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CHAPTER 5: Troubleshooting and Diagnostics
Figure 5-3. Activating RLB at the Remote Modem (Local Fiber Optic
Modem in a Digital Loopback).
5.3 Internal BERT Circuit Test
The Fiber Optic Modem has a built-in BERT circuit, consisting of a pattern
generator and a pattern tester. This circuit works in conjunction with the V.54
diagnostic loops and the remote BERT to verify normal system operation and
identify faulty equipment if the system fails.
The pattern transmitted is a proprietary, random pattern.
The pattern transmitted by the BERT can be received by another Fiber Optic
Modem (a two-BERT test) or looped back to the BERT for comparison (modem
self-test).
When used opposite another Fiber Optic Modem, the complete link can be
tested either with the PATT pushbutton pressed, or with an external BERT
transmitting the same 511-bit pattern (per V.52).
5.3.1 M
ODEM
S
ELF
-T
EST
This test verifies that the modem is operating correctly (see
Figure 5-4
).
To perform the test, proceed as follows:
1. Press the ANA pushbutton on the front panel. The TEST and DCD LEDs will
light up.
Local Fiber
Optic Modem
Remote Fiber
Optic Modem
DIG
Pressed
