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ENGINEERING

Fax and Context

Henry Petroski

Standards for Facsimile Transmission

Fax machines have an obvious need to communicate with one another. A given corporation could specify that all of its offices use the same brand of fax so that communications could flow smoothly among them, but communication across company lines would be impeded if fax machines were not compatible. Such compatibility would come if the different fax manufacturers agreed to common specifications, and the first standards for fax transmission were in place as early as 1968. Since communicating by fax, like telephoning, was an international issue, the United Nations, through its International Telegraph and Telephone Consultative Committee (known by the letters CCITT, because the official name in French is Comité Consultatif International Télégraphique et Téléphonique), promulgated the standards, which specified an analog frequency-modulation transmission scheme. According to the 1968 standard, an 8-1/2 by 11-inch page of information was expected to be transmitted within six minutes with a resolution of 100 dots per inch both horizontally and vertically.

Although technical standards spell out minimum expectations at the time a standard is written, they do not limit the levels of performance that manufacturers can seek. All technological artifacts evolve as new ways are discovered and developed for removing limitations on existing technology. In the case of fax machines, some obvious limitations were the speed and resolution with which faxes could be sent, not to mention the high cost of some of the early machines. As engineers continued to work on such problems to give their company's fax machines an advantage over the competition, the 1968 standards became too modest. The class of fax machines that met only those standards came to be known as Group 1 machines. In 1976, Group 2 machines were defined as those meeting a more severe standard, one in which analog transmission time at the same 100-by-100 resolution was only three minutes.





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