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22-8
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
• If no match with a permit action is encountered and all the configured classifiers’ ACEs
have been examined, the packet is assumed to be in the well known default class
(class-default).
Traffic Conditioning
A traffic stream is selected by a classifier, which steers the packets to a logical instance of a traffic
conditioner (marker, meter/policer).
Marking
Packet marking is a traffic conditioning action, performed on an identified flow at the ingress port. The
marking action could cause the DSCP / precedence bits to be re-written or left unchanged, depending on
user configuration.
The following types of markers are supported:
DSCP markers:
• Packet markers set the DS field of a packet to a particular code point, adding the marked packet
to a particular DS behavior aggregate. Based on configurations, each packet matching a
particular classifier may be marked with the specified DSCP value.The marker has the
capability of marking all the 64 possible DSCP values.
IP-Precedence markers:
• To maintain compatibility with the 3 bit IP precedence (Class of Service) contained in the TOS
byte of the IP header, the marker provides an option to mark a classified packet with a specified
IP precedence value. The marker has the capability of marking all the 8 possible IP-precedence
values. The remaining 3 bits of the DSCP field are set to zero.
Trusted Traffic:
• This is a class of traffic that has a service level agreement with an upstream router, and, as a
result, may not require the application of a marker.
Note If a marking action is not configured, that class of traffic is implicitly trusted. Alternatively, the user may
specifically configure the class of traffic as trusted.
Metering and Policing
Traffic matching a classifier may be metered using the Token Bucket Algorithm. The result of this
metering is used to decide whether to police a particular traffic stream or not.
Incoming packets are passed unaltered if the packet conforms to the traffic profile for that class. Out of
profile packets are discarded or marked down, depending on user configuration.
There are 32 instances of meters/policers available per physical interface. These may be distributed
between Multi-Field/Behavior Aggregate classifiers as required by the user.