336 Configuring Quality of Service
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Quality of Service (QoS) Overview
Quality of Service
(QoS) provides the ability to implement QoS and priority queuing within a
network. QoS improves network traffic flow based on policies, frame counters and context.
An implementation example that requires QoS include certain types of traffic such as Voice, Video
and real-time traffic which can be assigned a high priority queue, while other traffic can be assigned
a lower priority queue. The result is an improved traffic flow for traffic with high demand.
QoS is defined by:
•
Classification
— Specifies which packet fields are matched to specific values. All packets
matching the user-defined specifications are classified together.
•
Action
— Defines traffic management where packets being forwarded are based on packet
information, and packet field values such as VLAN priority (VPT) and DSCP (DiffServ Code
Point).
VPT Tag Classification Information
VLAN Priority Tags are used to classify the packets by mapping packets to one of the output
queues. VLAN Priority Tag to queue assignments are also user-definable. The table below details
the VPT to queue default settings:
Table 9-92. CoS to Queue Mapping Table Default values
CoS Value Forwarding Queue Values
0q2
1 q1 (Lowest Priority = Best Effort)
2 q1 (Lowest Priority = Best Effort)
3q2
4q3
5q3
6 q4 (Highest Priority)
7 q4 (Highest Priority)
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