Ever since we changed our customer's routers from 828 -> 878 we have problems when lines get down synced.
We always do vbr ATM shaping non real time, but when the configured SCR is higher then de actual sync rate, we get NO bit over the ATM interface. In conf mode, when you do "vbr-nrt ?" you can't give a higher number then the actual sync rate, but the value in startup-config keeps popping up in "show run". Fact is that we cannot predict if a line gets a lower sync rate due to line issues, so we have this situation from time to time. Cisco 828 does not have this issue.
Is this a bug or a feature? Tried on latest ios