ProCurve 2610-PWR Technical Information download pdf (Page 197)

Quality of Service (QoS): Managing Bandwidth More Effectively

Introduction

Term Use in This Document

outbound port For any port, a buffer that holds outbound traffic until it can leave the switch through that port. There

queue 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

Assigns a new QoS policy to an outbound packet by changing the DSCP bit settings in the ToS byte.

(DSCP re-

marking)

tagged port Identifies a port as belonging to a specific VLAN and enables VLAN-tagged packets belonging to that

membership 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 Comprised of a three-bit (high-order) precedence field and a five-bit (low-order) Type-of-Service field.

(ToS) byte 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 A device linked directly or indirectly to an inbound switch port. That is, the switch receives traffic from

device

upstream devices.

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

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

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.)

6-7

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ProCurve 2610-PWR Technical Information Page 197