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ISDN boxes outside

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Marco Moock

Oct 8, 2023, 6:40:24 PM10/8/23
That article mentions ISDN boxes outside of the house in the US.

I am from Germany and I don't know about them. Here ISDN terminators
(called NTBA) are mounted inside. They had the 2-wire Uk0 Bus at the
carriers side and the S0 bus on the customers side and were connected
to the TAE telephone socket, so no technician needed to come home when
ISDN was ordered.

What are exactly these ISDN boxes referred in the article?
What came out at the customers side?
An S0 bus or something else?

kind regards

Michael Trew

Oct 9, 2023, 9:11:16 AM10/9/23
I'm not quite sure. Most telco's have their newer plastic demarc box on
the outside of the home here. I've still seen older homes with the
2-wire solid core non-twisted pair (looks like a lamp cord) going inside
to the old ceramic fused demarc, which is grounded to the cold water
line, and mounted to a wooden stud in the cellar ceiling.

I coerced the AT&T tech to put the new plastic demarc box for the phone
and ADSL into the cellar of my home, instead of drilling an unsightly
plastic box into the exterior brick of my home. They put a new twisted
drop line in, and I replaced the interior wiring, with a whole-home ADSL
filter. Lucky for me, I have a clear phone line in all weather.

Fred Goldstein

Oct 9, 2023, 3:34:33 PM10/9/23
On 10/8/2023 8:14 AM, Marco Moock wrote:
Honestly, I don't recognize those boxes either, and I was very deeply involved in US ISDN.

In the US, the BRI handoff was at the U interface, not S/T, and the S/T bus was almost never used, except perhaps in some office Centrex arrangements. In most cases there was no physical NT1 either; the CPE typically just implemented the US 2B1Q format U interface.

Fred R. Goldstein      k1io    fred "at"
 Interisle Consulting Group 
 +1 617 795 2701


Oct 10, 2023, 8:13:16 PM10/10/23
On 10/8/23 8:14 AM, Marco Moock wrote:

> What are exactly these ISDN boxes referred in the article?

You seem to be describing a NT1, which converts from the 1-pair BRI from
the telco to the 2-part, multipoint, ST bus. The phones and routers were
on that ST bus.

But here, many ISDN installations used a single box with both parts
within it; it terminated the BRI, and also provided a router and/or POTS

The outside box might have been a NT1, or more likely the overvoltage
"protecter" on any line entering a building. It shunts a lightning
spike, etc. to ground.

Unlike the EU, US ISDN was an overall failure. It got use in several
specific markets; it was popular for radio broadcasters on remote
broadcasts, offering dual dependable, noise-free circuits without
expensive point-to-point leased circuits. Classical music stations loved

Other users include large Centrex accounts. ('Centrex' was a PBX-like
telco offering, offering 4-digit dialing within the company, and each
phone has its own 10 digit number. The switching was done by the Central
Office switch.) ISDN Centrex allowed phones with multiple-line buttons,
and other features. Centrex was very popular with US Government offices
in the DC region, because many agencies are sprawled over multiple
buildings, yet every fellow employee was a 4-digit dial away.

But residential ISDN phone service was not a success here; the Bells
regarded it as a premium service, and priced it as one. It was used for
Internet dialup, as its 64Kbs was better than a 28.8Kbs modem; it was
soon surpassed by DSL and Cable modem data.

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