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From: zweig@cs.uiuc.edu (Johnny Zweig)
Newsgroups: comp.dcom.telecom
Subject: Re: A Few ISDN Questions
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Date: 28 Feb 90 20:43:15 GMT
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casbs@csli.stanford.edu (Lynn Gale) writes:

>Will ISDN incorporate Fax functions?  RS-232?  What else besides voice?

ISDN is lower level than Fax -- it's higher level than rs-232; think
of it about the level of complexity of ethernet.  Basically a way of
moving bits.  Fax will certainly be one of the first available
applications since that involves moving many bits quickly.

>Is it known at this point in time what medium ISDN will run on?  In
>particular, what number of wire pairs are necessary and do they need
>to be shielded or unshielded?  (Thinking about wiring decisions with
>the future in mind...)
>If it takes, say, 4 pairs, what function(s) do each of the pairs
>perform?

It's complicated.  There are a couple of "reference points" which
serve different points of your house/business.  At the U-reference
point which is where the phone-company's wires/fibers/whatever come
into the building there are standards for 2- and 4-wires and for fiber
(the 2-wire one would be most common for ISDN to your house since most
houses only have one twisted pair in).

At the S- and T-reference points, there are 4 wires used for balanced
data transmission in each direction, with a dc-imbalance between the
average voltages in each direction, so you can tap the centers of the
send and receive transformers to get DC to power the equipment ==
extremely hip.  Unshielded twisted pair pairs (i.e.  ordinary telco
4-color cable) should be hip for that, at least according to this book
I have.


Johnny  -- not-an-Electrical-Engineer-but-I-play-one-on-the-Net