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