Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!helios!bcm!dimacs.rutgers.edu!rutgers!cbmvax!grr
From: grr@cbmvax.commodore.com (George Robbins)
Newsgroups: comp.dcom.modems
Subject: Re: comp.dcom.modems lexicon
Message-ID: <19660@cbmvax.commodore.com>
Date: 9 Mar 91 01:06:55 GMT
References: <3832.27d4dcf9@hayes.uucp> <1991Mar7.055236.16871@ims.alaska.edu> <19594@cbmvax.commodore.com> <1991Mar8.082523.25819@ims.alaska.edu>
Reply-To: grr@cbmvax.commodore.com (George Robbins)
Organization: Commodore, West Chester, PA
Lines: 51

In article <1991Mar8.082523.25819@ims.alaska.edu> floyd@ims.alaska.edu (Floyd Davidson) writes:
> In article <19594@cbmvax.commodore.com> grr@cbmvax.commodore.com (George Robbins) writes:
> >In article <1991Mar7.055236.16871@ims.alaska.edu> floyd@ims.alaska.edu (Floyd Davidson) writes:
> >
> >It's a misuse when all it refers to is enabling and disabling
> >local echo, while the modem is actually still modulating in
> >the full duplex mode. 
> 
> Not so.  See below.  (By the way, would you be so kind as to define
> "modulating in the full duplex mode".  :-)

In this case of the Bell 103/113/212 modem, something where you've
said "half/duplex or local echo", but are still using separate
transmit/receive carriers instead of a controlled carrier.
> 
> > Remember that things like teletypes didn't
> >really generate a "local echo", it's just the transmitter and
> >receiver were normally wired in series on the same circuit and
> >couldn't the receiver seeing what was trasmitted, unless you
> >manually bridged across it.
> 
> Maybe you will have to blame Ma Bell for that definition.  At
> the other end of that teletype loop there is a modem, though it
> was called a Teletype Terminal Unit at the time, which had two
> modes of operation:  half duplex and full duplex.  In some
> cases, such as the Western Electric 43A1 it had a switch, in
> others it was just wired differently.  In either case the modem
> put out an analog transmit signal and received an analog receive
> signal.  In other words the modem was "duplex" on the analog side
> no matter what was on the digital side.  The fd/hd switch or
> option only affected the digital side.

This is blatent revisionism.  8-) The original teletype circuit was
a telegraph current loop.  The "modems" reflect the adoption of FDM
multiplexing of multiple teletype channels over a single teletype
or telephone circuit and subsequently use of fairly standard modem
technology to extend teletype services though standard telephone
networks.

> (I am sitting six feet from four each eleven foot bays of
> Lenkurt telegraph equipment.  Some pretty old 25D stuff, there
> are about 200 modems, all of which have a half/full duplex
> option.)

Scary!


-- 
George Robbins - now working for,     uucp:   {uunet|pyramid|rutgers}!cbmvax!grr
but no way officially representing:   domain: grr@cbmvax.commodore.com
Commodore, Engineering Department     phone:  215-431-9349 (only by moonlite)