[asterisk-users] OT: Bandwidth calculations

[Gareth Blades]

Randy R wrote:
> Hi,
> 
> I know some of you are very experienced  as to the working of
> networks. I wondered whether there is some accepted way of determining
> bandwidth needs based on the network traffic over time. For example,
> looking at the figures for the network traffic through the server
> interface, we have hourly, daily and monthly figures. If everything
> were linear, taking the hourly figure and dividing it by 3600 (or the
> daily by divided 3600*24) would give us the required bps, but this
> average is pretty meaningless.
> 
> Those of you who have experience and education in this area, where can
> I look for guidance (links?) and do you have any rules of thumb you'd
> care to share? I'm actually looking for this for a web server not
> VoiP, but any info is welcome.
> 
> It seems obvious to me that taking the per second average and
> multiplying it by some kind of seat of the pants number must give a
> decent idea? WHat is that magic number?
> 
> Thanks in advance for any ideas.
> 
> /r
> 

It depends on the charging structure your ISP is using.

 From an ISP point of view when they purchase transit links all pricing 
is done on the 95th percentile basis. So for example you might purchase 
a 50Mbps connection over a 100Mbps interface. You would get a guaranteed 
50Mbps but could burst up to the full interface speed.
Bandwidth measurements are taken normally every 5 or 10 minutes. The 
95th percentile is calculated by discarding the top 5% results and the 
next highest reading is the 95th percentile. If this is below the 50Mbps 
then all is fine otherwise you will receive a bill for overusage.

For a web server this is probably a good start but would depend on how 
spiky your bandwidth graphs are. You might want to lower the speed if 
you tend to have lots of people downloading on a particular day of the 
week for example as the 95th percentile would be much greater than your 
average bandwidth.

If you just look at your bandwidth graphs you will probably get the best 
idea of a suitable figure.