From: utzoo!decvax!ucbvax!teletext Newsgroups: fa.teletext Title: LADT Article-I.D.: ucbvax.7713 Posted: Sun Jun 20 06:50:21 1982 Received: Tue Jun 22 01:17:12 1982 >From SIRBU@MIT-MC Sun Jun 20 06:48:38 1982 I disagree with Lauren's evaluation of LADT technology. In the first place, if it were really the same as the techniques used by AT&T to provide second phone lines, than clearly it is less expensive than a real second line. That establishes a bound on the cost; it's less than that of a second phone. However, LADT is really cheaper than FDM loop carrier. For one thing, when multiplexing two voice channels you need a reasonably linear mixer; for LADT, all you have is an FSK device that's operating above the voice band. That's easier to build. Indeed, the subscriber device is no more complicated than a 300 baud modem. Note also, that LADT offers an RS-232 interface to the subscriber, thus saving the cost of the modem. At the central office end, I agree that you need a rather expensive packet switch. The key question is, "Over how many subscribers is the cost of that switch distributed?" AT&T is expecting 60,000 for its Coral Gables trial. That will amortize a lot of capital. Finally, you note that there is increasing use of loop carrier for new phones. At the present time, roughly 70% of all subscriber loops are unloaded copper. The new subscriber loops use primarily digital carrier (T1). It's not to hard to imagine using LADT back to the T1 multiplexer and then multiplexing several subscriber's data channels over one 56 kbps voice line back to the CO. The use of subscriber loop carrier does not inhibit this technology. Marvin Sirbu