MTX – the first mobile switch
The AXE system provided the foundation for the growth of mobile telephony. Its flexibility made it possible to develop a switch for mobile systems, although this was not the intention from the beginning.
AXE was designed around ten building blocks or modules. The intention was to master complexity by dividing the system into independent modules with a standardized interface, much like Lego bricks. This made it possible to increase operational reliability, while providing scope for adding new functions. This flexibility proved to be strategic when a new switch for mobile systems needed to be developed.
In the mid-1970s, the Nordic PTTs put out a request for tender for a switch for the forthcoming Nordic Mobile Telephone system (NMT), which would be used in all Nordic countries. Ericsson was well positioned.
“Developing AXE as a modular system was very foresighted, since it made it possible for us to create new applications. In terms of technical expertise, Ericsson had a head start of several years on its competitors,” says Olle Ljungfeldt, general manager for NMT, TACS and GSM within Ericsson.
Olle Ljungfeldt was responsible for the technical parts of the bid for the first mobile telephone exchange, MTX. By changing a module, the AXE could be re-configured to handle mobile telephone calls. The sub-system for fixed subscribers was replaced by a new sub-system for mobile subscribers. A few other things also needed to be added or adjusted in other parts of the system, particularly with respect to maintenance.
In 1978, Ericsson was chosen as the switch supplier for Sweden, Denmark and Norway and eventually also for Finland and Iceland. The first prototypes were delivered in 1979, and the MTX switch was gradually taken into operation in the early 1980s. Three switches were supposed to handle traffic in Sweden “for the foreseeable future,” according to Televerket, the Swedish PTT. However, it was soon evident that 29 switches were needed in Sweden for NMT alone.
“That kind of miscalculation shows what people believed about the future of mobile telephony in the 1970s,” notes Olle Ljungfeldt.
The MTX switch was important for the success of the NMT system. NMT demanded an advanced switch that could support logic and control functions. The digital technology employed in MTX also provided fast switching between the NMT system’s base stations.
When the GSM system was developed around 1990, a switch was built that would provide more functions, offer less expensive mobile phones and above all support a greater volume of calls. The new switch was developed using AXE as a foundation and the expertise that had been acquired by those who developed the MTX switch.
Third-generation mobile systems also use a switch that is based on an enhancement of AXE.
“Obviously the switch for third-generation mobile systems doesn’t have much in common with the first AXE system for fixed telephony. The contents of the boxes has been changed and replaced, but the basic design and flexibility is the same,” says Olle Ljungfledt.
The first network diagram of the NMTsystems architecture.