Please read Part 1 of this blog first.

Why Service Providers need 95th Percentile
In an attempt to keep prices competitive and attract new customers, some service providers make efforts to bill customers based on usage.  This is how the 95th percentile became standard practice.  Here is how it works:  A customer’s bandwidth is measured (or sampled) from the switch or router and recorded in a log file. In many cases, this is done every 5 minutes. At the end of the month, the samples are sorted from highest to lowest and the top 5% (which equal to approximately 36 hours of a 30-day billing cycle) of data is thrown away. The next highest measurement becomes the billable utilization for the month.

Example Report
In the report below, 95th percentile is calculated separately for inBound  (top) and outBound (bottom) data.  The light green trend at the top are the data points that are dropped for billing because they are above the straight red line (95th percentile).

netflow95th

Notice above the ALT on the high light in the table (2010-01-05 11:40):  I can drill in on this data point and see who the top talkers, applications, etc. were at this interval in time. Scrutinizer is not limited to this simple traditional utilization based billing.

The Benefit to the Customer
The advantage to the customer is that they get the performance of a high-speed connection, while paying only for their actual usage. ISPs like it because they don’t have to worry about high-usage customers upsetting their overselling ratios.  Here is another good blog on 95th percentile that explains this concept pretty well.   It is possible however for 95th percentile to work to your disadvantage if the highest sample after the top 5% is dropped is still higher than your overall average bandwidth usage.  Some service providers use a flat rate billing system which Scrutinizer also supports.  Notice below we have filtered on all traffic in the 24.x.x.x subnet for any traffic involving http (TCP port 80), Scrutinizer can bill based on any combination of NetFlow fields.

netflowBilling

NOTE: you can’t use sFlow for the above as it only samples data.

Summary
NetFlow has many uses beyond network traffic analysis.  Network usage based billing with NetFlow is really getting back to one of the primary intended uses for the technology.  Best at NetFlow Reporting tools leave room for all your invoicing needs.

Mike Patterson author pic

Michael

Michael is one of the Co-founders and the former product manager for Scrutinizer. He enjoys many outdoor winter sports and often takes videos when he is snowmobiling, ice fishing or sledding with his kids. Cold weather and lots of snow make the best winters as far as he is concerned. Prior to starting Somix and Plixer, Mike worked in technical support at Cabletron Systems, acquired his Novell CNE and then moved to the training department for a few years. While in training he finished his Masters in Computer Information Systems from Southern New Hampshire University and then left technical training to pursue a new skill set in Professional Services. In 1998 he left the 'Tron' to start Somix which later became Plixer.

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