Path: utzoo!attcan!uunet!nih-csl!lhc!adm!husc6!wuarchive!cs.utexas.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request
From: hayes!tnixon@uunet.uu.net (Toby Nixon)
Newsgroups: comp.dcom.telecom
Subject: Re: Data Lines vs. Voice Lines
Message-ID: <12663@accuvax.nwu.edu>
Date: 26 Sep 90 18:10:01 GMT
Sender: news@accuvax.nwu.edu
Organization: Hayes Microcomputer Products, Norcross, GA
Lines: 33
Approved: Telecom@eecs.nwu.edu
X-Submissions-To: telecom@eecs.nwu.edu
X-Administrivia-To: telecom-request@eecs.nwu.edu
X-Telecom-Digest: Volume 10, Issue 684, Message 2 of 11


> This may be kind of a dumb solution, but why can't the phone company detect
> dead modem carrier and compress it the way they do with silence.  I realize
> that modem silence isn't as simple as people silence, but there must be some
> way to do this.  How about it?

CCITT Study Group XV is currently leading a study (along with Study
Groups VIII and XVII) on compression of fax and modem traffic on
digital trunks.  It would involve demodulation of the signal,
transmission of the original bits, and remodulation when the signal
reaches the other end.  This way, instead of wasting an entire 64kHz
DS0, the network can use only 2.4KHz for a V.22bis connection, 9.6KHz
for V.32, etc -- and pack them into DS0s to save bandwidth.

In the case of fax, the half-duplex nature of the link allows the
network to insert this mechanism at any line turnaround.  Also, the
fax T.30 handshake always indicates what kind of modulation scheme is
going to be used next, so the demodulator/remodulators can track the
protocol and keep the fax machines happy, without introducing any
appreciable delay.  With data, it's a bit trickier, because you don't
know for sure what the modulation scheme is going to be, and in the
case of full-duplex modems there's no natural place (like a
line-turnaround) where the network can switch in this mechanism.

It's an interesting project.


Toby Nixon, Principal Engineer     Fax:    +1-404-441-1213  Telex: 6502670805
Hayes Microcomputer Products Inc.  Voice:  +1-404-449-8791  CIS:    70271,404
Norcross, Georgia, USA             BBS:    +1-404-446-6336  MCI:       TNIXON
                                   Telemail: T.NIXON/HAYES  AT&T:     !tnixon
UUCP:   ...!uunet!hayes!tnixon     Internet:        hayes!tnixon@uunet.uu.net
MHS:    C=US / AD=ATTMAIL / PN=TOBY_L_NIXON / DD=TNIXON