🚀 go-pugleaf

>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