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T.6

An ITU standard for Group 4 fax machines. Introduced in 1984, Group 4 requires ISDN, DSL or other switched digital lines. It provides a greater compression ratio than Group 3 fax. See fax.



fax

(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 copy (a facsimile) of the original. A fax machine is made up of a scanner, printer and modem with fax signaling.

Group 1, 2, 3 and 4
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 resolutions are 203x98 dpi in standard mode, 203x196 in fine mode and 203x392 in super fine mode.

Group 3 is the common standard, 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, Switched 56 circuits or DSL lines. See fax/modem, Internet faxing and email.




A Different Kind of Fax Machine
This earlier portable fax machine from Reflection Technology weighed eight ounces, worked with most cellphones and stored 25 fax pages. Its virtual display simulated a 12" monitor, and its "virtual keyboard" (lever and buttons on top) let you select menu options. (Image courtesy of Reflection Technology, Inc.)






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