Information Technology Reference
In-Depth Information
as far as the standard's Channel testing method is concerned. If you change cables,
to use a longer or shorter cable for example, you must re-certify the Channel.
The Permanent Link was designed to allow a cable installation to be certified
once the horizontal cables were installed by the installation contractor. As a matter
of fact, the link was originally called the Contractor's Link. Naturally, the user and
patch cords were not in place at this stage and would have been impossible to test.
Nevertheless, the performance of the entire link (the Channel) is ultimately what the
user depends on, so this test was also included as an important benchmark of over-
all link performance.
Which link test should you use? Permanent Link certification is probably suf-
ficient in most cases of new installations. It will ensure that the 90 m (maximum) of
horizontal cable is performing to specifications. The Permanent Link test is consid-
ered the most reasonable performance testing standard for a turnkey cable system
installation, because the vendor may have little or no control over the cables used
to connect to the equipment.
Also, the build-out stage of construction is the best time to correct any problems
that are revealed by a Permanent Link test. After the network equipment is installed
and connected, it will be easiest and most useful to do Channel testing. The Channel
test is obviously very useful in dealing with network equipment vendors. You can rely
on your cable system completely when it has been certified as a Channel.
Performance Levels
Two types of performance levels should be considered in making field tests, the first
being the performance category of the cable system. You should determine long
before installation what category of performance you require and then test to that
level. The second type of performance is the accuracy level of the field tester you
intend to use to certify the cable.
We have discussed the cable performance categories at length in previous chap-
ters. The three categories of operation specified by TIA-568-C and related standards
are Categories 3, 5e, and 6. A new tighter version of Category 6, called AC6 or
Augmented Category 6, is tested to 500 MHz or better. Other standards, such as
some of the ISO documents, characterize similar performance levels, although with
some differences. For example, the ISO/IEC IS-11801 specifies identical categories
for uninstalled cable and components, but uses a class system for installed links.
Table 15.4 shows how the TIA categories correspond to the ISO classes. In most
instances, the TIA categories are the same or tougher in test parameters and may be
substituted with no problems. If you are in a situation that needs to reference these
other standards, you should adjust your testing accordingly. While most of these
