Yngve Rapp - The history of Ericsson

Fig. 6
Connected by command, any line or circuit to an
AXB 20 exchange can be measured from this Engineering
Control Board ECB
transmission and reception of signals,
etc. It also performs certain service
observation and supervisory functions,
e.g. regeneration, continuous test pattern
generation for functional checks,
check of distortion, time measurement,
etc.
The more complex switching functions
are performed by TTS (Telex Traffic
Handling Program Subsystem), which is
made up of software.
The TTS subsystem consists of a
number of function blocks, which may
be divided into five groups with the following
functions:
1. Handling of data relating to trunks,
subscriber lines, and to the TXS subsystem
2. Handling of central analysis functions,
e.g. analysis of selection signals,
route numbers, etc.
3. Handling of charging, accounting,
statistics
4. Handling of subscribers facilities, e.g.
hot line, broadcast/conference call,
call diversion
5. Handling of signal transmission during
the setting-up and clearing
phases of a connection.
Operation and maintenance functions
of TMS and TLS subsystems
The TMS subsystem administers chiefly
the operation and maintenance functions
which are implemented in software.
By commands to TMS, changes
are made in subscriber and circuit data,
and in routing, and other normally occuring
operational measures are carried
out.
Through TMS the mode of functioning
of the switching system is supervised on
the basis of the periodically recurring
character pattern. On encountering deviations
from the normal mode of functioning
TMS takes action in the form of
alarm and possibly change-over to the
parallel switching system.
TMS is engaged also in start-up of the
system, updating, program modifications,
etc.
The TLS subsystem comprises hardware
for measurements on trunks and
subscriber lines. The measurements are
made from an engineering control
board, to which an optional line is metallically
connected via a connection relay
in the line adapter circuit for that line.
Measurements, e.g. distortion measurements
of routes, are programmed to
be carried out automatically with the aid
of the corresponding maintenance
program.
From the engineering control board direct
measurements are made of line
current, voltage, and leakage resistance
for each line. The distortion on
the line can also be measured and read
directly on an instrument in the control
board (fig. 6).
Supplementary functions
Manual service
Operators' positions equipped with visual
displays for manual assistance in the
setting up of connections can be connected
to the switching system.
These positions can be connected to
the AXB 20 exchange from a remote
point via modems, which permits this
service to be located at any point in the
network. Examples of functions performed
at the operators' positions are
- international telex traffic to countries
requiring manual assistance
— information services
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