Black Box 32144, Manual

Page: 53 / 195

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CHAPTER 7: Diagnostics
7.3 Physical Inspection
The next step in isolating a
defective component is to inspect
the system. If you have been able to
trace the problem to a specific site,
examine that site. Check the
installation of the modem and
DTE. Are all cables in good
condition and fully connected?
Are all components in the system
receiving power? Inspect the
system as thoroughly as possible.
7.4 Overview of Modem Diagnostics
Once you have identified the
symptoms and conducted a
physical inspection of the sites in
question, you can use diagnostic
monitoring and testing to further
isolate the problem. The modem is
equipped with diagnostic
capabilities that will often enable
the user to locate faults quickly and
easily. The diagnostic features of
the modem fall into two
categories—local and remote—
as listed below.
There are six types of local
modem diagnostics:
• Analog loopback (ALB)
• Analog loopback self test
(ALBST)
• Analog loopback self test with
errors (ST/E)
• External analog loopback
(ALBX)
• External analog loopback self
test (ALXST)
• Digital loopback (DLB)
There are two types of remote
diagnostics:
• Remote digital loopback (RDL)
• Remote digital loopback self
test (RDLST)
The sequence in which
diagnostic tests should be
conducted depends upon the
symptoms that have been identified
as well as the availability of
personnel at the remote site and
external test equipment. The self
test pattern generator and pattern
detector built into the modem
alleviates the requirement for
external test equipment. With the
non-self tests, either a standard
DTE or an external bit error rate
test (BERT) is used to generate test
data and compare it with received
data.
Because more transmission
errors occur at higher speeds on
marginal transmission facilities,
begin testing at 14.4 Kbps. If errors
occur, reduce the speed and try
again. If you cannot correct the
problem, contact Technical
Support for assistance.