Upgrading Your Fiber Plant to 40 and 100 Gigabit Speeds

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Upgrading Your Fiber Plant to 40 and 100 Gigabit
Speeds-Mark Mullins
www.flukenetworks.com 2006-2017 Fluke
Corporation
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Upgrading Your Fiber Plant to 40 and 100 Gigabit
Speeds
Just Now Upgrading to 10 Gig? We Didn't Forget
About You
While upgrading backbone cable plants in the LAN
to support 10 Gig has been going on for several
years since the release of the 10GBASE-SR
standard for fiber, many enterprise businesses
did not previously require these types of speeds,
until now. Data centers are rapidly migrating to
25, 40 and even 100 Gigabit speeds to accommodate
an increasing amount of virtualized servers that
host more applications than ever before and vast
volumes of data that needs to be accessed,
transmitted and stored. At the same time, the
demand for high speed transmission in the LAN is
at an all-time high for both wired and wireless
connections. While many larger enterprise
businesses like universities and financial
institutions have already upgraded their LAN
backbones, there are still a vast number of
others that are just now coming to the
realization that 1 gigabit speeds are no longer
adequate. And with most of the information
disseminated now focusing on upgrading fiber
plants to support 40 and 100 gigabit speeds in
the data center, we decided that those just now
upgrading to 10 gig should not be forgotten and
could benefit from revisiting the key
considerations.
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Upgrading Your Fiber Plant to 40 and 100 Gigabit
Speeds
Cable Matters
When it comes to upgrading to 10 gigabit speeds
over fiber, it really comes down to whether or
not the cabling can support it. This has a lot to
do with the cable type and the overall channel
length. In multimode fiber commonly used in LAN
backbone infrastructures, signal degradation is
causes by modal dispersion. Modal dispersion
results in bit errors caused by light pulses
spreading over distance and arriving at the
receiver at different times. This is a limiting
factor for high speed transmission. Newer fiber
types have been specifically designed to inhibit
modal dispersion, and legacy 62.5µm multimode
fiber is not one of them. Those with this Fiber
Distributed Data Interface (FDDI)-grade fiber are
therefore limited to about 26 meters for 10
gigabit speeds--a rather impractical distance for
most LAN backbones that typically require
distances closer to 300 meters. To reach
required LAN backbone distances, the cable will
therefore have to be upgraded to laser-optimized
50µm multimode fiber with OM3 supporting 10
gigabit speeds to 300 meters and OM4 supporting
10 gigabit to 400 meters.
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Upgrading Your Fiber Plant to 40 and 100 Gigabit
Speeds
Cut Your Losses
In addition to cable type and distances, the key
parameter that truly tells us if the backbone
fiber can support 10 gigabit speeds is
attenuation. This parameter lets us know how much
signal loss can exist in an end-to-end channel
and still have enough signal strength to support
the application. While some installers may have
gotten away without calculating attenuations for
1 gigabit systems, this is not advisable once we
move to 10 gigabit speeds. The maximum amount of
attenuations in a 10 gigabit channel has
decreased to just 2.6dB (850 nm OM3 fiber) from
3.5dB for 1 gigabit applications. Attenuation is
a function of many factors--the light source used
in the transceivers, the cable type, the overall
channel length, and the number and quality of
connections and splices. The number one
contributor to loss and the most common problem
preventing the ability to support 10 gigabit
speeds is contamination of the fiber end
face.  Telecommunications rooms are not always
the cleanest environments, and any dust or debris
trapped between fiber end faces causes signal
loss, back reflection and even damaged equipment.
So regardless of the cable type, proper fiber
cleaning and inspection have to be a significant
part of ensuring support for 10 gig.
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Upgrading Your Fiber Plant to 40 and 100 Gigabit
Speeds
Certified Peace of Mind
Even after you've ensured the right cable type
and are convinced that you have abided by the
distance limitations and have done your best to
clean and inspect fiber end faces, the only way
to be 100 sure that you can support the IEEE
802.3 10GBASE-SR application is to certify the
fiber links. Tier 1 testing using an optical
loss test set like the CertiFiber Pro to
measures attenuation is one method of
certification, while Tier 2 testing using
an optical time domain reflectometer (OTDR) like
the OptiFiber Pro indicates the attenuation of
each component in fiber channel (i.e., cable,
connectors and splices) and events like fiber
bends that can also contribute to loss. Without
an OTDR, it can be difficult to identify and fix
the specific sources of loss. For ease of
certification, you want a tester that gives you a
PASS or FAIL based on the IEEE application
standard, as well as cabling standards specified
by TIA and ISO/IEC. A PASS or FAIL indication is
much easier and faster than calculating
attenuation or spending hours trying to interpret
OTDR traces. Thankfully both the CertiFiber Pro
and OptiFiber Pro provide this indication.
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