Information Technology Reference
In-Depth Information
Any complex system is subject to periodic failures, and LAN wiring systems are no
different. Throughout this topic, we have emphasized the installation of a reliable
wiring system. We have spent a great deal of time showing the proper components and
installation techniques that are required to create a properly functioning, reliable cable
plant. The precept for this careful construction is that when anything does go wrong,
it should very rarely be the cabling. (Some might say “never” rather than “rarely,” but
your LAN wiring is in an environment where it cannot totally be protected from those
uncaring souls without the proper respect for these thin little wires.)
The fact of the matter is that failures do happen. Fortunately, most of the fail-
ures happen during installation, where the link operation is not critical. Still, the
failed cable must be repaired, regardless of the circumstances. If the link has been in
operation, it is all the more important that we make the repairs quickly.
Cable link failures can be divided into two broad classes with respect to LAN wiring.
The classes of failures correspond to the types of test equipment for each. Failures involv-
ing basic cable function can be determined by the basic test equipment we talked about
in Chapter 15. This equipment can check cable link connectivity and DC wire map.
Failures involving performance- based cable function must be determined by the diagnos-
tic and measurement equipment we covered. This equipment tests the performance of the
cable link at the level of performance required for your particular LAN application. It
tests for split pairs, impedance, NEXT, length, attenuation, and other parameters that are
required for proper LAN operation. The basic function can be fine, but the link will still
not operate if it doesn't meet your performance needs. For example, you could probably
get DC connectivity on a barbed-wire fence, but you wouldn't be able to run data on it.
In this chapter, we will detail many of the types of cable link failures, whether
they are from installation errors or cable damage after installation. We will give
some approaches to finding the problem and repairing the cable link. Also, we will
say a little about a successful troubleshooting approach that you may find useful.
It is important to understand how LAN cabling can fail, in order to help you isolate
and troubleshoot problems with your cabling. In this section, we will examine the
common problems that may occur with an installed cable system and how to deter-
mine the best way to alleviate the problem.
Copper Cable Failure Modes
Copper cabling is the LAN wiring type that is most prone to failure, both during the
installation phase and after the cable has been “in the wall” for a while. Ideally, the
