There have been postings regarding telephones `tinkling'. It has also been posted in reply that this is attributable to line testing. They are tested by detecting the capacitor in the phone socket. Pre-socket phones are still tested OK, but the capacitor is actually in the phone. Hence it tinkles when tested.
Phones are not tested every hour, the current target is once a day, but in most places it'll be once every few days. New systems coming on stream in the future will permit the lines of people who complain about tinling to be excluded from the test cycle.
Conceptually Timed Break Recall (TBR) and Flash Hook are very similar; Flash Hook is used worldwide, TBR was invented by BT (GPT) for use in the UK. The difference is in the duration. TBR is 90ms, Flash Hook is anywhere between 200ms and a couple of seconds.
Cable telephones tend to use Flash Hook as they are using North American exchange equipment (for example, Cambridge Cable use the NT DMS100).
[for want of a better place to move it]
This may interest those who are trying to guess how Chargecard works. It is wholly cribbed from "The Cashless Services System" by N.G. Pope in "British Telecommunications Engineering" Vol 9, July 1990.
Customer dials 144. The call is routed to the nearest digital exchange, which adds 3 digits identifying the charging area of the caller. It routes it to the trunk exchange (Digital Main Switching Unit or DMSU) which routes it to one of 30 Cashless Services Processing Units (CSPUs) where it terminates. As far as conventional charging is concerned it is effectively a free call.
There is now a through transmision path from telephone to CSPU. Payphones are (internally) programmed to switch to MF after receiving 144. The CSPU sends a burst (1 second) of 1600Hz tone. If the originating phone is a payphone it will send its identity (9 MF digits) to the CSPU - (for stats on public payphone usage perhaps, it doesn't say?). Ordinary phones will not respond to the tone.
CSPU returns prompt to dial a/c number and PIN. 12 MF digits are received and stored. An X25 link connects CSPU to the Cashless Services Database (CSDB), and the incoming PIN is encrypted and compared with the encrypted PIN on the CSDB stored against the customer's actual record on the database. Validation takes about 100ms. CSPU returns a message to the caller to enter the required telephone number. The CSPU stores enough digits to route the call which is routed back to the DMSU and on through the PSTN (Public Switched Telephone Network). The CSPU remains in circuit throughout the call.
At the end of the call the CSPU sends an itemised billing record (from where to where, start time, duration etc) to the CSDB which then performs the billing calculation and passes it to the telephone input billing system (TIBS).
The article goes on to explain the hardware etc.
Earlier on it says
"There are various ways in which an automatic Chargecard service [could] be introduced into the network. Ideally the software would be built into the software of an intelligent local exchange with account number/PIN validation being carried out in an intelligent network database (INDB). This is considered to be the ultimate solution to the problem of providing the service. However in 1986 [when the service was envisaged] this solution was not a practical proposition and so an alternative had to be found. [The present system]"
(All information is from the public domain)