Teletypewriter Exchange Service

Teletypewriter Exchange Service. Commonly known as Telex, it was a switched network of teleprinters for text-based communication. Developed and operated by the Bell System in the United States, it became a global standard for business and diplomatic correspondence. The service allowed subscribers to dial each other directly, sending typed messages over dedicated circuits.

History and development

The origins of the service trace back to the late 1920s, with early experiments conducted by engineers at Western Electric. Commercial service was inaugurated in 1931, initially linking major cities like New York City and Chicago. The network expanded rapidly throughout the Great Depression and World War II, becoming vital for government and military logistics. International connections were later established through agreements with entities like the International Telecommunication Union and foreign carriers such as the British Post Office.

Technical operation

The system utilized Baudot code, a five-bit character encoding scheme, for transmitting data. Subscribers were equipped with a teleprinter, often a model like the Teletype Model 33, connected to the network via a dedicated leased line. Switching was initially manual through operators but was later automated using electromechanical crossbar switches in centers like the Western Union building in Manhattan. Transmission speeds were standardized at 45.45 or 50 baud, ensuring compatibility between machines from different manufacturers like Siemens AG and ITT Corporation.

Subscriber services and features

Customers accessed the network using a unique numeric address, similar to a telephone number. Key features included the ability to send messages to multiple destinations simultaneously and to receive communications 24 hours a day on unattended machines. Confirmation of delivery was provided via answerback codes, which automatically identified the receiving terminal. Services like TWX (Teletype Wide-area eXchange) offered by the Bell System and competing networks operated by the RCA Communications provided varied tariff plans.

Role in business and communication

The service revolutionized international commerce, becoming the backbone for industries like banking, shipping, and journalism. Major corporations, including General Motors and IBM, relied on it for transmitting contracts and invoices. News agencies such as the Associated Press and Reuters used it to distribute wire stories globally. It was also indispensable for diplomatic missions, with embassies and the United Nations maintaining constant links. Its use during events like the Cuban Missile Crisis underscored its strategic importance.

Decline and legacy

The advent of faster, more versatile technologies in the 1970s, such as the fax machine and early computer networks like ARPANET, began to erode its market share. The breakup of the Bell System following the United States v. AT&T Co. antitrust case further disrupted its operation. Most services in North America were officially discontinued by 1981, though they persisted longer in regions like Europe and Asia. Its legacy endures in modern protocols, influencing the development of email and instant messaging, and its infrastructure partially paved the way for digital data transmission.

Category:Telecommunications Category:Bell System Category:Obsolete telecommunications services