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ITU-T V.21:
Specifies full duplex transmission at 300 bit/s. Modulation rate:
300 baud.
(ITU-T V.22:
Alternative A specifies synchronous transmission at 1200 or
600 bit/s. Modulation rate: 600 baud.
Alternative B specifies asynchronous transmission at 1200 or
600 bit/s. Modulation rate 600 baud.
1200 bit/s data speed . Groups of 2 bits (dibit) are modulated
simultaneously, according to the following table:
Fig 15-1
Fig 15-2
00
90°
01
0°
11
270°
10
180°
600 bit/s
_. Phase shift by degrees
90°
01
270°
ITU-T V.22 bis
Specifies synchronous or asynchronous transmission at 2400 or
1200 bits bit/s. Modulation rate: 600 baud.
2400 bit/s data signaling rate: Groups of 4 bits (quadbit) are
modulated simultaneously. First, a phase quadrant change is
defined - relative to the first quadrant occupied by the previous
signal element - using the first two bits of the group.
See fig15-3.
Then the last two bits of the group are used to define one of the
four signal elements of the new phase quadrant (after phase
quadrant change).
See fig 15-4.
15-8
LZTR104006 R1.00
Zat14.4/14.4-7 and 19.2/19.2-7
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