Burstable billing

Burstable billing is a method of measuring bandwidth based on peak utilization. It also allows usage to exceed a specified threshold for brief periods of time without the financial penalty of purchasing a higher Committed Information Rate (CIR, "commitment") from an Internet service provider (ISP).

Most ISPs use a five minute sampling and 95% utilization when calculating usage.

95^th Percentile

The 95^th percentile is a widely used mathematical calculation to evaluate the regular and sustained utilization of a network connection. It is commonly used among all major internet transit and peering networks, as well as datacenters and ISPs for both capacity planning and/or calculating usage. It roughly means ‘you are paying based on the capacity for your busiest 5% of the week (eg, busiest 72 minutes out of a day)'. Some providers offer billing on the 90^th percentile as an incentive to attract customers with irregular bandwidth patterns.

The 95^th percentile is a good number to use for billing as it can allow the customer throughput bursts without additional financial compensation. Basically the 95^th percentile says that 95% of the time, the usage is at or below this amount. Conversely, usage could be above that amount up to 5% of the time.

There are important factors to percentile calculation:

Sampling interval, or how often samples are taken (called also "data points").

• A percentile is calculated on some set of data points.
• Every data point represents the average bandwidth used during the sampling interval (e.g., five minutes) and is calculated as the number of bits transferred throughout the interval divided by the duration of the interval (e.g., 300 seconds). The resulting value represents the average utilization rate for a single sampling interval and is expressed as bits per second (kbit/s/Mbit/s/Gbit/s). See data transfer rate.

Another options is Average Usage Billing Most datacenters and hosting providers use the “95th Percentile” or "burstable billing" method. while other utilizes Average Usage Billing. Throughout the month, these host take measurements of your bandwidth usage every 5 minutes. At the end of the monthly cycle, these measurements are added together and we divide this number by the number of measurements taken. Measuring of bandwidth in this manner results in a true “average” usage reading for your bandwidth bill.

Using this method allows hosts customers to take advantage of the natural peaks and valleys that occur from day to day bandwidth usage. Hosts with this bandwidth billing policy is designed to encourage customer to grow their businesses and push the envelope with their hosting environments! Here is an example:

Burstable rate calculation

Bandwidth is measured (or sampled) from the switch or router and recorded in a log file. In most 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.

Based on this model, the top 36 hours (top 5% of 720 hours) of peak traffic is not taken into account when billed for an entire month. Bandwidth could be utilized at a higher rate for up to 65 min a day with no financial penalty.

Criticism for end user billing

• With the 95^th percentile billing method there is potential for paying for bandwidth that is not used. However, this method will also allow brief access to peak bandwidth when required. For example, if a website is Slashdotted for an entire weekend (48 hours) then billing would be based on a higher rate just because of that single weekend. Whereas if the peak is shorter (less than 36 hours), the peak would not appear on a usage bill for the month.

• In the 95^th percentile billing method inbound and outbound traffic is usually calculated separately. The highest value is then used for billing rather than the sum.

• Customers sometimes mistake the 95^th percentile billing method for being able to use up to 95 percent of an assigned port (e.g. 9.5mbit of a 10mbit port, 95mbit of a 100mbit).

• Critics of the 95^th percentile billing method usually advocate the use of a flat rate system, billing per byte of data transferred, or using the average throughput rather than the 95th percentile.

See also

• MRTG - Used to review bandwidth usage and with patches, determine 95^th percentile values.
• Cacti - another tool for 95th percentile values also based on RRDtool

External links

• MRTG Help Site - Helpful page with example MRTG graphs and explanations.
• Torrus reporting setup guide - Implementation details and installation guide for monthly reports of traffic usage and 95th Percentile in Torrus
• RTG - Opensource server for get data from SNMP and save on relation database. Also includes graphic and report generator.