Cisco Catalyst 8540 MSR Configuration Manual page 850

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:
Weight
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.
Weight (class voice) = 255 * (200Mbps/(500Mps + 500Mps))
Weight = 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:
(Bandwidth of scheduler class A) =
In this formula, you can ignore scheduler-class 4 for LSIPC because it is for internal control traffic and
Note
it is negligible.
The following formula shows the calculation for the voice traffic (class voice) as 89.788 Mbps
(90 Mbps).
Bandwidth (class voice) =
Use the example configuration given in this document and shown in
weights assigned to each scheduler class and the bandwidth reserved for each class are calculated and
shown in
ATM Switch Router Software Configuration Guide
25-48
Bandwidth configured for class-map
=
A
Σ
Bandwidth of all class-maps + 500
16 + 240 + 128 + 64 + 25 + 44 + 51
Table 25-1.
Chapter 25
A
* 255
Schedule weight of Scheduler-class-A
Σ
of scheduler-class weights 0-2 and 4-7
51
Configuring ATM Router Module Interfaces
* 255
* 1Gbps
Figure 25-12. In this example, the
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