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Connecting up in V.22/V.22 bis
In V.22 bis, the modems decide during the connecting sequence
which transmission speed to use. The connecting sequence is
compatible with V.22 and is always started in 1200 bit/s.
lf the originating modem can transmit 2400 bit/s, it will send a
short sequence in a special pattern. If the answering modem
detects this and answers with a corresponding sequence, both
modems will after a short time, start transmission at a rate of
2400 bit/s. If however, one of the modems does not send this
sequence, the speed will remain 1200 bit/s.
ITU-T V.22 bis Handshake sequence at 2400 bit/s
Fig. 15-5 shows a connecting-up sequence where both modems
can transmit 2400 bit/s.
Call mode modem
Tr
itted line signa
4
Scrambled binary 1
Scrambled binary 1 |
Data
Connect to line
at 1200 bit/s
at 2400 bits
456ms | 100 ms
200 ms +10 ms
+10ms
+3. ms
600 ms +10 ms
106
Detect unscrambled
binary 1 in 155210 ms
_]|
107
Answer mode modem
A50ms 110 m
Begin 16 way
Detect 32 consecutive bits
decisions in receiver
of banary 1 af 2400 bis
Connect
Sted ore
ea
to line
c
signal
2100 Hz
Scrambled binary 1
S14
Scrambled binary 1
[Scrambled binary 1 [
Data
tor 3300
at 1200 bit/s
at 1200 bils
lat 2400 bit/s
+350 ms
75ms +20 ms
+t
200ms +10 ms
100ms :3 ms
7
Gooms
+10
? Detect 32
3
ms
£10
ms
Shey ta? bits of
10ms
+350 ms
aa
bmary 1 af 2400 bit
.
-
450ms -10 MS"
gegm 16 way
Gecrsrons In i
f
106
109
104 clamped | 104 unciam
to brary 1
|
(binary 1)
[Data
i
end of S1 signal in
lower channel
Fig 15-5
1 5-1
0
LZTR104006 R1.00
Zat14.4/14.4-7 and 19.2/19.2-7
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