The network operation teams are interested in knowing the sudden changes in the traffic throughput of their important POPs uplinks as this is an indication of a potential issue. In this note I will show how to create a TNPM wireline CME formula to calculate the drop percent in the inbound throughput. The key element of the formula is the ability to maintain the previous value of the formula in order to compare it with the current value. the CME formulas provide the ability to maintain the previous value of a the formula in an unbounded variable (a CME input variable which is not bounded to any other formulas/properties). Please note that the unbounded variable is not an officially documented feature however it is already used in some of the TNPM techpacks.
In our example, the unbounded variable is called "lastValue" and as shown below it is defined as an input variable however it is not bounded to any other formulas/properties. by calculating the delta value of the throughput and getting it is percent of the previous throughput value we can get the drop percent of the throughput. In the example below I am interested in the throughput values larger than 10Mbps however you can set it to any value you want.
Please note that the baseline thresholds can also be used to achieve something similar however I consider this method as a more controlled way of detecting sudden changes of a formula values. Of course if the required SNMP object returns an absolute value (not a counter eg. Number of PPP sessions) then you can use the "diff" function of the TNPM SNMP collection formulas instead of using the CME formulas.
Inbound Throughput Drop percent CME Formula:
| result deltaThput |
result := 0.0d.
lastValue isNil ifTrue: [lastValue := 0.0d].
deltaThput := lastValue - currentValue value.
(deltaThput > 0 and: [lastValue > 10000000]) ifTrue: [result := (100 * deltaThput) / lastValue].
lastValue := currentValue value.
Formula output example (Inbound Throughput):
Formula output example (Inbound Throughput drop percent):