Bandwidth Maths - Dedicated Server

I am bit lazy/busy, so wanted to just ask a simple quick fire question...
A lot of web hosting companies offer Bandwidth deals when you buy a package off them.  You pay a monthly fee and away you go.

Let say we bought a Windows 2003 IIS Server, a P4 2.4Ghz Celeron it comes with 1 IP Address and 1800GB/mo. Transfer (so the advert says).  The main idea is to run a small amount of IIS and large amount of FTP securly, maybe VPN to lots of connection points.

We have 400 computers connected at 512KB ADSL (in UK), pulling 10Mb Media files off this online (future) host.  Every week, the 10Mb file changes and the 400 computers have to re-download this file.  So this can generate 400 FTP connections to the server and I suspect there will be a limit of simulatanous connections, don't know at this stage.

My question:-

How much Bandwidth per month (or per week) do it need?

Would each of the 400 computers be maxed out at 512Kb/sec?  

How long do you think a transfer would take?  Or how long do you think it would take to send to 400 stations?

Formulas would be great.


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1800GB/mo would be more than enough data transfer.  Nevertheless, I would suggest that you change your approach a little.  In other words, why have each computer download the file from the remote server?  Why not just download it once to a network location and have the 400 computers copy it from there?  Also, assuming that you are able to make 400 simultaneous FTP connections (doubtful), 400 computers trying to download a 10MB file at the same time on a shared 512kbps connection would be terribly inefficient.  How long would it take?  Even if you were getting a full 512kbps, it would take hours.
DaveRowlandAuthor Commented:
Humeniuk.. thanks.. but I cannot change to that concept.  Currently we have 400 branches throughout the UK all pulling off this data, we wish to change it to a web solution as it is frame-relay to a server at the moment.

What I would like to find out is how much bandwidth I really need and try and get some figures together to promote a web solution versus an internal framerelay solution.  
Alright, that's not so bad then if they're in different locations.  If they were in the same office, you'd be in trouble :)

Data transfer really depends on usage and it's hard to get a handle on how much you would need based on what you've said - "a small amount of IIS and large amount of FTP securly, maybe VPN to lots of connection points" can mean just about anything.  However, 1800GB is quite a bit.  The FTP transfers you've mentioned would use only a very small part of that.  If that's the largest part of your traffic requirements, 1800GB/mo is overkill.
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DaveRowlandAuthor Commented:
hi, yes I guessed that was overkill, but that was just a random american host.  I am looking for some fugures / formulas, I wrote that question at 4am as I couldn't sleep.  Have a look at my other questions for more info on what I am doing.
DaveRowlandAuthor Commented:
Anyone got a bandwidth formula ?

to recap:-

10MB file x 400 connections to send the same file to would =4,000MB per update

A standard ADSL connection is 512Kbit/sec,,, so how long does it take to transfer 10MB file over ADSL?

so   'answer'  *  400 connections = time taken

Bandwidth, ie 30Gb/mo included type deals, are they normally recorded in MegaBits or MegaBytes?
Am I right to say : 30,000MB per month bandwidth =  7.5 * 4000MB, (7.5 updates possible of 4000MB total.)

How many does a generic IIS FTP server running on a webhost, how many connections can they really handle ?  25-50 at a time?  

I would like someone to fill the blanks and just check over this..

1:  How fast would it take to transfer 10Mb?  (when the server is connected to over 5 FTP connections(in a good host))
2: Will a server start failing connections when it nears 25-50 at a time?  what would be the limit on a top 100mbit connection on a good host
3:  Do hosts honour the Bandwidth agreements?  30GB sounds a lot but
4:  How long do you think it will take to update my 400 connections of 10mb via FTP, this would total 4,000MB of datatransfer?  The other side connections are multiple ADSL 512kbit modems.  Any formula?

Any one on here run an Dedicated ISP or a  You should know

I've never seen formulas used for this sort of thing.  Bandwidth fluctuates based on a number of factors including network traffic, internet traffic, etc.  which are largely unpredictable (beyond knowing that the daytime is busier than the night time).  Transfer times can also vary by file size, etc.  Different transfer methods work at different speeds, too.  HTTP transfer (using TCP) has more overhead and so is slower than FTP.  So don't look for absolute answers to these questions, because there aren't any.

To take a look at what I'm talking about, you can do a download speed test at the Broadband Reports website (see  I'm using a 3Mbit cable connection and I'll do three tests about 20 seconds apart.  The results:

Loaded 620871 Bytes in 2.01999998093 seconds
2458.9Kbps is your thruput

Loaded 10256 Bytes in 0.0700001716614 seconds
1172.11Kbps is your thruput

Loaded 334175 Bytes in 1.29999995232 seconds
2056.46Kbps is your thruput

You should also look at this info on how to test the speed of a host -

"The ultimate [speed] test is the download speed test. To do that you should ask the host for a test download file. That's about the best way to judge speed. The goal is to find a host that has the capability of sending at least a few hundred kBytes/second. If you're on a dial-up connection you'll not be able to test this yourself. Read on and you'll find a solution to this particular problem.

Because the host might try to fool you by giving you a test file located on a fast, almost empty server, it might be even better if you'd contact a current customer and ask him/her to post a test file on his account.

The file should be big enough to allow you to see the speed stability over time. A 10-15 Mb file should be enough. Another important aspect is the time of the test. The best times are rush hours actually, when the server are busy. These are are in the morning when most people read their emails (8am on the east coast of the US) and dinner time. Take care to compensate for time differences as not all servers host American websites. "

<< 1:  How fast would it take to transfer 10Mb? >>

10MB x 1024 = 10,240KB = 81,920kbits  (400 downloads = 32,768,000kbits)
Theoretically, it should take 150 seconds to download this file on a 512kbps connection assuming you get a sustained 512kbs throughout the dowload time (you won't) and there is no interference anywhere on the network and the internet isn't congested.

For the sake of comparison, my 3Mbps connection (3072kbps) should download the file in 26.67 seconds, but at an average download rate equal to the three tests above, it would take 33.3 seconds / 69.9 seconds / 39.8 seconds.

<< 2: Will a server start failing connections when it nears 25-50 at a time?  >>

You can throttle the bandwidth or simultaneous connections that an IIS server can make or you can set them to 'unlimited'.  Clearly there's no such thing as unlimited bandwidth or connections.  To some degree, I'm sure it's limited by total bandwidth available, but I don't know what the IIS limit is and couldn't find any reference to it on the Microsoft site.  In general, I think it would be advisable to stagger the download times rather than to try to make 400 simultaneous connections.

<< 3:  Do hosts honour the Bandwidth agreements?  >>
Good ones do.  I don't see the benefit to them of trying to cheat you of a few GB.  Bandwidth should be monitored and you should be able to check it on on ongoing basis.

<< 4:  How long do you think it will take to update my 400 connections of 10mb via FTP, this would total 4,000MB of datatransfer?  The other side connections are multiple ADSL 512kbit modems.  Any formula?  >>
Again, there are no absolutes.  Assuming 400 simultaneous connections (which I doubt is possible) and assuming that each of your ADSL connections was getting a full 512kbps and your server was operating at 100Mbps (and there was no other server traffic and no internet congestion), the server would be capable of 102,400kbps (1024 x 100Mbps) transfer, which is  half the collective 204,800kbps bandwidth of the 400 x 512kbps connections, it would take 320 seconds to transfer the total 32,768,000kbits.  Of course, you'll never realize these ideal conditions and this doesn't factor in the FTP packet ratio because I'm not sure what it is - I just know that it varies based on a few factors, including packet size (ie. assuming 40bytes per packet, smaller packets mean much more overhead than larger packets).

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DaveRowlandAuthor Commented:
Thanks for that
It has helped me work out the answers
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