Allied Telesis AT-S80 User Manual

Page 141

AT-S80 Management Software User’s Guide

Section I: Using the Menus Interface

141

For example, a tagged packet with a priority tag of 6 is placed in the
egress port’s highest priority queue of 3, while a packet with a priority tag
of 1 is placed in the lowest priority queue.

Note

QoS is disabled by default on the switch.

You can customize these priority-to-queue assignments using the AT-S80
management software. The procedure for changing the default mappings
is found in “Mapping CoS Priorities to Egress Queues” on page 143. Note
that because all ports must use the same priority-to-egress queue
mappings, they are applied at the switch level. They cannot be set on a
per-port basis.

CoS primarily relates to tagged packets rather than untagged packets
because untagged packets do not contain a priority level. By default, all
untagged packets are temporarily assigned a priority level of 0 as they
enter a port and, at the default settings, are placed in a port’s Q0 egress
queue, the queue with the lowest priority. But you can override this by
assigning a different temporary priority level to a port so that all of the
untagged packets are stored in a different egress queue. The procedure
for this is explained in “Changing the Temporary Priority Level of Untagged
Traffic” on page 146.

One last thing to note is that the switch does not change the priority level in
a tagged packet. The packet leaves the switch with the same priority it had
when it entered. This is true even if you change the default priority-to-
egress queue mappings.

Table 2. Default Mappings of IEEE 802.1p Priority Levels

to Egress Port Priority Queues

IEEE 802.1p Traffic Class

AT-FS750 Switch

Egress Port Priority

Queue