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25-48
ATM Switch Router Software Configuration Guide
OL-7396-01
Chapter 25 Configuring ATM Router Module Interfaces
Configuring VC Bundling with IP and ATM QoS
Because the enhanced ATM router module must schedule traffic received from both ATM VCs and
Layer 3 (broute) VCs, one half of the bandwidth is reserved for ATM connections. The bandwidth
configured on the maximum of four output policy maps must not be greater than 500 Mbps. Even if the
sum of bandwidths is more than 500 Mbps (but not more than 1Gbps) the weights calculated for IP QoS
classes is reserved for 500 Mbps maximum. The rest of the configured bandwidth is available only if
there is no ATM traffic (which also includes Layer 3 traffic of scheduler class 4 from EPIF modules).
The following formula is used to calculate the scheduler class weights for the IP QoS classes after an
IP QoS output policy is configured:
In the formula, the weights are scaled to 255, because that is the maximum weight that can be configured
for any scheduler-class.
The show epc ip-atm-qos command displays the mapping between the class maps and scheduler classes.
For example, using the following formula, class voice has a bandwidth of 200 Mbps, the total being 500
Mbps and the weight is calculated as 51.
This weight is assigned to scheduler class 8 (displayed using the show epc ip-atm-qos command.)
Next you must go back and calculate the minimum guaranteed bandwidth provided based on the
calculated scheduler weights using the following formula:
Note In this formula, you can ignore scheduler-class 4 for LSIPC because it is for internal control traffic and
it is negligible.
The following formula shows the calculation for the voice traffic (class voice) as 89.788 Mbps
(90 Mbps).
Use the example configuration given in this document and shown in Figure 25-12. In this example, the
weights assigned to each scheduler class and the bandwidth reserved for each class are calculated and
shown in Table 25-1.
Bandwidth configured for class-map
A
Weight
A
= * 255
Bandwidth of all class-maps + 500
Σ
Weight (class voice) = 255 * (200Mbps/(500Mps + 500Mps))
Weight = 51
Schedule weight of Scheduler-class-A
(Bandwidth of scheduler class A) =
* 255
of scheduler-class weights 0-2 and 4-7
Σ
51
Bandwidth (class voice) = * 1Gbps
16 + 240 + 128 + 64 + 25 + 44 + 51