| Fax
communications over PSTN |
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| n | Faxes follow
standard PSTN modem communications |
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| recommendations
or IEEE recommendations, as V.17 |
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| (02/91) (-
Wire modem for facsimile applications with rates up to 14 |
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| 400 bit/s) |
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| n | Faxes are
divided into groups: |
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| n | Group 1 (´68):
Analog scanning, 2400 bits/s |
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| n | Group 2 (´76):
Analog scanning, 4800 bits/s |
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| n | Group 3 (´80):
Digital scanning, 14400 bits/s |
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| n | Group 4 (´84):
Digital scanning, 64 kbit/s (ISDN) |
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| n | Example of
modules in group 3 transmitting fax: |
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| A4/US letter, |
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| 1144 lines |
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| Gray scales |
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| by dithering |
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| Modified |
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| Huffman |
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| QAM, V.27ter/ |
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| V.29 |
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| Scanning |
| Coding |
| Compression |
| Modem
(D/A) |
