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The following is an archive of a post made to our 'vox-tech mailing list' by one of its subscribers.

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Re: [vox-tech] Modem question . . . I think it is possible
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Re: [vox-tech] Modem question . . . I think it is possible



I don't think that the solution is practical.  I was more concerned with
whether it was in fact possible.  Of course, the NAT and PPP method is
superior but I was curious as if a modem could actually be split as asked.
It was more of an academic excercise and challenge then anything else.

On Fri, 20 Sep 2002, Harry Stangel wrote:

> Why do you need 2 channels?  Why not use one host as a 'master',
> running NAT and PPP out its modem, and the other host as a 'slave'
> connected to the 'master' host through their ethernet ports?
>
> Harry
>
> ----- Original Message -----
> From: "Chris McKenzie" <cjmckenzie@ucdavis.edu>
> To: <vox-tech@lists.lugod.org>
> Sent: Friday, September 20, 2002 2:32 PM
> Subject: [vox-tech] Modem question . . . I think it is possible
>
>
> > I know the post is a few days old but I was intrigued with the idea.
> > modems capable of the v.34 standard have something called an auxiliary
> > channel by which it can exchange information on such things as line
> > quality.  It can code using nonlinear, precoding, and 16-trellis along
> > with most modern being able to do 32 and 64 state trellis depending of
> > course on what type of bit (dibit etc) you want to transmit at.  Here is
> > the trick: Because of the ability to use such things as assymetrical
> > transmission and the use of trellis coding, and echo cancellation, each
> > modem will have an idea of sender and reciever.  For the first modem, the
> > other modem will be a sender and the other end of the ppp will be a
> > sender.  This essentially sets what could be a master slave model in order
> > to do correct splitting, with hopefully little interference (via the
> > trellis encoding).  Here is how it would work:
> >
> > Computer 1 is master
> > Computer 2 is slave
> >
> > ppp ISP is ISP
> >
> > Initiate the connection with the master to ISP and send a request for
> > 16-state trellis encoding at 14400 bps.  Ask for 16-state send and
> > 16-state receive.  Put the master on 32-state trellis recieve
> > without confirmation via the auxiliary making each other
> > baud recieved as null or noise.
> >
> > Place slave in 16-state trellis before connecting.  Because of the
> > trellis, it will interpret the data being sent as noise and adjust phase
> > correctly to the nulls.
> >
> > When it sends out a request, the ISP with 16 state trellis which is synced
> > with the master will interpret it as noise and ignore it.  However, the
> > master will take the signals in as extra data.  As long as the master can
> > split every other bit and maintain parity and whatever, it has now set up
> > two channels, one 16 bit with the other laptop and one 16 bit with the
> > ISP.  Each other end will take the 'excess' data as noise and ignore it
> > because it is not in sync.  You now have two linked connections over one
> > line.
> >
> > Truly, the slave still goes to the master which in turns goes to the ISP,
> > however, this would be a sane operation of 14400 bps and a technical modem
> > split.  Implementing it however, is another thing . . . shouldn't be that
> > difficult but also shouldn't be that worthwhile.  Anyway, that is all for
> > now.
> >
> >
> > Sincerely,
> > Christopher J. McKenzie
> >
> > cjm@ucdavis.edu
> > mckenzie@cs.ucdavis.edu
> > H: +1 818.9917724
> > C: +1 818.4293772
> > 1815 Mesa Ridge Ave
> > Westlake Village, CA 91362
> >
> > _______________________________________________
> > vox-tech mailing list
> > vox-tech@lists.lugod.org
> > http://lists.lugod.org/mailman/listinfo/vox-tech
>
> _______________________________________________
> vox-tech mailing list
> vox-tech@lists.lugod.org
> http://lists.lugod.org/mailman/listinfo/vox-tech
>

Sincerely,
	Christopher J. McKenzie

	cjm@ucdavis.edu
	mckenzie@cs.ucdavis.edu
	H: +1 818.9917724
	C: +1 818.4293772
	1815 Mesa Ridge Ave
	Westlake Village, CA 91362

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