LinuxSA Mailing list archives

  From: Robyn Manning <robynman@dove.net.au>
  To  : Daryl Tester <dt@picknowl.com.au>
        <linuxsa@linuxsa.org.au>
  Date: Sun, 26 Nov 2000 12:31:27 +1030

Re: ADSL Enabled Exchange Areas: Updated 20/11/2000

Hi guys

Ok now you've bamboozled me.

I have a 56k modem is that 56k bits or 56k baud?

Bits / second is ok but then what is baud?

Robyn

Daryl Tester wrote:
> 
> Jake Hawkes wrote:
> 
> > the way I remember, is that 2400 baud means 2400 symbols a second[1]. A
> > symbol may represent more than 1 bit, and with no "signal trickery", one
> > baud is on bit[2].
> 
> 2 out of 2 so far.
> 
> > Then you get very clever "signal tricksters" doing some hoopy maths, and
> > you get constellation patterns, representing a bunch of bits, the more
> > clever the constellation, the more bits per baud[3].
> 
> 3 out of 3 ... This is why you've graduated and become an
> international jet-setter, and I haven't.  :-)
> 
> QAM is "Quad Amplitude Modulation" (from memory)(and giving your
> constellation patterns mentioned above), and involves altering
> the signal strength to four discrete levels, giving you an
> additional two bits per baud (2 ^ 2 = 4).  From then on, I get
> rusty, as I haven't kept up with modem standards.
> 
> > Then, I believe more trickyness was brought in to do more clever
> > things.
> 
> Basically, to pack more bits per baud, but at the expense of
> frailty of data (hence the later schemes introduce error
> correction, and retraining), because the signal becomes
> really susceptible to phase variations and distortion that
> the human ear/brain combo is _really adept_ at filtering
> out.  The problem is worse with long cable runs and corroded
> connections, which unfortunately our country bretheren suffer
> from worse than city folk, which is why they have more problems.
> 
> But the upshot is, Telstra say "lines are only guaranteed for
> 2400 baud", and people say "2400 BPS in this day and age, that's
> ludicrous", and it degenerates from there.  And is Greg Lehey
> pointed out, any large organisation suffers from left hand/right
> hand syndrome, so once any technical spec. has been webified into
> the latest trendy font, technical accuracy goes out the window[1].
> Telecom used to state "2400 baud"; I've no reason to believe that
> Telstra state it differently.
> 
> > theressomethignwrongwithmyspacebar
> 
> ATLEASTYOURCAPSLOCKKEYISOK.
> 
> --
> Regards,
>   Daryl Tester,  Software Wrangler and Bit Herder, IOCANE Pty. Ltd.
> 
> "Who knows what men lurk in the heart of eval?"
> 
> [1] Not that I claim to be 100% accurate - my grey cells decay at
>     a faster rate than I am able to replace them.
> 
> --
> LinuxSA WWW: http://www.linuxsa.org.au/  IRC: #linuxsa on irc.linux.org.au
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