Allied Telesis AT-S63 User Manual

Page 323

AT-S63 Management Software Menus Interface User’s Guide

Section II: Advanced Operations

323

Table 7 lists the default mappings between the eight CoS priority levels
and the eight egress queues of a switch port.

For example, when a tagged packet with a priority level of 3 enters a port
on the switch, the packet is stored in Q3 queue on the egress port.

Note that 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 8.

Table 7. Default Mappings of IEEE 802.1p Priority Levels to Priority

Queues

IEEE 802.1p Priority

Level

Port Priority Queue

0 Q1

Q0 (lowest)

Q7 (highest)

Table 8. Customized Mappings of IEEE 802.1p Priority Levels to Priority