HP ProCurve 2810-24G, Management And Configuration Manual

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6-7
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:
Each switch port has four outbound traffic queues; “low”, “nor-
mal”, “medium”, and “high” priority. Packets leave the switch port on the
basis of their queue assignment and whether any higher queues are empty:
Table 6-1. Port Queue Exit Priorities
A QoS configuration enables you to set the outbound priority queue to
which a packet is sent. (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.)
outbound port
queue For any port, a buffer that holds outbound traffic until it can leave the switch through that port. There
are four outbound queues for each port in the switch: high, medium, normal, and low. Traffic in a port’s
high priority queue leaves the switch before any traffic in the port’s medium priority queue, and so-on.
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
Port Queue and
802.1p Priority Values
Priority for Exiting
From the Port
Low (1 - 2) Fourth
Normal (0, 3) Third
Medium (4 - 5) Second
High (6 - 7) First