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Automatic Tripping of B Subscriber's Answer-Back
As, with keyboard selection, the teleprinter motor starts early, this criterion
cannot be used for informing the A subscriber that he is connected to the B
subscriber. For the same reasons as above concerning the proceed-to-select
signal, it is desirable that the call-connected signal should be printed on the
subscriber's teleprinter. By automatically tripping the B subscriber's answerback
when the call is put through, a printed signal of this kind is obtained
which also informs the A subscriber whether he has been connected to the
correct B subscriber. In order that charging of the A subscriber shall not start
until he has been informed of the identity of the B subscriber, a delay in
starting can be arranged.
A time signal indicating hours and minutes is sent to the A and B subscribers
immediately before the automatic tripping of the B subscriber's
answer-back.
Signalling of Tariff Information
National calls are charged on subscribers' meters at the terminal exchange.
Since the registers are located at the transit centre, the tariff to be applied
for each individual connection should also be determined at the transit centre,
namely by the ARM exchange route marker. Since no tariff pulses can be
signalled on trunk circuits during an established connection, it is necessary,
before the connection is established, to signal the tariff from the transit centre
to the terminal exchange. Accordingly the tariff is signalled to the code receiver
at the terminal exchange (see signalling diagram) from the register
which receives the tariff information from the route marker.
The code receiver then sets up the tariff relays in the repeater. The signal
between register and code receiver consists of a teleprinter signal and is denoted
Z. For greater reliability in the transmission of the signal a 2-out-of-5
code has been used, i.e. the 10 telegraph signals among the 32 combinations
have been chosen which have two start pulses and three stop pulses. The ratio
of the number of start to stop pulses is then checked on reception in the code
receiver.
15 Classes of Subscribers Can be Connected to the
Terminal Exchange ARB
Classes in telex applications are used primarily to decide whether a connection
between two subscribers is permitted or not. In L M Ericsson telex
system the classes of the A and B subscribers are determined at the respective
terminal exchanges. To decide whether the connection is permitted, therefore,
it is necessary to transmit the A subscriber's class to the B subscriber's terminal
exchange, which is done in conjunction with the setting up of the connection.
The A subscriber's class is signalled by means of a teleprinter signal
denoted K from the terminal exchange to the register in the transit centre for
onward transmission to another register or code receiver. The transmission to
the first register takes place before the subscriber has sent the selection information,
so that it is possible to bar a special route or determine a special
route and a special tariff in the transit centre on the basis of the received
classification. Onward transmission of the classification to register or code
receiver is done in conjunction with the transmission of the numerical information.
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