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1. ON ITU-T (International Telecommunications' Union.)
The No. XIV Group of ITU-T, one of the four permanent
organizations of the International Telecommunications Uniib
(ITU), investigates and make recommendations on international
standards for facsimiles.
2. Definition of Each Group
- Group I (G1)
A-4 size documents without using formats which reduce the band
width of a signal sent over telephone lines. / Determined in 1968. /
Transmission for about 6 minutes at scanning line density of 3.85
lines/mm.
- Group II (G2)
Using reduction technology in the modulation/demodulation
format, an A-4 size document is sent at an official scanning line
density of 3.85 lines/mm for about 3 minutes. / Methods to
suppress redundancy are not used. / Determined in 1976.
- Group III (G3)
A method of suppressing redundancy in the image signal prior to
modulation is used. An A-4 size document is sent with about one
minute. / Determined in 1980.
- Group IV (G4)
Transmission is via the data network. A method is provided for
suppressing redundancy in signals prior to transmission, and
error-free reception of transmission is possible. / The scope of
these facsimile applications is not limited simply to transmission
of written statements. Through symbiotic linkages with other
communication methods, it can be expected to expand to include
integrated services.
3. Facsimile Call Time Series
As shown in the following diagram, the facsimile call time series is divided into five phases.
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