Ways to detect partys answering

[dsk]

To detect the other party's answering has been an issue for years.
Different systems has been used and often the same signal-type has been used for collecting coins during conversation. In this thread the party answer indication are the main issue!  I have tried to make a list, and would like to get comments, and additional information.
(combinations of the systems listed could be used, as in post-pay with voltage reversal...)

dsk

1) Reversal of line voltage.   (Available on ATA today)
2) DC signalling via ground connection 110V? USA/Canada only?
3) 12 or 16 kiloHerz pulse on the line (Europe only?)
    (The one on the picture was used here (Norway) when I served in 1982, and this one use a 16 kHz signal)
4) The caller starts the cycle by inserting coin, or pressing a button.
5) The exchange sends a short interruption in the power supply on the line.

[Jack Ryan]

In Australia we seem to have used each of your listed methods (and then some) with the exception of No 5.

I'll start with the CT1 and skip the early Automatic Electric, Gray and A/B payphones.

The CT1 and Redphone were for local calls only and used the reversal on answer to collect the coin(s) required. Local calls were (and still are) untimed so a single collection was made and there were no special provisions for ending the call.

Subsequent telephones supported STD (trunk calls, long distance) and ISD (international calls) and therefore needed to collect additional coins as needed. In general the exchange generated charge pulses at a rate determined by the distance and time (of day) of the call. The charge pulses were delivered to the payphone by:

1. 50Hz simplex (longitudinal) pulses
2. 12 or 16kHz pulses
3. DC pulses (not like in the US)

The payphones themselves validated and valued the coins and were programmed to know the unit charge (cost per charge pulse) of the time. The charge unit was the same as the cost of a local call.

The end of a call was defined as that time when, on the arrival of a charge pulse, there was insufficient funds remaining for one unit of call.

All of these phones were so called pre-pay but most, if no coin was present on answer, applied a tone to the received to:
1. prevent the caller from hearing a live or recorded message
2. indicate that a coin was required

If no coin was inserted within some seconds, the call terminated.

In addition, additional coins could be added at any time during a toll call.

The phones had other abilities to aid in operator assisted trunk calls but that's off the track a bit.

Jack