Hi all,

I've seen these many times but never actually understood which one was cheaper, more expensive or how much they actually would charge.

If we can take an example..

How much does one (1) GigaByte of transfer cost if the webhost is selling it for:

a) $2.00/GB at 95%
b) $2.00/GB at 50%

Basically...

when your billed at 95% your charged for the highest transfer rate you went, so say your consistant usage was only 100k a month but you advertised one day and had heavy usage of 900k for one day during that month. Your going to be charged 900k - 5% for the entire month, not your average which is actually 100k, with 50% your charged basically your average so even if a couple days out of the month you spike up your still only being billed for around 100k of average usage.

Now to translate that to gigs you basically figure there is 320gigs in 1024k of transfer.

So what you're saying is that..

With the 95% it would be

Monthly Cost = <GB Highest day> * 0.95 * <X Month days> * <Bandwidth cost per GB>

What would the formula for 50% be?

Something like that except rate per gig is only calculated at the last minute. With 95% method you can never be sure what your average cost per gig will be.

Bandwidth by the 95% method is *almost* always more (a lot) expensive and more risky. Imagine a Denial of service attack on your web site for several hours which saturates a 100mb network card.

For the people that are interested, I just did some calculations based on the formula above.

Ex #1:

If you're with a webhost charging you $2.00/GB at 95% and you use on average 1 GB per day and one day you advertise and you use 3 GB that day. In a 30 day month, you will use a total of 32 GB transfer.

Monthly transfer: 3 * 0.95 * 30 * 2.00 = 171
GB cost: 171 / 32 = 5.34

So, if you used 32GB that month and you used 3GB on your highest day, your monthly bandwidth cost will be $171 (which means you're paying more than $5/GB.

Keep in mind that if you actually use 3GB/day then this might not be very bad option for you. But then again, you might get a DOS attack one day.. You get the picture.. :eek2:

Originally posted by Mr. Amazon
With the 95% it would be

Monthly Cost = <GB Highest day> * 0.95 * <X Month days> * <Bandwidth cost per GB>


Uh... no. 95th percentile means that you get billed based on the data rate which you are below 95% of the time. 5% of a month is about 1.5 days, so 95th percentile billing would be based on the rate which you exceed for a total period of 1.5 days.

In the case of a site which runs at 100kbps continuously and spikes up to 900kbps for a single day, the 95th percentile level would just be 100kbps; however if your bandwidth went up to 900kbps for two days the 95th percentile level would be 900kbps.

Originally posted by cperciva


Uh... no. 95th percentile means that you get billed based on the data rate which you are below 95% of the time. 5% of a month is about 1.5 days, so 95th percentile billing would be based on the rate which you exceed for a total period of 1.5 days.

In the case of a site which runs at 100kbps continuously and spikes up to 900kbps for a single day, the 95th percentile level would just be 100kbps; however if your bandwidth went up to 900kbps for two days the 95th percentile level would be 900kbps.

So basically, same thing but instead of 1 day, it's 1.5 days?

Originally posted by Mr. Amazon


So basically, same thing but instead of 1 day, it's 1.5 days?

Not really... if your site spikes up to 900kbps on three separate occasions, each time for 12 hours, the 95th percentile level will be 900kbps, while no single day would have more than an average of 500kbps.

What if for example a site I have uses 100kbps most of the day, but every day between 2pm and 4pm goes up to 900kbps. That would be 30 * 2hs = 60hs, which is 2.5 days. Would I be charged for 900kbps for the whole month?

Originally posted by Mr. Amazon
What if for example a site I have uses 100kbps most of the day, but every day between 2pm and 4pm goes up to 900kbps. That would be 30 * 2hs = 60hs, which is 2.5 days. Would I be charged for 900kbps for the whole month?

Yes.

Of course, that's a rather unusual traffic pattern -- usually there would be a much lower difference between average and 95th percentile numbers.

Originally posted by cperciva
Yes.

Of course, that's a rather unusual traffic pattern -- usually there would be a much lower difference between average and 95th percentile numbers.

Hehe. I know, just trying to understand this whole thing. ;)

So how about the 50 percentile? How does that work? Is it the same thing, just 50 instead of 95?

Originally posted by Mr. Amazon
So how about the 50 percentile? How does that work? Is it the same thing, just 50 instead of 95?

As far as I can tell, 50th percentile is a myth invented by people who don't really understand the difference between average and 95th percentile billing. If you actually were being billed at the 50th percentile, it would mean the level which your traffic is above 50% of the time... but I'd personally read "50th percentile billing" as "we're clueless fools, and we bill based on average data rate".