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CHAPTER 5: Troubleshooting and Diagnostics
5.5 Communication Link Test
5.5.1 R
EMOTE
D
IGITAL
L
OOPBACK
The remote digital loopback test determines the performance of both the local
and remote Fiber Optic Modem, and the quality of the link between the local and
remote units.
1. Press the REM pushbutton on the front panel to provide a loopback at the
remote Fiber Optic Modem (see
Figure 5-2
). (This test can also be activated
via the pin on the DTE interface.) The TEST LED lights at both the local and
remote units.
2. Perform the BERT test as explained in
Section 5.3
.
3. If Step 2 indicates a fault, and if the modem test described in
Section 5.4
was
successful for both the local and remote modems, the line circuits are not
operating properly.
5.5.2 L
OCAL
D
IGITAL
L
OOPBACK
The test loops the received data back to the remote Fiber Optic Modem. (This test
is equivalent to activating remote loopback from the remote Fiber Optic Modem,
as shown in
Figure 5-7
). The operator at the remote end can determine the
performance of the local and remote Fiber Optic Modems and of the links
between them.
To activate this test, press the DIG pushbutton on the front panel.
Figure 5-7. Local Fiber Optic Modem in Digital Loopback.
Remote Fiber
Optic Modem
Local Fiber
Optic Modem
REM
Pressed
DIG
Pressed
