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--