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AT-S80 Management Software User’s Guide

Section I: Using the Menus Interface 99

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 101. 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 temporary 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 104.

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 Series

Egress Port Priority

Queue

1 2 ... 94 95 96 97 98 99 100 101 102 103 104 ... 241 242

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