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G3 FACSIMILE COMMUNICATIONS
the carrier frequency of the V.32 MODEM family is the main frequency
used by ATT in the United States and BT in the United Kingdom, be
adopted. At the assembly, deliberation turned into an argument between
US manufacturers and Japan who insisted on the different carrier fre-
quency of 1700 Hz.
The insistence by ATT in the United States and BT in the United Kingdom
was used, for example, for controlling data transmission due to the fact
that 1800 Hz was used as the carrier frequency. Various reasons such as a
secondary channel (backward channel) can be added easily to the low-fre-
quency range, and 1800 Hz is more advantageous in the design of a
MODEM device were put forward to advocate 1800 Hz.
On the other hand, some MODEM manufacturers, Japan and other coun-
tries insisted on 1700 Hz and counterargued that a V.33 MODEM was
already positioned as part of the V.29 MODEM family; and that, for the
1800 Hz agreed upon for the recommendation V.32 MODEM family, it
had not been confirmed that sufficient performance and reliability could be
obtained in band circuits of frequency 3000 Hz that are frequently seen in
submarine cable systems used exclusively for international lines. As a
result of deliberation, a data transmission test by an 1800 Hz carrier fre-
quency MODEM was conducted via a submarine cable system
mainly between ATT in the United States and KDD (Kokusai Denshi
Denwa Company, Ltd. in Japan) over a 3000 Hz band telephone line. As a
result of the test, it was proved that sufficient performance could be
obtained even when 1700 Hz was taken to be the carrier frequency; that
sufficient performance could be obtained even when the carrier frequency
was taken to be 1800 Hz; and that the equivalent performance and reliabil-
ity as that of a MODEM using a 1700 Hz carrier frequency could be
obtained. Due to these test results and the background that there is funda-
mentally no compatibility with V.29 at fallback speeds, 1800 Hz was
adopted as the carrier frequency in V.33. This concludes discussion of fall-
back speeds in V.33 and the carrier frequency. The following table cites
parameters relating to transmission systems.
5–72
Table 5-12 Various Parameters on V.33 MODEM
Data Transmission Speed
Modulation speed (baud rate)
Number of bits per modulation
Number of states per modulation
14400
12000
2400
2400
6
5
128
64
bps
Baud
bits
State
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