From: utzoo!decvax!ucbvax!teletext
Newsgroups: fa.teletext
Title: LADT
Article-I.D.: ucbvax.7711
Posted: Sat Jun 19 18:53:00 1982
Received: Sun Jun 20 06:07:28 1982

>From lauren@UCLA-Security Sat Jun 19 16:52:55 1982
I've been following LADT for quite some time.  It's actually nothing
more than the same technology used ("carrier") to provide a second
telephone line for a subscriber without adding another pair: multiplexing
another path "above" the "real" one.  It's main problems are that:

a) the equipment at the central office end is fairly expensive
b) the primary talk path is usually degraded since a sharp low pass
   filter is added on the line to separate the two paths.  

This latter problem can be solved through expensive digital carrier
systems, but I don't think Bell is considering that for LADT use.

The *really* big problem is that there is no evidence this service will
cost any less than just adding another "real" phone line.  In fact,
it will most likely cost FAR more since it will be rated as a data
service and requires more specialized equipment.  Current estimates of
its cost to the alarm industry have the alarm people screaming bloody
murder!  The established access charges for the new Bell packet network
are similarly very high and unsuitable for interconnecting "cheap"
videotext networks.

The main advantage of LADT will probably be that it saves telco trouble
by avoiding the need to install more outside plant just to serve
people who need second lines for videotext use.  However, there is no
reason to believe that the service will be priced in such a way
as to be of use to the "consumer" market -- in fact all available
info points in exactly the opposite direction.

--Lauren--

P.S.  One other problem is that increasingly, people's BASIC telephone
service is provided by carrier (especially in dense metro areas) -- in
most cases they're not even aware of it (most people do not notice
the lack of frequency response on the filtered lines, they EXPECT
lousy service!)  If lines are already provided by carrier, then adding
LADT becomes a real problem.  An amazing percentage of new phones in
many areas are already "added" via carrier technology.

--LW--