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I need to pick the brain of someone who knows about networks, specifically how the web functions over broadband.

With dial-up, when working out how long a web page would take to download, you took two factors into account for each file that needed to be downloaded - a fraction of a second for the computer to connect to the server (usually estimated at 0.5 seconds for these purposes), and then a number of seconds to download the file itself. So a 100k file might take 0.5 second for the connection and 30 seconds to download, meaning that file added 30.5 seconds to the load time for the site.

With broadband the 30 seconds to download the file is massively reduced. My question, though, is how long does the connection part of the process take? Is it the same (0.5 seconds per file), or is it comparably reduced, or is it so tiny as to be virtually unmeasurable?

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    How high is up?
    – John Saunders
    Jul 31, 2009 at 10:37
  • Moving to broadband from modem should reduce latency as it removes the digital-analogue conversion in the modem (and the corresponding shift back). You will see this with a simple ping. The delay in download should be significant but difficult to predict as broadband services have a wide range of download rates, are often contended and, at the higher end, the available bandwidth at the user end may exceed the per-download bandwidth of the server.
    – mas
    Jul 31, 2009 at 12:43
  • Why does it matter? This is an important question to answer in your question. In fact, I think there should be a section in the FAQ or on the "Ask a Question" page. In your particular case, are you trying to put an estimate on your web page for a warning to users who are about to download a file, or are you just curious about upgrading to broadband?
    – Ernie
    Jul 31, 2009 at 16:17
  • Double half of its speed!
    – William Hilsum
    Jul 31, 2009 at 21:42

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What you are talking about is latency vs bandwidth. "It's the Latency, Stupid." is an interesting read that talks about this in detail. mh is right that there are a lot of factors. But it general, dial-up modems and satellites have higher latency than most 'broadband' connections. So this could be noticeable for people browsing the web on a dial-up modem.

When you say "So a 100k file might take 0.5 second for the connection and 30 seconds to download, meaning that file added 30.5 seconds to the load time for the site.", that is not entirely accurate. With TCP, the transmission control, acknowledgments are sent to the other end of the connection to confirm that the data was received. The rate at which these are sent is the TCP window size. If the window size is small, and there is high latency, the full bandwidth is not used. So latency can actually effect large file transfers as well. This TCP Tuning Wikipedia article actually explains it well I think. You can read more about this here too.

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  • Small Disclaimer: I don't consider myself a TCP expert, so there might be inaccuracies, let me know ant I will update my post :-)
    – Kyle Brandt
    Jul 31, 2009 at 12:23
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When you say broadband, you are talking about a host of different technologies. Also, there are a lot of different ways a computer is connected to the Internet today. It may be WiMAX, 3G, WiFi, ADSL, Cable, Fibre and what nots. A wired link is usually faster and has less latency than a wireless link. You may actually wish to revisit some of your assumptions made for the estimation.

E.g.

If your users are connected via a home WiFI-ADSL router, a lot also depends on the speed of the router. If the router has a slow processor, it will have problems pushing maximum bandwidth and also higher latency as it takes longer to process the queues.

But for the purpose of your estimation, you seem to be trying to factor it in as a fixed overhead cost. This may be set as a variable K, which can be changed depending on the kinds of connection that you assume it to be.

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  • Disclaimer: Not a networking expert but working on some WiMAX stuff atm.
    – sybreon
    Jul 31, 2009 at 13:31
  • In other words: give up on your estimation of how long it will take to download your file through a broadband connection. ;)
    – Ernie
    Jul 31, 2009 at 16:13
  • Well, if you insist. :)
    – sybreon
    Jul 31, 2009 at 17:15
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How long is a piece of string?

Seriously, there are so many factors that can affect web speed, including - but by no means limited to - number of hops between nodes, router performance, compression overhead, concurrency, server performance and load, client performance, presence or absence of java and/or flash, and so on and so on and so on that there is really no such thing as a one-size-fits-all measurement.

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On just the broadband bit, forgetting the general internet overheads and home network connection bits, the variability you will see in broadband speeds will be due to the actions of other customers of your broadband supplier.

You may have bought 8MB/s of ADSL connected network bandwidth, which you then find out has a max speed of 6MB/s because of your distance from the telephone exchange. However, at the exchange, perhaps 200 broadband connections are grouped together, over a 32MB/s link to your providers backbone.

If, 4 or 5 other broadband users are downloading large files at the same time, your bandwidth will be reduced. You have no control over this. Its most likely to happen in the evenings, but i can, and does happen at random times. This is called contention. Contention ratios of 50x or 100x are quite common. 50x is better.

With Cable modem access, contention happens on the local loop as well.

However, as a rough guide, have a look at a broadband speed tester, and that will give you as good an answer as any for your data transfer times.

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