11 - ericssonhistory.com

the entire international number, destination code and national number proceded
by figures shift and the digit zero, the latter in order to indicate an
international call.
The signalling diagram thereafter shows the signalling in the case that the
destination country has Type B signalling with dial selection and non-automatic
tripping of the B subscriber's answer-back. After receipt of the callconnected
signal the international register in the outgoing exchange sends, in
this case, an answer-back trip signal to the B subscriber. The A subscriber
thus receives the same call-connected signal, i.e. the B subscriber's answerback,
on both national and international calls.
Signalling for Outgoing Fully Automatic
International Traffic
The signalling diagram in fig. 13 shows signalling on the chain of circuits
TxA—ARB-ARM—international centre in another country with Type A signalling
for fully automatic international traffic.
The diagram is based on the assumption of several international exchanges
for outgoing traffic in the same country and that all the international routes
do not exist in all international exchanges. After receipt of a proceed-to-select
signal GA, therefore, the A subscriber must send the destination code for the
called country. The destination code is preceded by figures shift and the
digit zero.
The diagram is also based on central charging in the international centre
by means of toll-ticketing equipment (the principle of charging on subscriber's
meters for part of the international traffic may, however, also be used in the
system).
Charging by toll-ticketing means that the backward channel to the terminal
exchange, as in the semi-automatic case, can be reversed to stop polarity for
signalling, in this case, of identity signal INTLX followed by an answer-back
trip signal. The toll-ticketing equipment receives the answer-back for identification
of the A subscriber, whose answer-back should therefore include the
subscriber's number.
The second proceed-to-select signal GA is sent to the A subscriber, who
then sends the B subscriber's number followed by either + (Combination 26)
or - (Combination 1). If the latter combination is sent, the punched card is
immediately set aside after clearing of the connection and the subscriber,
after a renewed call to a service position, can be informed of the charge for
the international connection.
Summary
As will be evident from this account L M Ericsson telex system contains
equipments of such flexibility that within the framework of CCITT's recommendations,
the exchanges can interwork with any other system. This applies
equally on the national and international planes.
On the national plane ARB and ARM exchanges are interworking with
other systems in Canada. Norway, Spain and Yugoslavia. Internationally a
number of countries with different signalling systems are interworking with
the intercontinental ARM exchanges in Montreal, Vancouver and Sydney,
all three of which are connected to the Round-the-World Commonwealth
Cable Scheme.
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