Why doesn't dialup modem maintain high initial download speed?

Discussion in 'Computer Support' started by Doc, Nov 30, 2007.

  1. Doc

    Doc Guest

    I find that when downloading a file, the initial kbps speed shown
    typically starts out much faster than it ends up. It might show a
    speed of 15 or 20 kbps and then eventually winds down to typically
    around 5 kbps.

    During those initial seconds when the speed is higher, it might d/l
    300 or 400 kb really quick, at a much faster pace than it does for the
    rest of the download.

    It seems that the modem is capable of taking the data much more
    rapidly than the speed at which it maintains the download, why doesn't
    it maintain the higher speed?
     
    Doc, Nov 30, 2007
    #1
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  2. Doc

    Pennywise Guest

    This happens to DSL as well, it's not true download speeds but the
    math the program uses (browser, download manager...) - best I can
    explain it.
    Cause the speed/time is correct, it's possible (if line quality is
    good) to increase speed to maintain 15 or 20 kbps when it drops, if
    conditions allow.

    Make sure you have hardware flow control enabled and it's not a
    Winmodem.

    control panel / modem, properties; Query the modem and see what AT
    commands are being used. If %E1 or %E2 aren't shown, you can play with
    them and see what happens.

    In the modem properties is a place to add additional AT commands, this
    is where you would put %E1 or %E2

    A modem will fall back if line quality goes bad, but will fall forward
    after a time if it's able. that's what the %E commands allow.

    "Command Description
    %E0 Disable line quality monitor and auto retrain.
    %E1 Enable line quality monitor and auto retrain.
    %E2 Enable line quality monitor and fallback/fall forward."
    http://readthetruth.com/modems.htm

    They can also be entered manually
    http://support.microsoft.com/kb/q124890/
     
    Pennywise, Nov 30, 2007
    #2
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  3. Doc

    Plato Guest

    That is due to the server the webpage or file is on. You cant do
    anything about that, except download from another source.
     
    Plato, Nov 30, 2007
    #3
  4. Doc

    chuckcar Guest

    You might check to see if there is a bottleneck on the "computer" side
    as opposed to the modem or the IP's side. try running system monitor
    (accessories/system tools) and adding (from edit/add menu)
    kernel/processor usage, file system/bytes read per second, file
    system/bytes written/second and finally memory manager/unused physical
    memory. If the first stays near 100%, you have too many programs running
    if the second or third are low or jump up and down a lot, you have a
    slow hard drive or one that is being used by something else. If the last
    is 0 or close to it, you need more ram or need to not run as many
    programs.
     
    chuckcar, Nov 30, 2007
    #4
  5. Doc

    PeeCee Guest



    Doc

    This is likely the affect of 'caching' by your Browser eg Firefox.

    5K/s is generally regarded as a near top speed for a dial up connection.
    What I suspect you are seeing is your Browser starting the download
    immediately you click the downlad button.
    Then in the time taken to navigate to the download folder of choice and
    clicking the last 'save' button the dial up connection will have downloaded
    several Kb of data.

    The speed that is then show in the progress window when you click the final
    button is the speed at which data is written to the file from the local
    cache ie hard drive speeds. Then as the cache is emptied and the data
    dribbles in through the dial up connection the speed calculator in the
    download progress window will adjust the speed displayed to show the average
    speed since the 'save' button was clicked.

    So if it takes 4 seconds for you to click the final save button you wil have
    roughly 20K of data cached and the speed reading will be 20K/s.
    At the next reading the dial up connection will have added another 5K so a
    total of 25K / 2 sec will give a speed of 12.5K/s, after 3 seconds it will
    average 10K/sec, 4 seconds 8.75K/s etc....
    I've taken intervals of 1 second, no doubt the actual intervals are a lot
    different, but you get the idea.

    Best
    Paul.
     
    PeeCee, Dec 2, 2007
    #5
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