RETURN Protocol Information


Facsimile Overview

FAX machines have been around a long time, having been invented by Scotland’s Alexander Bain in 1842. The earliest uses of facsimile transmission involved the transmission of maps and weather data.

A facsimile is an “image replica” of an original source. Although Television itself is technically a type of “facsimile”, the term today applies to machines that reproduce copies of an original document.

Today, the FAX machine is ubiquitous, with at least 80% of US citizens aware of what a FAX machine is, and over 60% having actually used a FAX machine. For many countries, the FAX machine is a necessity for communications. This is especially the case in Japan, where it is used to transmit the complex Japanese Kanji character set. Some estimates indicate that 90% of Japan’s overseas telecommunications consist of FAX transmissions.

In the early 1980’s the FAX machine became increasingly available. The ITU had released the Group 3 FAX recommendation, improving FAX transmission speed through the use of “modified Huffman coding”. Also, the modem modulation was improved to include the V.29 recommendation, with transmit speeds of up to 9600 BPS. Finally, as the ability of Japan to mass-produce electronic devices improved, the cost of FAX machines decreased dramatically. Prices of FAX machines today easily fall within the budget of the American consumer.

Today’s current Group 3 FAX standard supports Black and White transmission only (no greyscaling) at rates up to 14.4 KBPS. Other FAX standards (Group 4) are designed for use over ISDN facilities for even fast transmission and better resolution (picture quality). However, many proprietary forms of FAX transmission exist. I can remember a visit to Newsweek back in 1986, where they used a 768 KBPS facsimile machine to transmit pages to their printing centers.

The CCITT (now ITU) FAX standards define protocols (the procedures necessary to allow communications compatibility) for these machines. Go figure that the common, ordinary, FAX machine uses data communications protocols! Even more ironic is that a FAX machine’s control transmissions loosely follow the OSI (Open System Interconnection) model. Coincidence? I think not!

Knowledge of the FAX protocol is a handy thing. This is especially true, considering the amount of new LBRV (Low Bit-Rate Voice) algorithms and systems being designed and implemented today. Will that Voice-Over-IP (VoIP) algorithm be capable of transporting a FAX signal with a high degree of compatibility?