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Engaged tone

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  Engaged tone Jeff Layman <Jeff@invalid.invalid> - 2026-04-14 09:57 +0100
    Re: Engaged tone Theo <theom+news@chiark.greenend.org.uk> - 2026-04-14 12:14 +0100
      Re: Engaged tone JMB99 <mb@nospam.net> - 2026-04-14 20:07 +0100
      Re: Engaged tone Bob Latham <bob@sick-of-spam.invalid> - 2026-04-15 11:59 +0100
    Re: Engaged tone Scott <newsgroups@gefion.myzen.co.uk> - 2026-04-14 13:00 +0100
    Re: Engaged tone Richmond <dnomhcir@gmx.com> - 2026-04-14 13:22 +0100
      Re: Engaged tone Jeff Layman <Jeff@invalid.invalid> - 2026-04-18 22:17 +0100
        Re: Engaged tone Richmond <dnomhcir@gmx.com> - 2026-04-18 22:32 +0100
          Re: Engaged tone Jeff Layman <Jeff@invalid.invalid> - 2026-04-19 09:54 +0100
            Re: Engaged tone Richmond <dnomhcir@gmx.com> - 2026-04-19 14:11 +0100
              Re: Engaged tone David Woolley <david@ex.djwhome.demon.invalid> - 2026-04-19 17:24 +0100
                Re: Engaged tone Richmond <dnomhcir@gmx.com> - 2026-04-19 21:56 +0100
                  Re: Engaged tone David Wade <g4ugm@dave.invalid> - 2026-04-19 22:24 +0100
                    Re: Engaged tone Richmond <dnomhcir@gmx.com> - 2026-04-19 23:29 +0100
                      Re: Engaged tone Theo <theom+news@chiark.greenend.org.uk> - 2026-04-20 08:53 +0100
                    Re: Engaged tone David Woolley <david@ex.djwhome.demon.invalid> - 2026-04-20 09:23 +0100
                  Re: Engaged tone David Woolley <david@ex.djwhome.demon.invalid> - 2026-04-20 09:18 +0100
            Re: Engaged tone Andy Burns <usenet@andyburns.uk> - 2026-04-19 15:33 +0100

#39391 — Engaged tone

Years ago with POTS if you got a constantly engaged tone you could phone 
the operator and ask if there really was someone on the line. They could 
check and tell if there was a conversation going on or not, and perhaps 
the phone had been left "off the hook".

I assume that this is still possible with purely analogue lines in some 
way, but what about Digital Voice?

-- 
Jeff

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#39392

Jeff Layman <Jeff@invalid.invalid> wrote:
> Years ago with POTS if you got a constantly engaged tone you could phone 
> the operator and ask if there really was someone on the line. They could 
> check and tell if there was a conversation going on or not, and perhaps 
> the phone had been left "off the hook".
> 
> I assume that this is still possible with purely analogue lines in some 
> way, but what about Digital Voice?

Can operators listen in on digitally switched analogue calls?  I thought
that is something that needs a wire tapping permission (police warrant
etc)?

Theo

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#39398

On 14/04/2026 12:14, Theo wrote:
> Can operators listen in on digitally switched analogue calls?  I thought
> that is something that needs a wire tapping permission (police warrant
> etc)?


I suspect that it is if for technical reasons.

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#39401

In article <C4l*HH4DA@news.chiark.greenend.org.uk>,
   Theo <theom+news@chiark.greenend.org.uk> wrote:
> Jeff Layman <Jeff@invalid.invalid> wrote:

> > Years ago with POTS if you got a constantly engaged tone you
> > could phone the operator and ask if there really was someone on
> > the line. They could check and tell if there was a conversation
> > going on or not, and perhaps the phone had been left "off the
> > hook".
> > 
> > I assume that this is still possible with purely analogue lines
> > in some way, but what about Digital Voice?

> Can operators listen in on digitally switched analogue calls?  I
> thought that is something that needs a wire tapping permission
> (police warrant etc)?

When I worked for PO telephones and later BT, the groups switching
centre (GSC) had a department called "service obs". In my GSC there
were 3 or 4 ladies who listened in at random to the first minute or
so of a new call to measure the quality of service. These weren't
operator initiated calls these were Strowger auto calls.

In my case this was a none director GSC and I've no idea if service
obs exists today. 

Bob.

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#39393

On Tue, 14 Apr 2026 09:57:39 +0100, Jeff Layman <Jeff@invalid.invalid>
wrote:

>Years ago with POTS if you got a constantly engaged tone you could phone 
>the operator and ask if there really was someone on the line. They could 
>check and tell if there was a conversation going on or not, and perhaps 
>the phone had been left "off the hook".
>
>I assume that this is still possible with purely analogue lines in some 
>way, but what about Digital Voice?

'Years ago' ... Didn't Mr Strowger - who was an undertaker - invent
the automatic exchange because the operator was listening into his
calls and passing the business to another undertaker? 

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#39394

Jeff Layman <Jeff@invalid.invalid> writes:

> Years ago with POTS if you got a constantly engaged tone you could
> phone the operator and ask if there really was someone on the
> line. They could check and tell if there was a conversation going on
> or not, and perhaps the phone had been left "off the hook".
>
> I assume that this is still possible with purely analogue lines in
> some way, but what about Digital Voice?

I get an engaged tone when people hang up at the end of the call. I
think it comes from the router. It's probably the VOIP equivalent of
"Oops, something went wrong".

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#39405

On 14/04/2026 13:22, Richmond wrote:
> Jeff Layman <Jeff@invalid.invalid> writes:
> 
>> Years ago with POTS if you got a constantly engaged tone you could
>> phone the operator and ask if there really was someone on the
>> line. They could check and tell if there was a conversation going on
>> or not, and perhaps the phone had been left "off the hook".
>>
>> I assume that this is still possible with purely analogue lines in
>> some way, but what about Digital Voice?
> 
> I get an engaged tone when people hang up at the end of the call. I
> think it comes from the router. It's probably the VOIP equivalent of
> "Oops, something went wrong".

It seems strange that an engaged tone should be used when the connection 
has been terminated; if you hang on long enough does it change to a 
"call terminated" tone? What tone do you get when you dial an 
unobtainable number?

-- 
Jeff

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#39406

Jeff Layman <Jeff@invalid.invalid> writes:

> On 14/04/2026 13:22, Richmond wrote:
>> Jeff Layman <Jeff@invalid.invalid> writes:
>> 
>>> Years ago with POTS if you got a constantly engaged tone you could
>>> phone the operator and ask if there really was someone on the
>>> line. They could check and tell if there was a conversation going on
>>> or not, and perhaps the phone had been left "off the hook".
>>>
>>> I assume that this is still possible with purely analogue lines in
>>> some way, but what about Digital Voice?
>> I get an engaged tone when people hang up at the end of the call. I
>> think it comes from the router. It's probably the VOIP equivalent of
>> "Oops, something went wrong".
>
> It seems strange that an engaged tone should be used when the
> connection has been terminated; if you hang on long enough does it
> change to a "call terminated" tone? What tone do you get when you dial
> an unobtainable number?

I don't know, but I suppose if I got an engaged tone, I wouldn't know if
it was unobtainable or engaged.

What's an example of an unobtainable number?

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#39407

On 18/04/2026 22:32, Richmond wrote:
> Jeff Layman <Jeff@invalid.invalid> writes:
> 
>> On 14/04/2026 13:22, Richmond wrote:
>>> Jeff Layman <Jeff@invalid.invalid> writes:
>>>
>>>> Years ago with POTS if you got a constantly engaged tone you could
>>>> phone the operator and ask if there really was someone on the
>>>> line. They could check and tell if there was a conversation going on
>>>> or not, and perhaps the phone had been left "off the hook".
>>>>
>>>> I assume that this is still possible with purely analogue lines in
>>>> some way, but what about Digital Voice?
>>> I get an engaged tone when people hang up at the end of the call. I
>>> think it comes from the router. It's probably the VOIP equivalent of
>>> "Oops, something went wrong".
>>
>> It seems strange that an engaged tone should be used when the
>> connection has been terminated; if you hang on long enough does it
>> change to a "call terminated" tone? What tone do you get when you dial
>> an unobtainable number?
> 
> I don't know, but I suppose if I got an engaged tone, I wouldn't know if
> it was unobtainable or engaged.

So if you were given a phone number (making following a car accident and 
exchanging details with whoever gave you that number), and you phoned it 
and it was constantly engaged, you couldn't tell if it was genuinely 
engaged or, for example, an unobtainable fake number.

I guess a few years ago you could call the BT operator to check, but how 
do you do it now? There are websites which claim to be able to check 
whether or not any number is real.

> What's an example of an unobtainable number?

Not sure for certain how to find one. I tried the Experian confirmation 
utility at <https://www.edq.com/phone-verification/> by testing it with 
+44 800000000 and it reported:

"No coverage

Unable to detect the live status for the telephone network."

So I called 0800000000 and found it was a number for The Prudential!

I decided to change tack and search on "UK telephone reserved codes". At 
<https://en.wikipedia.org/wiki/List_of_dialling_codes_in_the_United_Kingdom#Code_prefixes>, 
it states that phone numbers beginning 04 and 06 are reserved codes, but 
doesn't explain what that means. Just for confusion, at 
<https://en.wikipedia.org/wiki/Telephone_numbers_in_the_United_Kingdom#Structure> 
it says that 04 and 06 are "Not in use"!

I tried 04123456789 from my mobile and got the engaged tone. I then 
tried 06123456789 and got the same thing. I don't use my mobile for many 
calls, and haven't to my knowledge called an unobtainable number before, 
although I've had an engaged tone calling numbers I know are ok. Looks 
like Voip calls and mobile calls treat unobtainable numbers in the same 
way. I wonder why; is it because they're digital? What about DV 
(non-Voip) calls?

-- 
Jeff

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#39408

Jeff Layman <Jeff@invalid.invalid> writes:

> On 18/04/2026 22:32, Richmond wrote:
>> Jeff Layman <Jeff@invalid.invalid> writes:
>> 
>>> On 14/04/2026 13:22, Richmond wrote:
>>>> Jeff Layman <Jeff@invalid.invalid> writes:
>>>>
>>>>> Years ago with POTS if you got a constantly engaged tone you could
>>>>> phone the operator and ask if there really was someone on the
>>>>> line. They could check and tell if there was a conversation going on
>>>>> or not, and perhaps the phone had been left "off the hook".
>>>>>
>>>>> I assume that this is still possible with purely analogue lines in
>>>>> some way, but what about Digital Voice?
>>>> I get an engaged tone when people hang up at the end of the call. I
>>>> think it comes from the router. It's probably the VOIP equivalent of
>>>> "Oops, something went wrong".
>>>
>>> It seems strange that an engaged tone should be used when the
>>> connection has been terminated; if you hang on long enough does it
>>> change to a "call terminated" tone? What tone do you get when you dial
>>> an unobtainable number?
>> I don't know, but I suppose if I got an engaged tone, I wouldn't
>> know if
>> it was unobtainable or engaged.
>
> So if you were given a phone number (making following a car accident
> and exchanging details with whoever gave you that number), and you
> phoned it and it was constantly engaged, you couldn't tell if it was
> genuinely engaged or, for example, an unobtainable fake number.
>
> I guess a few years ago you could call the BT operator to check, but
> how do you do it now? There are websites which claim to be able to
> check whether or not any number is real.
>
>> What's an example of an unobtainable number?
>
> Not sure for certain how to find one. I tried the Experian
> confirmation utility at <https://www.edq.com/phone-verification/> by
> testing it with +44 800000000 and it reported:
>
> "No coverage
>
> Unable to detect the live status for the telephone network."
>
> So I called 0800000000 and found it was a number for The Prudential!
>
> I decided to change tack and search on "UK telephone reserved
> codes". At
> <https://en.wikipedia.org/wiki/List_of_dialling_codes_in_the_United_Kingdom#Code_prefixes>,
> it states that phone numbers beginning 04 and 06 are reserved codes,
> but doesn't explain what that means. Just for confusion, at
> <https://en.wikipedia.org/wiki/Telephone_numbers_in_the_United_Kingdom#Structure>
> it says that 04 and 06 are "Not in use"!
>
> I tried 04123456789 from my mobile and got the engaged tone. I then
> tried 06123456789 and got the same thing. I don't use my mobile for
> many calls, and haven't to my knowledge called an unobtainable number
> before, although I've had an engaged tone calling numbers I know are
> ok. Looks like Voip calls and mobile calls treat unobtainable numbers
> in the same way. I wonder why; is it because they're digital? What
> about DV (non-Voip) calls?

I tried a number beginning with 01441 which should not exist as that
dialing code doesn't exist. I got a sound like this:

___ _ ___ _

Whereas when I called my own number I got:

__ __ __ __ __

So there is a difference.

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#39411

On 19/04/2026 14:11, Richmond wrote:
 > ___ _ ___ _
 >
This is "equipment engaged", and is the tone equivalent of "all lines to 
xxxx are busy, please try again later".  Done correctly, one length is 
louder than the other.

 > __ __ __ __ __
This is "subscriber engaged", where the phone is ringing or off hook.

"Number unobtainable", which is what you are looking for, is a 
continuous tone, although normally replaced by a voice announcement.

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#39412

David Woolley <david@ex.djwhome.demon.invalid> writes:

> On 19/04/2026 14:11, Richmond wrote:
>> ___ _ ___ _
>>
> This is "equipment engaged", and is the tone equivalent of "all lines
> to xxxx are busy, please try again later".  Done correctly, one length
> is louder than the other.
>
>> __ __ __ __ __
> This is "subscriber engaged", where the phone is ringing or off hook.
>
> "Number unobtainable", which is what you are looking for, is a
> continuous tone, although normally replaced by a voice announcement.

On my router there are two phone sockets and these have internal phone
numbers **11 and **12 , so if I phone **11 from phone 1 I get a tone
which is actually the equipment engaged tone above, but it must be
coming from my router I guess because such a call need not go outside
the router. Or maybe these tones are actually transmitted as error code
and are then always translated into tones by the VOIP receiver or
router?

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#39413

On 19/04/2026 21:56, Richmond wrote:
> David Woolley <david@ex.djwhome.demon.invalid> writes:
> 
>> On 19/04/2026 14:11, Richmond wrote:
>>> ___ _ ___ _
>>>
>> This is "equipment engaged", and is the tone equivalent of "all lines
>> to xxxx are busy, please try again later".  Done correctly, one length
>> is louder than the other.
>>
>>> __ __ __ __ __
>> This is "subscriber engaged", where the phone is ringing or off hook.
>>
>> "Number unobtainable", which is what you are looking for, is a
>> continuous tone, although normally replaced by a voice announcement.
> 

Aren't these SS7 call status tones

> On my router there are two phone sockets and these have internal phone
> numbers **11 and **12 , so if I phone **11 from phone 1 I get a tone
> which is actually the equipment engaged tone above, but it must be
> coming from my router I guess because such a call need not go outside
> the router. Or maybe these tones are actually transmitted as error code
> and are then always translated into tones by the VOIP receiver or
> router?
> 
well of course the call status is transmitted as a status code. The 
tones are generated locally! If the call isn't set up so you haven't 
selected a codec so you can't send a tone. Not sure if this is the 
current protocol defs...

https://datatracker.ietf.org/doc/html/rfc3261

Dave

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#39414

David Wade <g4ugm@dave.invalid> writes:

> On 19/04/2026 21:56, Richmond wrote:
>> David Woolley <david@ex.djwhome.demon.invalid> writes:
>> 
>>> On 19/04/2026 14:11, Richmond wrote:
>>>> ___ _ ___ _
>>>>
>>> This is "equipment engaged", and is the tone equivalent of "all lines
>>> to xxxx are busy, please try again later".  Done correctly, one length
>>> is louder than the other.
>>>
>>>> __ __ __ __ __
>>> This is "subscriber engaged", where the phone is ringing or off hook.
>>>
>>> "Number unobtainable", which is what you are looking for, is a
>>> continuous tone, although normally replaced by a voice announcement.
>> 
>
> Aren't these SS7 call status tones
>
>> On my router there are two phone sockets and these have internal phone
>> numbers **11 and **12 , so if I phone **11 from phone 1 I get a tone
>> which is actually the equipment engaged tone above, but it must be
>> coming from my router I guess because such a call need not go outside
>> the router. Or maybe these tones are actually transmitted as error code
>> and are then always translated into tones by the VOIP receiver or
>> router?
>> 
> well of course the call status is transmitted as a status code. The
> tones are generated locally! If the call isn't set up so you haven't
> selected a codec so you can't send a tone. Not sure if this is the
> current protocol defs...
>
> https://datatracker.ietf.org/doc/html/rfc3261
>

You say 'of course' as if it is obvious, but it isn't obvious to
me. When I had an analogue line the tone would have been sent as a sound
over the line in the same way as a voice. So how do I know that if I
make a call to an analogue line the tone isn't created in the system
somewhere and then sent as a sound (though digital) in the same way as
voice?

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#39415

Richmond <dnomhcir@gmx.com> wrote:
> David Wade <g4ugm@dave.invalid> writes:
> 
> >> 
> > well of course the call status is transmitted as a status code. The
> > tones are generated locally! If the call isn't set up so you haven't
> > selected a codec so you can't send a tone. Not sure if this is the
> > current protocol defs...
> >
> > https://datatracker.ietf.org/doc/html/rfc3261
> >
> 
> You say 'of course' as if it is obvious, but it isn't obvious to
> me. When I had an analogue line the tone would have been sent as a sound
> over the line in the same way as a voice. So how do I know that if I
> make a call to an analogue line the tone isn't created in the system
> somewhere and then sent as a sound (though digital) in the same way as
> voice?

Because that's not how SIP works. Status is sent by messages that look a bit
like HTTP, and that is sent over the control channel long before audio is
negotiated.

Status is necessary to be sent out of band because your handset needs it -
eg with just an audio channel you can't make it ring, or tell it the audio
has ceased. Also status is needed when the endpoint isn't a human - eg if
an autodialler makes a call it needs to know if the call was accepted,
engaged, etc. The status does that easily without having to interpret tones
on the line.

In-band signalling was proved to be a bad idea since the 70s era Blue Box
and 'phreaking' became a problem (in the US), which is why signalling is now
out of band.

Theo

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#39417

On 19/04/2026 22:24, David Wade wrote:
> Aren't these SS7 call status tones

SS7 doesn't use inband tones for signalling; these are purely for the 
humans.  Some analogue carrier systems used 2600 Hz tones for signalling 
end of of call, which is the derivation of the name of the newsgroup 
alt.2600 (see blue box references in another reply).  That is a much 
higher pitch than normal call progress tones.

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#39416

On 19/04/2026 21:56, Richmond wrote:
> Or maybe these tones are actually transmitted as error code
> and are then always translated into tones by the VOIP receiver or
> router?

That would be the normal way of doing it with SIP.  There is no point in 
keeping up a media path on a failed call.

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#39410

Jeff Layman wrote:

> I decided to change tack and search on "UK telephone reserved codes". At 
> <https://en.wikipedia.org/wiki/ 
> List_of_dialling_codes_in_the_United_Kingdom#Code_prefixes>, it states 
> that phone numbers beginning 04 and 06 are reserved codes, but doesn't 
> explain what that means. Just for confusion, at <https:// 
> en.wikipedia.org/wiki/Telephone_numbers_in_the_United_Kingdom#Structure> 
> it says that 04 and 06 are "Not in use"!

Prior to ph[ONE]day, I had an 04 prefix mobile number from Vodafone 
(along with a full credit-card sized SIM).

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