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Modem 34336
7.3 Physical Inspection
The next step in isolating a defective component is inspecting the system.
If you can 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 identify the symptoms and conduct 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 enabling
you 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, or ST)
• 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 you should conduct diagnostic tests depends upon the
symptoms you identified, the availability of personnel at the remote site, and
external test equipment. The self-test pattern generator and pattern detector
built into the Modem alleviate the requirement for external test equipment.
With the non-self tests, use either a standard DTE or an external bit error rate
test (BERT) 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 the highest available speed. If errors
occur, reduce the speed and try again. If you cannot correct the problem,
contact your supplier.