11 - ericssonhistory.com

to be tripped. The calling subscriber's "answer-back", which includes the subscriber's
number, is used for identification purposes because these calls are
not periodically metered at the originating exchange, as are national calls, but
are toll-ticketed at the international centre. The Commission is thus able to
present an itemised account for this high-rate international traffic.
This ticketing process is manual, but eventually the function will be automatic
and calls will then be established completely automatically on some
routes.
Following receipt of the calling subscriber's "answer-back", the international
exchange sends the printed service code GA to the calling subscriber
as an indication that he may now key the international number. The call then
proceeds in much the same way as for a national call.
For international inward calls the international exchange is treated as
though it is a service position connected to the Sydney national telex transit
exchange and 5-digit selection information, preceded by the usual "Figures
Shift" register opening character, is fed into the national telex exchange register
to set up the call in the usual way.
Subscriber Terminal Equipment
As part of planning for the introduction of automatic telex service, the
Australian Post Office studied teleprinters submitted against a Post Office
specification from manufacturers all over the world. Finally the well-known
Siemens T Type 100 page printer was chosen as the standard machine for the
telex service and was introduced into the network in early 1960, with the
intention that by the time the telex network was automatised, all machines
would be of this type.
The machine, as offered, simplified the design of the subscriber's terminal
control unit since the machine itself incorporates calling and clearing keys
and circuit features such as centrifugally operated contacts in the machine to
prove that the motor is running.
Among the optional features of the machine is the ability to add attachments
such as a tape reperforator enabling incoming line signals to be copied
on perforated tape, or for information to be prepared in both page and tape
form as an off-line process using this machine. Also available is a tape transmission
attachment and more than 50 % of all Australian telex subscribers
hire machines incorporating both these attachments.
The terminal control units designed by the Post Office have two functional
arrangements. The first of these is for machines without tape reperforation
and transmission attachments and, in the case of single current signalling
units, uses a very simple 2-relay control unit which is incorporated as part of
the machine. For machines having tape attachments, a more complex terminal
unit is used which permits the subscriber to prepare tape in a local circuit.
The tape prepared may also be proofed by running it through the tape transmitter
receiving page copy on the page section of the machine. This unit incorporates
safeguards permitting an incoming call to take priority over local
tape preparation but preventing the destruction of the tape in local preparation
by giving warning of an impending call with a 3-second time delay before
actual connection of the call. This allows the operator to clear tape under
preparation before the incoming call is received.
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