Selection and Testing of Electronic Components for LM

134
ence this as congestion or a "silent
connection". They then make a new and
normally successful call attempt, and
thus the traffic handling disturbances
must be considered as negligible.
Fig. 9 shows the system restart rate for
the very first AKE 13 exchange, Rotterdam
DC, from when it was first put
into operation until the end of 1976. The
great reduction in the number of restarts
is a result of the successive improvement
and stabilization of the
system and also the clearance of faults
in the exchange itself. A number of
faults were revealed during the period
immediately after the system had been
put into operation, when new programs
were taken into use and more lines connected
in. Hence the number of system
restarts per month increased until
March 1972, and then started to decrease.
When a system restart is carried out a
printout is obtained, stating the type of
fault. Atthesametime data are recorded
on magnetic tape that define the system
statewhen thefaultoccurred. Thisgives
valuable information for further fault
tracing.
In conclusion it can be said that the
system restart function is an excellent
aid for maintaining the operational reliability
of the system, since it limits the
effects of a fault and also provides the
basic data for clearing program and
handling faults. Furthermore the possibility
of initating a system restart manually
means that the operating staff
have been given a tool that enables
them to clear up a complex fault situation.
Successive improvements
The AKE 13 system has been delivered
to some of the most technically
advanced administrations in the world.
In meeting their different requirements
AKE 13 was successively supplemented,
so that it now constitutes a
system that meets the most divergent
demands, especially as regards operation
and maintenance. The administrations'
experience of AKE 13 has also
provided views that have resulted in
new facilities and improved handling
methods.
As new techniques become available
the possibility arises of adding new system
components, which increase the
capacity of the system, enlarge its field
of use, improve its operational reliability
and simplify its handling. Processor
APZ 150 is one example of this development.
This modern processor was
used for the first time in Stockholm
(Hammarby exchange) in June 1976.
Three more exchanges with APZ 150
were taken into service in 1976, in
Odense (Denmark), Oslo (Norway) and
Helsinki (Finland). By using integrated
circuit engineering and semiconductor
memories it has been possible, for
example, to reduce the space requirements
and increase the traffic handling
capacity. A list of the most important
improvements that APZ 150 has brought
the AKE 13 system is given on the opposite
page.
Another example of the continuous development
of the AKE system is the introduction
of regional computers. Thus
the LM Ericsson type APN 163
minicomputers are used in AKE 13 for
several applications, for example forthe
signalling terminals in the latest AKE
generation of the CCITT signalling system
No. 6, and for the display-based
operator system ANE 403. Minicomputer
APN 163, which is also used in several
applications outside the telecommunications
field, has been designed with
special regard paid to the stringent demands
on reliability that a telephone
exchange makes. The list of instructions
for APN 163 has also been designed
to meet the requirements of SPC
exchanges. Since the minicomputer
has been designed by LM Ericsson it
has been possible to integrate its operation
and maintenance with that of the
remainder of the exchange.
The use of regional computers provides
valuable flexibility at the interface between
the central functions in the control
part of the AKE system and the functions
of the peripheral units, which are
often affected by external conditions. In
certain cases it has also been possible
to relieve the central control system of
routine but capacity demanding functions,
which would otherwise have reduced
the overall traffic handling
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