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When searching for solutions for your data center, you often hear the phrase “95th Percentile” when quoted for bandwidth (transit).

To put it another way, the 95th percentile indicates that your bandwidth use is lower than the amount reported for at least 95% of the month’s span. If, on the other hand, you need more bandwidth for five percent of the month, you will not be charged any additional fees. You will likely be provided with a network port that is 100 megabytes, 1 gigabyte, 10 gigabytes, or even 1000 gigabytes. You will be able to utilize the entire capacity of the port in bursts, and you will not be charged any additional fees (provided that you do not do so for more than five percent of the month).

95th Percentile of the month is…

One month is about 730 hours long. According to this, five percent of the month is around thirty-six and a half hours every month. It is consequently possible for you to exceed your committed data rate (CDR) for a maximum of 36 and a half hours per month without incurring any additional fees.

For Example

Let’s say, for instance, that you are being offered a price for a 50 megabytes CDR displayed on a 1 gigabyte network port and billed at the 95th percentile. This implies that you anticipate spending less than 95% of the month at a speed of 50 megabytes per second or less, but you could be content to use up to 1024 megabytes per second for up to 5% without worrying about incurring additional expenses.

As a result, the following are examples of potential situations for data centers:

If you moved data at a guaranteed total download and upload speed of 50 megabits per second, you would not be charged any additional fees.

If you wanted to download any files, you could do so at the maximum speed of the port, up to 1 gigabit per second. However, as long as you did not download at a rate over 50 megabits per second for more than 36.5 hours each month, you would not be charged any additional fees. The fact that the file downloads more quickly means that it takes less time to download, which frees up more time for more burstable bandwidth consumption. This is a precious feature, particularly when anything is taken into consideration.

After doing calculations, if it is determined that you have utilized more than 50 megabits per second for more than 95% of the time, the monitoring and billing system will “cut the top 5% off” and provide you with a new CDR that is in the 95th percentile. Any excess would then be charged to you at the rate specified per megabyte. It is essential to ensure that excess expenses (also known as “overage”) are recognized in advance.

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How can you determine the bandwidth you need at the 95th percentile?

This is a ubiquitous question and, with monitoring, is easier to determine.

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

Can you get a guarantee that you will never exceed the CDR and, therefore, avoid incurring charges?

Indeed. On your edge router and/or firewall, it is possible to restrict the amount of bandwidth used from the outside. This is an excellent alternative if you acquire a 50 megabytes CDR and are OK with a download and upload speed of no more than 50 megabits per second. However, this does imply that you are not making full use of the port that has been allocated to you and that a download of 10 gigabytes will only be completed at around 6 megabytes per second, as compared to the theoretical download speed of 125 megabytes per second or more.

We often consider imposing rate limits on specific apps operating for a long time for our customers while allowing other programs to utilize the port’s total capacity. One example would be downloads.

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