Qos Features And Components - Cisco 500 series Administration Manual

Configuring Quality of Service

QoS Features and Components

QoS Features and Components
Cisco 500 Series Stackable Managed Switch Administration Guide
The QoS feature is used to optimize network performance.
QoS provides the following:
• Classification of incoming traffic to traffic classes, based on attributes,
including:
- Device Configuration
- Ingress interface
- Packet content
- Combination of these attributes
QoS includes the following:
• Traffic Classification—Classifies each incoming packet as belonging to a
specific traffic flow, based on the packet contents and/or the port. The
classification is done by ACL (Access Control List), and only traffic that
meets the ACL criteria is subject to CoS or QoS 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
The QoS mode that is selected applies to all interfaces in the system.
• Basic Mode—Class of Service (CoS).
All traffic of the same class receives the same treatment, which is the single
QoS action of determining the egress queue on the egress port, based on
the indicated QoS value in the incoming frame. This can be the VLAN
Priority Tag (VPT) 802. 1 p value in Layer 2 and the Differentiated Service
Code Point (DSCP) value for IPv4 or Traffic Class (TC) value for IPv6 in
Layer 3. When operating in Basic Mode, the switch trusts this external
assigned QoS value. The external assigned QoS value of a packet
determines its traffic class and QoS.
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