User manual

CHAPTER 4: GENERAL INFORMATION AND FEATURES
4.3 2W/4W Leased Line
We had talked modem operate in the previous section. There are two-wire leased lined
and four-wire leased line.
2W leased line achieves full duplex with only a pair of lines. There comes up the
problem of interference. In V.21, V.22, V.22bis operating modes, the Modem used
the frequency split method. Whereas, in V.32/V32bis/V.34 mode, it must provides
"echo cancellation", because originate and answer modems occupy the same
frequency band.
4W leased line offers two independently unilateral transmission channel, therefore, it
can achieve full duplex communication with less interference.
Obviously, the line quality of 4W leased line is better than that of 2W leased line.
However, the modem does an excellent job with both 2W and 4W leased lines and
even dial line.
DTE MODEM MODEM DTE
∼
DTE
MODEM MODEM
DTE
∼
∼
2W Leased Line
4W Leased Line
FIG. 4-3: 2W/4W leased line.
4.4 Answer Mode VS. Originate Mode
While using the dial line, there must be a modem initiating the call, once the exchange
recognizes the number, it connects the circuit to the answering modem with ring
signals. Answering modem can pick up the call manually or automatically. Afterward,
it issues the answer tone to connect with the originate modem. Usually, we call the
modem which dials the call as originate mode and the other one as answer mode.
According to the role of the connection the training sequence and working frequency
band of either modem is different from each other even operating with leased line.
With 2/4-wire full-duplex operation such as V.21, V.22, V.22bis, V.23, V.32, V.32bis,
V.34, Bell 103, and Bell 212A, there should be an originate mode and an answer
mode.
You may find the information of originate/answer settings in the “ORG/ANS MODE”
column of “CONGIF MODEM” MENU. Note that the modem will automatically
determine either mode whenever you use the “AT” commands, front panel dialing, or
auto answering.
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