Telegraph code

A telegraph code is a character encoding used to transmit information through telegraphy machines. The most famous such code is Morse code.

Manual telegraph codes

Morse code can be transmitted and received with very primitive equipment. It encodes each letter of the alphabet as a series of dots and dashes. International Code developed from Morse's original listing and makes a binary code. The speed of sending is directly related to the length of the shortest (dot) element: a dash is three dots long, an inter-character gap is the same (3 dots) long, and inter-word and sentence gaps should be 5 or 7 dots long (change from earlier standard - 5 dots). The speed of sending is also referred to as words per minute, and is classically based on the 'paris' formula - as 'paris' is considered to be an average length word. See main article on Morse Code.

Morse code can even be used to transmit Chinese characters. There already existed dictionaries which numbered the Chinese characters. It is simply a case of sending the numbers by Morse Code, and these numbers are then looked up in the dictionary at the receiving end.

In practice, this is a slow process, unless done by an expert Chinese telegrapher who can remember the numbers of the all the 5,000 odd characters which are in common use.

Automatic telegraph codes

Manufacturers developed teleprinters to allow typed messages to be transmitted and received without Morse code training. At the time, hardware costs depended on the length of the longest code. With an alphabet of 26 uppercase letters, the code had to be at least 5 bits long. To reduce hardware cost, teleprinter manufacturers adopted the fixed-length 5 bit Baudot code (rather than trying to use variable-length Morse code).

Users were not satisfied with the limited character set available in Baudot code. Demand for lowercase letters and more punctuation marks led to teleprinters with a 6 bit TeleTypeSetter (TTS) code, and later, 7 bit ASCII code.

(Demand for accented vowels led to the 8 bit ISO 8859-1. Demand for Cyrillic, Hebrew, Arabic, Greek, and other letters led to many variations of ISO 8859. Demand for using more than one of these sets of letters at the same time led to the 16 bit Unicode. Demand for Chinese characters led to 20 bit Unicode, which clearly is impossible for any typewriter like formed character mechanical teleprinter, although dot-matrix printers can print Chinese characters.)

Commercial codes

Telegraph companies charged based on the length of the message sent. Therefore, to save money, elaborate commercial codes were developed that encoded common phrases as words or numbers. Another aim of the telegraph codes was to reduce the risk of misunderstanding by avoiding having similar words mean similar things.

Those sending telegraph messages were also able to encrypt the messages to ensure secrecy.

Examples of these codes include the A.B.C Telegraphic Code and Bentleys Second Phrase Code. In addition to more general commercial codes, there were a number of codes targeted at particular industries e.g. railways, cotton.

In codes such as the A.B.C. Telegraphic code, code words could contain what would be recognised today in programming terms as parameters e.g. in the 'Freight and tonnage requirements' section, antitacte means 'Mozambique, loading at not more than two places, to -, steamer for about - tons general cargo at - per ton on the d/w capacity to cargo'. The telegrapher would then fill in the 3 parameters, the destination, the number of tons and the price per ton.

The regulations of the International Telegraph Convention distinguished between 'code telegrams' which it describes as 'those composed of words the context of which has no intelligible meaning' and 'cipher telgrams' which it describes as 'those containing series of groups of figures or letters having a secret meaning or words not to be found in a standard dictionary of the language'. Codes such as the A.B.C. Telegraphic code, therefore, included both numbers and code words so the user could chose between the two.

Example code words:

 - From the A.B.C Telegraphic Code
    - paromella - in leaaving the dock (harbour) struck the pier, damaging the stern
    - arimaspen - Phaeton with 6 B.H.P. two cylinder motor to seat four passengers speed - miles per hour
    - haubarer - Charterers will allow the option of carrying horses for ship's benefit

 - From Bentley's Complete Phrase Code 
    - oyfin - has not been reinsured
    - azkhe - clean bill of health
    - atgam - have they authorised?

 - From the telegraphic cipher code specially adapted to the cotton trade
    - dress - the supply from India will be less than expected
    - insane - at what price, free on board and freight, can you offer us cotton for shipment by steamer sailing this week?
    - puncher - we anticipate rate of interest will be reduced by Bank of England

In computer networking terminology one would say the commercial code is layered on top of Morse code, which in turn is layered on top of binary code, which in turn is layered on top of a physical telegraph wire.

International Code of Signals (radiotelegraph)

In 1931, the International Code of Signals, originally created for ship communication by signalling using flags, was expanded by adding a collection of five-letter codes to be used by radiotelegraph operators.

See also

• Chinese telegraph code