🚀 go-pugleaf

<6d7e5b47@om52.acorn.co.uk> Anthony Frost wrote:

> ...
>  > The whole point about ISDN is that its a digital transmission network
>  > therefore the conventional MODEM-PSTN-MODEM setup is useless because you
>  > don't need to convert to analouge, you just send the straight digital data
>  > stream down the line.
> 
> Nope. A modem is a device to convert the signals from a serial port into
> something the transmission line can handle and back again. An ISDN TA is
> a device to convert the output of a serial port etc....  

A MODEM is a MOduator/DEModulator, i.e. somthing that modulates a signal so
that it can be sent down a transmission line, and demodulates the modulated
signal back to a digital signal.

In an ISDN set up the connection to the BT ISDN socket is already digital,
and the TA simply performs data formatting and timing, and no modulation or
demodulation. In fact the only MODEM in a normal ISDN2 set up is the line
termination box that belongs to BT, and that is a 144Kbps full duplex modem
that puts 2B+D on a normal copper pair. A a modem, it links only to the
exchange a few (not many) miles away, and then te network caries the signals
digitally.

As such an ISDN TA is not actually a modem. However, as you say, it
typically "pretends" to be one in that it obeys basic Hayes command sets and
as far as the computer (Archi, etc) is concerned is simply a very quick

Hayes compatible modem (from an "interface to the computer" point of view).

As said, demon to support ISDN access.

-- 
 _                                  FREE Nokia Orange 5.1, talk60 weekend
(_) _| _ . _  _   Tel 07050 ADRIAN  ** Only via our web pages - Sep96 **
( )(_|(  |(_|| )  Fax  0500 222258  http://www.rhanna.demon.co.uk/aa/ E&OE