Fax

A fax (short for facsimile, which in turn Tele facsimile ) or also called remote copy, the transfer of one or more documents in the form of a gridded into lines and pixel image over the telephone network or wireless (eg, weather fax ).

When the transmitter and receiver serve mostly analog fax machines. Send and receive faxes, you can also from and to a PC using

• Fax server and modem,
• ISDN card or telephone system or
• Fax over IP.

Here, each fax document is an image file.

To fax the standards G2 or G3 (see CCITT Recommendation T.4 Standardization of Group 3 Facsimile Apparatus for Document Transmission and T.30 protocol ) used. For fax between lines, there is the standard G4.

Technology and standardization

For ISDN exists with the standard G4 a standard for a digital fax, of a significantly higher rate (64 kbit / s) than the standard G3 analog ports (up to 14.4 kbit / s, Super G3 to 33.6 kbit / s ) operates, but is rarely used in practice.

For the transmission of fax over IP are the ITU- T Recommendations T.37 and T.38 for asynchronous synchronous transmission.

The MIME type image/g3fax and the file extension. G3 are named according to the standard G3.

Programs that receive faxes on your PC and then can be considered are, for example:

• Under the X Window System xli and kfax;
• Under Mac OS X, the native reception service (accessible via System Settings → Printers and Fax ) (which appears in German system language under the name preview) in conjunction with a viewing program like the one provided Preview.app or to be acquired GraphicConverter.app; or FAXstf program for receiving and viewing;
• Microsoft Windows NT4, 2000 and XP, the operating system belonging Fax service along with an image viewer.
• Little known is that the Fax service in Microsoft Windows Vista Home Basic and Home Premium is no longer included and also can not be re-install. In the variants Business, Ultimate and Enterprise, however, the new " Windows Fax and Scan " is available.
• In Windows 7 Home Premium from the scan and fax services is available again.

There are also fax software with TIFF-/FAX- (Type FAX Image, derived from Fax: FAX / fax = * / ≈ TIF [F ] [/ BTF / BigTIF { F} ]. ? ), GIF, or SFF files works.

Coding and compression of data

In black / white faxing the image information after being read by a photodiode line loss with the algorithms MH (Modified Huffman, RLE - based), MR ( Modified READ, also known as " Fax Group 3" or one-dimensional coding called, see also Error Correction mode) or MMR ( Modified Modified READ, also known as " Fax Group 4" or two-dimensional code called ) compressed. Compression rates depending on the image data, but in general provides the best MMR compression, followed by MR. The relatively simple to implement MH coding is still used today to communicate with older fax machines or fax software via the CAPI interface.

The image information in color faxes are normally transmitted with lossy JPEG compression. Lossless JPEG compression is provided for, but is used as well as not. The color information are coded in the Lab color space. Grayscale images contain only the L component.

To start a connection, before sending the message content, be transmitted and receiving device to vote on the encoding used. It takes up to about 10 seconds.

Paper formats and resolutions

When negotiating the parameters ( English negotiation) at the beginning of a connection, the recipient is also notified to the paper used by the transmitter. This determines the length of the scanned line (scan line ). Together with the number of sampled pixels per line determines the resolution. After T.4 following horizontal resolutions are possible:

• For ISO A4, Letter and Legal 1728 pixels on a scan line of 215 mm ( ± 1% ) ( b / w and color)
• 3456 pixels on a scan line of 215 mm ( ± 1% ) ( b / w and color)
• 2592 pixels on a scan line of 215 mm ( ± 1% ) (for Colour Fax )

• 2048 pixels on a scan line of 255 mm ( ± 1% ) ( b / w and color)
• 4096 pixels on a scan line of 255 mm ( ± 1% ) ( b / w and color)
• 3072 pixels on a scan line of 255 mm ( ± 1% ) (for Colour Fax )

• 2432 pixels on a scan line of 303 mm ( ± 1% ) ( b / w and color)
• 4864 pixels on a scan line of 303 mm ( ± 1% ) ( b / w and color)
• 3648 pixels on a scan line of 303 mm ( ± 1% ) (for Colour Fax )

Vertical resolution is 3.85 lines / mm, 7.7 lines / mm and 15.4 lines / mm for black / white faxing and 7.7 lines / mm and 15.4 lines / mm for color faxing. In Annex E to T.4 for color faxing not only the resolutions 200 dpi and 400 dpi, but an additional 300 dpi, which corresponds to 11.55 lines / mm, admitted. For color faxing the restriction that horizontal and vertical resolution must match.

The two most commonly used black / white formats are:

Color faxes are not widespread.

Easy To Convert and shows that the line widths and resolutions listed in T.4 are inaccurate or inconsistent. Thus a 1728 pixel wide 200 -dpi line must be about 219.5 mm long; when printing a color fax, this can lead to problems. A scan line of 215 mm width corresponds to the U.S. letter and legal formats, but can not be represented 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 faxes (for example, TIFF), for faxes often horizontal resolutions of 200, 203 or 204 dpi and vertical resolutions of 98/100 dpi and 196/200 dpi can be used.

The paper size will only determine the horizontal dimensions of the fax. The length of a fax page is not fixed. It can be a few lines or extend over several sheets of paper, so that for example a two-page fax on three or more sides of the paper must be printed.

Most of the devices are not able to print on one side over its entire width or scan. The Faxstandard encountered this fact by the transfer of some millimeters of the lateral edges is not guaranteed.

ID

Due to the nature of the alleged documents faxes to set the sender number was reserved exclusively for the service technicians of the equipment manufacturer in fax machines in Germany until the end of 1992 and the correct setting has been checked at the entry in the Fax Phone Book. To protect against unauthorized changes the sender number was adjustable only in a hidden service mode. ( See also: Security through obscurity ).

Send report

After sending a fax, a transmission report can be printed. Most can be set on the device, if this report is to never, ever, printed as a summary report after a certain number of items or in case of error. A special form is the qualified transmission report. Here additionally, the contents of the sent document is printed in a smaller format with. This should increase the probative value of a fax. In general, however, for every argument in court that it is subject to the evaluation of the evidence by the judge. Also a qualified transmission report is thus not quite sure proof that a particular letter has a particular recipient at all and / or reached the indicated deadline.

Fax protocol

The T.30 protocol is the basis of the G3 fax technology standards, which enables communication between fax machines, fax modems, fax cards and fax servers.

In this protocol, the connection, the transfer of phone number, date and time and the acknowledgment of receipt is defined. The transmission can be used with a data transfer rate of 2400 bit / s up to 33,600 bit / s.

Welcome response from a called fax.? / I

When sending a fax data is converted into sound. In order to understand the equipment, sets the FAX protocol, such as transmitter and receiver respond (handshake) with each other.

CED ( Called terminal identification)

DIS (digital identification signal)

DCS (digital command signal)

Training and TCF (Training check function)

CFR ( Confirmation to receive)

Training, data, and EOP (End of procedure )

MCF (message confirmation )

DCN ( Disconnect)

Fax transmissions via radio

Fax transmissions can also take place via radio.

The German Weather Service ( DWD) operates long-and short -wave transmitter in Pinneberg near Hamburg. There, weather reports and forecasts as a radio teletype ( RTTY ), and weather maps in facsimile ( modulation F1C, wefax ) are sent.

Faxing as teleletter

The teleletter is a historic letter service, in which the transport of a letter is replaced by faxing the mail via the telephone network or satellite radio or was. Here, a customer without a fax machine to give up a letter on a post form in a teleletter place and have it relayed to a receiving teleletter point, from where it is then sent by post or express delivery reaches the recipient or ready set by mailbox or pick up. In Germany and most other countries of the teleletter service has now been set as technically obsolete.

Points of contact with other technologies

There are also combination solutions in which an email is sent to a gateway, which then sends it as a fax (see Mail2Fax ). Since the fax is sent over the public switched telephone network, these solutions are mostly free of charge. Are also the other way round it. Some e -mail providers offer fax numbers to convert incoming faxes to files and forward them as e -mail attachment to the receiver, which thus does not need a separate fax machine ( Fax2Mail ). These are funded either by the revenue from the service number or fees charged to the owner of the fax number will be charged.

As a further development, the integration of the fax machine in so-called multi -function devices can be observed include the scanner, printer, photocopier and fax functionality.

Analog modems ( which is the only fax interface to and from the PC ) are also faxtauglich usually. Faxes are sent out via a virtual fax print driver from any printed program, receive incoming faxes from the modem drivers, sometimes in a buffer memory of the modem when the PC and available when you start the computer available.

Military fax machines and standardization

For the military use of fax machines and facsimile machines, this means that the devices are free from compromising radiation and with all common tactical data key devices (eg, Elcrobit 3-1 after SAVILLE ) can be used. So used, for example, the former Office of Communications of the Bundeswehr ( ANBw ) or the Center for Intelligence of the Bundeswehr and the image Writes patrols and Bildfunk squads from 1995, the abstrahlsichere facsimile device type ANTFAX 10 Bosch Telecom or the Easy employed in Denmark and the Netherlands Fax 9100 e from Siemens with V.24/V.28-Schnittstellen. These correspond to the force in NATO STANAG 5000 only ( Zone 0 - NATO SDIP 27 Level A ( formerly AMSG 720B ) ) are military Faxes before Van Eck phreaking NATO standard. . The German Luftwaffe, the German Foreign Office and government agencies worldwide also took advantage of the backup module DSM fax from Siemens for secure fax transmissions, which performed for commonly used fax machines, fully automatic encryption and decryption of fax signals to the crypto chip SCA95 according to the RSA cryptosystem. The authorization was carried out through personalized smart cards. Even today, fax machines come in the military and security agencies worldwide. The U.S. fax machine TS -21 BLACKJACK has, for example, a Shannon -Fano coding.

History

The Scottish clockmaker Alexander Bain in 1843 constructed a copying telegraph, which made it possible to transfer, manuscripts and drawings, so black and white images electrically. So that even before ever in Europe for the first time the Morse code was used in 1848. His system was thus decisively improved mainly by Frederick Collier Bakewell in 1847 that he aufspannte the image to be transferred to a rotating roll and pixel by pixel by a metal pin groped helically. Registration was performed on the receiving side in a similar manner. The first commercial telefax service between Paris and Lyon in 1865 set up ( " Pantélégraphes "). This tele- autographic method was significantly improved later by Elisha Gray, Arthur Korn and Max Dieckmann, which get quite a good image transmissions during the First World War. Many others were also active in this area, as well as Rudolf Hell. Mid-1920s were transmitted by radio with this system also pictures. The Light System for transfer writing yet delivered even with highly degraded transmission channel readable font.

The early picture telegraph was used only occasionally due to effort and cost, such as in police administration and newspaper editors. First prototypes of a new publicly available fax generation can be found in Germany in the 1970s, at that time still under the name telecopier. In underestimating the possibilities of even privately used equipment technology initially was no marketing.

In 1974, with the Infotec 6000 Infotec first time a fax to the free market. The technology of Infotec 6000 was the basis for today still valid group -3 standard.

In Japan, telefax could enforce easier because the usual Telegraph with its only about 60 characters, the Japanese writing system, especially the kanji, could not completely transferred. The value written in kanji text had re-written in Latin alphabet ( transcribed ) are. Therefore, there was higher demand for a pictorial transfer method.

1979, the Fax service was officially launched by the German Federal Post Office. [ Evidence ?]

First, there was a lack of a world standard. Between Japan and Germany officially no fax traffic was possible because standard differences. Unofficially, but converters were installed.

Native was the fax machine to the German offices but only in the late 1980s. Especially when the thermal paper initially required for the reception could be replaced by normal writing paper, it went rapidly upwards. Already from the beginning of the nineties was hardly more of an office without a fax machine.

Number of fax ports in the Federal Republic of Germany:

Source: Technical Telecommunications Central Office, Darmstadt

In the German procedural law, the fax machine became more important after the authorities on time -maintaining access a document also recognized when the pleading was sent within the deadline by fax. In civil law, there remained, however, that a facsimile is simply a (remote) copy and therefore legal or contractual requirement of written form within the meaning of § 126 BGB fails to maintain. The writing requires the receipt of a declaration of intent with the original name signature. A variety of civil declarations, such as the cancellation of contracts according to § 355 BGB, can now be given legal effect by fax. The facsimile is sufficient in text form within the meaning of § 126b BGB.

With the widespread use of the Internet in the mid- nineties, the fax service has been increasingly supplanted by e-mail. The private use of fax machines shifts in favor of online fax services which are indeed to take part free of charge.

The proof capability of faxing is limited. Since only one image of the handwritten signature is transmitted (very low resolution, no information on printing and office management and speed ), these signatures are unsuitable for Schriftvergleichung so that a proof of authenticity can only be poorly managed. Another problem is that the other station is not reliably identified. This is used by dubious companies that unsolicited advertising or even dubious to fraudulent contract deals send ( suppressed fax number ). In the classical telex this problem was already solved: By simply pressing the details of the remote station could be requested.