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

[Harry Stangel]

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
>
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