11 - ericssonhistory.com

• Belgium, Holland,
Norway
Type A with printed service signals, sending of
register identity, automatic tripping of B subscriber's
answer-back together with sending of
time.
• France Type A with printed service signals, sending of
day number and time. Tripping of both A and B
subscriber's answer-back.
• Canary Islands U 20 signalling on ARQ.
On an incoming call to the international transit centre in Madrid the outgoing
country receives Type B signals.
The outgoing country can choose
• whether to get the call-confirmation sent and proceed-to select signals as
two separate signals or as a combined signal
• to send selection signals in the form of teleprinter signals or dial pulses.
As will appear from the above, the primary purpose of an international
transit centre is to interwork with different countries in accordance with the
existing variant types of signalling systems.
Signalling Diagrams
Signalling on Subscriber Line
See fig. 8 for outgoing traffic, i.e. traffic from A subscriber (TxA), fig. 9
for incoming traffic, i.e. traffic to B subscriber (TxB). The signalling diagrams
Fig. 8
Signalling on calling subscribers line
Terminal exchange
Calling subscriber equipment consisting
of teleprinter and control unit
Subscriber's line which*may be either
a single current line or
double current line
Forward signalling path, i.e. from subscriber
to exchange
Backward signalling path, i.e. in opposite
direction
Proceed-to-select signal
Selection information, called subscriber's
number
Time signal, hours and minutes, e.g. 21.10
Called subscriber's answer-back
etc. Called subscriber's number
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