Fiber Optics Cable Testing
Fiber is now beginning to appear in traditional 'UTP territory'.
There have been continual improvements in optical fiber performance,
fiber cable designs, connectivity technology, and test equipment.
Not only are these fiber products more craft friendly than
ever, they are also less expensive. New advancements in transceiver
products will make fiber even more attractive in the LAN environment.
Fiber optic cable comes in two basic types: multimode or
single mode. Multimode fiber has a relatively large core diameter
(typically 50 or 62.5 microns). Light from LED sources can
be efficiently coupled into multimode fiber. Multimode fiber
is most often used in LED-based LAN systems. Single-mode fiber
has a very small core diameter (8.3 microns). Single-mode
fiber propagates only one optical mode, significantly increasing
bandwidth. Single-mode fiber is primarily used in laser-based
long haul and interoffice applications. Single-mode fiber
is beginning to be used in LAN as backbone cabling and to
"future proof" networks.
How is fiber tested? Historically, the quality of fiber cable
was so good and bandwidth more than adequate that some network
designers specified that only a simple continuity check was
required for fiber cable certification. Today's higher speed
networks demand more from the fiber and are making this simple
approach obsolete. Industry standards bodies including the
TIA/EIA, IEEE, ISO and ANSI have published standards that
define maximum supportable distance and maximum channel attenuation
for LAN. See Fiber Standards for pass/fail limits by application.
Therefore when installing cable to support a standardized
network application (i.e. Ethernet, FDDI, and ATM), it is
appropriate to test cable and compare the results to the appropriate
standard. In practice, network designers and architects are
frequently unaware of the standards or chose to use their
own user-defined pass/fail criteria. This can result in a
cabling plant that is either not tested as thoroughly as necessary,
jeopardizing network performance, or tested too severely which
can needlessly add to the cost and time of the cable installation
and testing.
What is really required?
It is best to comply with the appropriate fiber application
standard, all of which require direct attenuation measurement.
These standards have been painstakingly developed and approved
by a large group of leading companies in the industry. You
can be confident of acceptable network performance when you
certify that the cabling plant meets the requirements of the
standard. If you are installing cable and the transmission
standard is unknown or is a new transmission protocol for
which a standard has not yet been published, it is recommended
that you follow the guidelines as set forth by the networking
equipment manufacturer or a general building standard. That
means TIA/EIA-568-B in North America or ISO/IEC 11801 in Europe.
Other regional and country-specific standards exist.
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