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This fax machine from 1999 used relatively new inkjet printing technology on normal paper.
Like many fax machines, this 1990 model used thermal printing on relatively expensive thermal paper which came in rolls. The roll was inserted into a compartment in the machine.

Fax (short for facsimile), sometimes called telecopying or telefax (short for telefacsimile), is the telephonic transmission of scanned printed material (both text and images), normally to a telephone number connected to a printer or other output device. The original document is scanned with a fax machine (or a telecopier), which processes the contents (text or images) as a single fixed graphic image, converting it into a bitmap, and then transmitting it through the telephone system in the form of audio-frequency tones. The receiving fax machine interprets the tones and reconstructs the image, printing a paper copy.[1] Early systems used direct conversions of image darkness to audio tone in a continuous or analog manner. Since the 1980s, most machines transmit an audio-encoded digital representation of the page, using data compression to transmit areas that are all-white or all-black, more quickly.

Initially a niche product, fax machines became ubiquitous in offices in the 1980s and 1990s.[2] However, they have largely been rendered obsolete by Internet-based technologies such as email and the World Wide Web, but are still used in some medical administration and law enforcement settings.[3]

History

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Wire transmission

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See also: Wirephoto

Scottish inventor Alexander Bain worked on chemical-mechanical fax-type devices and in 1846 Bain was able to reproduce graphic signs in laboratory experiments. He received British patent 9745 on May 27, 1843, for his "Electric Printing Telegraph".[4][5][6] Frederick Bakewell made several improvements on Bain's design and demonstrated a telefax machine.[7][8][9] The Pantelegraph was invented by the Italian physicist Giovanni Caselli.[10] He introduced the first commercial telefax service between Paris and Lyon in 1865, some 11 years before the invention of the telephone.[11][12]

In 1880, 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.[13] An account of Henry Sutton's "telephane" was published in 1896. Around 1900, German physicist Arthur Korn invented the Bildtelegraph, widespread in continental Europe especially following a widely noticed transmission of a wanted-person photograph from Paris to London in 1908,[14] used until the wider distribution of the radiofax.[15][16][17] Its main competitors were the Bélinographe by Édouard Belin first, then since the 1930s the Hellschreiber, invented in 1929 by German inventor Rudolf Hell, a pioneer in mechanical image scanning and transmission.[18]

Input (left) and output (right) of a telautograph transmission

The 1888 invention of the telautograph by Elisha Gray marked a further development in fax technology by making it possible for users to send signatures over long distances. This was used for verifying identification or ownership over long distances.[19][20][21]

On May 19, 1924, scientists of the AT&T Corporation "by a new process of transmitting pictures by electricity" sent 15 photographs by telephone from Cleveland to New York City, such photos being suitable for newspaper reproduction. Previously, photographs had been sent over the radio using this process.[22]

The Western Union "Deskfax" fax machine, announced in 1948, was a compact machine that fit comfortably on a desktop, using special spark printer paper.[23]

Wireless transmission

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Main article: Radiofax
Children read a wirelessly transmitted newspaper in 1938.

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. Also in 1924, Herbert E. Ives of AT&T transmitted and reconstructed the first color facsimile, a natural-color photograph of silent film star Rudolph Valentino in period costume, using red, green and blue color separations.[24]

Beginning in the late 1930s, the Finch Facsimile system was used to transmit a "radio newspaper" to private homes via commercial AM radio stations and ordinary radio receivers equipped with Finch's printer, which used thermal paper. Sensing a new and potentially golden opportunity, competitors soon entered the field, but the printer and special paper were expensive luxuries, AM radio transmission was very slow and vulnerable to static, and the newspaper was too small. After more than ten years of repeated attempts by Finch and others to establish such a service as a viable business, the public, apparently quite content with its cheaper and much more substantial home-delivered daily newspapers, and with conventional spoken radio bulletins to provide any "hot" news, still showed only a passing curiosity about the new medium.[25]

By the late 1940s, radiofax receivers were sufficiently miniaturized to be fitted beneath the dashboard of Western Union's "Telecar" telegram delivery vehicles.[23]

In the 1960s, the United States Army transmitted the first photograph via satellite facsimile to Puerto Rico from the Deal Test Site using the Courier satellite.

Radio fax is still in limited use today for transmitting weather charts and information to ships at sea. The closely related technology of slow-scan television is still used by amateur radio operators.

Telephone transmission

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External images
image icon LDX system, Scanner and Printer
image icon Magnafax Telecopier by Xerox

In 1964, Xerox Corporation introduced (and patented) what many consider to be the first commercialized version of the modern fax machine, under the name (LDX) or Long Distance Xerography. This model was superseded two years later with a unit that would set the standard for fax machines for years to come. Up until this point facsimile machines were very expensive and hard to operate. In 1966, Xerox released the Magnafax Telecopiers, a smaller, 46 lb (21 kg) facsimile machine. This unit was far easier to operate and could be connected to any standard telephone line. This machine was capable of transmitting a letter-sized document in about six minutes. The first sub-minute, digital fax machine was developed by Dacom, which built on digital data compression technology originally developed at Lockheed for satellite communication.[26][27]

Analog 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 varied 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 that 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.

Digital transmission and height of popularity

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By the late 1970s, many companies around the world (especially Japanese firms) had entered the fax market, and prices for long-distance faxing in 1978 were significantly lower than they had been in 1968, both at high and low speeds. Faxes had become useful to large newspapers and multinational corporations, and some digital methods were being developed. However, the rise of the market was fairly slow. Individual manufacturers had purposefully developed incompatible transmission methods in order to prevent their customers from buying from competitors.[28] The CCITT (later ITU-T) Recommendation T.3, defining group 2 fax machines, was the first to offer interoperability in 1976, with a speed of three minutes per page.[29]

In 1980, the CCITT's Recommendation T.4 promised groundbreaking interoperability for digital fax machines, with transmission times of just 40 seconds per page.[29] Accompanying this, a new wave of more compact, faster and efficient fax machines hit the market, leading to two decades of ubiquitous faxing in business contexts. Xerox continued to refine the fax machine for years after their ground-breaking first machine. In later years it would be combined with copier equipment to create the hybrid machines we have today that copy, scan and fax. Some of the lesser known capabilities of the Xerox fax technologies included their Ethernet enabled Fax Services on their 8000 workstations in the early 1980s.

In 1985, Hank Magnuski, founder of GammaLink, produced the first computer fax board, called GammaFax. Such boards could provide voice telephony via Analog Expansion Bus.[30]

In the 21st century

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Laser fax having a compact, built-in laser printer, 2001.[31]

Although businesses usually maintain some kind of fax capability, the technology has faced increasing competition from Internet-based alternatives. In some countries, such as Germany, because electronic signatures on contracts are not yet recognized by law, while faxed contracts with copies of signatures are, fax machines enjoy continuing support in business.[32] In Japan, faxes are still used extensively as of September 2020 for cultural reasons, including widespread preference for handwriting over typing.[33][34][35][36] They are available for sending to both domestic and international recipients from over 81% of all convenience stores nationwide. Convenience-store fax machines commonly print the slightly re-sized content of the sent fax in the electronic confirmation-slip, in A4 paper size.[37][38][39] Use of fax machines for reporting cases during the COVID-19 pandemic has been criticised in Japan for introducing data errors and delays in reporting, slowing response efforts to contain the spread of infections and hindering the transition to remote work.[40][41][42]

In many corporate environments, freestanding 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).[43] 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.

Professional laser fax machine for office use with the Super G3 standard for faster transmission.

The once ubiquitous fax machine has also begun to disappear from the small office and home office environments.[citation needed] Remotely hosted fax-server services are widely available from VoIP and e-mail providers. Users can send and receive faxes using them with their existing e-mail accounts instead of dedicated hardware and fax lines. Personal computers have also long been able to handle incoming and outgoing faxes using analog modems or ISDN. These solutions are often ideally suited for users who only very occasionally need to use fax services. In July 2017 the United Kingdom's National Health Service was said to be the world's largest purchaser of fax machines because the digital revolution has largely bypassed it.[44] In June 2018 the Labour Party said that the NHS had at least 11,620 fax machines in operation[45] and in December the Department of Health and Social Care said that no more fax machines could be bought from 2019 and that the existing ones must be replaced by secure email by March 31, 2020.[46]

Leeds Teaching Hospitals NHS Trust, generally viewed as digitally advanced in the NHS, was engaged in a process of removing its fax machines in early 2019. This involved quite a lot of e-fax solutions because of the need to communicate with pharmacies and nursing homes which may not have access to the NHS email system and may need something in their paper records.[47]

In 2018 two-thirds of Canadian doctors reported that they primarily used fax machines to communicate with other doctors. Faxes are still seen as safer and more secure and electronic systems are often unable to communicate with each other.[48]

Hospitals are the leading users for fax machines in the United States where some doctors prefer fax machines over emails, often due to concerns about accidentally violating HIPAA.[3]

Capabilities

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There are several indicators of fax capabilities: group, class, data transmission rate, and conformance with ITU-T (formerly CCITT) recommendations. Since the 1968 Carterfone decision, most fax machines have been designed to connect to standard PSTN lines and telephone numbers.

Group

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Analog

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Group 1 and 2 faxes are sent in the same manner as a frame of analog television, with each scanned line transmitted as a continuous analog signal. Horizontal resolution depended upon the quality of the scanner, transmission line, and the printer. Analog 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.3 and T.30. 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

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The Dacom DFC-10—the first digital fax machine[26]
The CCD single-row image sensor in a fax machine. Only about one quarter of the length is shown. The thin line in the middle consists of photosensitive pixels. The read-out circuit is at left.

A major breakthrough in the development of the modern facsimile system was the result of digital technology, where the analog signal from scanners was digitized and then compressed, resulting in the ability to transmit high rates of data across standard phone lines. The first digital fax machine was the Dacom Rapidfax first sold in late 1960s, which incorporated digital data compression technology developed by Lockheed for transmission of images from satellites.[26][27]

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 6 and 15 seconds to transmit a single page (not including the initial time for the fax machines to handshake and synchronize). They require sufficient random access memory to store two lines of scanned bits at a time.[29] The horizontal and vertical resolutions are allowed by the T.4 standard to vary among a set of fixed resolutions:
    • Horizontal: 100 scan lines per inch
      • Vertical: 100 scan lines per inch ("Basic")
    • 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")
    • Horizontal: 300 scan lines per inch
      • Vertical: 300 scan lines per inch
    • Horizontal: 400 or 408 scan lines per inch
      • Vertical: 400 or 391 scan lines per inch ("Ultrafine")
  • Group 4 faxes are designed to operate over 64 kbit/s digital ISDN circuits. They conform to the ITU-T Recommendations
    • T.563 (Terminal characteristics for Group 4 facsimile apparatus),
    • T.503 (Document application profile for the interchange of Group 4 facsimile documents),
    • T.521 (Communication application profile BT0 for document bulk transfer based on the session service),
    • T.6 (Facsimile coding schemes and coding control functions for Group 4 facsimile apparatus) specifying resolutions, a superset of the resolutions from T.4,[49]
    • T.62 (Control procedures for teletex and Group 4 facsimile services),
    • T.70 (Network-independent basic transport service for the telematic services), and
    • T.411 to T.417 (concerned with aspects of the Open Document Architecture).

Fax Over IP (FoIP) can transmit and receive pre-digitized documents using ITU-T recommendation T.38 to send digitised images over an IP network using JPEG compression. T.38 is designed to work with VoIP services and often supported by analog telephone adapters used by legacy fax machines that need to connect through a VoIP service. 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 related to the e-mail–to–fax service that still uses fax modems at least one way.

Class

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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 (also known as Class 1.0) fax devices do fax data transfer, while 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.[50]
  • What is commonly known as "Class 2" is an unofficial class of fax devices that perform T.30 session management themselves, but the T.4/T.6 data compression is performed by software on a controlling computer. Implementations of this "class" are based on draft versions of the standard that eventually significantly evolved to become Class 2.0.[51] All implementations of "Class 2" are manufacturer-specific.[52]
  • Class 2.0 is the official ITU-T version of Class 2 and is commonly known as Class 2.0 to differentiate it from many manufacturer-specific implementations of what is commonly known as "Class 2". It uses a different but standardized command set than the various manufacturer-specific implementations of "Class 2". The relevant ITU-T recommendation is T.32.[52]
  • Class 2.1 is an improvement of Class 2.0 that implements faxing over V.34 (33.6 kbit/s), which boosts faxing speed from fax classes "2" and 2.0, which are limited to 14.4 kbit/s.[52] The relevant ITU-T recommendation is T.32 Amendment 1.[52] Class 2.1 fax devices are referred to as "super G3".

Data transmission rate

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Several different telephone-line modulation techniques are used by fax machines. They are negotiated during the fax-modem handshake, and the fax devices will use the highest data rate that both fax devices support, usually a minimum of 14.4 kbit/s for Group 3 fax.

ITU standard Released date Data rates (bit/s) Modulation method
V.27 1988 4800, 2400 PSK
V.29 1988 9600, 7200, 4800 QAM
V.17 1991 14400, 12000, 9600, 7200 TCM
V.34 1994 28800 QAM
V.34bis 1998 33600 QAM
ISDN 1986 64000 4B3T / 2B1Q (line coding)

"Super Group 3" faxes use V.34bis modulation that allows a data rate of up to 33.6 kbit/s.

Compression

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As well as specifying the resolution (and allowable physical size) of the image being faxed, the ITU-T T.4 recommendation specifies two compression methods for decreasing the amount of data that needs to be transmitted between the fax machines to transfer the image. The two methods defined in T.4 are:[53]

An additional method is specified in T.6:[49]

Later, other compression techniques were added as options to ITU-T recommendation T.30, such as the more efficient JBIG (T.82, T.85) for bi-level content, and JPEG (T.81), T.43, MRC (T.44), and T.45 for grayscale, palette, and colour content.[55] Fax machines can negotiate at the start of the T.30 session to use the best technique implemented on both sides.

Modified Huffman

[edit]
Main article: Modified Huffman coding

Modified Huffman (MH), specified in T.4 as the one-dimensional coding scheme, is a codebook-based run-length encoding scheme optimised to efficiently compress whitespace.[53] As most faxes consist mostly of white space, this minimises the transmission time of most faxes. Each line scanned is compressed independently of its predecessor and successor.[53]

Modified READ

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Modified READ, specified as an optional two-dimensional coding scheme in T.4, encodes the first scanned line using MH.[53] The next line is compared to the first, the differences determined, and then the differences are encoded and transmitted.[53] This is effective, as most lines differ little from their predecessor. This is not continued to the end of the fax transmission, but only for a limited number of lines until the process is reset, and a new "first line" encoded with MH is produced. This limited number of lines is to prevent errors propagating throughout the whole fax, as the standard does not provide for error correction. This is an optional facility, and some fax machines do not use MR in order to minimise the amount of computation required by the machine. The limited number of lines is 2 for "Standard"-resolution faxes, and 4 for "Fine"-resolution faxes.

Modified Modified READ

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Main article: Group 4 compression

The ITU-T T.6 recommendation adds a further compression type of Modified Modified READ (MMR), which simply allows a greater number of lines to be coded by MR than in T.4.[49] This is because T.6 makes the assumption that the transmission is over a circuit with a low number of line errors, such as digital ISDN. In this case, the number of lines for which the differences are encoded is not limited.

JBIG

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In 1999, ITU-T recommendation T.30 added JBIG (ITU-T T.82) as another lossless bi-level compression algorithm, or more precisely a "fax profile" subset of JBIG (ITU-T T.85). JBIG-compressed pages result in 20% to 50% faster transmission than MMR-compressed pages, and up to 30 times faster transmission if the page includes halftone images.

JBIG performs adaptive compression, that is, both the encoder and decoder collect statistical information about the transmitted image from the pixels transmitted so far, in order to predict the probability for each next pixel being either black or white. For each new pixel, JBIG looks at ten nearby, previously transmitted pixels. It counts, how often in the past the next pixel has been black or white in the same neighborhood, and estimates from that the probability distribution of the next pixel. This is fed into an arithmetic coder, which adds only a small fraction of a bit to the output sequence if the more probable pixel is then encountered.

The ITU-T T.85 "fax profile" constrains some optional features of the full JBIG standard, such that codecs do not have to keep data about more than the last three pixel rows of an image in memory at any time. This allows the streaming of "endless" images, where the height of the image may not be known until the last row is transmitted.

ITU-T T.30 allows fax machines to negotiate one of two options of the T.85 "fax profile":

  • In "basic mode", the JBIG encoder must split the image into horizontal stripes of 128 lines (parameter L0 = 128) and restart the arithmetic encoder for each stripe.
  • In "option mode", there is no such constraint.

Matsushita Whiteline Skip

[edit]

A proprietary compression scheme employed on Panasonic fax machines is Matsushita Whiteline Skip (MWS). It can be overlaid on the other compression schemes, but is operative only when two Panasonic machines are communicating with one another. This system detects the blank scanned areas between lines of text, and then compresses several blank scan lines into the data space of a single character. (JBIG implements a similar technique called "typical prediction", if header flag TPBON is set to 1.)

Typical characteristics

[edit]

Group 3 fax machines transfer one or a few printed or handwritten pages per minute in black-and-white (bitonal) at a resolution of 204×98 (normal) or 204×196 (fine) dots per square inch. The transfer rate is 14.4 kbit/s or higher for modems and some fax machines, but fax machines support speeds beginning with 2400 bit/s and typically operate at 9600 bit/s. The transferred image formats are called ITU-T (formerly CCITT) fax group 3 or 4. Group 3 faxes have the suffix .g3 and the MIME type image/g3fax.

The most basic fax mode transfers in black and white only. The original page is scanned in a resolution of 1728 pixels/line and 1145 lines/page (for A4). The resulting raw data is compressed using a modified Huffman code optimized for written text, achieving average compression factors of around 20. Typically a page needs 10 s for transmission, instead of about three minutes for the same uncompressed raw data of 1728×1145 bits at a speed of 9600 bit/s. The compression method uses a Huffman codebook for run lengths of black and white runs in a single scanned line, and it can also use the fact that two adjacent scanlines are usually quite similar, saving bandwidth by encoding only the differences.

Fax classes denote the way fax programs interact with fax hardware. Available classes include Class 1, Class 2, Class 2.0 and 2.1, and Intel CAS. Many modems support at least class 1 and often either Class 2 or Class 2.0. Which is preferable to use depends on factors such as hardware, software, modem firmware, and expected use.

Printing process

[edit]

Fax machines from the 1970s to the 1990s often used direct thermal printers with rolls of thermal paper as their printing technology, but since the mid-1990s there has been a transition towards plain-paper faxes: thermal transfer printers, inkjet printers and laser printers.

One of the advantages of inkjet printing is that inkjets can affordably print in color; therefore, many of the inkjet-based fax machines claim to have color fax capability. There is a standard called ITU-T30e (formally ITU-T Recommendation T.30 Annex E [56]) for faxing in color; however, it is not widely supported, so many of the color fax machines can only fax in color to machines from the same manufacturer.[57]

Stroke speed

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Stroke speed in facsimile systems is the rate at which a fixed line perpendicular to the direction of scanning is crossed in one direction by a scanning or recording spot. Stroke speed is usually expressed as a number of strokes per minute. When the fax system scans in both directions, the stroke speed is twice this number. In most conventional 20th century mechanical systems, the stroke speed is equivalent to drum speed.[58]

Fax paper

[edit]
Paper roll for direct thermal fax machine

As a precaution, thermal fax paper is typically not accepted in archives or as documentary evidence in some courts of law unless photocopied. This is because the image-forming coating is eradicable and brittle, and it tends to detach from the medium after a long time in storage.[59]

Fax tone

[edit]

A CNG tone is an 1100 Hz tone transmitted by a fax machine when it calls another fax machine. Fax tones can cause complications when implementing fax over IP.

Internet fax

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See also: Internet fax

One popular alternative is to subscribe to an Internet fax service and send and receive faxes from a personal computers using an existing email account. No software, fax server or fax machine is needed. Faxes are received as attached TIFF or PDF files, or in proprietary formats that require the use of the service provider's software. Faxes can be sent or retrieved from anywhere at any time that a user can get Internet access. Some services offer secure faxing to comply with stringent HIPAA and Gramm–Leach–Bliley Act requirements to keep medical information and financial information private and secure. Utilizing a fax service provider does not require paper, a dedicated fax line, or consumable resources.[60]

Another alternative to a physical fax machine is to make use of computer software which sends and receives faxes utilizing fax servers and unified messaging. A virtual (email) fax can be printed out and then signed and scanned back into a computer to be emailed. Also the sender can attach a digital signature to the document file.

With the surging popularity of mobile phones, virtual fax machines can now be downloaded as applications for Android and iOS. These applications make use of the phone's internal camera to scan fax documents for upload or they can import from various cloud services.

[edit]
  • T.4 is the umbrella specification for fax. It specifies the standard image sizes, two forms of image-data compression (encoding), the image-data format, and references, T.30 and the various modem standards.
  • T.6 specifies a compression scheme that reduces the time required to transmit an image by roughly 50-percent.
  • T.30 specifies the procedures that a sending and receiving terminal use to set up a fax call, determine the image size, encoding, and transfer speed, the demarcation between pages, and the termination of the call. T.30 also references the various modem standards.
  • V.21, V.27ter, V.29, V.17, V.34: ITU modem standards used in facsimile. The first three were ratified prior to 1980, and were specified in the original T.4 and T.30 standards. V.34 was published for fax in 1994.[61]
  • T.37 The ITU standard for sending a fax-image file via e-mail to the intended recipient of a fax.
  • T.38 The ITU standard for sending Fax over IP (FoIP).
  • G.711 pass through - this is where the T.30 fax call is carried in a VoIP call encoded as audio. This is sensitive to network packet loss, jitter and clock synchronization. When using voice high-compression encoding techniques such as, but not limited to, G.729, some fax tonal signals may not be correctly transported across the packet network.
  • RFC 3362 image/t38 MIME-type
  • SSL Fax An emerging standard that allows a telephone based fax session to negotiate a fax transfer over the internet, but only if both sides support the standard. The standard is partially based on T.30 and is being developed by Hylafax+ developers.

See also

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References

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Further reading

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Fax

View on Grokipedia
from Grokipedia

Fax, short for , is a for transmitting scanned printed material, such as text or , over lines to a receiving device that reconstructs the as a graphic . The process involves optical scanning of the original line by line, conversion of light and dark areas into or analog signals modulated as audio tones, transmission via , and reconstruction by the receiving fax machine using thermal, inkjet, or to produce a . The concept originated in the 1840s with Alexander Bain's electric printing telegraph, which synchronized pendulum-driven scanners to transmit images over telegraph wires, predating the telephone by decades. Further advancements included Elisha Gray's 1888 telautograph, which electrically replicated handwriting and signatures over distances, laying groundwork for visual transmission. Commercial viability emerged in the 1960s with Xerox's Magnafax Telecopier, enabling rapid document exchange and fueling widespread adoption in business during the 1970s and 1980s through standardized Group 3 protocols that achieved speeds up to 9.6 kbit/s. Despite displacement by email and digital alternatives from the 1990s onward due to superior speed, cost, and editability, fax endures in sectors like healthcare, law, and government for its legal reliability, requirement of wet-ink signatures, and operation without internet dependency.

History

Precursors and Early Inventions

The earliest known precursor to facsimile transmission was the electrochemical telegraph patented by Scottish inventor Alexander Bain on May 27, 1843, under British Patent No. 9745 for "improvements in producing and regulating electric currents." Bain's device, often termed the , employed a synchronized mechanism with a metal to scan raised type on a flat metal surface, generating electrical pulses proportional to the contact; these pulses traveled over telegraph wires to a receiver that used an to deposit iron particles via onto moving paper, reproducing text facsimiles at speeds up to three letters per minute over distances of about 600 kilometers. Limited by its reliance on physical and inability to handle continuous tones or images reliably, Bain's system prioritized textual content and faced legal challenges from telegraph monopolies, preventing widespread adoption. In 1847, English physicist Frederick Bakewell advanced the concept with his image telegraph, which replaced Bain's with a rotating for scanning and synchronized drums at sender and receiver, enabling transmission of simple drawings, , and basic images via similar electrochemical means over telegraph lines. Bakewell's apparatus achieved the first documented successful transmission of non-textual visuals in 1847, though it remained experimental due to errors over long distances and sensitivity to line noise. Italian priest and physicist Giovanni Caselli refined these principles in his , patented in 1860 and publicly demonstrated in 1861 at the Florence International Exhibition before King , using a spring-driven and improved via a to transmit , signatures, and simple sketches over wire at up to 90 characters per minute. Caselli's system saw limited commercial trials in from 1865 to 1870, verifying documents via official signatures over distances up to 400 kilometers, but was curtailed by the expansion of optical and standardization on . Early 20th-century innovations shifted toward wireless and photographic applications, with French inventor Édouard Bélin's Bélinograph, developed from 1907 and adapted for radio transmission by 1914, incorporating photoelectric scanning of images on film to send signals via over radio waves, enabling the first wireless photo transmissions for news services. Similarly, German engineer Rudolf Hell patented the in 1929, a field-sequential system using mechanical scanning and to transmit text and weather maps over shortwave, finding niche use in and despite bandwidth limitations. By the 1920s, wire-based systems integrated with networks, as demonstrated by AT&T's telephotography trials on May 19, 1924, which transmitted 15 photographs from to New York over standard phone lines using photoelectric drums and subcarrier modulation, marking a transition from dedicated telegraph wires to versatile voice circuits for image relay.

Commercial Development and Standardization

The development of international standards by the (ITU, then CCITT) in the marked the transition of facsimile technology from specialized military and governmental applications to broader commercial viability, primarily through analog transmission over standard lines. The standard, formalized in 1968 as Recommendation T.2, enabled machines to scan and transmit documents at resolutions of about 4 lines per millimeter, typically requiring 6 minutes per page on 8.5 by 11-inch paper. This standard addressed interoperability challenges, allowing fax devices from different manufacturers to communicate reliably, though early machines remained expensive and bulky, limiting initial adoption to large businesses and news agencies for transmitting press releases and urgent dispatches. In 1976, the Group 2 standard (Recommendations T.3 and T.30) improved efficiency by halving transmission times to approximately 3 minutes per page through higher scanning rates and better modulation, further encouraging commercial uptake in sectors like and corporate offices during the late 1960s and 1970s. Japanese manufacturers, including , played a pivotal role in making machines more affordable and office-friendly; 's innovations, such as the RIFAX 600S launched around 1974 in collaboration with , introduced early digital scanning elements that presaged faster systems, transmitting A4 pages in about 60 seconds. These advancements, combined with regulatory approvals for phone-line compatibility, spurred adoption by news services for real-time reporting and businesses for contract exchanges, though costs still confined widespread use to enterprises rather than households. The 1980 introduction of the Group 3 standard revolutionized commercial faxing by incorporating digital compression and redundancy reduction, slashing transmission times to under 1 minute per page while supporting higher resolutions up to 8 lines per millimeter. Recommended as T.4, this digital protocol—pioneered with significant Japanese input—facilitated global interoperability and paved the way for mass-market machines, as terminals could now handle error correction and modulation schemes like V.27, reducing costs and errors over analog lines. By standardizing these features, Group 3 enabled fax to become a staple for and media, with manufacturers rapidly scaling production for office environments.

Peak Adoption and Widespread Use

The adoption of fax machines surged in the 1980s and early 1990s, transforming before widespread . In the United States, the number of installed fax machines grew from 250,000 in 1980 to 5 million by 1990, reflecting rapid driven by compatible standards and expanding networks. Worldwide, the installed base exceeded 10 million machines by 1989, with annual sales in the U.S. alone reaching 1.6 million units in 1990. This growth created strong network effects, as the utility of fax increased with the number of users, encouraging businesses to adopt the technology for reliable document transmission. Falling prices were a primary driver of this expansion. In the late , fax machines typically cost around $10,000, limiting use to large organizations. By the late , prices ranged from $600 to over $4,000 depending on features, and by 1990, basic models were available for under $500, making them affordable for small businesses and offices. U.S. installations rose from 300,000 in 1983 to 2.5 million by , underscoring the accessibility gains. Fax's speed and reliability outperformed traditional mail for time-sensitive documents, with transmissions completing in minutes per page compared to days or weeks for postal services, and low error rates due to error-correction protocols in Group 3 standards. This capability accelerated global trade by enabling swift exchange of contracts, invoices, and orders in and manufacturing, where pre-digital verification required physical or rapid copies. Businesses reported fax as the fastest-growing tool in the , integral to daily operations before dominance.

Decline and Transition to Digital Alternatives

The adoption of and internet-based communication in the early accelerated the decline of traditional fax machines, as these digital alternatives provided faster transmission, negligible marginal costs, and easier integration with computer workflows compared to analog phone line-dependent faxing. Worldwide sales of standalone fax machines, which peaked at approximately 15 million units in 2000, dropped to 13 million in 2001 and continued to fall sharply thereafter, reflecting a broader shift away from dedicated hardware. By the , annual global unit sales had contracted to under 1 million, with revenue from physical fax machines estimated at around $858 million in 2024 and projected to decline further. This period also saw the emergence of hybrid multifunction devices in the early , combining fax capabilities with scanning, printing, and direct transmission, which facilitated a partial transition rather than abrupt replacement. These all-in-one machines allowed users to digitize documents for while retaining fax functionality for compatibility, bridging the gap as internet proliferated and reduced reliance on physical transmission. Despite the precipitous drop in hardware sales, fax technology has not achieved full , with the global fax services market valued at $3.31 billion in 2024, underscoring ongoing demand in niches where faxed signatures retain legal equivalence to originals under certain regulations. This persistence highlights the inertial effects of entrenched systems, even as digital tools dominate general .

Technical Operation

Fundamental Principles of Facsimile Transmission

The process of facsimile transmission begins with optical scanning of a document, where incident light illuminates the surface and reflected intensity variations are detected by photoelectric elements, such as arrays in contact image sensors or charge-coupled devices (CCDs), converting the analog optical into a proportional electrical signal. This signal is sampled spatially into a grid of pixels representing or binary reflectance levels, typically at horizontal resolutions of 200 (DPI) and vertical resolutions ranging from 100 to 200 DPI, balancing detail capture with transmission feasibility over analog channels. The sampled electrical signal, which encodes sequential lines of pixel data, is then modulated onto an audio-frequency carrier to produce varying tones compatible with the limited bandwidth of (PSTN) lines, constrained to approximately 300–3400 Hz for voice-grade transmission. or schemes shift the carrier frequency or amplitude according to pixel values—higher frequencies or amplitudes for dark areas, lower for light—ensuring the modulated mimics audible tones that propagate without excessive over copper twisted-pair lines. At the receiving end, recovers the signal from the incoming tones, which drives a mechanism to reconstruct the by selectively marking corresponding to detected intensities, with overall fidelity governed by the (SNR) along the channel—SNR below 20–30 dB introduces detectable artifacts like speckle or line breaks due to corrupting threshold decisions. in signal encoding, such as repeated transmission of pulses or margin data, provides causal resilience against transient , enabling partial error recovery without full digital correction schemes. Bandwidth limitations impose inherent trade-offs: increasing resolution elevates the data rate (e.g., from ~1 bit per at 200 DPI to higher for finer sampling), demanding either prolonged transmission times—up to minutes for letter-sized pages—or reduced vertical resolution to fit within the channel's Nyquist-limited capacity of roughly 2400–2800 , prioritizing speed over sharpness in noisy or constrained environments.

Analog Fax Systems

Analog fax systems, primarily embodied in the ITU and Group 2 standards, operated by scanning documents line-by-line and transmitting continuous analog audio signals over standard lines to represent black and white areas. In these systems, a detected reflected light from the document, converting brightness variations into an electrical signal modulated via (FSK), where a lower typically denoted black lines and a higher frequency signified white spaces or background. This waveform was sent directly without , allowing compatibility with voice-grade analog phone networks but limiting fidelity to binary contrast rather than grayscale. Horizontal resolution standardized at 1728 elements per line for A4-width documents (equivalent to 8 pixels per millimeter across 215 mm), while vertical resolution depended on scan speed. The ITU standard, formalized in 1968 under Recommendation T.2, achieved transmission speeds of approximately six minutes per A4 page, with a vertical resolution of about 4 lines per millimeter (roughly 96-102 lines per inch). , approved in 1976, improved efficiency by reducing page transmission time to around three minutes through higher scan rates and better modulation, while maintaining or slightly enhancing resolution to support finer detail in business documents. Both groups relied on mechanical or early electromechanical scanning—often rotating drums or flatbeds—with recording at the receiver using thermal, electrolytic, or activated by demodulated signals to mark lines proportionally. A key limitation of analog fax stemmed from the uncoded continuous signal's vulnerability to channel impairments, such as thermal noise, , or over copper telephone lines, which could shift frequencies and erroneously interpret white as black (or vice versa), manifesting as random speckles or "" artifacts on the output. These errors accumulated causally with distance and line quality, lacking inherent correction mechanisms, and degraded image clarity progressively—issues inherent to analog propagation without quantization or redundancy. Transmission rates equated to roughly 0.17-0.33 pages per minute, constraining use to low-volume applications like urgent memos despite widespread adoption in offices during the . This noise susceptibility underscored the causal necessity for digital encoding in later standards to enable detection and retransmission, rendering pure analog systems obsolete by the mid-1980s.

Digital Fax Systems

Digital fax systems represent a shift from continuous analog signals to discrete processing, primarily in Group 3 and subsequent classifications adopted from the late onward. The scanned document image, initially captured as varying intensities, undergoes analog-to-digital conversion followed by binarization to yield a bilevel (black-and-white) pixel grid, typically at resolutions of 200x100 or 200x200 . Binarization employs fixed thresholding, assigning pixels above a threshold to white and below to black, or error-diffusion dithering to approximate tones through patterned clusters, thereby preserving legibility in text-heavy documents while minimizing data complexity. This binary encoding facilitates substantial efficiency gains over analog predecessors by enabling schemes that represent consecutive identical pixels as single values with lengths, exploiting the predominance of uniform runs in printed materials to compress data by factors of 10 to 50 for typical pages. Transmission times thus drop to under one minute per page at 9600 bits per second, compared to several minutes in analog systems, due to reduced bandwidth requirements and immunity to analog drift. The transition was propelled by 1980s advancements in very-large-scale integration (VLSI) chips and digital signal processors, which integrated scanning, binarization, encoding, and modulation into compact, cost-effective hardware capable of real-time operation without bulky analog components. Error resilience in digital fax stems from discrete bit streams framed with checksums or cyclic redundancy checks, permitting receiver-side detection of bit flips induced by line noise; erroneous frames prompt selective retransmission requests, yielding effective bit rates below 10^{-5} under standard conditions, far surpassing analog susceptibility to signal degradation. This causal mechanism—discrete verification versus cumulative analog distortion—underpins the reliability that drove fax adoption to over 250,000 machines in the U.S. by 1980, escalating to millions by decade's end.

Standards and Protocols

ITU-T Recommendations and Group Classifications

The develops recommendations to standardize facsimile transmission for global interoperability, primarily through the T series for terminals and procedures. Recommendation T.30 specifies the procedures for document facsimile transmission in the general switched telephone network, including Phase A call establishment, Phase B capabilities negotiation via Digital Information Signal (DIS) and Digital Command Signal (DCS) frames, Phase C image data transfer, and Phase D post-message procedures such as error correction and confirmation. This protocol enables handshaking between terminals to exchange capabilities like resolution, paper size, and compression methods, ensuring reliable document exchange over analog public switched telephone networks (PSTN). Facsimile apparatus is classified into Groups 1–4 by recommendations, reflecting progression from analog to fully digital systems. (T.2) employs analog scanning and frequency-modulated transmission at 1440 lines per minute, yielding six minutes per A4 page with 96 lines per inch vertical resolution. Group 2 extends this with partial for improved horizontal resolution up to 8 lines per mm but remains largely analog and obsolete. (T.4), the most widely deployed for PSTN, scanned images at resolutions from 203 x 98 to 203 x 392 , supporting automatic operation and transmission times under one minute per page via modulation schemes like V.27ter at 2400–4800 bps. (T.6) targets error-free digital networks such as ISDN, using two-dimensional coding without modulation for direct binary data transfer between terminals, bypassing T.30 handshaking in point-to-point scenarios. For software-driven facsimile on personal computers, modem classes define protocol partitioning between hardware and host. Class 1 modems handle basic modulation/demodulation per ITU-T V-series (e.g., V.17 at 14.4 kbps for high-speed Group 3, V.27ter at 4800/2400 bps for fallback), with the host implementing T.30 procedures and error correction. Class 2 and enhanced Class 2.0 integrate more T.30 elements into the modem firmware, simplifying software via AT commands for capabilities exchange and buffering, while supporting the same V-series modulations for Group 3 compatibility. These classes facilitate PC-to-fax interoperability without dedicated hardware. Group 3 standards dominated PSTN facsimile traffic by the mid-1980s due to their efficiency over analog lines.

Compression Algorithms

Compression in facsimile transmission relies on exploiting statistical redundancies in bi-level (black-and-white) images to minimize data volume, thereby reducing transmission time over bandwidth-limited analog lines. These algorithms encode runs of identical pixels and predict adjacent line correlations, aligning with principles where lower entropy signals—such as those with long horizontal runs in text—yield higher compression ratios. Typical document images, dominated by predictable patterns like uniform white spaces and short black runs in characters, compress more efficiently than halftoned photographs, which introduce noise-like variability and shorter runs, limiting ratios to under 5:1 compared to 5-10:1 or more for text-heavy pages. The foundational algorithm, Modified Huffman (MH) coding defined in ITU-T Recommendation T.4, employs one-dimensional combined with variable-length Huffman codes tailored to fax statistics. It scans each line independently, encoding the lengths of alternating white and black runs using a 1D table optimized for common short black runs (e.g., 0-63 pixels) and longer white spaces, with makeup codes for extended runs and termination codes to signal line ends. This achieves average compression ratios of approximately 8:1 for scanned text documents by capitalizing on horizontal predictability, though performance drops for vertically complex images. To enhance efficiency for correlated lines, T.4 introduces Modified READ (MR) as a hybrid 1D/2D scheme, where most lines use MH but every Kth line (typically K=2) employs 2D coding to the prior line's pixels, encoding vertical transitions (pass modes for unchanged runs, vertical mode for differences, or horizontal fallback). Modified Modified READ (MMR), specified in T.6 for Group 4 fax, extends this to full 2D coding without periodic 1D resets or end-of-line markers, using a sliding window to resolve line ambiguities via fill bits. These 2D methods improve ratios to around 15:1 for bi-level images with vertical continuity, such as graphics, by reducing inter-line redundancy. For superior lossless bi-level compression, T.82 (JBIG1) employs with adaptive templates and , analyzing local contexts across multiple lines to predict pixel values probabilistically, often outperforming MMR by 20-30% on documents with repeated symbols like text or logos. This standard supports optional modes for sparse or noisy images but saw limited adoption in early fax due to computational demands, remaining niche for high-end or archival uses. variants, such as Matsushita's skip coding for predominantly white sparse documents, further optimize by bypassing empty regions, though they lack .

Data Transmission Rates and Modulation

Group 3 facsimile standards, as defined in Recommendation T.4, support digital data transmission rates primarily between 2400 bit/s and 14400 bit/s for image data transfer over analog public switched networks (PSTN). The initial phase synchronization and capability negotiation occur at lower rates using V.21 modulation at 300 bit/s, employing binary frequency-shift keying (BFSK) to ensure compatibility across varying line conditions. Higher rates for the main image transmission phase are achieved through optional modulation schemes, with V.27ter being mandatory for basic Group 3 compliance at 2400 or 4800 bit/s. Modulation techniques in Group 3 fax leverage (PSK) and (QAM) variants to maximize throughput within the PSTN's effective bandwidth of 300 to 3400 Hz, which constrains symbol rates to avoid excessive . V.27ter utilizes differential binary and quaternary PSK (DBPSK/DQPSK) at a symbol rate of 1200 or 2400 , enabling robust performance over noisy lines by emphasizing phase differences rather than absolute phases. V.29, an optional scheme, employs 8-level quadrature PSK approaching QAM at 7200 or 9600 bit/s with a 2400 symbol rate, trading some error resilience for higher . The fastest standard rate, via V.17 introduced in 1990, reaches 14400 bit/s using trellis-coded modulation (TCM)—a convolutional-coded form of 16-QAM or PSK—operating at 2400 to 3000 with fallback to 7200, 9600, or 12000 bit/s based on channel equalization and assessments. Transmission reliability is enhanced by adaptive fallback during the phase, where the sending terminal transmits test signals; if rates exceed thresholds (e.g., more than 10% bit errors in V.17 training checks), it downgrades to slower modulations like V.27ter to maintain integrity over impaired lines affected by factors such as or . Empirical measurements indicate that under typical PSTN conditions, a standard A4 page at basic resolution (203 x 98 dpi) transmits in 12 to 30 seconds at 9600 bit/s, extending to 45-60 seconds at 2400 bit/s or in poor-quality scenarios requiring retransmissions. These rates reflect a balance between speed and correction, as higher-order QAM schemes like V.17's demand cleaner channels but offer up to 6 times the throughput of baseline PSK when line quality permits.

Equipment and Features

Fax Machine Hardware Characteristics

Traditional fax machines feature an optical scanner that employs a (CCD) to detect black and white areas on documents by reflecting light off the page line by line. Illumination is provided by a bright light source, often LED arrays in later models, with the scan head moving across the document via mirrors and lenses to focus the reflected light onto the CCD. Many units include an (ADF) for handling multiple sheets, typically supporting 20 to 50 pages in sequence depending on the model. Printing hardware in fax machines commonly utilizes thermal print heads that generate heat to form images on heat-sensitive paper, eliminating the need for ink or toner in basic configurations. Advanced models incorporate inkjet or mechanisms for output on plain paper, enabling higher quality and compatibility with standard . These printers operate line by line, with thermal heads advancing paper incrementally during reception. Early commercial fax machines from the , such as the Magnafax Telecopier introduced in 1966, were bulky devices weighing approximately 46 pounds and occupying space comparable to contemporary office photocopiers. By 1980, advancements led to the Canon FAX-601, the first compact desktop model suitable for office tabletops. Operational power draw for these machines typically ranges from 10 to 50 watts, varying with activity such as scanning or printing. Internal components include a control panel for user input, a for signal conversion, and circuitry managing scan-to-print workflows.

Printing and Paper Technologies

Early facsimile machines predominantly employed direct , which utilized heat-sensitive paper rolls to produce images by applying heat and pressure from a print head, causing the coated chemical layer to darken without requiring or toner. This method, common from the 1970s through the early 1990s, relied on continuous rolls of specialized that were automatically cut to the transmitted page length, offering simplicity and low initial cost but resulting in images prone to fading over time due to exposure to light, heat, or moisture. In contrast, emerged as an intermediary technology, employing a heated to melt and transfer or onto plain paper, enabling compatibility with standard office stock while maintaining thermal-based mechanisms. By the mid-1990s, the industry shifted toward plain paper facsimile machines using inkjet or technologies, which provided superior archival quality as toner or adhered permanently to uncoated , resisting degradation unlike thermal media. Laser-based systems, in particular, became prevalent for their ability to fuse toner electrostatically onto plain at high speeds, aligning with the growing demand for durable output in business environments. This transition addressed limitations of thermal rolls, such as the need for supplies and poor long-term readability, though it introduced dependencies on standard quality to minimize issues like jams, which can arise from mismatched sheet thickness or humidity-affected stock in sheet-fed mechanisms. Fax printing resolution standardized at approximately 203 (dpi) horizontally across Group 3 systems, with vertical resolution typically at 98 dpi for basic mode or 196-204 dpi for fine mode, ensuring consistent rasterized output regardless of the printing method. These specifications, defined in recommendations, maintained interoperability while accommodating the physical constraints of thermal heads or arrays, though plain systems often achieved sharper edges due to higher precision in toner application.

Audio Tones and Signaling

Fax machines employ distinct audio tones during the initial handshaking phase to establish connections over analog lines, as defined in Recommendation T.30. The calling station transmits a Comfort Noise (CNG) tone, consisting of a Hz signal burst lasting 0.5 seconds, repeated approximately every 3 seconds with intervening silence. This periodic tone alerts the receiving end to the presence of a fax device without requiring immediate response, allowing the called station time to prepare. Upon detecting the CNG, the answering station responds with a Called Station Identification (CED) tone: a continuous 2100 Hz ±15 Hz signal for 2.6 to 4 seconds, followed by a brief . The CED serves multiple functions, including disabling echo suppressors or cancellers in the transmission path to prevent signal and confirming the answering device as a fax . These tones facilitate by ensuring both ends recognize the call type and prepare for subsequent digital flag sequences in Phase A of the T.30 protocol, transitioning to capabilities exchange without data modulation. On analog lines, these acoustic signals contribute to reliable connection establishment, with traditional fax failure rates typically around 5% or less, far outperforming VoIP environments where tone mishandling can exceed 20% failures. Empirical from analog deployments underscore the tones' effectiveness in minimizing no-answer or detection errors, as the frequencies are chosen to traverse standard PSTN filters without .

Modern Developments

Internet Fax and FoIP

, commonly referred to as Fax over IP (FoIP), facilitates the transmission of Group 3 facsimile documents across IP networks by interfacing traditional analog fax signals with digital packet-based transport, thereby reducing dependency on (PSTN) lines. The core protocol for real-time FoIP is defined in ITU-T Recommendation , which specifies procedures for converting demodulated fax data from standards such as V.17 or V.27ter into compressed digital packets for conveyance over UDP, with reconstruction and remodulation at the receiving end to maintain compatibility with conventional fax terminals. This approach mitigates and impacts through error correction mechanisms like (FEC) and redundancy, enabling reliable end-to-end delivery without the signal degradation often encountered in VoIP pass-through methods using codecs like G.711. In contrast to real-time FoIP, store-and-forward Internet fax employs email-based gateways that convert incoming fax pages into standardized image formats, such as TIFF-F, for attachment to SMTP messages addressed via protocols like RFC 3192's minimal fax addressing scheme, with retrieval often via POP3 or IMAP at the destination. These gateways demodulate, store, and reformat the fax data server-side before forwarding, decoupling sender and receiver timing and allowing integration with existing infrastructure for asynchronous delivery. SIP signaling typically negotiates sessions in real-time FoIP setups, embedding media descriptions in SDP to switch from voice to fax modes mid-call, as outlined in related RFCs for IP fax relay. Adoption of FoIP protocols accelerated after 2000 amid the expansion of VoIP deployments, driven by enterprises seeking to consolidate voice and fax traffic over IP backbones for lower long-distance costs and simplified network management, with implementations becoming prevalent in fax servers and gateways by the mid-2000s. Early boardless FoIP solutions emerged around 2000, enabling scalable, hardware-agnostic faxing over IP without dedicated analog ports, further propelling integration in IP-centric environments.

Cloud-Based and AI-Enhanced Fax Services

Cloud-based fax services, developed as SaaS platforms since the early 2010s, allow transmission of documents over the without dedicated hardware, converting files to fax-compatible formats for delivery to recipients' numbers or inboxes. Providers like eFax enable API-based integration for automated, high-volume faxing directly into enterprise applications, supporting compliance standards such as HIPAA. OpenText's Core Fax similarly offers APIs for inbound and outbound fax collection, facilitating seamless embedding in cloud environments. The market for fax services, encompassing variants, attained a value of USD 3.31 billion in 2024, driven by demand for scalable digital alternatives amid analog infrastructure declines. These services prioritize across distributed networks, achieving network uptime guarantees of 99.5% or higher, which mitigates transmission failures common in analog setups due to line , congestion, or equipment faults. In contrast, traditional analog faxing often experiences delivery rates below 80% when routed over modern VoIP lines without specialized protocols. By 2024-2025, AI integrations have augmented these platforms with optical character recognition (OCR) for automated data extraction from incoming faxes, reducing manual processing and error rates in document handling. Tools like those from WestFax apply AI to evaluate delivery routes dynamically, selecting optimal paths to enhance success rates and minimize retries. Additional features include AI-driven verification for recipient authentication and anomaly detection to bolster security against spoofing, though efficacy depends on implementation quality and underlying data training. Such enhancements address legacy fax inefficiencies empirically, with processing speeds for large volumes exceeding manual methods by processing complex documents in seconds via minimal human oversight.

Regulatory Transitions and End-of-Life for Analog Systems

In the United States, the (FCC) issued Order 19-72A1 on August 2, 2019, granting forbearance to telecommunications carriers from certain legacy regulations under Title II of the Communications Act, thereby permitting the retirement of analog copper-based (POTS) lines without mandatory replacement obligations. This regulatory shift, requested by USTelecom, eliminates requirements for carriers to maintain or offer new discounted POTS services, accelerating the transition to digital Voice over Internet Protocol (VoIP) networks amid declining copper infrastructure maintenance costs and rising digital investments. By 2025, major carriers such as have planned widespread POTS retirements, directly impacting analog fax machines that depend on these lines for transmission, as providers cease support for legacy endpoints. The order necessitates migration of fax operations to VoIP-compatible systems or cloud-based alternatives, with the FCC reducing carrier notification periods for service discontinuations from 180 to 90 days as of March 20, 2025, to expedite the process. Analog fax devices, reliant on continuous tone signaling and uncompressed audio paths inherent to POTS, often face interoperability challenges over VoIP, including packet loss-induced transmission errors or failure to negotiate Group 3 protocols without specialized adapters like Fax-over-IP gateways. This enforced digital pivot, while aimed at modernizing networks, has revealed transitional vulnerabilities, such as service disruptions for non-migrated users and increased urgency for businesses in sectors like healthcare to validate compatibility before carrier cutoffs. Internationally, similar copper network shutdowns underscore the global end-of-life for analog systems. In the , BT mandated migration from (PSTN) by December 31, 2025, prohibiting new analog line installations since September 2023 and urging businesses to adopt All-IP services to avoid fax and voice outages affecting an estimated 2 million entities. Comparable timelines apply elsewhere, with Canadian providers halting new copper installations and European telcos like planning PSTN decommissioning by 2030, compelling fax-dependent operations to hybrid digital solutions amid risks of operational downtime during uneven regional rollouts. These policies, driven by infrastructure obsolescence and efficiency gains, prioritize network upgrades but impose adaptation costs on legacy users, potentially stranding non-upgraded analog hardware without viable fallback options.

Applications and Persistence

Key Industries and Use Cases

In the healthcare sector, fax technology persists as a primary method for transmitting records, referrals, and prescriptions, with approximately 70% of providers relying on it for such exchanges as of 2025. This includes up to 90% of communications involving electronic health records (EHR) systems, where fax ensures compatibility with legacy infrastructure and regulatory standards like HIPAA. Over 70% of hospitals specifically use fax for record transmission annually. The legal industry employs fax for affidavits, court filings, and sensitive document delivery, where it provides a timestamped record of transmission. A 2019 Association of Corporate Counsel survey indicated that 63% of legal departments continued using fax for such purposes. Recent data shows 76% of surveyed lawyers deem faxing necessary for certain -related documents. Government agencies and financial institutions depend on fax for official verifications, loan approvals, and regulatory submissions requiring physical-like originals. These sectors contribute to the broader trend where 17% of global businesses relied on fax for critical operations in 2024, per . In , fax supported bureaucratic processes until regulatory shifts began phasing it out around mid-2024.

Factors Driving Continued Reliance

One primary factor sustaining fax usage is its established legal validity and regulatory acceptance. Faxed documents, including signatures, are enforceable in most U.S. states and many international jurisdictions as original writings under statutes like the , providing verifiable transmission logs via confirmation reports that demonstrate receipt and timestamp accuracy. In contrast, emails often lack such inherent authentication, rendering them less admissible in court without additional corroboration, as they can be forged or disputed more easily due to absent direct verification. This legal precedence persists because fax protocols embed proof-of-delivery mechanisms that courts recognize as reliable evidence, aligning with compliance needs in regulated sectors where digital alternatives may require extra validation steps. Fax's technical reliability in constrained environments further entrenches its role, particularly where is intermittent or bandwidth-limited. Operating over public switched telephone networks (PSTN), fax achieves near-100% transmission success rates in analog setups, unaffected by email's vulnerabilities like spam filters, server downtime, or , which can delay or block up to 20-30% of emails in high-volume scenarios. As of 2025, this direct circuit-switched connection yields error rates below 1% for standard Group 3 faxes, outperforming email's variable delivery amid cybersecurity threats and infrastructure gaps in rural or developing regions. Such robustness stems from fax's point-to-point handshaking protocol, which confirms page integrity before disconnection, bypassing digital intermediaries prone to failure. Network effects and systemic inertia amplify fax's persistence, as its universal compatibility over existing telephony infrastructure requires no software installation or agreements, enabling seamless exchange among disparate parties. This Metcalfe-like scaling—where value grows with connected endpoints—contrasts with fragmented digital platforms demanding uniform adoption, perpetuating fax in ecosystems where upgrading legacy hardware across supply chains imposes prohibitive coordination costs. Cultural entrenchment in business practices, especially in regions like or with conservative document-handling norms, reinforces this lock-in, as unilateral shifts risk communication breakdowns with non-compliant counterparts.

Security Considerations

Perceived Security Advantages

Traditional fax systems, operating over dedicated analog telephone lines, are perceived as more secure than internet-based alternatives due to their isolation from IP networks, which eliminates exposure to remote cyberattacks such as , , or unauthorized data via digital channels. This point-to-point transmission model confines data to physical phone lines, requiring direct access—such as or physical tampering—for interception, a process that demands specialized equipment and proximity, thereby raising the barrier to unauthorized access compared to email's vulnerability to mass scanning and spoofing. In regulated sectors like healthcare, faxing maintains preference for transmitting sensitive information under frameworks such as HIPAA, where it supports compliance through verifiable audit trails, including transmission confirmation reports and physical receipt verification via printed documents or manual handoff, reducing risks of unconfirmed delivery or alteration. Prior to widespread digital adoption around 2018, analog fax systems reported fewer cyber-related breaches than email equivalents, attributable to the absence of networked endpoints that facilitate remote exploitation, with healthcare providers citing this analog detachment as a key factor in sustained use for ().

Known Vulnerabilities and Exploitation Risks

In August 2018, researchers at demonstrated a set of vulnerabilities dubbed "Faxploit" in the T.30 fax protocol, which underpins most traditional fax communications. These flaws, including buffer overflows in the handling of DHT (discrete Huffman table) and COM (comment) markers during image decoding, could be triggered by sending a specially crafted malicious fax—often disguised as a PDF—from a standard fax machine or software . Successful exploitation enabled remote code execution (RCE) on the receiving fax device, allowing attackers to install , exfiltrate data from connected networks, or pivot laterally within corporate infrastructures, as demonstrated on vulnerable HP OfficeJet printers affecting tens of millions of devices. The T.30 protocol transmits data in over analog phone lines without inherent , exposing content to interception by anyone monitoring the line, such as through wiretaps or compromised infrastructure. This lack of persists even in hybrid setups where faxes route through VoIP gateways, unless explicitly mitigated, rendering sensitive documents—like medical records or financial data—vulnerable to during transit. Additionally, the protocol's one-way confirmation mechanism heightens risks of misdirection; faxes sent to incorrect numbers due to dialing errors or spoofing can result in unintended disclosures without sender notification, a common issue in high-volume environments. Operational and physical access risks compound these technical flaws, particularly in sectors like healthcare where fax usage remains prevalent despite digital alternatives. Unattended fax machines or shared printers allow unauthorized individuals to retrieve printed outputs containing confidential information, bypassing digital access controls. Post-2025 regulatory shifts away from analog PSTN networks toward digital alternatives have not eliminated these vulnerabilities; legacy fax servers and Fax over IP (FoIP) implementations often retain T.30 compatibility, inheriting exploitation paths, while real-world incidents underscore ongoing threats—such as the potential for RCE in unpatched systems to facilitate broader data breaches in regulated industries.

Criticisms and Limitations

Efficiency and Cost Drawbacks

Fax transmission typically requires 1 to 3 minutes per page under standard conditions, significantly slower than delivery, which occurs in seconds. This delay arises from the analog-to-digital conversion and error-correction protocols inherent in Group 3 fax standards, which negotiate rates and retransmit corrupted data packets. Transmission failure rates average 4-6% in typical setups, rising to higher levels on degraded phone lines or VoIP connections due to signal noise, , or incompatible codecs. These failures necessitate manual retries, compounding time losses and disrupting workflows, particularly in high-volume environments where poor line quality—common in rural or aging infrastructure—exacerbates bit errors during modulation. Operational costs include consumables such as or ink, which add $0.03 to $0.10 per page depending on machine type and volume, contrasting with the negligible of digital alternatives like . Maintenance for hardware, including toner replacements and repairs, further elevates expenses, with analyses indicating legacy fax systems impose hidden resource drains through downtime and supply procurement. Manual processes introduce human errors, such as incorrect dialing, misfeeding documents, or mishandling printed outputs, which limit and increase rework. These inefficiencies stem from reliance on physical intervention for loading, monitoring, and retrieving faxes, preventing and hindering integration with larger document systems.

Environmental and Resource Impacts

Traditional fax machines, reliant on thermal or plain printing, have historically driven substantial consumption. In the United States alone, conventional fax operations were estimated to consume over 200 billion pages annually as of 2014, prior to accelerated digital adoption, with an average business machine using approximately 5,000 sheets per year. This volume contributes to landfill accumulation, as comprises about 26% of , and thermal fax often resists standard due to its chemical coatings. Energy demands of further compound resource use, with each page requiring localized heat application that exceeds the negligible power for digital scanning or viewing equivalents—studies indicate can demand up to 65 times the energy of online alternatives per document. However, analog fax devices maintain a low technological footprint, with minimal compared to server infrastructure for cloud services, offsetting some inefficiencies in low-volume contexts. While paper production for faxes indirectly pressures forests—global pulp and paper accounting for up to 40% of industrial wood harvest—sustainable practices in major producers like have decoupled much of this from net , as tree volumes continue to rise amid managed harvesting. The ongoing shift to cloud-based faxing, as highlighted in 2025 provider assessments, substantially curtails these impacts by obviating altogether, yielding up to 80% reductions in and associated in transitioned operations.

Cultural and Economic Impact

Transformation of Business Communication

The widespread adoption of fax machines during the enabled businesses to transmit documents such as contracts, invoices, and orders across global distances in minutes via standard lines, markedly surpassing the days-to-weeks delays inherent in postal mail systems. This shift supported just-in-time and practices in and , where rapid confirmation of terms could prevent production halts or missed shipments, thereby enhancing operational responsiveness without reliance on emerging digital networks. For instance, firms exchanged legal briefs and banks requested title verifications instantaneously, streamlining workflows previously bottlenecked by physical transport. In export-oriented sectors like , fax integration correlated with accelerated coordination, as firms leveraged the technology to bypass time zone barriers and negotiate deals in real-time, contributing to productivity gains amid the decade's liberalization. Empirical adoption patterns show fax usage surging alongside international commerce volumes; by the late , machines processed millions of pages daily in offices worldwide, facilitating a tenfold or greater reduction in document exchange latency compared to for multi-page agreements. Such efficiencies underpinned causal improvements in velocity, with businesses reporting reduced holding costs and faster market responses in fax-reliant industries. Fax democratized these capabilities for small and medium-sized enterprises (SMEs), which acquired cost-effective standalone units—often under $1,000 by mid-decade—without needing proprietary networks like systems dominated by larger corporations. This accessibility mitigated entry barriers in global documentation flows, allowing SMEs to engage in cross-border transactions previously feasible only for entities with extensive or diplomatic channels, thus broadening participation in without exacerbating divides tied to infrastructure.

Legacy in a Digital Age

The persistence of fax technology exemplifies , where historical adoption and regulatory entrenchment create inertia that resists displacement by superior digital alternatives, often prioritizing compliance over efficiency. In sectors like healthcare, U.S. HIPAA regulations mandate verifiable transmission methods that fax fulfills due to its established audit trails and perceived legal validity, leading to 70–90% of inter-provider communications still relying on it despite widespread adoption. Similarly, legal and operations favor fax for its simplicity in handling wet-ink signatures and avoiding email's spam-filter vulnerabilities, illustrating how rules codified around legacy systems—such as those predating widespread infrastructure—lock in suboptimal practices, delaying broader innovation. As of 2025, fax endures in niche applications through hybrid models blending analog roots with cloud-based delivery, reflecting adaptation amid the FCC's phase-out of traditional analog systems via Order 19-72A1, which mandates upgrades to digital protocols like T.38 over IP. The global digital fax market is expanding at a 10.2% CAGR, driven by services converting faxes to email or secure portals, while overall fax services are projected to reach $4.48 billion by 2030 at a 5.17% CAGR, underscoring survival via incremental modernization rather than wholesale replacement. This trajectory highlights fax as a cautionary case of technological lock-in, where sunk costs in infrastructure and training—compounded by network effects in industries with universal fax compatibility—perpetuate use even as email and APIs offer faster, cheaper options, critiquing an overreliance that stifles causal progress toward more scalable systems. Proponents view fax's resilience as a virtue of proven reliability in adversarial environments, such as where digital risks undermine alternatives, while detractors decry it as emblematic of wasteful stagnation, with approximately 17% of global businesses tethered to it for critical tasks amid viable hybrids. favors the hybrid path, as growth in online fax platforms demonstrates pragmatic evolution over rigid persistence, offering a lesson that regulatory inertia can be mitigated through layered without abandoning core functionalities outright.

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