How is bandwidth calculated?

Yeah, I have heard somewhere that they take average speed guranteed to customer and then times it # of seconds per month or something like that. That doesn't sound too good, so I was wondering how its really done? Or do they just guesstimate?

Also, can anyone explain to me by they charge by the 95%? Thanks.

Well that depends on the particular ISP/IPP.

Most ISPs do either burstable or fixed limit. Fixed limit is simple, the router only gives you the kbps you pay for. On burstable, they usually give you more, say a full T1, and you pay based on the 95th percentile (MattWil, this should also answer your question). That means they look at the router logs and see how much you used the connect over the entire month. They throw out the top 5% of usage, and the top after that is how much you pay.

Now, with IPPs its a little different. MANY IPPs are lazy and use server logs corolated to file sizes to determine outbound bandwidth. As its almost impossible to accurately messure imbound bandwidth, most IPPs disregard it. Internet Background Noise is a big reason for this. The more acurate way to measure bandwidth for IPPs is router logs. But, here's the problem with that. If you're on a shared enviornent your IPP could be using domain based virtual hosting on a single IP. Then its impossible to distinguish between the different clients on the same IP. If the IPP gives you your own IP, though, they can use router logs if they want to be accurate.

Any ISP/IPP worth their salt should tell you exactly how they calculate their bandwidth. It may be burried in their docs somewhere, look but if you can't find it ask. If they won't tell, I'd take my business elsewhere.

Hope this helps.

I know how they measure used traffic, my question was/is how do they calculate allowed traffic. Like you go buy some hosting right, and there you see bandwidth 100gb/month. Quesion is - what is that figure based on?

Oh, my bad.

Well, that again depends on who exactly you are dealing with. I spent quite some time researching starting an IPP and I here's how I always calculated it. Take the how much you pay for a certain ammount of bandwidth then pad the price up a bit. Say if I have a T3 (45 mbps) for $28,000 a month (picked for ease of math). Thats roughly 14,000 gigabytes a month if my math is right. So when you divide it out, thats $2 a gig. So I'd charge $2.50 to $3.00 a gig. So on a $30 a month plan, I'd give about 10 gig.

Problem with this method is that it doesn't exactly lead to competitive prices. So many IPPs do do some statistical analysis and see that their average customer uses about 60% of what they purchase and adjust their figures accordingly. They also tend to have high overage charges. I've seen some with a $2 charge per 100 mB overage, or $20 a gB. The highest I can recall is $2 per 50 mB overage, ouch!

If you want to look at ISPs, don't get me started. The phone system is a circuit switched network. That means that data travels over it at the speed of light. If you have a friend on the other side of the country, do a direct modem connect to them sometime. Try to ping them over that, then compare it to when you do the same on the Internet. You'll be surprised by the results. ISPs terribly oversell their bandwidth, particularly dialups. The reason you have a 250 ping on a modem and a 50 on DSL is that you get held up at the routers. After all, both use the same medium, copper phone line, just DSL uses more frequencies, thus more bandwidth.

Sweet, thx for the info. Actually it is pretty close to what I have figures out, but always good to know someone did a research and came up with the same results. thx again.
P.S. I think you're overesteemating price of t3 about 10 times I think you can get it for $3000/month, and for $30k/month you could probably get (if youre very lucky) oc-3

Well, I picked that figure for ease of math. Anyways, the price of bandwidth varies depending on where you are. Where I live its $1800/mth for a T-1, but 50 miles from here its $400/mth.

Where geographically is a T3 $3000/mth and an OC-3 $30k? I might move.

Well, I heard from a frend of a friend that he could get it in cali. 'm not sure about exact location, and yeah I would've moved either (probably). I have a pretty good deal right now though, cable with 1.5-1.8mbits down, but only 400mbits up (200-250kbytes && 50 kbytes)