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how to calculate internet connection speed per number of users

Posted on 2008-10-02
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What is the best way, for consulting purposes to determine a recommended internet connection speed per number of users ?
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Question by:eschonian
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by:Jerrod_W
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Depends on the nature of the business. If you are constantly going to be uploading and downloading large files, I would recommend at least T-1 for 20+ users.  On the same note, if most of the work is going to be done internally, you wouldn't really "need" more than DSL for 50 or so people.
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by:eschonian
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Well here is the deal, I got 32 + remote users. An exchange server, an ACT web server, and vpn connections all the time. Currently we have a cable connection, a fast one, but everyone is screaming it's so slow ?? Was looking for some sort of calculation to get the boss to upgrade...
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by:Jerrod_W
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Any time you have incoming traffic on a cable connection, its gonna bog down the entire pipeline. With cable the bandwidth comes and goes on one channel. If you get a T-1, the incoming and outgoing traffic will operate independent of one another. I'll try to find some hard numbers to post. In the meanwhile, who is your provider and what plan do you have (if you know)?
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by:eschonian
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I understand all that. I remember when i was getting my MC-something or other. There was a calculation they had in the book for x number of users * this amount of bandwidth per user... etc...
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by:eschonian
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BTW we have Armstrong Cable it's one of those mega big down but only like 100 KB up...
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Mark Wills earned 250 total points
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Generally speaking Cable is not going to cut it. You really have to go to a multi-channel technology. Either the ATM (e.g. T1) or DSL. The advantage of DSL is you can effectively create your own channel splitting through multiple lines for the same price as T1. The Routers / Switches (and not hubs) / Multiplexers look at line demand and balance the load across multiplexed channels. Cable is one of those technologies like a tree - fine if you are close to the trunk, and hideous if you are out amongst the leaves.

Really have to consider the "real life" and not the text book. The text book gives wonderful rates, but you really have to measure in terms of achievable throughputs.

If you are carrying voice as well, then it is going to bog down a bit more, and in some clever systems, will degrade data in favour for voice to ensure quality. Digital data is easier to compress and get a giher data count than the line normally indicates.

Now with Exchange and Web Server then there are added pressures - they are kind of "open" to listen to anything coming their way. and there is a ton of noise out there. If you need some quick improvement, then hive those two facilities off to a hosted service, and alleviate some local load.

As for "office" speed, then need to understand a bit more about your architecture and nature of data demand from various locations. Typically once a connection if up and established, the data volumes for say a Terminal user (ie data entry) is considerably less than that of (potentially) a report user if the report engine is client side. So that is the next thing to consider - what is client side and what is (or could be ) server side. Generally as much server side as possible for data processing so that the "results" are distributed as opposed to the data sources so that the client generates the results.

Then there is concurrency. In a multi-channel technology, with each channel working at peak efficiency, then you have a round-robin type of effect - as each request is fulfilled, it becomes available. Most T-1's are 24 channel - normally with a few resereved for specific functions (such as voice or QOS routing of phone etc). So with say 20 channels available, there is considerable scope to accommodate many times that as concurrent requests - with just a small shift in timing of those requests.

That is basically called oversubscribing - and that is the "magic" number. Most PABX'x for example use a rule of thumb of (limit) 24:1 (ie demand to availability) - which is really a bit high...

What you need to watch is : large file copies over the network, movie / music downloads, "unapproved" internet, office workers sharing / colaborating on that "majic" 20meg powerpoint and so on... Not to mention a few sitting in youtube - it can kill a network

Ideally, you have a baseline - by type of traffic and ideally type of user - then you can start calculating capacity properly. At the moment the only baseline you have is users saying it is too slow - need more specific examples of "when" and "what" is too slow (other than the typical user response "everything").

So, a "rule of thumb" ? is a very, very hard question to answer without a bit more understanding of what you actually do (e.g. publisher selling e-books and videos on line is a lot more that an accounting practice, or say a law firm with very high document management). Have a quick (?) look at : http://www.microsoft.com/technet/archive/itsolutions/ecommerce/maintain/optimize/capplan.mspx?mfr=true  to understand some of the interactions in determining traffic management

For application work, normally start with a very generic calculation like :

Internet Explorers will typically show just under 4KB/s on a download. So let's use that as a baseline. So, say you have 50 concurrent users, then you are needing something like 200KB/sec - so your current capacity is only half of a very broad rule of thumb.

In reality, a typical screen / page based application  is closer to 64kb/s (assuming sub-per second acceptable paint refresh), and can be double that. However, screens like SAP r/3 can be 20kbps because the way in which the screen is painting (that number is re-inforced in  http://whitepapers.zdnet.co.uk/0,1000000651,260499785p,00.htm). All of which still happens to fit in the above calc, and seems to be an acceptable (high-ish) mix of reasonable Internet activity, mail, screens, some downloads, etc...

But what you really have to do is to look at the type and nature of traffic, in terms of size, get an "appropriate" acceptable response time (and 1 second works extremely well for a screen "paint" ), divide and calculate bits or Bytes per second, then multiply out by users and there you have it. You question is kind of asking it back to front, but that's what you get with Comms - constant catch-22.
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