Telephone geeking - UXD5 exchanges

[j r powell]

Visited a friend's parents' house in the Cheshire countryside yesterday, and
to my surprise his village was served by a BT UXD5 exchange - an early
digital exchange type from the 1970s which I'd previously thought was only
used in the highlands of Scotland and far-flung Welsh villages.
Is it common to find them just a few miles from "civilisation" (as I did),
or was this a rare anomaly?

This was the first time I'd ever used one "from the inside", and in addition
to the loud Strowger-esque call progress tones and characteristic
high-pitched whine constantly present in the background noise, I was
surprised to hear the exchange put on a loud "siren" sound (known to some US
phreaks as the "cry-baby") after the phone was left off-hook for a minute or
so - something I've never heard from a UK POTS line before.

[Andy Burns]

I was surprised to hear the exchange put on a loud "siren" sound
(known to some US phreaks as the "cry-baby") after the phone was left
off-hook for a minute or so - something I've never heard from a UK POTS
line before.

The "howler" you mean? I thought all UK phone lines did that, mine does
and I'm certainly not on a UXD5.

[j r powell]

Post by Andy Burns

I was surprised to hear the exchange put on a loud "siren" sound
(known to some US phreaks as the "cry-baby") after the phone was left
off-hook for a minute or so - something I've never heard from a UK POTS
line before.

The "howler" you mean? I thought all UK phone lines did that, mine does
and I'm certainly not on a UXD5.

I've never heard it on any BT System X or Y lines.
Behaviour has always been:
X = Dialtone -> "Please hang up and try again" repeating message ->
permanent silence
Y = Dialtone -> NU tone -> silence -> loud clunk -> permanent silence

[Paulg0]

Post by j r powell
Y = Dialtone -> NU tone -> silence -> loud clunk -> permanent silence

The howler usually starts after about 3 or 4 minutes of the final silence
you mention

Paul

[j r powell]

Post by Paulg0
The howler usually starts after about 3 or 4 minutes of the final silence
you mention

It doesn't around here, honest!
My parents' house had (perhaps unusually) one System X and one System Y
line. The latter belonged to me, and I frequently left it off hook for hours
while doing homework. It never "howled" at me.
I'm certain the System X line never did either, and nor does the one in my
current place of residence.
Perhaps it's a regional thing, or a feature included with some special class
of service?

There should be no technical need for customers to keep their phones
on-hook - even the Strowger exchanges included a mechanism whereby an
off-hook line would be disconnected from the switching train in order to
free up the capacity for use by other customers.

[Phil]

Post by j r powell

Post by Paulg0
The howler usually starts after about 3 or 4 minutes of the final
silence you mention

It doesn't around here, honest!
My parents' house had (perhaps unusually) one System X and one System Y
line. The latter belonged to me, and I frequently left it off hook for
hours while doing homework. It never "howled" at me.
I'm certain the System X line never did either, and nor does the one in
my current place of residence.
Perhaps it's a regional thing, or a feature included with some special
class of service?
There should be no technical need for customers to keep their phones
on-hook - even the Strowger exchanges included a mechanism whereby an
off-hook line would be disconnected from the switching train in order to
free up the capacity for use by other customers.

My System X line definitely does provide howler, I heard it on Tuesday
when I nudged the phone on my desk off hook.

There was a period of time (Early 90s???) when BT disabled howler on
System X lines. I was told this was because it was "louder than peak
audio level" and therefore might damage subscribers equipment and/or
ears. I never really believed this explanation, but it certainly is
true that howler is louder than normal peak audio (It is not delivered
via the ADC.)

[Gaius]

Post by Phil
There was a period of time (Early 90s???) when BT disabled howler on
System X lines. I was told this was because it was "louder than peak
audio level" and therefore might damage subscribers equipment and/or
ears. I never really believed this explanation, but it certainly is
true that howler is louder than normal peak audio (It is not delivered
via the ADC.)

The original - Strowger - howler was more correctly known as "Graduated
Howler". It started at a moderate level, but stepped up by several dB
(10?) after about 30sec or so. It did this several times until it was
truly ear splitting. This was done to avoid (guaranteed) hearing damage
that would have occurred if the final level had been connected directly
to a handset held to the ear.

The early earpiece inserts were much more robust than the later rocking-
armature type, and could be driven much harder.

Later howlers, including System X, produced much lower peak powers to
avoid hearing and (I guess) equipment damage.

[Ken Wheatley]

Post by j r powell

Post by Paulg0
The howler usually starts after about 3 or 4 minutes of the final
silence you mention

It doesn't around here, honest!
My parents' house had (perhaps unusually) one System X and one System Y
line. The latter belonged to me, and I frequently left it off hook for
hours while doing homework. It never "howled" at me.
I'm certain the System X line never did either, and nor does the one in
my current place of residence.
Perhaps it's a regional thing, or a feature included with some special
class of service?

I suppose they (system x and y) are getting on a bit.

SIN 351 says of the howler "To draw attention to a telephone left
on-line. May be applied to attachments which hold after the distant end
has cleared or after an unsuccessful call. The howler can sometimes be
applied automatically, in which case it will start 3 minutes after the
parked state has been achieved."

I suppose the 'can sometimes' implies that use is not universal, but
that surprises me.

[j r powell]

I suppose the 'can sometimes' implies that use is not universal, but that
surprises me.

'can sometimes' surprised me for the opposite reason of course - I played
with phones as a kid and never heard the thing until this week. None of the
old Strowger tone plants I've seen/heard produced it either.

If it's "not delivered via the ADC" on System X/Y, as someone suggested,
then what generates it and how is it put onto the line?

[Phil]

Post by j r powell

Post by Ken Wheatley
I suppose the 'can sometimes' implies that use is not universal, but
that surprises me.

'can sometimes' surprised me for the opposite reason of course - I
played with phones as a kid and never heard the thing until this week.
None of the old Strowger tone plants I've seen/heard produced it either.
If it's "not delivered via the ADC" on System X/Y, as someone suggested,
then what generates it and how is it put onto the line?

On System X it is applied via the test access system which provides
'copper' access to the subscriber's line via relays. It is generated
by, er, I forget, it'll come to me in a moment.

[Gaius]

Post by j r powell
Visited a friend's parents' house in the Cheshire countryside yesterday, and
to my surprise his village was served by a BT UXD5 exchange - an early
digital exchange type from the 1970s which I'd previously thought was only
used in the highlands of Scotland and far-flung Welsh villages.
Is it common to find them just a few miles from "civilisation" (as I did),
or was this a rare anomaly?

The software for the UXD5 is mainly written in a dialect of Coral66
known as POcoral. There's not many people still around who are familiar
with this.

The last I heard, UXD software maintenance had been outsourced to a
cottage industry of a couple of guys who were about the only people
still competent to do this. I wonder what happens when they retire ?

[j r powell]

Post by Gaius
The software for the UXD5 is mainly written in a dialect of Coral66
known as POcoral. There's not many people still around who are familiar
with this.

Yep I knew that :) They've always been the last to receive new services (eg
1471) as a result, and were even rumoured to have been limited to LD
signalling on trunk lines to/from the rest of the network for many years
(supposedly because they were surrounded by Strowger when first installed,
and therefore designed to speak the same "language").

Post by Gaius
The last I heard, UXD software maintenance had been outsourced to a
cottage industry of a couple of guys who were about the only people
still competent to do this. I wonder what happens when they retire ?

Presumably the entire BT network will have cut over to 21CN by then.

[Mark]

Post by j r powell

Post by Gaius
The software for the UXD5 is mainly written in a dialect of Coral66
known as POcoral. There's not many people still around who are familiar
with this.

Yep I knew that :) They've always been the last to receive new services (eg
1471) as a result, and were even rumoured to have been limited to LD
signalling on trunk lines to/from the rest of the network for many years
(supposedly because they were surrounded by Strowger when first installed,
and therefore designed to speak the same "language").

Post by Gaius
The last I heard, UXD software maintenance had been outsourced to a
cottage industry of a couple of guys who were about the only people
still competent to do this. I wonder what happens when they retire ?

Presumably the entire BT network will have cut over to 21CN by then.

I wouldn't bet on it. The PSTN migration to 21CN by BT is on-hold
with no revised date for completion.

[Denis McMahon]

... I was surprised to hear the exchange put on a loud "siren" sound
(known to some US phreaks as the "cry-baby") after the phone was left
off-hook for a minute or so - something I've never heard from a UK POTS
line before.

Howler. Still happens on my BT Central Portsmouth exchange, just under 4
mins after going off-hook when I tested.

Rgds

Denis McMahon

[Peter]

Post by j r powell
Visited a friend's parents' house in the Cheshire countryside yesterday, and
to my surprise his village was served by a BT UXD5 exchange - an early
digital exchange type from the 1970s which I'd previously thought was only
used in the highlands of Scotland and far-flung Welsh villages.
Is it common to find them just a few miles from "civilisation" (as I did),
or was this a rare anomaly?

It was based on the Monarch digital PABX. I guess there will still be
quite a few of those kicking around in many offices all over the UK

[j r powell]

Post by Peter
It was based on the Monarch digital PABX. I guess there will still be
quite a few of those kicking around in many offices all over the UK

Only about 50 left according to a BT guy I spoke with earlier today, and
since each unit typically only provides a few hundred lines at most, they
must comprise just a tiny percentage of BT's network.

[j r powell]

Post by j r powell

Post by Peter
It was based on the Monarch digital PABX. I guess there will still be
quite a few of those kicking around in many offices all over the UK

Only about 50 left according to a BT guy I spoke with earlier today, and
since each unit typically only provides a few hundred lines at most, they
must comprise just a tiny percentage of BT's network.

UXD5s, that is. I'm not sure how many of its PABX siblings are still in
service.

[Graham.]

Post by Peter
It was based on the Monarch digital PABX. I guess there will still be
quite a few of those kicking around in many offices all over the UK

Only about 50 left according to a BT guy I spoke with earlier today, and since each unit typically only provides a few hundred
lines at most, they must comprise just a tiny percentage of BT's network.

There were some smallish switches serving some town centres in the '90s
in areas where the main exchange hadn't been modernised.
Used mainly by retailers for EFT machines (credit card terminals)
IIRC the machine dialled 11 to be instantly connected to the PAD.
I'm sure someone told me they were Monarchs, and the word "cardway" had something
to do with it.

[Michael R N Dolbear]

Post by j r powell

Post by Peter
It was based on the Monarch digital PABX. I guess there will still be
quite a few of those kicking around in many offices all over the UK

Only about 50 left according to a BT guy I spoke with earlier today, and
since each unit typically only provides a few hundred lines at most, they
must comprise just a tiny percentage of BT's network.

http://www.scotland.gov.uk/Publications/2004/06/19531/39258
http://www.scotland.gov.uk/Publications/2004/06/19531/39264

In Scotland in 2004 there were " 420 UXD5 exchanges covering some
4.5% of the Scottish population, mainly in rural and remote areas. "

That was 600 persons - average per UXD5 exchange

Whether it's a " tiny percentage" then or now depends on whether you
measure by route miles or circuit miles since the exchanges were put in
*because* a village was 20 or 50 miles from anyplace larger.

What were they replaced *with* ?

[George Weston]

Post by Michael R N Dolbear

Post by j r powell

Post by Peter
It was based on the Monarch digital PABX. I guess there will still

be

Post by j r powell

Post by Peter
quite a few of those kicking around in many offices all over the UK

Only about 50 left according to a BT guy I spoke with earlier today,

and

Post by j r powell
since each unit typically only provides a few hundred lines at most,

they

Post by j r powell
must comprise just a tiny percentage of BT's network.

http://www.scotland.gov.uk/Publications/2004/06/19531/39258
http://www.scotland.gov.uk/Publications/2004/06/19531/39264
In Scotland in 2004 there were " 420 UXD5 exchanges covering some
4.5% of the Scottish population, mainly in rural and remote areas. "
That was 600 persons - average per UXD5 exchange
Whether it's a " tiny percentage" then or now depends on whether you
measure by route miles or circuit miles since the exchanges were put in
*because* a village was 20 or 50 miles from anyplace larger.
What were they replaced *with* ?

Dunno - but going backwards, they replaced UAXs, which did the same job
electro-mechanically.
It makes me chuckle when using the GIS system at work, when I see
telephone exchange addresses still labelled "(name of village) UAX".

George

[j r powell]

Post by Michael R N Dolbear
http://www.scotland.gov.uk/Publications/2004/06/19531/39258
http://www.scotland.gov.uk/Publications/2004/06/19531/39264
In Scotland in 2004 there were " 420 UXD5 exchanges covering some
4.5% of the Scottish population, mainly in rural and remote areas. "
That was 600 persons - average per UXD5 exchange
Whether it's a " tiny percentage" then or now depends on whether you
measure by route miles or circuit miles since the exchanges were put in
*because* a village was 20 or 50 miles from anyplace larger.
What were they replaced *with* ?

The figure of 420 UXD5s sounds like a more reasonable one to me, so perhaps
BT guy was mistaken.
Having said that, an old BT exchange list I found shows one in an area I'm
familiar with which is now System Y, so perhaps they've had to replace some
as neighbourhoods have expanded et al, due to their limited line capacity
(unlikely in those far-flung rural areas though).

There were also at least two variants - UXD5 A (late-1970s) and B
(mid-1980s).
Seems that the former is considerably more limited (eg. in supporting fewer
lines and relying upon electromechanical meters for billing).
http://www.dope.org/9x/uk/misctext/UXD5B.TXT

[s***@gmail.com]

I worked on the development of UXD5 firmware back in the late 80's when I was at GEC in Coventry. I didn't know any were still in use !

[m***@privicy.net]

Post by s***@gmail.com
I worked on the development of UXD5 firmware back in the late 80's when I was at GEC in Coventry. I didn't know any were still in use !

Posting to Usenet via Google Groups is generaly a Bad Idea (tm),
However it does have the <cough> advantage of infinate retention over
those of us who post by more direct means, so it would be a good idea
to quote what you are replying to for us non-googlers

Anyway I looked it up, it's from 2011
https://groups.google.com/d/msg/uk.telecom/cWJKhwHHMVU/aEy88Fi0X14J

Jamie Powell, I wonder what became of him. He used to play havoc in
uk.tech.broadcast