Selection and Testing of Electronic Components for LM

Table 2
Extended AKE 13 exchanges Exchange
Fig.2
Helsinki
Copenhagen
Mexico City
Mexico City
Rotterdam DC
Rotterdam DC
Rotterdam INT
Turku
Turku
Ålborg
Ålborg
Time
Jan -77
Nov -75
Sept -75
Sept -76
Mar -73
July-74
May -76
Feb -75
April -77
Aug -74
Feb -77
Size of the extension
4 processors 9 600 multiple pos.
2 „ 7 200
2 „ 7 200
1 „ 3 600
1 200
1 ,, 3 600
1 „ 1 200
800
1 600
3 000
1 200
data processing capacity of the system
can thus be extended in step with the
increase in the number of lines, fig. 1.
This means that the central, most complex
and, for the operation most important
part of the system need never be
larger than what is required for handling
the traffic on the lines connected at the
time.
The factor that is most important for the
reliability is the synchronous duplication
of the control system. It provides
— the fastest possible fault detection
through continuous comparison of
the function of the duplicated units
— the possibility of easily separating
software faults and hardware faults
— simple and reliable fault localization
— the minimum loss of traffic handling
capacity when a fault occurs
— the possibility of introducing new
functions without disturbing the
traffic
Thanks to the duplication it is possible
to reload the whole system without disturbing
the traffic. The two sides in the
system, A and B, which normally work in
synchronism, are separated by means
of a command, fig. 2. Side A is then
loaded with exchange programs and
data from a tape unit. Side B continues
the traffic handling without interruption.
When the loading is completed, the
newly loaded side A takes over the traf­
Size of the exchange after
the extension
6 processors 15 000 multiple pos.
6 ,, 20 400
4 „ 15 000
5 .. 18 600
2 „ 6 000
3 „ 9 600
2 ,, 3 600
2 „ 6 400
2 „ 8 000
4 „ 8 400
4 „ 9 600
fic handling and side B is put in the
standby state. If any operational disturbance
should then occur because of
faults in the newly loaded software,
there will be an automatic changeover
to side B and the traffic handling will
again be carried out by the original
software. When it has been proved that
the newly loaded side A works
satisfactorily, updating of side B is
ordered and also a return to synchronously
duplicated operation. The updating
is carried out by copying the contents
of the A-side stores.
This facility, which through separation
of the system sides enables programsto
be loaded and verified without interruption
of the traffic handling, can also be
used when making major changes in the
software.
The possibilities offered by the synchronous
duplication and multi-processor
arrangement have been utilized
in the methods for installation and testing
of extensions that have been used
successfully in AKE exchanges already
in operation, table 2.
The system can be extended by the
addition of new data processing blocks
without it being necessary to change
the contents of the program stores
already in service. If the extension does
not include any new functions it is sufficient
to make certain minor adjust-