Why is broadband advertised as upto 10x dial up?

Discussion in 'Broadband' started by mrlipring, Sep 20, 2003.

  1. mrlipring

    mrlipring Guest

    i regularly got 5.5kb/sec on my old phone line.

    It depends on the modem and the quality of the phone line. 56kbit/second is
    10.28 * faster than the 576kbit that dsl modems on a half meg connection
    will connect at.

    analogue modems are a very old technology. bear in mind that it's possible
    to get way in excess of a half meg connection through your phone line. even
    with a relatively crap line, half meg is doable.
     
    mrlipring, Sep 20, 2003
    #1
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  2. mrlipring

    Jacob Rosse Guest

    Well I get upto about 4k/s on a 56k modem on dialup and upto 64k/s on
    broadband. That's about 15 times the speed which actually fits with my
    download times. This is the first time I have seen advertising claims sell
    a product short.

    Anyway how come a 56k modem never ever reaches anywhere near 7k/s and yet
    broadand often reaches its limit?
     
    Jacob Rosse, Sep 20, 2003
    #2
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  3. You are unlikely to be getting 64k/s via a 512 ADSL link without using some
    form of compression.
    Check your true speed via the speed test here :-
    http://www.adslguide.org.uk/
     
    Paul Woodsford, Sep 20, 2003
    #3
  4. mrlipring

    Chris Jones Guest

    Well I get upto about 4k/s on a 56k modem on dialup and upto 64k/s on
    I agree - with my 56k, I used to get about 4k/sec max, but broadband gets a
    steady 60 kb/sec. It really is 15 times the speed, not "up to 10 times".
     
    Chris Jones, Sep 20, 2003
    #4
  5. mrlipring

    Killa Guest

    Modem connections support compression so I was quite used to getting
    downloads of text newsgroups at anywhere between 7 and 9 KB/s on a
    dialup. In that context to say ADSL is 10 times faster is not selling
    the product short - in fact they should only be saying up to 7 times
    faster for downloading text.
    Maybe you had a crap modem - I've regularly max'ed out a 115.2k serial
    port with a V.90 modem with compression enabled. In fact with a modem
    with a 230.4k serial port I've gone over 170kbps on a V.90 modem - not
    often, but with a download that is compressible, it can happen.
     
    Killa, Sep 20, 2003
    #5
  6. I agree! Exactly my experiences.
     
    Brian McIlwrath, Sep 20, 2003
    #6
  7. mrlipring

    Draxen Guest

    Analogue modems can get that "fast" if you're downloading something easily
    compressible, ie text. But most of us all download already compressed files,
    zips, jpegs, mp3s, divx video so few of us ever enjoyed the dubious
    pleasures of on-the-fly modem compression to it's full extent.

    Although they work over the same lines I believe analogue modems have to
    operate in a "noisier" medium, there's less signal to noise so error
    correction kicks in and that incurs an overhead in your available bandwidth.
    That was one of the big selling points of ISDN, it was a pure digital medium
    so you got max possible bandwidth.

    I'm not sure if xDSL counts as a digital transport though... We do still use
    modems on the services so that suggests to me there is still some form of
    analogue <> digital conversion going on. If anyone knows I'd be interested
    in learning if DSL is "pure" digital.
     
    Draxen, Sep 21, 2003
    #7
  8. Hi,
    I'm no expert on this, but as I uderstand it ADSL is not pure digital.
    The DSLAM in the exchange is a special kind of modem, just like your normal
    analogue modem. The signal for ADSL is split into a number of channels each
    occupying a particular frequency range. The channels occur at frequencies
    between about 300 KHz and 2.2 MHz (I'm not sure of the exact figures, but
    its about that).

    So whereas with a normal modem, you only have a single channel, and it
    transfers data sequentially, with ADSL, the multiple channels allow you to
    transfer many streams of data in parallel.

    However, all of this data is encoded into analogue signals for transmission
    accross the phone line using Frequency Modulation. So it's a bit like
    connecting 10 standard modems to the phone line, but with each one operating
    in its own frequency band, then distributing the data accross the modems.
     
    Martin Cooper, Sep 21, 2003
    #8
  9. ^^^^^^^^^^^^
    you mean
    Data-rate=Bandwidth*(log2(1+signal-to-noise ratio))??
    :)
     
    robert w hall, Sep 21, 2003
    #9
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