 to acknowledge receipt of the transmission character set. The Murray Code unlike the Morse code, is com- of the information in some areas the telex message was accepted as posed in such a manner that all characters contain the same number a legally binding. The first telex machines were connected to the of units and each unit takes exactly the same time to transmit. The telephone network alongside a telephone, by setting up a telephone unequal dot and dash of Morse code is replaced by equal duration call and then transferring the line to a teleprinter. As the need for the 'mark' and 'space'. Each character requires 5 units giving 32 char- service grew in business the need for a separate telex network acters in total. The character set is extended by defining two shift became apparent. Initially the telex networks were switched via characters, figures shift and letters shift. manual switchboards, but as they were exclusive to business use the This code makes up the basis of CCITT International Alphabet networks were quickly converted to automatic working in the late Number 2 which is fundamental to the operation of all telex ma- 1950s. chines (see Figure 59.1). As the telex service grew, the need for a more comprehensive character set was required, particularly when operating over high frequency radio circuits. The CCITT Interna- Characteristics of telex tional Alphabet Number 5, with its 7 unit error detecting code and automatic retransmission to correct errors, was adopted for telex Telex differs from telephony in that it carries the written rather than working and a translation defined between both character sets. In spoken communication and is almost exclusively used in the busi- essence this meant that a TELEX machine sending in CCITT ITA 2 ness world. A key element of telex communication is the production would be translated via a code conversion to CCITT ITA 5. of a local record, exactly duplicating the message sent to and When a character is sent to line it is preceded with one start received at the dista