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AXB 20—Description of System
Eric Strindlund, Lars-Åke Andersson, Lennart Brennick
A summary account is given of the structure of system AXB 20 with the emphasis
on its most characteristic property- the functional modularity both in hardware and
software.
The applications and general properties of the system are summarized in a preceding
article in this number.
UDC 621 394 3
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Fig. 1
System AXB 20 has a four-level functional
structure:
System structure
Telex and data traffic are in rapid
growth. At the same time a technical development
is taking place in the field of
telex and data switching exchanges,
with the emphasis on electronics, time
division multiplex being used in the
switching network and stored program
control in the central processing system.
An important property of the system is
its ability for flexible adaptation to
changed conditions, e.g. to changes of
traffic volume, new signalling systems,
new subscriber facilities, new types of
teleprinter, etc.
System AXB 20 possesses this flexibility
to a high degree owing to the functional
modularity that has been introduced
throughout the hardware and software.
This means that an AXB 20 exchange is
easy to handle primarily from the operation
and maintenance point of view, but
also during the various stages preceding
cut-over, i.e. specification, production,
documentation, and installation.
The modularity also facilitates extensions
of the system.
The modular structure of AXB 20 is of
fundamental significance and will
therefore be illustrated from three
aspects.
Operative modularity
The operative modularity of the system
means that it is flexible in providing for
needs of increased traffic capacity, increased
line capacity, rerouting of traffic,
etc.; in other words, it is easily
adaptable to changes in the traffic envi-
••rment in which the exchange works.
Administrative modularity
The functional modularity of AXB 20,
which results in simplified administration
of the exchange both before and
after cut-over, is here called administrative
modularity.
After cut-over of the exchange the administrative
modularity permits simplified
routines for maintenance, service
supervision, programming, fault tracing,
etc., which together signify higher
reliability.
During the stages before an exchange is
put into operation administrative modularity
implies more rational methods
for technical adaptation, production,
documentation, installing, training,
etc., which in total result in a better and
more economical system.
Technical modularity
Technical modularity is no new concept
in telecommunications. It isthe property
which has made it possible to create
global telecommunication systems with
their interworking and interchangeable
local exchanges, trunk exchanges and
transmission systems. This technical
flexibility has been achieved by using
well defined interfaces between the
component parts of the system. This
principle has been adopted in system
AXB 20, which is correspondingly made
up of function blocks with strictly defined
interfaces.
System AXB 20 can therefore be easily
adapted to new functional requirements
and, owing to its exchangeable functional
modules, there is no practical difficulty
in the introduction later on of
new solutions or system components if
warranted by the technical development.
The basic structural principle which
runs through the whole of AXB 20, as
shown schematically in fig. 1, is thus a
consistently implemented functional
modularity. At the highest level, the
system level, AXB 20 consists of the
switching systems for telex and asynchronous
data and of the control
system APZ 210. Some of the basic features
of these systems are presented below.