tion split the radio speech channel to keep the mobile units in speech when necessary. CCITT document facsimile equipment 60/5 Table 60.2 Document facsimile types Network Public telephone (analogue) Public data (digital) CCITT Group/ G1/T.2 G2/T.3 G3/T.4/T.30 G4 Class 1/T.563 recommendation Transmission time 6 min (4 min option) 3 min Around 30 sec (at Around 5 sec (at 9.6kbit/s) 64kbit/s) Data rate Analogue 14.4-2.4kbit/s 64-2.4kbit/s Modulation AM/VSB (vestige of V.17/V.29/V.27 te None (line driver and upper sideband) coder to suit network) White 1300Hz (US 1500Hz) Maximum carrier reversing phase Black 2100Hz (US 2400Hz) 26dB below white Synchronisation +10 parts in 106 +5 parts in 106 Derived from data rate and sequence Index of co-operation Not specified Not specified (176 option) (264/528 option) (549) Scan line frequency Not specified Not specified (around 100Hz) (around 600Hz) Horizontal resolution Not applicable 1728 pels/215mm 200 pels/25.4mm (8.04 pels/mm) (option 240/300/400) Scan line length 215mm 215/255/303mm 219/260/308mm Vertical resolution 3.85 lines/mm 3.85 lines/mm 3.85 lines/mm Square with horizontal (2.57 opt) (7.7 lines/mm option) Data compression One dimensional MH 2 dimensional MMR encoding 2 dim MR & MMR Uncompressed Uncompressed 60.3 CCITT document facsimile equipment to be used they must be available in both send and receive machines and are usually negotiated automatically. This is principally for the transmission of business and commercial papers, letters, drawings and general office documentation around 60.4.1 Scanner A4 size (210mm X 297mm). The pages are often black or dark coloured text or handwritten characters on white or pastel back- In a typical CCD scanner a section of the original is illuminated by grounds, although machines handle a wide range of original docu- a fluorescent or cold cathode tube. The facsimile line to be scanned ments. is focused onto a 1728 (A4 width) or 2048 (B4) element CCD single CCITT has produced and continues to develop recommendations line image sen