When configuring the Quality of Service (QoS) policies, adequate bandwidth must exist for all required applications. The sum of all bandwidth used on each major application represents the minimum bandwidth requirement for any given link. This should consume no more than 75 percent of the total bandwidth available on that link. When there is available bandwidth that the total amount intended (or configured) to be used, the router will not apply the service policy.
For manifestations of the problem, refer to the bolded lines in this example:
service-policy output TSA-ATM <----This is the line that will not be add by IOS
With the bandwidth percent configured, Cisco IOS® Software determines the percent based off the Sustainable Cell Rate (SCR) value in the vbr-nrt statement. In this case, the value is 1536k.
This is how bandwidth works:
1536 times 50 percent = 768k
1536 times 25 percent = 384k
1536 times 15 percent = 230k
768 plus 384 plus 230 = 1382
To add these percentages: 1536 times (50 plus 25 plus 15) percent = 1536 times 90 percent = 1382.
The router determines the available bandwidth to be used as being 75 percent of the SCR. In this case, the amount of bandwidth available would be 1536 times 768 = 1152. This is less than the bandwidth configured for use (1382). Therefore, the router will not apply the service policy.