Allied Telesis AT-S79 User Manual

Page 145

AT-S79 Management Software User’s Guide

Section I: Using the Menus Interface

145

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-S79
management software. The procedure for changing the default mappings
is found in “Mapping CoS Priorities to Egress Queues” on page 147. Note
that because all ports must use the same priority-to-egress queue
mappings, these mappings are applied at the switch level. They cannot be
set on a per-port basis.

You can configure a port to ignore the priority levels in its tagged packets
and instead use a temporary priority level assigned to the port. For
instance, perhaps you decide that all tagged packets received by port 4
should be assigned a priority level of 5, regardless of the priority level in
the packets themselves. The procedure for overriding priority levels is
explained in “Configuring CoS” on page 150.

CoS relates primarily to tagged packets rather than untagged packets
because untagged packets do not contain a priority level. By default, all
untagged packets are placed in a port’s Q0 egress queue, the queue with
the lowest priority. But you can override this and instruct a port’s untagged
frames to be stored in a higher priority queue. The procedure for this is
also explained in “Configuring CoS” on page 150.

Table 2. Default Mappings of IEEE 802.1p Priority Levels

to Egress Port Priority Queues

IEEE 802.1p Traffic Class

AT-GS950 Series

Egress Port Priority

Queue