[sdiy] Information Content of Signals

[John L Marshall]

To make matters worse, the teen Bells (used to be baby Bells but they are
now awkward and arrogant.) routinely split a DS0 into two telephone lines.
One subscriber may have a full DS0, allowing modems to work close to full
speed. Another subscriber, paying the same rate, shares a DS0 and the best
the modem can do is half speed.

Take care,
John
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Pacific Northwest Synthesizer Meeting
August 9, 2003
www.sound-photo.com
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----- Original Message ----- 
From: "Magnus Danielson" <cfmd at swipnet.se>
To: <madhun2001 at yahoo.com>
Cc: <grichter at asapnet.net>; <synth-diy at dropmix.xs4all.nl>
Sent: Saturday, May 17, 2003 7:07 AM
Subject: Re: [sdiy] Information Content of Signals


> From: Tim Ressel <madhun2001 at yahoo.com>
> Subject: Re: [sdiy] Information Content of Signals
> Date: Sat, 17 May 2003 04:26:56 -0700 (PDT)
>
> > I have also wondered about this, but from a different
> > direction. I want to know how they can get 53kbps on a
> > phone line with 3khz bandwidth. Oh I know they use
> > this funky phase-constellation thingie.
> >
> > I have heard that they stopped at 53kbps not because
> > of the limitation of phiscics, but because the FCC set
> > a limit there.
>
> This is not quite true. The 56k modems is very funky, they try to make the
> A/Ds use the bits efficiently, but you can only get it as far as you like.
> However, due to peculiarities in the DS1 system you may not even know how
7 of
> the 8 bits behaves, since you may end up getting the 8th bit robbed, and
you
> need the last bit for balance, and then you must rob the 7th bit for
balance
> and then only 6 bits is free choice, and this happends with 1/24th of a
chance
> and then on every 6th sample. Don't come and say transparent
communications!!!
>
> The 56k modems had more design issues than people originally thought.
Brrr!
>
> Cheers,
> Magnus