T200 telex and data switching system

The T200 Switching System by Hasler Ltd, Berne was one of the world's first (if not the first) stored-program-controlled public line-switching systems with digital transmission at bus-level. The first technical description for a stored-program-controlled telex exchange was produced in 1966, and led to an order from Cable and Wireless (Hong Kong), who were already a major customer of Hasler’s TOR (Teletype (Telex) over Radio) equipment. The order was placed in December 1967. The first T201 system entered service in Hong Kong in 1972. This subsequently led to three generations of switching systems developed from the original T200 system, operational for 48 years in fifteen countries around the world, all based on the principle of majority processing for security and redundancy, with three processors running synchronously.

The last T203 system was switched off on 31 August 2020. It was run by SwissTelex Ltd in Lugano (Breganzona), Switzerland. Its processor has been transferred to the Swiss Museum of Communication in Berne.

Initial development

The first T201 exchange was based on solid state technology (TTL) and used duplicated Ampex core memories for central storage. It entered public service in Hong Kong in February 1972.

At the same time, a project was being formulated in Switzerland for an Integrated Telecommunications Network (Integriertes Fernmelde-System). The decision was taken to base this project on the T200 system.

Hardware

Hasler had developed its own T200 processor system, achieving a high reliability level based on redundancy, with three processors running synchronously supervised by unique patented majority circuitry us 3,921,149, W.Kreis and P.Laederach of Hasler Berne Switzerland, "Computer Comprising Three Data Processors", published 1975-11-18 .

The core memory comprised a maximum of 64k lines, each of four data bytes, plus an additional control byte for parity checking, etc. Ampex magnetic tapes were the only mass storage devices, and were used mainly for program loading, call data recording and memory dumps for software failure analysis. All vital System components were redundantly equipped for achieving a specified system availability of 99.997%. Hasler had adequate know-how in state of the art hardware development and kept to project schedules for all hardware units.

Software

A dedicated assembler language, TELMOS, making best use of the T200's instruction set was developed to use the limited storage space down to bit-level with optimal real-time usage, and to meet the challenge of developing a comprehensive software package for a capacity of 4096 Telex lines. The software comprised the real-time operating system, call handling using various signalling types and subscriber facilities (such as abbreviated dialling, advice of call duration), routing control, on-line network database management, call recording to magnetic tapes, network management, overlay programs for batch processing of print-outs, and additional utilities such as magnetic tape copying, hardware testing and diagnostics.

At the start of the project Hasler lacked software expertise and capacity for creating such a complex real-time system and in 1970 had to call on the British consultancy company, Scicon Ltd, to accelerate progress.

After some delays, the first T201 Exchange in Hong Kong, was put into service provisionally on 2nd February 1972 in the (old) Mercury House in Central. The new Mercury House in Wanchai was still in building and was only ready in August 1972 to host the second T201 exchange with the final software package. This was put into service in 1973, after which the first T201 exchange was moved to New Mercury House and put into service in 1974, increasing the total line capacity to 8192 telex lines. Specific to the Hong Kong site Hasler had also provided an advanced solution for the connection of Kowloon subscribers. T201 line processors installed in Kowloon Ocean Terminal could be connected to the T201 Exchanges in Hong Kong using PCM technique over a 2.4 Mb/s radio-link across the harbour. Each link provided a capacity for 1024 telex lines.

T202

The T202 was developed to cope with rapidly increasing demand for more traffic handling capacity and higher software functionality. The addressable range for the central memory was increased, discs were added for random-access mass storage, the traffic handling capacity was doubled by the concept of load sharing between twin processors, and the line equipment upgraded for switching 300Bd anisochronous data, which was required by the Swiss PTT for the implementation of its new network.

The first T202 Exchange was brought into service as a Gateway Exchange for the Overseas Telecommunications Commission (OTC/A) in Sydney, Australia. The system was equipped from the start with twin processors in view of over-optimistic growth predictions for telex in Australia.

In 1979 C&W Hong Kong started to operate its first T202 System (HK-D) with twin-processors also required to cope with new value-added Telex services such as Store & Forward, Instore and automated Customer Enquiry Services. Telex had been and was still growing at a high rate with Hong Kong's international business booming. In 1982 a second T202 Exchange (HK-E) was installed in Kowloon, which permitted C&W to switch off the former 3 T201 Systems previously configured as concentrators connected to HK-D.

In 1972, the Swiss Postal and Telephone Authority (PTT) placed orders for T202 Telex Systems for its telex and data network.

In 1975 the first T202 system was brought into service in Sydney, Australia. It had an increased capacity, with twin processors for load sharing).

T203

The Swiss project for an Integrated Telecommunications Network (Integriertes Fernmelde-System (IFS)) mentioned already had in the meantime developed a new T203 processor, which was released for production in May 1981. Since the basic T200 concepts had been maintained, it was decided to upgrade the Telex systems with a significantly improved performance to space ratio and reduced energy consumption. The replacement of the outdated core memories by solid-state memories (64kB chips) was another important factor. The T203 generation led to a break-through for the T200 product-line. In 1985 a cooperation agreement was signed with the Nanjing Telecommunications Equipment Factory, which on behalf of MPT, the telecommunications authority of the People's Republic of China, decided to base the whole Chinese Telex network on the T200 system. The first T203 Exchange in Taiyuan was put into service in late 1985. Later MPT led Hasler to upgrade the T203 to a TM203 providing combined Telex and Telegram switching. By 1997 17 T203 Systems (of which 12 were TM203) had been deployed in China.

The first Swiss T203 telex system was brought into service at Wallstrasse in Basle [d23] in 1984. By 1989 the Swiss PTT's telex network was entirely based on T203 Exchanges. Note: In 1983, the IFS-project dropped the objective for a Swiss made network for the alternative to use international technology which had become available in the meantime. The world players Siemens, ITT, LME (with Hasler) made the race. The T203 Product Line however survived for many years to come in Telex.

In the meantime the IFS project had launched the development of the T203 Processor. This incorporated a solid state central memory. The processor was finally released for production in 1980, and a year later, development started on a T203 telex and data-switching system (taking over this processor from IFS). In 1983, the Swiss Integrated Telecommunications System project was cancelled. The Swiss IFS Network would in future be based on international technology (Siemens, ITT, LME).

In 1985. the first T203 Telex System was brought into service at Wallstrasse in Basle. The Swiss PTT's network of T203 systems would run to eight by 1989, including the exchange at Lugano which would eventually form the backbone of the network.

The same year, the first of fifteen systems in the People's Republic of China was installed.

T203+

The extended product life span provided by the T203 generation also provided a perspective for new options to respond to needs for interworking with new services and for otimising network and operations costs. New interworking features over X.25 ports included Teletex/Telex Conversion (TTCF) [e10], Packet Assembly Disassembly [e12 ] for Messaging Systems interworking with Telex Networks (e.g. EasyLink in UK with Mercury's T203) and the same for Videotex and Corona [d25] in Switzerland. Integrated R101 multiplexers and intelligent T203 line processors configured as Telex Concentrators (TCON)[e11] for up to 256 lines also had a potential for significant savings on equipment space and cost. Another feature of the T200 Software was the possiblity to form Virtual Telex Networks (VTN) for Telex customers in foreign countries enabling the formation of efficient international Telex Hubs. This scheme was increasingly implemented by operators chosing to abandon Telex operation with obsolete exchanges at high maintenance cost.

Maturity and Decline

In 1987, Hasler Ltd merged with two other telecommunications manufacturers into the Ascom Group, and three years later, management decided on the implementation for its telex business of a ‘slow market retreat strategy‘ with the aim of:

* ensuring contractual commitments towards customers (till 2005!);
* continuing to exploit T200 business opportunities offering risk-free investments;
* reducing staff from 125 to 25
* gradual outsourcing of T200 software maintenance and support, leading to a management buyout.

In 1997, all Swiss telex services were connected to the T203 system in Lugano, and in 2006, SWISSTELEX was founded in Lugano, as a platform for interworking with any other network.

In 2020, the T203 Telex-System in Lugano was switched off – the last of approximately fifty T200 systems world-wide, and the last T203 Processor was moved to the Museum of Communication in Berne.

The last 20 years – Creation of SwissTelex Ltd As planned in 1994 by Telecom PTT all telex services had been transferred to the T203 system (installed in 1987) of the now privatised SWISSCOM's Telex Competence Centre in Lugano and a new strategy was set up to enable the connection of Telex Subscribers of foreign countries. In 2006 SWISSCOM encouraged a management buy-out handing over the rights and obligations to the SwissTelex Ltd to provide the Telex-Service in Switzerland, with the option to provide Virtual Telex Networks for other countries under regulated terms.

The T203 becomes a Telex Hub for foreign VTN The first VTN in Switzerland was created as early as 1999 for Sweden’s subscribers and by 2015 the T203 hosted foreign Telex subscribers from 20 countries, e.g. Mercury UK/2006, Germany/ 2007, BT/2008. The last T203 Central System (triplicated processor in the middle) On 31st August 2020, the T203 Telex-System in Lugano was switched off – the last of approx. 50 T200 systems having been in service world-wide.

The triplicated Processor of the last T203, as a landmark of Swiss telecommunication history was subsequently transfered to the Museum of Communication in Berne, host of old Hasler’s museum since 2003. Hasler's role in telegraphy had started in 1852.

T200-Systems have been deployed in:
Switzerland: CH-PTT (8 systems), Swiss Federal Railways (SBB)
Europe: Cyprus, Paris, Ireland, UK (Mercury Communications), Poland 6 systems, Czech Rail, Austria (M203 Telegram)
Asia: Hong Kong (6 systems), China (15 systems, mostly TM203 for Telex & Telegram), Manila, Singapore (Teletex CF, then Telex), Bombay & Madras (Telex & Telegram), Djakarta
Australia: Sydney, Melbourne (Teletex-CF)
Africa: Malawi