Quality of Service (QoS)
©2008 Allied Telesis Inc. All rights reserved.
39.32
AlliedWare Plus
TM
Operating System Software Reference C613-50003-00 REV E
Software Version 5.2.1
approximately half the value of the Max
th
setting that you have already set for that
particular color. See the
mls qos queue-set threshold command on page 40.33
.
■
Select a value for the Queue Length Averaging Factor. We suggest you initially use the
default value of 9. See
mls qos queue-set averaging-factor command on page 40.30
.
Egress Queue Mapping
On the switch you can use the
“match ip-dscp” on page 40.11
to select frames of a particular
type. You can then assign these frames with a particular User Priority value then map them to
one of eight egress queues. This facility enables you to accept frames that are already carrying
meaningful priority information to be automatically assigned to an appropriate egress queue.
For example, you could decide to send frames with a User Priority value of 7 to queue 3, and
frames with a User Priority value of 2 to queue 7.
Egress Queue Mapping
Frames entering a port at layer two may be tagged or untagged. VLAN tagged frames contain 3
additional fields as shown in
Figure 39-13
below. The User Priority field enables you to map
incoming frames to any one of eight egress queues. This facility enables you can accept frames
that are already carrying meaningful priority information to be automatically assigned to an
appropriate egress queue. For example, you could decide to send frames with a User Priority
value of 7 to queue 3, and frames with a User Priority value of 2 to queue 7.
Figure 39-13: User Priority Field
Mapping an Untagged frame to an Egress Queue
Frames entering a port with no VLAN tag and hence no User Priority Field, can be mapped to
one of the eight Egress queue by using the
mls qos queue command on page 40.29
. For
example, you could decide to send all untagged frames to a low priority egress queue such as
queue 7.
Mapping an IEEE 802.1P value to an Egress Queue
Immediately after ingress, a VLAN-tagged Ethernet frame can be assigned to an appropriate
egress queue, based on the priority value that is set within the frame’s VLAN Tag Information
Field (TIF). To create the mapping between the TIF and a ports egress queue see the
mls qos
map cos-queue to command on page 40.23
.
VLAN_UPriority
C
F
I
VLAN I D
User
Priority
