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Fax

Fax (short for facsimile, from Latin fac simile, "make similar", i.e. "make a copy") is a telecommunications technology used to transfer copies (facsimiles) of documents, especially using affordable devices operating over the telephone network. The word telefax, short for telefacsimile, for "make a copy at a distance", is also used as a synonym. Although fax is not an acronym, it is often written as "FAX". The device is also known as a telecopier in certain industries. When sending documents to people at large distances, faxes have a distinct advantage over postal mail in that the delivery is nearly instantaneous, yet its disadvantages in quality have relegated it to a position beneath email as the prevailing form of electronic document transfer except where the legal status of a sent fax and its accompanying sending report are desired. 

Overview 

A "fax machine" usually consists of an image scanner, a modem, and a printer.

Although devices for transmitting printed documents electrically have existed, in various forms, since the 19th century (see "History" below), modern fax machines became feasible only in the mid-1970s as the sophistication increased and cost of the three underlying technologies dropped. Digital fax machines first became popular in Japan, where they had a clear advantage over competing technologies like the teleprinter, since at the time (before the development of easy-to-use input method editors) it was faster to handwrite kanji than to type the characters. Over time, faxing gradually became affordable, and by the mid-1980s, fax machines were very popular around the world.

Although many businesses still maintain some kind of fax capability, the technology has faced increasing competition from Internet-based systems. However, fax machines still retain some advantages, particularly in the transmission of sensitive material which, due to mandates like Sarbanes-Oxley and HIPAA, cannot be sent over the Internet unencrypted[citation needed]. In some countries, because electronic signatures on contracts are not recognized by law while faxed contracts with copies of signatures are, fax machines enjoy continuing support in business.

In many corporate environments, standalone fax machines have been replaced by "fax servers" and other computerized systems capable of receiving and storing incoming faxes electronically, and then routing them to users on paper or via an email (which may be secured). Such systems have the advantage of reducing costs by eliminating unnecessary printouts and reducing the number of inbound analog phone lines needed by an office.

Capabilities 

There are several different indicators of fax capabilities: Group, class, data transmission rate, and conformance with ITU-T (formerly CCITT) recommendations.

Fax machines utilize standard PSTN lines and telephone numbers.

Group 

Analogue 

Group 1 and 2 faxes were sent in the same manner as a frame of analogue television, with each scanned line transmitted as a continuous analogue signal. Horizontal resolution depended upon the quality of the scanner, transmission line, and the printer. Analogue fax machines are obsolete and no longer manufactured. ITU-T Recommendations T.2 and T.3 were withdrawn as obsolete in July 1996.

* Group 1 faxes conform to the ITU-T Recommendation T.2. Group 1 faxes take six minutes to transmit a single page, with a vertical resolution of 96 scan lines per inch. Group 1 fax machines are obsolete and no longer manufactured.
* Group 2 faxes conform to the ITU-T Recommendations T.30 and T.3. Group 2 faxes take three minutes to transmit a single page, with a vertical resolution of 96 scan lines per inch. Group 2 fax machines are almost obsolete, and are no longer manufactured. Group 2 fax machines can interoperate with Group 3 fax machines.

Digital 

Group 3 and 4 faxes are digital formats, and take advantage of digital compression methods to greatly reduce transmission times.

* Group 3 faxes conform to the ITU-T Recommendations T.30 and T.4. Group 3 faxes take between six and fifteen seconds to transmit a single page (not including the initial time for the fax machines to handshake and synchronize). The horizontal and vertical resolutions are allowed by the T.4 standard to vary among a set of fixed resolutions:
o Horizontal: 100 scan lines per inch
+ Vertical: 100 scan lines per inch
o Horizontal: 200 or 204 scan lines per inch
+ Vertical: 100 or 98 scan lines per inch ('Standard')
+ Vertical: 200 or 196 scan lines per inch ('Fine')
+ Vertical: 400 or 391 (note not 392) scan lines per inch ('Superfine')
o Horizontal: 300 scan lines per inch
+ Vertical: 300 scan lines per inch
o Horizontal: 400 or 408 scan lines per inch
+ Vertical: 400 or 391 scan lines per inch ('Ultrafine')
* Group 4 faxes conform to the ITU-T Recommendations T.563, T.503, T.521, T.6, T.62, T.70, T.72, T.411 to T.417. They are designed to operate over 64 kbit/s digital ISDN circuits. Their resolution is determined by the T.6 recommendation, which is a superset of the T.4 recommendation.

Fax Over IP (FOIP) can transmit and receive pre-digitized documents at near realtime speeds. Scanned documents are limited to the amount of time the user takes to load the document in a scanner and for the device to process a digital file. The resolution can vary from as little as 150 DPI to 9600 DPI or more. This type of faxing is not like the e-mail to fax service that still uses fax modems at least one way.

Class 

Computer modems are often designated by a particular fax class, which indicates how much processing is offloaded from the computer's CPU to the fax modem.

* Class 1 fax devices do fax data transfer where the T.4/T.6 data compression and T.30 session management are performed by software on a controlling computer. This is described in ITU-T recommendation T.31.
* Class 2 fax devices perform T.30 session management themselves, but the T.4/T.6 data compression is performed by software on a controlling computer. The relevant ITU-T recommendation is T.32.
* Class 2.1 fax devices are referred to as "super G3"; they seem to be a little faster than the other 2 classes.
* Class 3 fax devices are responsible for virtually the entire fax session, given little more than a phone number and the text to send (including rendering ASCII text as a raster image). These devices are not common.

History 

Wire transmission 

Scottish inventor Alexander Bain worked on chemical mechanical facsimile type devices and in 1846 was able to reproduce graphic signs in lab experiments. Frederick Bakewell made several improvements on Bain's design and demonstrated his device at the 1851 Great Exhibition in London. Bain and Bakewell's systems were inferior and could reproduce only poor quality images. They lacked synchronization between the transmitting mechanism and the receiving mechanism. In 1861, the first practical operational electro-mechanical commercially exploited telefax machine, the Pantelegraph, was invented by the Italian physicist Giovanni Caselli. He introduced the first commercial telefax service between Paris and Lyon some 11 years before the invention of workable telephones.[1][2]

In 1881, English inventor Shelford Bidwell constructed the scanning phototelegraph that was the first telefax machine to scan any two-dimensional original, not requiring manual plotting or drawing anymore. Around 1900, German physicist Arthur Korn invented the Bildtelegraph, widespread in continental Europe especially since a widely noticed transmission of a wanted-person photograph from Paris to London in 1908, used until the wider distribution of the radiofax. Its main competitors were the Bélinograf by Édouard Belin first, then since the 1930s the Hellschreiber, invented in 1929 by Rudolf Hell, a pioneer in mechanical image scanning and transmission.

Wireless transmission 

As a designer for the Radio Corporation of America (RCA), in 1924, Richard H. Ranger invented the wireless photoradiogram, or transoceanic radio facsimile, the forerunner of today's "Fax" machines. A photograph of President Calvin Coolidge sent from New York to London on November 29, 1924 became the first photo picture reproduced by transoceanic radio facsimile. Commercial use of Ranger's product began two years later. Radio fax is still in common use today for transmitting weather charts and information. Also in 1924, Herbert E. Ives of AT&T transmitted and reconstructed the first color facsimile, using color separations. 

Telephone transmission 

Prior to the introduction of the once-ubiquitous fax machine, one of the first being the Exxon Qwip[3] in the mid-1970s, facsimile machines worked by optical scanning of a document or drawing spinning on a drum. The reflected light, varying in intensity according to the light and dark areas of the document, was focused on a photocell so that the current in a circuit would vary with the amount of light. This current was used to control a tone generator (a modulator), the current determining the frequency of the tone produced. This audio tone was then transmitted using an acoustic coupler (a speaker, in this case) attached to the microphone of a common telephone handset. At the receiving end, a handset's speaker was attached to an acoustic coupler (a microphone), and a demodulator converted the varying tone into a variable current which controlled the mechanical movement of a pen or pencil to reproduce the image on a blank sheet of paper on an identical drum rotating at the same rate.[4] A pair of these expensive and bulky machines could only be afforded by companies with a serious need to communicate drawings, design sketches or signed documents between distant locations, such as an office and factory.