Selection and Testing of Electronic Components for LM

128
Fig. 3
Standardization of program packages
merits in the data stores of the data processing
blocks in service, in order to
show the changed configuration of the
control system.
When extending an exchange, the additional
data processing block and
switching equipment are tested by
means of special installation test programs,
which are run in the new processor
before the new units are connected
to the data processing blocks that are
already in service.
Division into function blocks
Several of the basic characteristics of
AKE 13 have been obtained by dividing
the system into function blocks. The
blocks contain program sequences with
functionally associated data and also
hardware units. The interfaces between
the various blocks are clearly defined
and the interworking between blocks is
carried out with the aid of special signals.
Experience has shown that this structure
is essential for the design, maintenance
and production of such a large
and complex SPC system as AKE 13. To
develop clear, lucid and well adapted
documentation for a large program
system is generally considered as one of
the most difficult and resource-demanding
tasks in the production of
software. However, thanks to the division
into blocks it has been possible to
apply the same product handling and
documentation rules for the AKE 13
software as have long been used successfully
for LM Ericsson's earlier exchange
systems. This has been
advantageous both for the operation
and the maintenance of the AKE 13
systems.
Standardized software
When designing software a natural aim
is to create software that can be used
for as many exchanges as possible.
Standardization means simplified document
handling and improved program
quality because of the wider field of
application. This has a favourable
effect on both exchange and product
maintenance.
Thanks to the division into function
blocks it has been possible to build up
an extensive program library over the
years. As regards the switching system
this library comprises approximately
200 blocks with standard functions and
a further 200 blocks containing market-dependent
functions. Altogether
this means a total program volume of
approximately 700 000 words for the
switching system. The standard blocks
cover all signalling systems that have
been specified by CCITT, including No.
6, and a comprehensive operation and
maintenance system for the exchange
switching system. The operating system
in APZ 150 is general for all exchanges,
and it has therefore been possible to
create a standardized system file forthis
system that applies for all exchanges,
both as regards the revision status of
the blocks and their placing (allocation)
in the program store. The operating system
is handled as a superior product
and its status is marked with a revision
state indication for the whole operating
system. The revision state is changed
when functions are added to the operating
system. The operating system in
service can be exchanged for a more
modern one without the environment,
i.e. the software in the switching system,
being affected.
It is also possible to standardize the
switching system software in the same
way. This has been done for several
administrations. The aim has been to
create, for each administration, as large
a share of standard allocated program
volume as possible. The blocks that are
uniaue for a particular exchanqe are