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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
Figure 22-3 shows queue-implementation for each physical interface. Each queue can be assigned to a
particular output traffic class.
Figure22-3 Queue Implementation

Buffer Management

Each queue is associated with a threshold buffer group, which essentially defines a set of parameters for
buffer management and drop behavior.
Threshold group parameters are defined as follows:
Discard limit value:
•This is the maximum queue length (in bytes), beyond which the packet will be tail-dropped.
Marking limit value:
•This is the point in the queue (in bytes), after which packets in the queue will have the EFCI bit
set.
Note The threshold group parameters are configured in bytes and are r ounded up so as to be multiples of an
ATM cell payload (48 bytes).
The Catalyst 8540 has a maximum of four buffer groups, and the above parameters may be defined for
each of these buffer groups through user configuration.
Scheduling
Each of the four traffic classes are served by the scheduler according to it’s configured weight.
Scheduling is done using the Weighted Round Robin Algorithm.
The WRR scheduler guarantees a minimum bandwidth to each class, based on the assigne d weight. Idle
bandwidth is shared among the classes in a fair manner.
Input
interface 1
Input
interface 2
Queue 3
Queue 2
Queue 1
Queue 0
= Class 3 (IP traffic)
= Class 2 (IP traffic)
Output
interface
= Class 1 (IP traffic)
= Class 0 (Non-IP traffic
default traffic)
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