Information Technology Reference
In-Depth Information
cable for shorts or opens. The cable link was working before the failure, so we don't
have to be too concerned about other miswires.
Of course, if the application is a Category 5e 100 Mbps one, we would want
to use a cable scanner set for Category 5e tests, since cable operation at the higher
frequencies could be impaired without affecting DC continuity. If the cable checks
good, the physical connection is no longer suspect. Next, you could look at the com-
puter setup, interface card, server setup, and all the other network items that could
cause a logical connection to fail.
Another way to logically divide the problem is through substitution of known-
good components. Alternatively, you could use substitution to verify the proper
operation of suspected components including the computer and hub. For example,
you could move a known-good computer to the suspected-bad outlet, or move the
suspected computer to a known-good outlet. Substitution causes you to guess which
component might be bad and then test your guess. It can be done with very little test
equipment, but it requires you to proceed very methodically and with no precon-
ceived assumptions.
The third step, testing each portion of the whole, you might notice has fol-
lowed immediately after we logically divided the problem. You must be very certain
what you test, or your tests may be invalid. For example, what if we had tested the
Permanent Link instead of the Channel in our prior example? Does that test all of
the cable? No, it does not! If the problem had been a failed user or patch cord, we
would have missed it.
So, be methodical, be sure you understand the problem, carefully structure
your testing so that it eliminates as many variables as possible, and make no
absolute assumptions.
