by Alex van den Bogaerdt

Our internet provider does usage based billing. Part of the bandwidth is at a fixed price, the remaining bandwidth is subject to UBB.

The UBB works as follows: every sample period the current bandwidth is calculated. When it is above the UBB rate, the excess is used to build an average over a month. This average is used to calculate the bill.

I do trust the provider however I do not necessarily trust their billing system. Therefore I need a way to check the bill.

Normal usage would be to graph from the 1st of the previous month until the 1st of the current month. RRDtool does all the calculations, using CDEF statements. I use bash to collect the prices from a database, then start the RRDtool script with those variables filled in.

The data that I used to create the image has been altered to protect our privacy and the providers pricing policy (meaning: its bogus data). It does show however how it works. If I create the graph using correct values for start and end times, the only difference should be caused by rounding and by different polling times.

If you are interested in the script generating this, get it here.