Testing and Certifying LAN Wiring - LAN Wiring - page 381

TABLE 15.4
Comparison of TIA/EIA Categories and ISO/IEC Classes

TIA-568-C Category 5 Category 5e Category 6 Category 7*

ISO/IEC IS-11801 Class D Class D Class E Class F *

*Category 7 and Class F are proposed extensions to the performance models.

standards on an international level are coordinated (also called harmonized ) to use
the same procedures, nomenclature, and limits, they may also contain deviations in
language and some parameters that are appropriate in that region of the world. In
addition, the standards bodies that promulgate these documents revise them on dif-
fering time cycles, and they may not be exactly synchronized to implement changes
at the same time that the overall international community deems necessary.
TIA-568-C identifies two performance levels for field testers, Accuracy Levels
I and II. Accuracy Level II is the toughest, and is justified when you intend to oper-
ate your cable drops at or very near the length or performance limits, including user
cords and jumpers. Table 15.5 shows the minimum requirements for the two levels.
These accuracy levels are provided to ensure that the test instrument can actually
measure the cable link parameters that need to be certified. Accuracy Level II is
intended to closely mimic the laboratory test equipment and turns out to be more
than was needed for reasonable measurements.
A third accuracy standard is now specified in TIA-568-C, called Accuracy
Level IIe. It allows for measurement to Category 5e.
It is difficult to say which type of tester you need for certification. The potential
problems actually occur only at or very near the acceptable performance limits. In a
cable plant that uses very high quality cable and components and that has relatively
short cable runs, you may never approach the limits required for your category of
operation. However, if you use low-quality materials and questionable installation
practices, you may see a lot of links at the performance limits. The Accuracy Level II
is difficult to achieve, as its intent is to very closely emulate the performance of gen-
eral-purpose laboratory analyzers costing 10 to 20 times as much.
Now that TIA has endorsed Level IIe accuracy, that is really all you need to
properly verify link performance. For routine use, it may be sufficient to get an
Accuracy Level I tester or one that does not achieve Accuracy Level IIe on all param-
eters. Some testers may offer different performance levels on Permanent Links and
Channels, because the Channel test requires the use of the 8-pin modular connector
at the test interface. As a LAN manager, you may choose to get a less expensive
Accuracy Level I tester for your own casual troubleshooting use, and depend on an
installation contractor for Accuracy Level II-e tests when necessary.