HP 3500 Series Advanced Traffic Management Manual page 230

Quality of Service: Managing Bandwidth More Effectively
QoS Traffic Marking
Table 5-3. Mapping 802.1p Priorities to Outbound Port Queues on the Switch and Downstream Devices
Configured
802.1p Priority
1
2
0
5-12
Configuring a new 802.1p priority value allows you to set the outbound priority
queue to which a packet is sent. For example, you can configure an 802.1p
priority of 0 through 7 for an outbound packet. When the packet is sent to a
port, the QoS priority determines the outbound queue to which the packet is
assigned as shown in Table 5-2.
Table 5-2. 802.1p Priority Settings and Outbound Queue Assignment
802.1p Priority Setting Outbound Port Queue
1 and 2 Low priority (1, 2)
0 or 3 Normal priority (3, 4)
4 and 5 Medium priority (5, 6)
6 and 7 High priority (7, 8)
If a packet is transmitted in an untagged-VLAN environment, the 802.1p
priority settings in Table 5-2 control only the outbound queue to which the
packet is sent on the local switch. Because no VLAN tag is used, an 802.1p
priority value is not added to the 802.1Q field in the packet header for use by
downstream devices.
However, if your network uses only one VLAN and does not require VLAN-
tagged ports, you can preserve 802.1p priority settings in outbound traffic by
configuring the ports on links between devices on which you want 802.1p
priorities to be honored as tagged VLAN members.
If a packet is transmitted in an 802.1Q VLAN-tagged environment, the QoS-
configured 802.1p setting is also added to the VLAN packet header as an 802.1p
priority for use by downstream devices and applications (as shown in Table
5-3).
In an 802.1Q VLAN environment with VLAN-tagged ports, if QoS is not config-
ured on the switch but is configured on an upstream device, the priorities
carried in the packets determine the outbound port queue on which packets
are forwarded.
Outbound Port 802.1p Priority Added to
Queue in the Tagged VLAN Packets
Switch Exiting the Switch
Queue 1 1 (low priority)
Queue 2 2
Queue 3 0 (normal priority)
Queue Assignment in Downstream Devices
With:
8 Queues 4 Queues
Queue 1 Queue 1
Queue 2
Queue 3 Queue 2
2 Queues
Queue 1