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Chapter 3 - Modem Testing
2 for DIP switch setting information).
Computer or Terminal Local MultiModem
Digital Analog
CONNECT
UUUUUUUU
UUUU
Figure 3-3. Local Analog Loopback Test
Digital Loopback Test
The digital loopback test is an on-line test that loops data sent
from one modem across the phone line to another modem, and
then back to the first modem. This test checks the phone line
and modem integrity.
This digital loopback test is used on modems configured for
four-wire leased lines. To perform this test, the DLB switch on
the modem’s circuit board must be set to the DLB position (see
Figure 2-3 in Chapter 2).
In this test the local modem is placed in digital loopback mode.
Data is entered and transmitted from the remote modem (which
is not in digital loopback mode), sent across the phone line to
the local modem, and looped back to the remote modem.
UUUUUUUUU
UUUUU
Computer or Terminal Local MultiModem Remote MultiModem
Computer or Terminal
Digital
Analog
Digital
Analog
OK
Figure 3-4. Digital Loopback Test