fax
A fax (short for facsimile, which in turn Tele facsimile ) also fax called, is the transfer of one or more documents in the form of a gridded in lines and pixel image over the telephone network or wireless (eg. As weather fax ).
Fax machines for analog connections are mostly used as senders and receivers . Faxes can also be sent and received from and to a PC using one of the following solutions:
Each fax document is an image file.
The standards G2 or G3 are used for fax transmission (see CCITT Recommendation T.4 Standardization of Group 3 Facsimile Apparatus for Document Transmission and T.30 protocol). The G4 standard exists for faxes between ISDN connections . According to a survey by the opinion research company YouGov , one in five employees in Germany used the technology in 2015 to send professional documents. One reason for this is that fax transmissions in Germany are a cost-effective and time-saving alternative to registered mail , because they are mostly recognized in court - depending on the judge - as prima facie evidence of transmission. Fax transmission is also an inexpensive feature of many printers and copiers.
history
The Scottish watchmaker Alexander Bain constructed a copy graph as early as 1843, which allowed handwriting and drawings , i.e. black and white images, to be transferred electrically. That was before Morse code was used for the first time in Europe in 1848. His system was mainly improved by Frederick Collier Bakewell in 1847 by mounting the image to be transferred on a rotating roller and scanning it pixel by pixel with a metal pin in a helical manner. Registration was carried out in a similar way on the receiving end. The first commercial fax service was established between Paris and Lyon in 1865 with Pantelegraphen , a development by the Italian physicist Giovanni Caselli , which partly combined concepts of the Bainian and Bakewellian devices. This teleautographic method was later improved by Elisha Gray , Arthur Korn and Max Dieckmann , who managed to transmit images quite well during the First World War . Many others were also active in this area, including Rudolf Hell . Mid-1920s were also pictures by using this system broadcasting transmitted. The Hell system for text transmission still delivered legible text even when the transmission channel was severely disturbed.
The early picture telegraph was only used selectively due to the effort and expense involved, for example in police administration and newspaper offices. The first prototypes of a new, publicly accessible fax generation can be found in Germany in the 1970s , at that time still under the name of fax machines . In misjudgment of the possibilities of a device technology also used privately, there was initially no marketing.
In 1974 Infotec launched the Infotec 6000 for the first time, a fax machine on the open market. The technology of the Infotec 6000 was the basis for the Group 3 standard that is still valid today.
In Japan, telecopiers were able to establish themselves more easily because the previously common teleprinters with only about 60 characters could only incompletely transmit the Japanese script , especially the Kanji . The text written in Kanji had to be rewritten (transcribed) in the Latin alphabet. Therefore, the demand for an image transmission method was higher there.
In 1979 the fax service was officially introduced by the Deutsche Bundespost .
At first there was a lack of a world standard. Due to differences in standards, no fax traffic was officially possible between Japan and Germany. Unofficially, however, converters were installed.
However, the fax machine did not become familiar in German offices until the late 1980s. Especially when the thermal paper that was initially required for reception could be replaced by normal writing paper, things picked up rapidly. As early as the early 1990s, an office could hardly do without a fax machine.
Number of fax connections in the Federal Republic of Germany:
| year | Number of connections |
|---|---|
| 1981 | 4,367 |
| 1982 | 7,307 |
| 1983 | 10,211 |
| 1984 | 13,212 |
| 1985 | 17,533 |
| 1986 | 25,000 |
| 1989 | 375,000 |
| March 1993 | 1,100,000 |
Source: Central Telecommunications Office , Darmstadt
In German procedural law, the fax machine gained in importance after authorities recognized the timely receipt of a document even if the document was sent by fax within the deadline. In substantive civil law, on the other hand, the fact that a fax is only a (remote) copy and therefore does not comply with the statutory or contractual requirement of the written form within the meaning of Section 126 BGB. The written form requires the receipt of a declaration of intent with an original signature. A large number of declarations under civil law, such as the revocation of distance sales contracts in accordance with Section 355 of the German Civil Code, can now be made legally effective by fax. The fax letter is sufficient in text form within the meaning of § 126b BGB.
With the general spread of the Internet from the mid-1990s, fax services were increasingly replaced by e-mail . The private use of fax machines is shifting in favor of online fax services, some of which can even be used free of charge.
The evidential value of faxes is limited. Since only an image of the manual signature is transmitted (very low resolution, no information about pressure, writing and speed), these signatures are unsuitable for a comparison of scripts, so that it is difficult to provide proof of authenticity. Another problem is that the other station cannot be reliably identified. This is used by dubious companies that send unsolicited advertising or even dubious to fraudulent contract offers (with suppressed fax numbers). With traditional telex this problem was already solved: the details of the other station could be requested by simply pressing a button.
Technology and standardization
For ISDN , the G4 standard is a standard for digital faxes that can be used at a significantly higher speed (64 kbit / s) than the G3 standard for analog connections (up to 14.4 kbit / s; Super G3 up to 33.6 kbit / s). s) works, but is rarely used in practice.
For transmission via Fax over IP related ITU-T Recommendations T.37 for asynchronous and T.38 for synchronous transmission.
The MIME type image / g3fax and the file extension .g3 are named after the G3 standard .
Programs with which faxes can be received on the PC and then viewed are for example:
- under the X Window System xli and kfax ;
- under Mac OS X the system's own reception service (accessible via System Preferences → Printer and Fax ) in conjunction with a viewing program such as the Preview.app supplied (which appears under the name Preview in the German system language ) or the GraphicConverter.app that can be purchased ; or the FAXstf program for receiving and viewing;
- under Microsoft Windows NT4, 2000 and XP the fax service belonging to the operating system together with a picture viewer
- Little is known that the fax service is no longer included in Microsoft Windows Vista Home Basic and Home Premium and cannot be installed later. In the Business , Ultimate and Enterprise versions , however, the new "Windows Fax and Scan" program is available.
- In Windows 7 from Home Premium , the scan and fax service is available again.
There is also fax software that works with TIFF - / FAX- ( FAX Type Image , derived from the fax: FAX / *. Fax = / ≈ TIF [F] [/ BTF / BigTIF {F}]?), GIF - or SFF - Files works.
Coding and compression of the data
In black and white faxes, the image information is read out by a line of photodiodes without loss using the algorithms MH ( Modified Huffman , RLE-based), MR (Modified READ, also referred to as "Fax Group 3" or one-dimensional coding, see also Error Correction Mode ) or MMR (Modified Modified READ, also called "Fax Group 4" or two-dimensional coding) compressed. The compression rates depend on the image data, but in general MMR provides the best compression, followed by MR. The relatively easy to implement MH-coding is still used today to work with older fax machines or fax software via the CAPI - interface to communicate.
The image information in color faxes are usually lossy JPEG - transfer compression. JPEG lossless compression is intended, but almost not used. The color information is coded in the Lab color space . Grayscale images contain only the L component .
At the beginning of a connection, before the message content is transmitted, the sending and receiving device agree on the coding used. This takes up to 10 seconds.
Paper sizes and resolutions
When the parameters are negotiated at the beginning of a connection, the recipient is also informed of the paper format used by the sender . This determines the length of the scanned line ( scanline ). Together with the number of scanned image points per line, the resolution results. According to T.4, the following horizontal resolutions are possible:
- for ISO A4, Letter and Legal
- 1728 pixels on a scan line of 215 mm (± 1% tolerance) (in black and white and color)
- 3456 pixels on a scan line of 215 mm (± 1% tolerance) (in black and white and color)
- 2592 pixels on a scan line of 215 mm (± 1% tolerance) (only for color fax)
- For ISO B4
- 2048 pixels on a scan line of 255 mm (± 1% tolerance) (in black and white and color)
- 4096 pixels on a scan line of 255 mm (± 1% tolerance) (in black and white and color)
- 3072 pixels on a scan line of 255 mm (± 1% tolerance) (only for color faxes)
- For ISO A3
- 2432 pixels on a scan line of 303 mm (± 1% tolerance) (in black and white and color)
- 4864 pixels on a scan line of 303 mm (± 1% tolerance) (in black and white and color)
- 3648 pixels on a scan line of 303 mm (± 1% tolerance) (only for color fax)
Possible vertical resolutions for faxes are:
- 3.85 lines / mm (only black and white)
- 7.7 lines / mm
- 15.4 lines / mm
In Annex E to T.4, not only the resolutions 200 dpi and 400 dpi, but also 300 dpi, which corresponds to 11.55 lines / mm, are permitted for color faxes. With color faxes, the restriction applies that the horizontal and vertical resolution must match.
The two most common black and white formats are:
- 1728 pixels at 203 or 204 dpi horizontally; 98 dpi vertical (low resolution)
- 1728 pixels at 203 or 204 dpi horizontally; 196 dpi vertical (high resolution)
Color faxes are not very common.
Simple recalculation and conversion shows that the line widths and resolutions listed in T.4 are imprecise or contradictory. For example, a 1728 pixel wide 200 dpi line must be around 219.5 mm long; this can lead to problems when printing a color fax. A scan line with a width of 215 mm corresponds to the US formats letter and legal , but cannot be displayed on A4. To display a line with 1728 pixels on A4, a resolution of 209 dpi is required. In various file formats that are suitable for storing fax documents (for example TIFF ), horizontal resolutions of 200, 203 or 204 dpi and vertical resolutions of 98/100 dpi and 196/200 dpi are often used for fax documents.
The paper format only determines the horizontal dimensions of the fax document. The length of a fax page is not specified. It can be a few lines or extend over several pages of paper, so that, for example, a two-sided fax document has to be printed on three or more pages of paper.
Most devices are unable to print or scan a page across its entire width. The fax standard counteracts this fact by not guaranteeing the transmission of a few millimeters of the page margins.
Identifier
Due to the supposed document character of faxes, the setting of the sender number in fax machines in Germany was reserved exclusively for the service technicians of the device manufacturer until the end of 1992 and the correct setting was checked when entering the fax telephone book. To protect against unauthorized changes, the sender number could only be set in a hidden service mode. ( See also: Security through obscurity .)
Delivery report
A transmission report can be printed out after sending a fax. In most cases it can be set on the device whether this report should never, always, be printed out as a collective report after a certain number of shipments or only in the event of an error. The “qualified transmission report” is a special form. The content of the sent document is also printed out here in reduced form. This is supposed to increase the evidential value of a fax. In general, however, it applies to every submission in court that it is subject to the judge's assessment of the evidence . Even a qualified transmission report is therefore not legally reliable proof that a specific letter reached a specific recipient at all and / or on the specified date.
Fax protocol
The T.30 protocol is the basis of the G3 fax standard , which enables communication between fax machines, modems, cards and servers.
This protocol defines the establishment of the connection, the transmission of the phone number , date and time and the acknowledgment of receipt. The transmission can take place with a data transmission rate of 2400 bit / s to 33,600 bit / s.
When a fax is transmitted, data is converted into tones. So that the devices understand each other, the fax protocol defines how the sender and recipient react to one another ( handshake ).
CNG ( calling tone )
- With the protocol according to group 3 (see above), the sender should report to the receiver with a signal of the frequency 1100 Hz, each 0.5 seconds long and 3 seconds long pauses to signal a fax transmission.
CED (called terminal identification / identification of the called party)
- The receiving fax machine answers the call with an approx. 3 second long 2100 Hz tone (see sound sample, first signal).
DIS ( digital identification signal / digital identification signal )
- Immediately after the CED tone, the called device emits a 2-second signal and repeats it every 3 seconds if the caller does not respond. In V.21 FSK modulation (300 bit / s), the signal contains information about the device and its reception characteristics (see sound sample, second and third signal).
DCS ( digital command signal / digital command signal )
- The caller in turn transmits his / her performance features. In this way, both devices determine the best possible transmission standard for mutual communication.
Training and TCF ( training check function / training check function )
- The caller sends test data, which it ends with a TCF signal.
CFR ( Confirmation to receive )
- The called fax acknowledges with CFR if it could understand the data.
Training , data and EOP ( end of procedure)
- The caller sends the data and completes the transmission with EOP .
MCF ( message confirmation )
- The recipient confirms receipt with MCF .
DCN ( disconnect )
- The caller ends the data connection.
Fax transmissions over the air
Fax transmissions can also be made by radio.
The German Weather Service (DWD) operates long and short wave transmitters in Pinneberg near Hamburg . There weather reports and forecasts are sent as radio telex (RTTY) and weather maps as facsimile (modulation type F1C, Wefax ) .
Fax transmission as a tele letter
The Tele letter is a historic letter service, in which the transport was replaced by faxing a letter to the Post over the telephone network or satellite radio. A customer without a fax machine can use a mail form to send a letter to a mailbox and have it sent to a receiving mailbox, from where it can then be sent to the recipient as a printout by post or express delivery or made available for collection. In Germany and most other countries, the mail service has now been discontinued as "technically obsolete".
Points of contact with other techniques
There are also combined solutions in which an e-mail is sent to a gateway , which then forwards it as a fax (see Mail2Fax ). Since the fax is sent over the public telephone network, these solutions are usually chargeable. There is also the opposite way. Some e-mail providers offer fax numbers in order to convert incoming faxes into files and forward them as an e-mail attachment to the recipient, who therefore does not need their own fax machine ( Fax2Mail ). These are financed either through the income from the service number or through fees with which the owner of the fax number is charged.
A further development is the integration of the fax machine in so-called multifunctional devices that include scanner , printer , photocopier and fax functionality.
Analog modems (formerly the only fax interface to and from the PC) are also usually fax compatible. Faxes are sent via a virtual fax printer driver from every printing program, incoming faxes are received by the modem driver, sometimes also in a buffer memory of the modem when the PC is switched off and are available after the computer is started.
Around 1980 in Austria, analogue pictures were transmitted between newspaper offices and news agencies via telephone lines.
Weather satellites transmit - for example, NOAA satellites from NASA using the analog method Automatic Picture Transmission (APT), or MetOp satellites from EUMETSAT digitally using Low Rate Picture Transmission (LRPT) - images of the clouds to earth.
Military fax machines and standardization
For military use of fax machines or fax machines, this means that the machines are free from compromising emissions and can be used with all common tactical data encryption devices (e.g. Elcrobit 3-1 according to SAVILLE ). For example, the former Office for Communications of the Bundeswehr (ANBw) or the Center for Communications of the Bundeswehr and the BildSchreibTrupps and BildFunkTrupps used the radiation- proof fax machine of the type ANTFAX 10 from Bosch Telecom or the Easy Fax 9100, which is also used in Denmark and the Netherlands E from Siemens with V.24 / V.28 interfaces. These correspond to the STANAG 5000 valid in NATO . Military fax machines are protected against Van Eck phreaking in accordance with NATO standards (Zone 0 - NATO SDIP 27 Level A (formerly AMSG 720B)). The German Air Force, the Foreign Office and authorities around the world also use the data security module DSM Fax from Siemens for secure fax transmissions, which encrypts and decrypts fax signals fully automatically with the SCA95 crypto chip using the RSA cryptosystem for standard fax machines . The authorization was carried out using personalized chip cards. Fax machines are still used today by the military and security agencies. The US fax machine TS-21 BLACKJACK , for example, has Shannon-Fano coding .
See also
literature
- Markus Aigner: The fax manual. Technology, tips and trends . Richard Pflaum Vlg GmbH, Munich 1995, ISBN 3-00-000017-8 .
- L. Heil: Fax machines . In: Concise dictionary of electrical telecommunications . 1970, 3rd Volumes Q-Z, pp. 1644-1645
- F. Schiweck: Facsimile telegraphy on telephone lines . 1956-1957
- History of facsimile . Times Facs. Corp., 1950
- Schröter: Handbook of picture telegraphy and television . 1932
Web links
- Faxes from the Museum Foundation Post and Telecommunications
- Historical fax and writing technology
- What can be done against unwanted faxes (fax spam)? IHK Stuttgart
- History and Practice of Analog Ham Radio Fax
- The forefather of the fax machine: inventor Rudolf Hell is 100 years old. On: Wissenschaft.de from December 15, 2001.
- Standardization of Group 3 facsimile terminals for document transmission
Individual evidence
- ↑ The fax is far from extinct . September 17, 2015. Retrieved September 17, 2015.
- ↑ Joseph Scheppach: Beaming for letters. In: Technology Review June 2018, pp. 96–97
- ↑ Albrecht Darimont: Telecommunication with the PC: A practice-oriented guide for the use of the personal computer in modern telecommunication networks . Springer-Verlag, 2013, ISBN 978-3-322-83680-9 , pp. 68 ( google.de [accessed on April 29, 2017]).
- ↑ Joint Senate of the Supreme Courts of the Federation, decision of April 5, 2000, file number 1/98
Remarks
- ↑ The German designations of the protocol modules are only translations of the English. Terms for understanding readers who do not understand English; therefore be careful when using it. Translations or names of the literature are preferable. If such are found, please insert them instead.