Management Software Menus Interface User’s Guide
Section II: Advanced Operations 309
Table 8 lists the mappings between the eight CoS priority levels and the
four egress queues of a switch port.
For example, if a tagged packet with a priority level of 3 entered a port on
the switch, the switch would store the packet in Q1 queue on the egress
port.
Priority 0 is mapped to CoS queue 1 instead of CoS queue 0 because
tagged traffic that has never been prioritized has a VLAN tag User Priority
of 0. If priority 0 was mapped to CoS queue 0, this default traffic goes to
the lowest queue, which is probably undesirable. This mapping also
makes it possible to give some traffic a lower priority than the default
traffic.
You can change these mappings. For example, you might decide that
packets with a priority of 5 need to be handled by egress queue Q3 and
packets with a priority of 2 should be handled in Q1. The result is shown in
Table 9.
Table 8. Default Mappings of IEEE 802.1p Priority Levels to Priority
Queues
IEEE 802.1p Priority
Level
Port Priority Queue
0 Q1
1 Q0
2 Q0
3 Q1
4 Q2
5 Q2
6 Q3
7 Q3
Table 9. Customized Mappings of IEEE 802.1p Priority Levels to Priority
Queues
IEEE 802.1p Priority
Level
Port Priority Queue
0 Q1
1 Q0
2 Q1
3 Q1