22-7
ATM Switch Router Software Configuration Guide
OL-7396-01
Chapter 22
Configuring Quality of Service
About IP QoS on the Enhanced Gigabit Ethernet and Enhanced ATM Router Module Interfaces
Figure 22-1 Architectural Model
Packet Classification
Packet classifiers select packets in a traffic stream based on the content of some portion of the packet
header.
Classifiers are implemented in a ternary content addressable memory (TCAM). TCAM has the capability
of providing variable length matches. The order in which classifiers are defined within a policy map is
the order in which entries will be programmed in TCAM.
There are two types of classifiers:
Multi-field (MF) classifiers:
•
Classify traffic streams identified by the source and/or destination IP addresses, TCP/UDP
source and/or destination ports, and/or Layer 4 protocol
•
Are configured using one or more IP standard or extended, named or numbered Access Control
Lists (ACLs)
Behavior Aggregate (BA) classifiers:
•
Classify traffic streams based on the differentiated services code-point (DSCP) or IP precedence
bits in the TOS byte of the IP header
Note
In the IP QoS context, the permit and deny actions in the access control entries (ACEs) have different
meanings than with security ACLs:
•
If a match with a permit action is encountered (first-match principle), the specified
traffic conditioning action for that classifier is taken.
•
If a match with a deny action is encountered, the classifier being processed is skipped,
and the next classifier’s ACL(s) is/are processed.
MF-Classifier
Marker
BA-Classifier
Queuing
Scheduling
Congestion
Control
Ingress Traffic Conditioner
QoS Data Path
Switch Fabric
Queue
Selector
Forwarding Engine
Meter/Policer
Optional
Classifier
Egress Traffic Conditioner
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