Telecom Dictionary - Definitions of terms
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facsimile (FAX): 1. A form of telegraphy for the transmission of fixed images, with or without half-tones, with a view to their reproduction in a permanent form. In this definition the term telegraphy has the same general meaning as defined in the Convention. 2. The process by which fixed graphic images, such as printed text and pictures, are scanned, and the information converted into electrical signals that may be transmitted over a telecommunications system and used to create a copy of the original, or an image so produced. Note 1: Wirephoto and telephoto are facsimile via wire circuits. Radiophoto is facsimile via radio. Note 2: Technology now exists that permits the transmission and reception of facsimile data to or from a computer without requiring hard copy at either end. Note 3: Current facsimile systems are designated and defined as follows:
- Group 1 Facsimile: The mode of black and white facsimile operation, defined in ITU-T Recommendation T.2, that uses double sideband modulation without any special measures to compress the bandwidth. Note 1: A 216 × 279-mm document, i.e., an 8½ × 11-inch document, may be transmitted in approximately 6 minutes via a telephone-type circuit. Additional modes in this group may be designed to operate at a lower resolution suitable for the transmission of 216 × 279-mm documents in 3 to 6 minutes. Note 2: The CCITT frequencies used are 1300 Hz for white and 2300 Hz for black. The North American standard is 1500 Hz for white and either 2300 or 2400 Hz for black.
- Group 2 Facsimile: The mode of black and white facsimile operation, defined in ITU-T Recommendation T.3, that accomplishes bandwidth compression by using encoding and vestigial sideband, but excludes processing of the document signal to reduce redundancy. Note: A 216 × 279-mm document, i.e., an 8½ × 11-inch document, may be transmitted in approximately 3 minutes using a 2100-Hz AM/PM/ VSB, over a telephone-type circuit.
- Group 3 Facsimile: The mode of black and white facsimile operation, defined in ITU-T Recommendation T.4, that incorporates means for reducing the redundant information in the signal by using a one-dimensional run-length coding scheme prior to the modulation process. Note 1: A 216 × 279-mm document, i.e., an 8½ × 11-inch document, may be transmitted in approximately 1 minute or less over a telephone-type circuit with twice the Group 2 horizontal resolution. The vertical resolution may also be doubled. Note 2: Group 3 Facsimile machines have integral digital modems. Note 3: An optional two-dimensional bandwidth compression scheme is also defined within the Group 3 Facsimile Recommendation. Note 4: When any CCITT or CCIR Recommendation is modified by the ITU-T, the modified document is designated as an ITU-T Recommendation.
- Group 3C Facsimile: The Group 3 digital mode of facsimile operation defined in ITU-T Recommendation T.30. Note: Group 3C is also referred to as Group 3 Option C or as Group 3-64 kb/s.
- Group 4 Facsimile: The mode of black and white facsimile operation defined in ITU-T Recommendation T.563 and CCITT Recommendation T.6. Note 1: Group 4 Facsimile uses bandwidth compression techniques to transmit, essentially without errors, a 216 × 279-mm document, i.e., an 8½ × 11-inch document, at a nominal resolution of 8 lines/mm in less than 1 minute over a public data network voice-grade circuit. Note 2: When any CCITT or CCIR Recommendation is modified by the ITU-T, the modified document is designated as an ITU-T Recommendation.
- Type I Facsimile: The mode of digital black and white facsimile operation defined in MIL-STD-188-161 used for transmission of bi-level information (e.g., text and simple graphics). Note: Type I facsimile is interoperable with the black-and-white facsimile mode of STANAG 5000 and is designed for operation over noisy communications links such as tactical channels.
- Type II Facsimile: The mode of gray-scale facsimile operation defined in MIL-STD-188-161 used for transmission of multi-level information (e.g., photographs). Note: Type II facsimile is interoperable with the black-and-white facsimile mode of Type I or STANAG 5000 equipment and is designed for operation over noisy communications links such as tactical channels.
Facsimile - (FACSimile) Originally called "telecopying," it is the communication of a printed page between remote locations. Fax machines scan a paper form and transmit a coded image over the telephone system. The receiving machine prints a facsimile of the original. A fax machine is made up of a scanner, printer and modem with fax signaling. (see Fax)
Fax standards were developed starting in 1968 and are classified by Groups. Groups 1 and 2, used until the late 1980s, transmitted a page in six and three minutes respectively. Group 3 transmits at less than one minute per page and uses data compression at 9,600 bps. The Group 3 speed increase led to the extraordinary rise in usage in the late 1980s. Group 3 resolution is 203x98 dpi in standard mode, 203x196 in fine mode and 203x392 in super fine mode.
Group 3 is still the standard today, but Group 4 machines can transmit a page in just a few seconds and provide up to 400x400 resolution. Group 4 requires 56 to 64 Kbps bandwidth and needs ISDN or Switched 56 circuits. See fax/modem and e-mail.
Fax (Telecopying) - The telephonic transmission of scanned-in printed material (text or images), usually to a telephone number associated with a printer or other output device. The original document is scanned with a fax machine, which treats the contents (text or images) as a single fixed graphic image, converting it into a bitmap. In this digital form, the information is transmitted as electrical signals through the telephone system. The receiving fax machine reconverts the coded image and prints a paper copy of the document.
Almost all modems manufactured today are capable of sending and receiving fax data. Fax/modem software generates fax signals directly from disk files or the screen. Even if a document is text only, it is treated by the computer as a scanned image and is transmitted to the receiver as a bitmap. Faxing a message online works well if the recipient wants only to read the message. However, if the document requires editing, it must be converted into ASCII text by an OCR (optical character recognition) program, or it must be retyped manually into the computer. A more efficient method of sending documents that require modification is through the e-mail system. E-mail files are already ASCII text so they can be edited immediately in any text editor or word processing program.
The Internet now provides a new and cheaper way to send faxes in some cases. A number of free and commercial companies provide arrangements for using the Internet rather than the public telephone system for most or part of the path to the fax point. Some services also provide the ability to broadcast a fax to multiple addresses.
Fax Board - Fax capability built onto a printed circuit board. Today, most fax boards are fax/modems, which also provide data transmission. See fax/modem.
Fax Group - An encoding format used for fax transmission. There are two types: Fax Group 3, also known as G3, and Fax Group 4, also known as G4. Fax Group 3 and 4 are two of the encoding formats for Tagged Image File Format (TIFF) files. The more commonly used format, Fax Group 3, is Recommendation T.4 of the
CCIT, now known as the ITU-T (for Telecommunication Standardization Sector of the International Telecommunications Union). Fax Group 3 supports one-dimensional image compression of black and white images, On a standard fax machine, Fax Group 3 uses redundancy reduction to enhance speed and is able to transmit a page in one minute or less. Fax Group 3 can achieve compression ratios of 10:1 for office documents and 15:1 for engineering drawings with a resolution of 200 dots per inch (dpi).
Less frequently used, Fax Group 4 (G4) is ITU-T Recommendation T.6 and supports two-dimensional image compression, compressing the line width as well as the line length. Fax Group 4 can achieve compression ratios of 15:1 for office documents and 20:1 for engineering drawings with a resolution of 400 dpi. Unlike Fax Group 3, Fax Group 4 can use Integrated Services Digital Network (ISDN) for transmission.
Fax Logger - Automatically storing copies of incoming and outgoing faxes onto some storage medium.
Fax/Modem - A combination fax board and data modem available as an external unit that plugs into the serial port of the computer or as an expansion board for internal installation. It includes a switch that routes the call to the fax or data modem. Incoming faxes are printed on the computer's printer. Most all modems today are fax/modems.
A fax/modem requires software that generates the fax transmission from typed-in text, a disk file or from a screen image. Fax/modems often transmit a sharper image than a fax machine, which obtains its source material by scanning the page.
Group 3 fax/modems provide various levels of processing based upon their service class. Class 1 devices perform basic handshaking and data conversion and are the most flexible, because much of the work is done by the computer's CPU. Class 2 devices establish and end the call and perform error checking. There are a variety of de facto Class 2 implementations and one Class 2.0 standard. As PCs have become more powerful, future service classes with more features are unlikely.
Fax Modem Switch - A device that allows a single phone line to be shared for a fax machine and a modem. When a call comes in and it is a fax call, the call is automatically routed to the fax machine or fax.modem. If the call is a modem call, it is routed to the correct modem.. Some devices handle voice, fax and data modem switching. May require a security access code (SAC) in the dialing string to automatically switch to the modem.
Fax Server - A computer in a network that provides a bank of fax/modems, allowing users to fax out and remote users to fax in over the next available modem. The fax server may be a dedicated machine or implemented on a file server that is providing other services.
A fax server (or faxserver) is a system installed in a local area network (LAN) server that allows computer users who are attached to the LAN to send and receive fax messages. Fax messages can be stored as printable word processing, graphics, database, or spreadsheet files. Scanned documents can be sent as fax messages, allowing a computer and scanner to effectively emulate a dedicated fax machine.
A fax server is composed of a computer with a fax program, a
fax modem(a modem capable of sending and receiving fax signals as well as conventional Internet data), a connection to the Internet or a telephone line, and connections to the LAN users.
There are several advantages to a fax server when compared with an ordinary fax machine. A single fax server can emulate multiple fax machines (one for each network user), thereby reducing overhead. Some functions can be automated. For example, a business fax server can automatically send invoices and purchase orders to customers and suppliers at specified times. Received faxes can be automatically stored as files on the server, and retrieved later by network users. In addition, a fax server can function without paper, reducing clutter and eliminating the need to continually check paper trays.
The term "fax server" is sometimes used to describe a program that enables a computer to send and receive fax messages.
Fax Switch - A device that tests a phone line for a fax signal and routes the call to the fax machine. When a fax machine dials a number and the line answers, it emits an 1100Hz signal (CNG tone) to identify itself. Some devices handle voice, fax and data modem switching and may require keying in a security access code (SAC) to switch to the modem. See CNG tone<.
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