Public telephones and telephone exchanges

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djl
Beiträge: 17
Registriert: Do 27. Jan 2022, 00:31

Public telephones and telephone exchanges

Beitrag von djl »

Hello. Sorry again for speaking English.
I'm curios, in the old days of the pay (public phones) how the telephone exchange knew when to take the coin. How it the exchange communicated that to the telephone?
djl
Beiträge: 17
Registriert: Do 27. Jan 2022, 00:31

Re: Public telephones and telephone exchanges

Beitrag von djl »

Danke schon!
I didn't know what term too look for, but there is a good start!
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Roehricht
Beiträge: 6594
Registriert: Di 13. Aug 2013, 04:00
Wohnort: 25474 Hasloh

Re: Public telephones and telephone exchanges

Beitrag von Roehricht »

Hi ,
The brtish payphone system used to work total different to the continental ones which is obvious feature is dial first , than insert the coins.

The british system used the pay tone system. The exchange send a high pitched series of rapid pips after the desired station answered , that´s the pay tone upon you have to insert a coin. At the phone side , the coins generate different frequencies according to its value. This method is derived from the older age were phone calls switched by hand from the lovely switchboard girls. When they say. "30 p for the next 3 minutes" , they hear the right sound which came from three 10 p coins you had insert.
In the phone exchange is a a tone receiver attached to the dedicated payphone switches which give way to the speech path to the remote party after insert coins.
The pay pips were generated at the central time register for select the appropiate tariff to the dialled number. Another paytone remaind to insert more coins before the remaining time elapse. The speech path is turn on be reverse the a/b wires from the exchange side. (silent reversal)

The latest modern payphone use a digital modulated subcarrier for singnalling interchange. Those are the coinless pay phones with the BT unit cards and credit cards phones.

73
Wolfgang
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haupes
Beiträge: 169
Registriert: Di 13. Aug 2013, 20:15

Re: Public telephones and telephone exchanges

Beitrag von haupes »

In the USA in the 1970s, people found a way to make free calls by creating a control tone sequence with a toy whistle: https://en.wikipedia.org/wiki/John_Draper#Phreaking
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Roehricht
Beiträge: 6594
Registriert: Di 13. Aug 2013, 04:00
Wohnort: 25474 Hasloh

Re: Public telephones and telephone exchanges

Beitrag von Roehricht »

Hallo,
In the USA in the 1970s, people found a way to make free calls by creating a control tone sequence with a toy whistle:
Yes, people over there were quite crative to find a way for free phone calls. :mrgreen:

Way back in those days USA used the old CCITT signalling system no.5. called inband system. It employs tone frequencies so manipulations were easy to optain. It was replaced by system no.7 when digital switches come in service which makes manipulation much more difficult. Many years both systems run parallel due to step-by-step modernisation. Signalling system no.7 go on living in IP systems.
Look here:
https://en.wikipedia.org/wiki/Signaling_System_No._5

The brits used different signalling systems all over the years. They develope countermeasures against "Phone Phreakers" quite early with success.

https://www.britishtelephones.com/pwover1.htm

73
Wolfgang
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