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ATM Switch Router Software Configuration Guide
OL-7396-01
Chapter22 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 ma rked 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 servic e 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 t raffic profile for that class. Out of
profile packets are discarded or marked down, depending on user configura tion.
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.