Tips for Taking on Tier 1 and Tier 2 Fiber Testing

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Tips for Taking on Tier 1 and Tier 2 Fiber
Testing-Mark Mullins
www.flukenetworks.com 2006-2017 Fluke
Corporation
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Tips for Taking on Tier 1 and Tier 2 Fiber
Testing
Unlike required Tier 1 testing for attenuation
(insertion loss), length and polarity that can be
achieved with an optical loss test set (OLTs),
few technicians in the field find themselves
faced with Tier 2 testing and the need for
an Optical Time Domain Reflectometer (OTDR). But
every now and then, there is that one customer or
consultant who specifies Tier 2
testingespecially as fiber networks have
ever-tighter loss budgets and less room for
error. Or there may be the need to gain more
insight into the performance of a link component
for troubleshooting purposes. Regardless of the
reason for taking fiber testing to the top tier,
its good to understand the technology and best
practices surrounding Tier 2 testing.
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Tips for Taking on Tier 1 and Tier 2 Fiber Testing
Not a Replacement
First of all, it is important to acknowledge
that Tier 2 testing does not replace the total
insertion loss measurements taken during Tier 1
testing. Tier 2 testing requires Tier 1 and is
used as a complementary evaluationusing both
methods provides the most completed picture of
the fiber installation. In other words, just
because Tier 2 testing may be required doesnt
mean you can skip Tier 1. You still need to
measure the total fiber losses of the
link. However, Tier 2 testing does do something
that Tier 1 cannotan OTDR characterization of
the link. OTDRs use pulsed laser diodes to
transmit high-power light pulses into the fiber
and high-gain light detectors to measure any
light reflected back. These measurements detect
events in the fiber that either reduce or reflect
the power of the source pulse. While a small
amount of backscatter is expected in any fiber
link, when the light meets a connection, break,
crack, splice, sharp bend or end of the fiber, it
reflects a certain amount of light expressed in
dB.
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Tips for Taking on Tier 1 and Tier 2 Fiber Testing
Not a Replacement
The OTDR characterization is achieved by
plotting the reflected light versus the distance
along the fiber, providing a graphical signature
for technicians to determine precisely where in
the link the reflection occursthe ideal
troubleshooting tool. It is also an extremely
useful way to measure the loss of a specific
splice or connector within a link to ensure that
is no larger than what is required by the
standard, that it meets performance values
specified in manufacturer claims, or that it is
within the range needed to support future
applications.
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Tips for Taking on Tier 1 and Tier 2 Fiber Testing
Know the Procedure
The first step in Tier 2 testing is (you guessed
it!) to first complete Tier 1 testing. Once
youve completed Tier 1 testing to verify that
the fiber links meets the loss budgets as
specified by TIA and ISO/IEC standards for a
given application, connect the OTDR to one end of
the link using a launch fiber and attach a tail
fiber to the connector at the far end. Similar
to using test reference cords when using an OLTS
in Tier 1 testing, launch fibers must be used at
both ends of the link when testing with an OTDR.
The launch cable connects between the OTDR and
first connector enabling the tester to overcome
dead zone limitations so it can measure the loss
and reflectance of the first connector in the
link. The tail fiber serves a similar purposeit
allows the tester to properly see and test the
last connector at the far end of the link. Once
youve configured the OTDR with the appropriate
limits and connected both launch and tail fibers,
perform your test. Then disconnect the OTDR,
leaving the launch and tail fibers in place and
connect the OTDR to the far-end tail fiber. Now
test a 2nd time to look at the link in the
opposite direction. Calculate the average loss of
both bidirectional results for the link, compare
to the limits, and review pass or fail results.
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Tips for Taking on Tier 1 and Tier 2 Fiber Testing
Easier than You Think
Are you surprised by how simple Tier 2 testing
seems? Dont be. Legacy OTDRs used to require
years of technical experience to read and
interpret traces, but todays OTDRs contain
comprehensive software that automate analysis and
test parameter set-up, among other advanced
analytical capabilities. Fluke
Networks OptiFiber Pro makes it even simpler to
fully characterize your fiber links with its
SmartLoop capability. SmartLoop enables automated
testing and analysis of two fibers in a single
test. This patent pending process automatically
separates the two fibers for individual pass/fail
analysis, display, and reporting. Not only does
this cut the testing time by at least half, it
also enables bi-directional testing without
moving the OTDR to the far end of the link. In
addition to getting the job done quicker,
SmartLoop OTDR further enhances the ease and
speed of testing in environments where the far
end is difficult of even dangerous to reach
because the OTDR never has to be moved to the far
end.
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