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Burstable Bandwidth and the 95th Percentile – What does it really mean?

Burstable bandwidth can provide real value for some clients, but how does it all work?

Every day, the provision of scalable and robust connectivity is becoming more important to the enterprise. Organisations are increasingly adopting cloud technologies such as Salesforce, Amazon Web Services and Office 365, building out IP telephony solutions requiring QoS and in some cases, creating their own web facing applications.

Now, not only is the availability of the connection critical, but that connectivity must perform optimally in order to ensure that no bottlenecks or undue latency issues impact user experience.

So when we purchase bandwidth, we want to balance these requirements with the commercial concerns relating to enterprise class connectivity services.

Burstable Bandwidth a facility that allows organisations to automatically consume greater bandwidth than the contracted amount for short periods of time at no additional cost. 95th Percentile Billing means that the top 5% of consumption readings in a given month are discarded before calculating what is owed by the client and here’s how it works:

  • A log of 30 days worth of traffic samples at the default frequency (every 5 minutes is typical) is accumulated and the log is sorted in descending order
  • The top 5% of samples are dismissed
  • The value of the largest remaining sample becomes the effective bandwidth usage value for the month.

So how does it work in practice?

You acquire a 10Mbps synchronous network (€50 per Mb for this example) with burstable bandwidth limited to 40Mbps. Now, over a period of 30 days, your ISP will take a measurement of usage every 5 minutes (that’s 8,640 measurements). At the end of the billing cycle, the ISP removes the top 5% (432 measurements) and discards them. The next highest measurement is then taken and that figure is used for billing.

So, let’s say that after removing the first 5% (which is 36 hours by the way), the highest remaining reading is 9Mbps. In this case there is no additional charge as it falls under your contracted rate of 10Mbps. Billing is as follows:

10Mb x €50 = €500 (nice and simple!)

However, if this reading was 17Mb, then the ISP will take the 7Mb excess and bill this at a premium (usually about 20%). In this case, you will be billed as follows:

(€500 normal billing) + (7Mb x €50 x 120%) = €920

When is 95th percentile billing a good idea?

Using burstable bandwidth is a good idea when you know your normal working requirements are below a certain level, but want to facilitate short term bursts of activity without paying for increased bandwidth. For example, you may have a daily routine that hogs bandwidth for half an hour or a regular month end activity that requires a 12 hour data dump. You may even want to mitigate DDOS impacts. Once you are confident that you won’t consistently use the excess, then it’s a great facility.

When is it not?

Put simply, if your organisation consistently uses higher bandwidth than the contracted rate for over 5% of the month, then you need to either fix the limit (remove bursting) or increase the capacity. Another potential hazard is if consumption in a given period is unduly high and not properly monitored, you may get an unwelcome surprise when you get your next bill!

About the author

Brian has worked in the IT managed services and hosted services arena for over 20 years. He has worked successfully with clients in both corporate and SME spaces. He ensures that our technical solutions meet the business requirements of our clients. Brian also works closely with the technical teams to constantly improve our service portfolio and bring these developments to our client base.

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