11 - ericssonhistory.com

The capital cost of the telex system per subscriber line is very much greater
than for a telephone system of the same size mainly because of the high cost
of the teleprinter terminal compared with that of a telephone terminal.
Since capital charges play an important part in determining rentals, the
rental charged for telex subscriber service is much higher than for telephone
service. Consequently connection to the telex system is generally not justified
unless the subscriber has a line loading much higher than is usual for a telephone
subscriber. This affects trunking of telex switching systems which must
be designed for heavy subscriber loadings.
Historical Background of Telex Service
Historically, subscriber-operated teleprinter switching systems awaited the
development of a reliable and inexpensive teleprinter suitable for use in widely
dispersed subscribers' offices. The start/stop principle was used in the 1920's
in the United States and Europe to develop such teleprinters, which resembled
an office typewriter in operation and required a minimum of auxiliary
equipment.
Large telegraph switching networks developed in the 1930's. using these
newly-developed start/stop page printers. The first of these was established
by the Bell system in the United States in the year 1930. This network used
direct current subscriber loops and voice frequency telegraph trunk connections
and was designated the TWX system. This system continued to grow
as a manual network until, by 1962, it had approximately 60,000 subscribers.
The network in this year was converted to automatic operation through
partial integration with the telephone switching system using tone signalling
subscribers terminals.
In Europe fully automatic switching networks operating on a telegraph
basis had been developed in the thirties, the first of these being the German
network using the well known dial selection "neutral" supervision step-bystep
switching technique which was followed later by many other countries.
The Netherlands developed an automatic switching system for telegraphy
using the common control switching technique and with the then novel feature
of the use of the keyboard of the teleprinter for selection. Further the system
provided for printed service code indications to be sent to the calling subscriber's
machine as part of the supervisory signalling of the system.
In Australia the two main lines of overseas development were examined
• that of the Bell system in the United States toward integration with the
telephone switching network using tone signalling terminal units with the
teleprinter, and
• that of the rest of the world, toward internationally compatible automatic
teleprinter switching networks using exclusively telegraph trunks.
The decision was made to adopt the latter course. Important reasons for
this decision were that the Australian automatic trunk telephone network was
some years behind the degree of automatisation achieved by the Bell system
and automatic teleprinter switching on this basis would not have been possible
on many routes for some years. Predominantly long distance telex traffic
20