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Old 18th May 2019, 1:34 am   #1
Chris55000
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Default GPO/BT Call Progress Tones?

Hi!

I didn't get my own mobile until only a few years ago so relied on call–boxes much later than most people I knew when I was younger, and I remember the residential phone books always had the phone call progress tones described in the "General Information" pages as follows:–

A) Dial Tone (continuous purring or higher–pitch continuous tone) – Dial number desired, not forgetting area code;

B) Ringing Tone (a repeated burr–burr) – The equipment is trying to call the dialled number;

C) Engaged Tone (A repeated single note) – the called number is busy – please try again a few minutes later;

Now on one or two occasions I heard two variations of this – one was a repeated "up" and a "down" tone and the second was a very short "pip" followed by a much longer "beep", again continuouly repeated, at roughly the same pitch – I never saw these mentioned in the phone books! Can any 'phone experts enlighten me?

D) Number Unobtainable Tone (a continuous note) – the called number or line is not in service;

E) Pay Tone (a series of rapid pips) – instructs call–box users to insert money to begin or continue the call.

Those were the official descriptions that were printed, if my memory serves me correctly.

What happened if you picked the phone up and carried on listening whilst any of these tones (apart from ringing–tone of course!) were in progress – did they carry on indefinitely?

Does anyone recall ever hearing any unusual tones/sounds on the lines apart from those described above, and what about announcements? – I remember that phone books said "occasionally recorded announcements may be used instead of tones in some areas", but I don't think I ever once heard any!

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Old 18th May 2019, 7:50 am   #2
Dave Moll
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Default Re: GPO/BT Call Progress Tones?

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What happened if you picked the phone up and carried on listening whilst any of these tones (apart from ringing–tone of course!) were in progress – did they carry on indefinitely?
I wouldn't exclude ringing tone from the list, as there was (and still is) a limit to how long it will continue if the called party doesn't answer. I know this from times when I was trying to make contact with a place where I sometimes stay that didn't have a telephone, but there was a callbox outside, so it was a matter of letting it ring until someone happened to be within earshot of the box. My recollection is that it gave up after about fifty rings, but it depends on what exchange equipment is involved.
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Old 18th May 2019, 8:02 am   #3
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Default Re: GPO/BT Call Progress Tones?

I think the alternative engaged tone you're referring to is "equipment busy tone" as I understand it. I believe this is when the call could not be routed/connected to the called party due to insufficient capacity - probably a shortage of trunk lines or similar.
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Old 18th May 2019, 8:41 am   #4
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Default Re: GPO/BT Call Progress Tones?

I believe the "uneven" sounding engaged tone is "equipment busy" rather than "called party engaged".

I've heard "The number you have called, is unavailable" announcements.

I've also heard on occasion some pretty "rough" approximations to the various tones.
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Old 18th May 2019, 11:11 am   #5
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Default Re: GPO/BT Call Progress Tones?

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I believe the "uneven" sounding engaged tone is "equipment busy" rather than "called party engaged".
This was always known as Equipment Engaged Tone or EET.

With the advent of push button "dialing" dial tone was renamed proceed tone, but the name never caught on.

Dial tone was changed from 50Hz square wave to 400Hz sine wave because MF4 dialing didn't work well in the face of 50Hz harmonics which were present until the first keyed digit was accepted.
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Old 18th May 2019, 11:15 am   #6
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Default Re: GPO/BT Call Progress Tones?

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Quote:
Originally Posted by Chris55000 View Post
What happened if you picked the phone up and carried on listening whilst any of these tones (apart from ringing–tone of course!) were in progress – did they carry on indefinitely?
I wouldn't exclude ringing tone from the list, as there was (and still is) a limit to how long it will continue if the called party doesn't answer.
I wouldn't say "was". I remember as a nasty kid ringing a building site with an outside bell from a local call box and leaving it ringing for around 2 hours on a Sunday. Eventually someone came to use the call box and nicked my 4d.
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Old 18th May 2019, 11:26 am   #7
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Default Re: GPO/BT Call Progress Tones?

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what about announcements?
Of course, these days if you ring an invalid number from BT (I don't know about other providers) the NU tone has been replaced by a woman who repeats over and over again (for about a minute) "The number you have called has not been recognised." Also the engaged/busy tone now has a message superimposed upon the tone saying that the number is busy and encouraging you to use the ring back service (for which there is normally a charge), though this message isn't repeated, continuing with just the tone until it times out.
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Old 18th May 2019, 11:32 am   #8
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Default Re: GPO/BT Call Progress Tones?

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Dial tone was changed from 50Hz square wave to 400Hz sine wave because MF4 dialing didn't work well in the face of 50Hz harmonics which were present until the first keyed digit was accepted.
I hadn't realised that was the reason for the change. I had thought of it as simply a by-product of the move from mechanical to electronic exchanges.
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Old 18th May 2019, 12:50 pm   #9
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Default Re: GPO/BT Call Progress Tones?

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Originally Posted by Herald1360 View Post
I believe the "uneven" sounding engaged tone is "equipment busy" rather than "called party engaged".

I've heard "The number you have called, is unavailable" announcements.

I've also heard on occasion some pretty "rough" approximations to the various tones.
The 'uneven' engaged tone is known as 'congestion tone' or 'path engaged tone' - effectively indicating that there was a lack of available equipment somewhere along the route of the call.

The tone have changed over the years. Early exchanges didn't even have dialling tone - I can just remember some in service like that. And ringing tone wasn't always 'double beat' - some had single beat ringing as late as 1974!

For those with a line off CNet - various demonstrations of tones are available as follows -
0352 82 86 has a 1930 GPO recording about the tones then in use on larger exchanges (not the smaller rural exchanges)
Other demonstration codes - some Australian/New Zealand tones are similar to the UK tones - note that the modern UK Busy Tone is faster
01-283 AVEnue 0812 UK Number Unobtainable Tone (NU Tone)
01-283 AVEnue 0813 UK Congestion Tone
01-283 AVEnue 0814 UK Dialling Tone
01-283 AVEnue 0815 UK Pay on Answer paytone
01-283 AVEnue 0816 UK Ringing Tone
01-283 AVEnue 0817 UK Older 400/25 c/s Ringing Tone
01-283 AVEnue 0818 UK Older 400/17 c/s Ringing Tone
01-283 AVEnue 6111 Australian Busy Tone
01-283 AVEnue 6112 Australian Number Unobtainable Tone
01-283 AVEnue 6113 Australian Congestion Tone
01-283 AVEnue 6116 Australian Ringing Tone
01-283 AVEnue 6411 New Zealand Busy Tone
01-283 AVEnue 6412 New Zealand Number Unobtainable Tone
01-283 AVEnue 6413 New Zealand Congestion Tone
01-283 AVEnue 6414 New Zealand Old Overflow Busy Tone Used on 11th step of Group selectors. Remained in use on NZUAX13s long after being replaced on other exchanges.
01-283 AVEnue 6416 New Zealand Ringing Tone

If you've not got a CNet line (they have no rental or charges!_) you can reach the numbers by dialling 01352 83 8111 the after the announcement dial the above numbers - to save redialling the PSTN number, just press # then the next number you want to dual. Calls charged at normal landline rates and included in most 'free calls' packages as it is a normal 01... number
Don't all dial at once!

The current BT Network Tones/Announcement definitions can be found at here
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Old 18th May 2019, 2:13 pm   #10
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Default Re: GPO/BT Call Progress Tones?

The NZ NU tone is an interesting one! It sounds like the Morse code for "H" repeated over.

Given that the Australian and NZ numbers start with their country codes, it left me wondering whether there is any significance to "08" of the UK ones.
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Old 18th May 2019, 2:43 pm   #11
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Default Re: GPO/BT Call Progress Tones?

I can't but think that the "new" voice announcements waste time, surly the modern populace can tell the difference twixt but a few tones. You can decode the tone in less than a second, an announcement takes ages in comparison. Progress!
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Old 18th May 2019, 4:04 pm   #12
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Default Re: GPO/BT Call Progress Tones?

I can still remember around 1980 when the equipment was old there used to be an announcement that often came up when calling a London number from the home counties.
"All lines from (town name) are engaged".
It was very frustrating when calling a busy switch board in the London area.
You occasionally got a line just to find that the line to the busy switch board was engaged.
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Old 18th May 2019, 4:46 pm   #13
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Default Re: GPO/BT Call Progress Tones?

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Originally Posted by Dave Moll View Post
The NZ NU tone is an interesting one! It sounds like the Morse code for "H" repeated over.

Given that the Australian and NZ numbers start with their country codes, it left me wondering whether there is any significance to "08" of the UK ones.
The NZ NU is effectively an 'H' in Morse

No significance. Just happened that there was a 284-44xx number in use when the UK tones were set up. The Au and NZ codes were add at later date and it was thought appropriate to use the country code as the first two digits.

There is an interesting website https://www.3amsystems.com/World_Tone_Database which shows the tones/cadences of tones from countries all around the World and give the settings for setting them up on either a Linksys ATA or an Asterisk computer based PC for use with VoIP. If you would like the old GPO UK settings for an ATA - PM me.
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Old 18th May 2019, 4:58 pm   #14
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Default Re: GPO/BT Call Progress Tones?

The Bedford number 01234 567890 probably gets more than its share of "test" calls, and you get "The number you have dialled has not been recognised" but don't be fooled! The BT lady is not being entirely truthful, the announcement is not "early media", it is a completed chargeable call.
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Old 18th May 2019, 6:58 pm   #15
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Default Re: GPO/BT Call Progress Tones?

It is a long time ago, but I can't remember any parts of the call route in an exchange with tones on them other than the first selector and final selector. Used ot have a special tag block with the S and Z pulses, and the tones, all done in 0.9mm, 21swg, wire.

I think even the busy, NU, etc tones were all passed back to the first selector to stop equipment being held when not carrying a call.

You needed a special relay to do the tones, mu-metal sleeving on the core or something.
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Old 18th May 2019, 7:37 pm   #16
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Default Re: GPO/BT Call Progress Tones?

In past-times the UK phone-network would include very short 'pips' of in-band audible tones for various signalling purposes during call-setup and cleardown.

Though these have not been used for a few decades, it's still quite common for the sound-effects-people in radio-dramas to include them in "calling someone on the phone" scenes.
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Old 18th May 2019, 7:52 pm   #17
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Default Re: GPO/BT Call Progress Tones?

As I remember, the tones were generated by the ringing generator. The cam operated spring sets for the cadence were fascinating to watch, in an anoraky sort of way. All electronic now, enabling voices as well as tones.
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Old 19th May 2019, 10:33 am   #18
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Default Re: GPO/BT Call Progress Tones?

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As I remember, the tones were generated by the ringing generator. The cam operated spring sets for the cadence were fascinating to watch, in an anoraky sort of way. All electronic now, enabling voices as well as tones.
As late as the 1960/70's as the provision of STD was extended, some smaller exchanges had the tones produced by 'vibrating' relays but to have tones that would pass over amplified circuits, the very low frequency tones were increased and 'standardised' Small rural exchanges were changed over from the vibrating generation to small 'Ringer 2A' machines that produced the tones and ringing.
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Old 19th May 2019, 10:41 am   #19
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Default Re: GPO/BT Call Progress Tones?

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Originally Posted by G6Tanuki View Post
In past-times the UK phone-network would include very short 'pips' of in-band audible tones for various signalling purposes during call-setup and cleardown.

Though these have not been used for a few decades, it's still quite common for the sound-effects-people in radio-dramas to include them in "calling someone on the phone" scenes.
Those tones were initially AC1 signalling system tones and in later years, other AC signalling systems - AC3, AC9, AC13 etc - all for passing the tones over amplified /carrier/co-axial circuits that had no DC path for signalling backwards and forwards. In theory, callers were not supposed to hear them as they were not part of the 'call progress' tone system.
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Old 30th May 2019, 7:39 pm   #20
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Default Re: GPO/BT Call Progress Tones?

Hi!

Another memory has come back to me on the subject of GPO/BT Call Progress Tones, and that was I'm sure the Pay Tone changed format from a continuous series of rapid pips to a single burst, about 2–3 s long, of fainter but even more rapid pips, then if money wasn't inserted promptly enough (within 2–3 s!) you got silence then the 400 Hz N.U. tone and had to replace the receiver and restart the call again!

Can any Member confirm the Pay Tone changed in spec recently? The current BT S.I.N. 350 no longer lists "Pay Tone", so I wonder if it's now been abolished from the PSTN?

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Last edited by Chris55000; 30th May 2019 at 8:00 pm.
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