HP ProCurve Series 6120 Blade Switches Advanced Traffic Management Guide

5-7
Quality of Service (QoS): Managing Bandwidth More Effectively
Introduction
Overview
QoS settings operate on two levels:
■ Controlling the priority of outbound packets moving through the
switch: 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 5-1.
Table 5-1. 802.1p Priority Settings and Outbound Queue Assignment
(In an 802.1Q VLAN environment with VLAN-tagged ports, if QoS is not
configured on the switch, but is configured on an upstream device, the
priorities carried in the packets determine the forwarding queues in the
switch.)
■ Configuring a priority for outbound packets and a service (prior-
ity) policy for use by downstream devices:
• DSCP Policy: This feature enables you to set a priority policy in
outbound IP packets. (You can configure downstream devices to read
and use this policy.) This method is not dependent on VLAN-tagged
ports to carry priority policy to downstream devices, and can:
re-marking
(DSCP re-
marking)
Assigns a new QoS policy to an outbound packet by changing the DSCP bit settings in the ToS byte.
tagged port
membership
Identifies a port as belonging to a specific VLAN and enables VLAN-tagged packets belonging to that
VLAN to carry an 802.1p priority setting when outbound from that port. Where a port is an untagged
member of a VLAN, outbound packets belonging to that VLAN do not carry an 802.1p priority setting.
Type-of-Service
(ToS) byte
Comprised of a three-bit (high-order) precedence field and a five-bit (low-order) Type-of-Service field.
Later implementations may use this byte as a six-bit (high-order) Differentiated Services field and a
two-bit (low-order) reserved field. See also “IP-precedence bits” and DSCP elsewhere in this table.
upstream
device
A device linked directly or indirectly to an inbound switch port. That is, the switch receives traffic from
upstream devices.
Term Use in This Document
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)