Burstable billing
From Wikipedia, the free encyclopedia
Burstable billing is a method of measuring your bandwidth based on peak utilization. It also allows a user to use more than the agreed bandwidth 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 the burstable rate.
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[edit] 95th Percentile
The 95th percentile is a widely used mathematical calculation to evaluate the regular and sustained utilisation of a network pipe. It is commonly used among bandwidth providers, e.g. datacenters and upstream providers, for both capacity planning and/or calculating metered use and roughly means ‘for most of the time this was the throughput on the line’.
The 95th percentile is a good number to use for billing as it can allow the customer throughput bursts without any financial penalty. Basically the 95th percentile says that 95% of the time, the usage is below this amount. Conversely, 5% of the time, usage is above that amount.
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 through the sampling interval, calculated as the number of bytes (or KB/MB/GB etc.) transferred divided by the sampling interval length in seconds (effectively representing the average utilisation for single sampling interval).
[edit] Burstable rate calculation
Your bandwidth is measured from the switch or router and recorded in a log file, which in most cases is done every 5 minutes. At the end of the month, your usage statistics are sorted, and the top 5% (which equal to approximately 36 hours of a 30-day billing cycle) of data is thrown away, and that next measurement becomes your 'billable utilization' for the month.
Usually only a few services are billed using 95th percentile pricing: Dedicated T1 and Colocated servers. While your average DSL, Cable and Wireless provider usually bills on the total bandwidth used over the entire billing period.
Based on this model, the top 36 hours (top 5% of 720 hours) of peak traffic are not taken into account when billed for an entire month. What this means is that you could run at the full rate for up to 65 min a day with no financial penalty.
[edit] Critics
- Critics argue that the 95th percentile billing method favors the datacenter and/or the upstream provider, advocates will reply that it benefits the customer.
- With 95th percentile billing one has to take into account that there is potential for paying for bandwidth you did not use. But on the other hand the 95th percentile will also allow you to briefly "dip into" peak bandwidth when you require to. For example, if your website was slashdotted for an entire weekend (48 hours) then you would be billed based on a higher rate just because of a single weekend. Whereas if the peak is shorter, you would not notice the peak on your bill.
- Inbound and outbound traffic percentile are calculated separately and sometimes the highest value is used for billing rather than the sum.
- Customers sometimes mistake 95th percentile for being able to use up to 95 percent of their assigned port (e.g. 10mbit, 100mbit).
- Critics of the 95th percentile billing method usually advocate the use of a flatrate or a billing per GB of transfer.
[edit] See also
- MRTG - Used to review bandwidth usage and with patches, determine 95th percentile values.
[edit] External links
- MRTG Help Site - Helpful page with example MRTG grabs and explanations.
