All About Alien Crosstalk Measurement

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All About Alien Crosstalk Measurement-Barry
Lindsley
www.flukenetworks.com 2006-2017 Fluke
Corporation
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All About Alien Crosstalk Measurement
Alien crosstalk is a relatively new measurement
thats widely misunderstood. Im often asked why
its an important measurement and if its
required to be measured by the standards. Also
misunderstood is the sampling criteria for alien
crosstalk measurements, which are applied so that
not all links have to be tested?
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All About Alien Crosstalk Measurement
What is Alien Crosstalk?
Alien crosstalk is the coupling of noise from
one cable link to another. This happens if one
cable is surrounded by many other cables in a
bundle. We identify the cables that surround a
cable in a bundle as Disturbers. Cables that can
suffer from noise coupling from other cables are
identified as the Disturbed cable or (Victim).
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All About Alien Crosstalk Measurement
Why is it important? 
The surrounding cables (Disturbers) will impact
the ability of the disturbed cable (Victim) to
transmit data. This becomes more important as we
increase the bandwidth requirement of cables for
faster applications. You might think that using
shielded cables i.e. (where there is at least an
outer shield) then alien crosstalk would not be a
problem. However, if the shield is not terminated
correctly even a shielded system can fall foul of
alien crosstalk.
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All About Alien Crosstalk Measurement
How do we Measure Alien Crosstalk? (With a
DSX-5000) 
Basically we measure alien crosstalk between
each pair of each Disturber cable to each pair of
the Disturbed cable in a cable bundle. That means
16 PSANEXT (Power Sum Alien Near End Crosstalk)
measurements between each disturber cable to the
disturbed cable. We do this at the near-end for
each disturber to the disturbed cable pair in the
bundle. First we identify the potential
Disturbed cable that is surrounded by Disturbers,
not including cables connectors that are
adjacent to gaps. For Disturbers, we pick cables
in the same bundle that surround the Disturbed
cable. These are the cables where the connectors
are likely to cause the majority of the ANEXT.
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All About Alien Crosstalk Measurement
How do we Measure Alien Crosstalk? (With a
DSX-5000) 
The connector shown in green identifies a
potential good disturbed cable connector. The
connectors shown in red, identify cable
connectors in a patch panel that would not make
good disturbed cables. The connectors shown in
blue identify potential good Disturber cable
connectors in the same bundle as the Disturbed
cable. We make an ANEXT measurement with the
Master unit of the DSX-5000 connected to the
Disturbed (victim) at the near-end with a
terminator at the far. The DSX-5000 remote unit
is connected to the near-end of the Disturber
with a terminator attached at the far end. The
Master unit and remote are then connected
together via the RJ45 communication ports to
enable them to synchronise the tests being made.
The measurements are then made on the Disturbed
(Victim) as below for each Disturber.
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All About Alien Crosstalk Measurement
How do we Measure Alien Crosstalk? (With a
DSX-5000) 
For each test the Main unit of the DSX-5000
CableAnalyzer tester remains connected to the
Disturbed (Victim) cable. Each time a measurement
of Disturbed (Victim) is completed for one
Disturber, the remote unit and the terminator are
moved to the next Disturber to make the next
test, this is continued until all the Disturbers
in the bundle have been measured for that
Disturbed cable. Alien Crosstalk also requires a
measurement to be made from the far-end. This is
the PS AACR-F (Power Sum Alien Attenuation
Crosstalk Ratio Far End) measurement. This is
performed in the same way as PS ANEXT but the
setup is different. The Main unit is connected to
the Disturbed cable connector as before. However,
the remote unit is connected at the far end and
the terminator at the near end as in the diagram
below. In addition, the communication cable
between the master and remote unit is connected
through one of the horizontal RJ45 links.
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All About Alien Crosstalk Measurement
How do we Measure Alien Crosstalk? (With a
DSX-5000) 
For each test the Main unit of the DSX-5000
tester remains connected to the Disturbed
(Victim) cable. Each time a measurement of
Disturbed (Victim) is completed for one
Disturber, the remote unit and the terminator are
moved to the next Disturber to make the next
test, this is continued until all the Disturbers
in the bundle for one Disturbed cable have been
completed.
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All About Alien Crosstalk Measurement
What do the standards say about Alien crosstalk
measurement requirements?
The ANSI/TIA-568-C.2 and ANSI/TIA-1152 identify
that PS ANEXT and PS AACR-F measurements are
required for compliance of Category 6A systems
and are not optional. The values and methodology
are described in ANSI/TIA-568-C.2. The ISO/IEC
118012011 Edition 2.2 and IEC 61935-1 define PA
ANEXT and AACR-F as normative for Field testing.
i.e. normally required if not met by design
(Specified in section A.2.11). If the coupling
attenuation of ClassEA or F permanent links or CP
links is at least 10dB better than the
corresponding channel coupling attenuation
requirements (see clause 6), and Class
FA permanent links or CP links are at least 25dB
better than the corresponding channel coupling
attenuation requirements (see clause 6) then the
requirements are met by design. Unfortunately,
there is no way for you know the coupling
attenuation, even with a field tester!
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All About Alien Crosstalk Measurement
What do the standards say about the number of
sample tests required on an installation?
The ISO/IEC 14763-2 defines that an equal number
of short, medium and long links should be test to
an equivalent acceptance quality level (AQL) of
0.4 as defined in ISO 2859-1 for link
populations up to 500,000 links. So the maximum
number of Disturbed bundles you would have to
measure would be between 3 and 315. However, did
you know that according to IEC 61935-1 in
sections 5.4.2 through 5.4.6 if you measure the
ANEXT and AFEXT and process the data as described
in 5.4.7 for the links with the highest insertion
loss (read longest links) if your results for
three of these links show a margin of 5 dB for PS
ANEXT and PS AACR-F, then you can stop testing
the highest insertion loss links (longest links).
This is also the case if you measure three of the
lowest insertion loss links (read shortest links)
and also the median insertion loss links (read
median length links).
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All About Alien Crosstalk Measurement
What do the standards say about the number of
sample tests required on an installation?
So I hope that is much clearer! You are required
to test an installation for Alien Crosstalk.
There is a method of testing which is to measure
the PS ANEXT and PS AACR-F on a Disturbed link in
a minimum of three bundles for each of the short,
median and long links. If these pass with 5dB or
greater margin then you can stop. If not, you
have to continue testing to an AQL sample size of
0.4.
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