Dell POWERCONNECT 5524, User Manual

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Dell PowerConnect 55xx Systems User Guide
641
QoS Features and Components
The QoS feature is used to optimize network performance. It provides
classification of incoming traffic into traffic classes, based on one or more
attributes, including:
– Device configuration
– Ingress interface
– Packet contents
QoS includes the following features:
• Traffic Classification — Classifies each incoming packet, as belonging to
a specific traffic flow, based on the packet contents and/or interface. The
classification is done by an ACL (Access Control List), and only traffic
that meets the ACL criteria is subject to classification.
• Assignment to Hardware Queues — Assigns incoming packets to
forwarding queues. Packets are sent to a particular queue for handling as a
function of the traffic class to which they belong.
• Other Traffic Class-Handling Attribute — Applies QoS mechanisms to
various classes, including bandwidth management.
QoS Modes
A single QoS mode is selected and applies to all interfaces in the system. The
modes are:
•
Basic Mode — Class of Service (CoS)
.
– Traffic is divided into classes that determine how it is treated. All
traffic in a class is treated with the same QoS action. The QoS action
for the class of traffic determines the egress queue on the egress port,
based on the indicated QoS value in the incoming frame.
The QoS value in the incoming frame is:
•
Layer 2 Packets — VLAN Priority Tag (VPT) 802.1p value
• Layer 3 IPv4 Frames — Differentiated Service Code Point
(DSCP) value
• Layer 3 IPv6 Frames —Traffic Class (TC) value
When operating in Basic mode, the switch trusts this
externally-assigned QoS value.