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| ITA2 | |
|---|---|
| Name | International Telegraph Alphabet No. 2 |
| Aliases | Baudot code, Murray code |
| Introduced | 1924 |
| Designer | Émile Baudot (basis), Donald Murray (adaptation) |
| Used by | Western Union, Royal Navy, French Post Office, Soviet Union |
| Type | 5‑bit binary code |
ITA2
ITA2 is a five‑bit teleprinter code used for serial communication in early telegraphy and radioteletype systems. It evolved from earlier electromechanical signaling schemes and became a de facto standard for many postal, telegraph, naval, and aeronautical services through much of the twentieth century. ITA2 enabled compact binary transmission of Latin‑script text and control functions over long‑distance links operated by organizations such as Western Union, British Post Office, US Navy, and International Telecommunication Union.
The code’s lineage traces to the pioneering switching work of Émile Baudot and subsequent refinements by Donald Murray for typewheel teleprinters and paper‑tape systems. Early deployments occurred alongside apparatus from manufacturers like Morse Telegraph Company and ITT Corporation, and in services run by entities including Western Union and national postal administrations such as the British Post Office and the French Post Office. During the interwar and World War II periods, militaries and navies—e.g., the Royal Navy and the US Army Signal Corps—integrated five‑bit teleprinter codes into tactical and strategic communications. Post‑war aviation and maritime radiotelephony organizations including International Civil Aviation Organization and the International Maritime Organization used five‑bit radioteletype links derived from the same family of codes. Standards bodies like the International Telecommunication Union and national standards agencies codified operation and signaling parameters for teletype and radioteletype services.
The code uses fixed five‑bit patterns to represent letters, figures, and control functions, requiring shift characters to toggle between alphabetic and numeric/punctuation modes. Mechanically implemented in electro‑mechanical teleprinters from makers such as Murray, Siemens, ITT, and Remington, the signaling used asynchronous serial transmission with start and stop bits and specified bit timing. Circuitry and relays in equipment like the Teletype Model 33 interpreted bit patterns to actuate typebars, drums, or printers. Error characteristics were influenced by line quality on circuits operated by carriers including AT&T and Western Union, and by modulation schemes used on radio channels such as amplitude modulation and single‑sideband employed by stations like Radio Moscow and BBC World Service.
Multiple national and manufacturer variants adapted the five‑bit repertoire for language needs and control sequences. For example, versions deployed by the Soviet Union accommodated Cyrillic mappings used in equipment produced by firms like Moskabel', while Western European operators adjusted character sets for diacritics in French and German for companies such as Siemens and Oliven. Teleprinter models including the Model 15 and Model 33 implemented variant shift tables; bespoke adaptations appeared in specialized systems for organizations like NASA and the US Air Force for telemetry and command messages. Amateur radio operators and hobbyist communities later adopted modified versions for noncommercial radioteletype experimentation, referencing documentation from groups such as the American Radio Relay League.
Five‑bit teleprinter codes were widely used for commercial telegraphy by Western Union, for diplomatic channels in foreign ministries, for naval communications aboard vessels of the Royal Navy and United States Navy, and for aeronautical weather and flight information via services coordinated by International Civil Aviation Organization. Broadcast stations including BBC World Service and Radio Free Europe used radioteletype to distribute news and monitoring services. In industrial settings, railways and utilities employed teleprinter lines managed by entities such as London Transport and national railways for operational dispatch. During conflicts, intelligence organizations and signals units used teletype traffic in theaters overseen by commands like Allied Expeditionary Force and Soviet High Command.
Interoperability depended on agreed signaling parameters (baud rate, start/stop bits, current reversal) and standardized shift conventions promulgated by bodies such as the International Telecommunication Union and national carriers like AT&T and British Post Office. Character repertoire differences required interworking tables when routing between networks operated by Western Union, Soviet Post Office, or regional radio services; gateways and translation equipment were produced by manufacturers including ITT and Siemens. Modern conversion to computer formats involved mapping five‑bit patterns to character sets like ASCII and EBCDIC and using software libraries derived from archival specifications held in repositories such as the National Archives (UK) and the US National Archives and Records Administration.
The five‑bit teleprinter tradition influenced later serial encodings, teletypewriter conventions in equipment from Teletype Corporation, and early computer teletypes used in UNIX and academic computing at institutions such as MIT and Bell Labs. Concepts such as shift states and fixed‑width binary symbols anticipated mechanisms in digital codes like Morse code‑derived protocols and contributed to line‑oriented terminal design in mainframe contexts operated by IBM and DEC. Preservation efforts by museums including the Science Museum (London), the Smithsonian Institution, and specialist societies maintain operational teleprinters for education and research. Category:Telegraphy