Information Technology Reference
In-Depth Information
Initial operation of the workstation is a good indication that the cable is all
right, but it's not positive proof that the cable is in perfect condition—particularly
if your workstations are still using 10 or 16 Mbps technology, and you plan to go
to higher speeds. Also, it is not unusual for some of the station drops to remain
unused until some later date. How will you know if those drops will work when you
need them?
Would you have a light fixture installed and not try the switch? Probably not.
You need to test each drop of your cabling system as well. The best way to test cable
is to use proper test equipment that looks only at the cable performance. In that
way, you avoid the nagging little network problems that obscure the real issues.
Cable often gets blamed for problems that are really network hardware problems
and bad software configurations.
The best time to do the testing is before furnishings and people have been
moved in. At this point, all outlet jacks are accessible, without the need to move
desks and other furniture. Any inspections and repairs that are needed can be done
quickly and without disturbing anyone. Of course, modular furniture will have to
be in place because the cable must be installed in the furniture modules before it can
be tested.
TIA has offered TSB-72, now incorporated into TIA-568-C, as a means to pro-
vide an intermediate point for interconnection to modular furniture. See the details
in Chapter 10, “Open-Office Wiring.”
The testing of installed cable links is often referred to as “certification” of the instal-
lation. Certification is normally performed by the installer and involves testing each
individual cable link to a recognized standard. The end result of the certification is
a report that shows the actual measurements of each cable link and the pass or fail
determination.
A dilemma initially existed in providing a method of testing and certifying
installed telecommunications cable. The original EIA/TIA-568 standard specifically
stated that the performance standards for cable and connecting hardware did not
apply to installed systems. The reason for this was that it was known that an
installed cable run had performance that was below that of cable tested at the fac-
tory. As a matter of fact, a correlation problem seemed to exist between cable tested
with a factory RF network analyzer and with the field test instruments. Whether the
field testers gave actual measurements of the parameters or judged the cable on
pass/fail criteria, there were differences that might cause factory-certified cable to
fail a field test.
