What is 95th Percentile (Burstable) Billing?

When you’re looking around for data centre solutions you’ll often come across the term “95th Percentile” when being quoted for bandwidth (transit).

In simple terms, 95th Percentile means that your bandwidth usage is lower than the quoted amount for at least 95% of the month.  Should you need more bandwidth for 5% of the month, however, you won’t be charged any more. You will probably be given a network port that is 100Mb, 1Gb, 10Gb, or even 100Gb and you can use the full capacity of the port in bursts and (providing you don’t do so for more than 5% of the month) you won’t be charged extra.

95% of the month is…

An entire month is ~730 hours.  Based on that, 5% of the month is ~36 1/2 hours a month. You could, therefore, go above your committed data rate (CDR) for up to 36 1/2 hours a month and not be charged any extra.

An example quote.

Say, for example, you are being quoted for 50Mb CDR billed at 95th Percentile, presented on a 1Gb network port.  This would mean you expect to spend less than 95% of the month at 50Mb/s or less, but you could quite happily use up to 1024Mb/s for up to 5% of the month without the worry of extra charges.

Therefore, projected data centre scenarios might include:

Should you transferred data at an absolute solid 50Mbit/s total download and upload, you wouldn’t be charged any extra.

If, for example, you wanted to download some files you could do this at the full speed of the port (up to 1Gb/s) but, providing you didn’t download at a rate above 50Mb/s for more than ~36.5 hours a month, you would not be charged any extra. This is very useful – especially bearing in mind, as the file downloads quicker, it spends less time downloading it and therefore leaving more time for more burstable bandwidth use.

If after calculations it turns out you used more than 50Mb/s for more than 95% of the time the monitoring and billing system would “chop the top 5% off” and give you a new 95th percentile CDR. You would then be charged any excess at the given rate per Mb. It is important to make sure that excess (or “overage”) charges are known upfront.

How do you know how much bandwidth you need at 95th percentile?

This is a very common question and, without monitoring, is actually difficult to determine.

You may know how much data you transfer in a month but that doesn’t help here. You could transfer all of that data at a full 1Gb/s and it might only happen within two days every month. In this case, your 95th percentile would be 1Gb/s as you’ve saturated the port for more than the ~36.5 hours.  Likewise, if the total data you transfer is spread across the entire month the CDR may be less.

Is there a way to guarantee you’ll never go over the CDR and avoid charges?

Yes. It’s possible to limit the external bandwidth use on your edge router and/or firewall.  If, for example, you purchase 50Mb CDR and you are happy to download and upload at no more than 50Mb/s (Megabits), this is a good solution. It does mean, however, you aren’t using the full capacity of the port you’ve been provisioned and that 10GB download will only download at around ~6MB (Megabytes) a second, as opposed to a potential 125MB a second.

Often we look at rate-limiting certain long-running applications for our clients but leaving other things to use the full port capacity. Downloads for example.

How do deeserve estimate usage?

We look at the data centre solution we’re deploying and initially use educated estimates, making the client aware of any charges and that usage may rise accordingly.

During the first few months of deploying the service, we closely monitor bandwidth use and let our clients know the usage we are seeing. This is usually apparent pretty quickly if we think the bandwidth use will exceed the initial estimates.

Example monitoring.

This is an example graph from the deeserve monitoring platform, showing the average traffic, total traffic, and the 95th percentile value for a 100Mbit port.

All values are reported in Kb (Kilobits) or KB (Kilobytes). We divide these numbers by 1024 to get the Mb (Megabits) or MB (Megabytes) values.

As you can see, the average traffic throughput for the entire month was just 975Kbit/s (which is around 0.9Mbit/s). The 95th Percentile, however, is being calculated at around 3.91Mbit/s. Total traffic that was transferred is just under 287GB for the month.

Providing the CDR purchased was, therefore, 4Mb or more and there would be no further charges.

If you’re currently looking for a data centre solution, whether it’s managed colocation (where you own the kit but use our data centre racks) or a fully dedicated IT support solution on dedicated hardware (where we offer a monthly cost and lease all hardware and software to you), please get in touch with us today to see how we can help to create a custom IT solution tailored to your exact business needs.

Posted on: 7th September 2020.