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Alien Crosstalk for the
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Inexperienced User
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Agenda
�What is alien crosstalk
�Where does alien crosstalk occur in the link
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�Standards & guidelines defining alien crosstalk
�Creating a quality plan to address requirements
�Link performance requirements
�Link certification
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What is Alien Crosstalk
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What is Alien Crosstalk
� Alien crosstalk (AXT) is a unwanted disturbing signal coupling
from one balanced twisted-pair component, channel or
permanent link to another
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� The term “Alien” is used because unlike pair to pair crosstalk,
alien crosstalk is a disturbing noise source that originates from
outside the affected link’s cable and components
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History - Alien Crosstalk
� In 2006 the IEEE ratified 10GBASE-T and later published
IEEE 802.3-2008 defining a version of Ethernet with a nominal
data rate of 10 Gbit/s, ten times faster than Gigabit Ethernet
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� Achieving 10GBASE-T over copper required new encoding
schemes, 500MHz bandwidth and full duplex transmission
� Due to these changes alien crosstalk, which has always been
present in twisted pair copper networks and cannot currently be
cancelled, became a significant noise source capable of
disrupting 10GBASE-T
� In response the industry defined new standards and guidelines
for acceptable levels of alien crosstalk and developed test
methods for measuring alien crosstalk
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Reflected Mode of Alien Crosstalk
� Near end alien crosstalk is a reflected mode that is
sourced and received at the same ends of the
disturbing and disturbed links
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Transmitted Mode of Alien Crosstalk
� Far end alien crosstalk is a transmitted mode that
is sourced and received at opposite ends of the
disturbing and disturbed links
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Where Does Alien Crosstalk
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Occur in the Link
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Where Does Alien Crosstalk Occur
� Alien crosstalk occurs between the cables and components
of a disturber link and a disturbed (victim) link
� Alien crosstalk coupling increases as the components and
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cables of the two links approach each other
� Alien crosstalk is extremely dependent upon installation
practices such as patch cord positioning, cable bundling,
use of tie-wraps, pathway fills and component placement
� Alien crosstalk is not simply limited to a single disturbing
link, multiple disturbing links may add to the total alien
crosstalk present on a disturbed link
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Alien Crosstalk in the Horizontal Link
� Alien crosstalk occurs when
different cables run in parallel for
an extended distance in close
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proximity
� Long, tightly bound cable bundles
present an ideal location for
significant levels of alien crosstalk
� A worst case condition exists
when a disturbed (victim) cable is
surround by six disturbing cables
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Alien Crosstalk in Cords
� Alien crosstalk occurs when
different equipment and patch
cords are routed together in
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close proximity
� Bound cords present an ideal
location for significant levels
of alien crosstalk in the first
few metres of the link
� Management bar lay and
waterfalls also present
opportunity for alien crosstalk
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Alien Crosstalk in Components
� Alien crosstalk occurs where
components of different links
come into close proximity
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� Patch panels present an ideal
location for significant levels
of alien crosstalk
� A worst case condition exists
when a disturbed port is
surrounded on three or four
sides by disturber ports
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Standards & Guidelines
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Defining Alien Crosstalk
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Standards Defining Alien Crosstalk
� ISO/IEC 11801 Ed 2.0 Amendment 1 provides channel
and alien crosstalk requirements for Class EA, Class F and
Class FA
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� BS EN 50173-1 A1 provides channel and alien crosstalk
requirements for Class EA, Class F and Class FA
� ANSI/TIA-568-C.2 provides channel, permanent link and
alien crosstalk requirements for Category 6A
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Guidelines Defining Alien Crosstalk
� Guidelines provide methods for re-characterizing installed
Class E and Category 6 cabling to ensure 10GBASE-T
operation
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� ISO/IEC TR 24750 and CLC/TR 50173-99-1:2007 both
provide channel and alien crosstalk recommendations for
installed Class E
� TIA TSB-155 provides channel, permanent link and alien
crosstalk recommendations for installed Category 6
� Class E and Category 6 cabling is not recommended for
new installations supporting 10GBASE-T operation
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Creating a Quality
Plan
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Cable Considerations
� UTP Class EA and Category 6A cables with improved alien
crosstalk performance may be constructed with an inner
seperator, a larger outside wall thikness and an increased
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cable diameter.
� Cable alien crosstalk performance can be compromised by
deforming the outer jacket or inner separator due to tie
wraps, excessive conduit/pathway fill or exceeding
recommended bend radius
� Pathway and conduit fill ratios increase for the same
number of cables if the cable diameter increases
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Cord and Component Considerations
� UTP Class EA and Category 6A equipment and patch
cords typically have a larger outside wall thickness to
reduce alien crosstalk
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� Cord alien crosstalk performance can be compromised by
deforming the outer jacket due to tie wraps and exceeding
recommended bend radius
� Compacting cords in management bars and trays brings
cords into closer proximity increasing alien crosstalk in the
critical first few meters of the link
� UTP Class EA and Category 6A patch panels are typically
lower density than Class E and Category 6
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Reducing Alien Crosstalk
� Minimize the number of cables in a bundle, reducing the
number of possible disturbers
� Un-bundle the horizontal link in the first 15 metres
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allowing the cables to separate
� Eliminate cable ties if possible, if not reduce cable tie
tension and space cable ties farther apart
� Randomly lay cable in trays to prevent any two cables from
running in close proximity their entire length
� Use F/UTP or S/FTP cables and cords to significantly
reduces alien crosstalk
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Reducing Alien Crosstalk (cont)
� Separate equipment and patch cords and eliminate cable
ties to reduces the alien crosstalk coupling in the first few
metres of the link
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� Lay cords randomly in management bars to prevent any
two cords from running in close proximity their entire
length
� Reduce the number of cords in a waterfall and maximize
the radius to reduce cord compaction
� Use fully shielded components to significantly reduce alien
crosstalk
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Alien Crosstalk Consideration
� Alien crosstalk is extremely dependent upon installation
practices such as patch cord positioning, cable bundling,
use of tie-wraps, pathway fills and component placement
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� Alien crosstalk certification is unique, its a selective process
using statistical data about the installation to identify and
certify the links deemed most prone to alien crosstalk
interference
� Certifying alien crosstalk on each Class EA/F/FA and
Category 6A link or re-certifying alien crosstalk on each
Class E or Category 6 link may not be necessary nor
plausible due to test times
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Alien Crosstalk Consideration (cont)
� Alien crosstalk testing consumes significantly more time
than channel or link testing
� Worst case instrument test time for a single disturbed link
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testing PSANEXT and PSAACRF at both ends of the link
# of Disturbing Links Worst Case Instrument Test Time
1 1.5 minutes
2 3 minutes
4 6 minutes
8 12 minutes
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Additional Guidance
� Seek guidance from cable and component manufacturers
for installing and certifying Class EA/F/FA or Category 6A
links
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� Seek additional guidance from cable and component
manufacturers for identifying and selecting disturbed and
disturbing links for alien crosstalk certification
� Consult ISO/IEC TR 24750, CLC/TR 50173-99-1:2007
or TIA TSB-155 for determining the Class E or Category 6
alien crosstalk environment and alien crosstalk mitigation
techniques
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Create a Quality Plan
� Create a quality plan that considers how the selection and
installation of cable and components affects the alien
crosstalk environment
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� The quality plan should identify changes to the installation
brought on by Class EA/F/FA or Category 6A components
� The quality plan should address alien crosstalk certification,
including identification & selection of test links and criteria
for obtaining satisfactory performance
� A Class E and Category 6 quality plan should address alien
crosstalk mitigation practices
� Obtain agreement from all parties
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Create a Quality Plan (cont)
�A good quality plan that
considers and incorporates the
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elements in the previous slides
will reduce installation and
certification time while
increasing confidence in
installation’s ability to meet
alien crosstalk requirements
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Link Performance Requirements
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Performance 10GBASE-T Class E & Category 6
� Pair measurements � Alien crosstalk added
� Wiremap 1-500MHz
� Delay/Delay Skew/Length* � PSANEXT
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� Resistance** � Average PSANEXT
� PSAACRF
� Pair to pair performance
� Average PSAACRF
extended to 500MHz
� Marginal Computation
� Insertion Loss
� Return Loss
� NEXT & PSNEXT
� ACR-N & PSACR-N**
* Not a recognized Class E measurement
� ACR-F & PSACR-F ** Not a recognized Category 6 measurement
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Performance Class EA & Category 6A
� Pair measurements � Alien crosstalk 1-500MHz
� Wiremap � PSANEXT
� Delay/Delay Skew/Length* � Average PSANEXT
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� Resistance** � PSAACRF
� Average PSAACRF
� Pair to pair performance
1-500MHz
� Insertion Loss
� Return Loss
� NEXT & PSNEXT
� ACR-N & PSACR-N**
* Not a recognized Class EA measurement
� ACR-F & PSACR-F ** Not a recognized Category 6A measurement
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Performance Class F
� Pair measurements � Alien crosstalk added
� Wiremap 1-600MHz
� Delay/Delay Skew � PSANEXT
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� Resistance � Average PSANEXT
� PSAACRF
� Pair to pair performance
� Average PSAACRF
1-600MHz
� Insertion Loss
� Return Loss
� NEXT & PSNEXT
� ACR-N & PSACR-N
� ACR-F & PSACR-F
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Performance Class FA
� Pair measurements � Alien crosstalk 1-1000MHz
� Wiremap � PSANEXT
� Delay/Delay Skew � Average PSANEXT
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� Resistance � PSAACRF
� Average PSAACRF
� Pair to pair performance
1-1000MHz
� Insertion Loss
� Return Loss
� NEXT & PSNEXT
� ACR-N & PSACR-N
� ACR-F & PSACR-F
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Power Sum Alien NEXT (PSANEXT)
� PSANEXT sums four near end alien crosstalk measurements from
each pair of the disturbing link to a single pair of the disturbed link
� Four PSANEXT results are calculated at the end of a disturbed link for
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a total of 8 results if both ends are tested
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Power Sum Alien ACRF (PSAACRF)
� PSAACRF sums four far end alien crosstalk measurements from each
pair of the disturbing link to a single pair of the disturbed link
� Four PSACRF results are calculated at the end of a disturbed link for a
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total of 8 results if both ends are tested
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Average PSANEXT & PSAACRF
� Average PSANEXT is the average of the PSANEXT
results on each of the disturbed link pairs
� Average PSAACRF is the average of the PSAACRF results
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on each of the disturbed link pairs
� One Average PSANEXT or PSAACRF result is calculated
at the end of a disturbed link for a total of 2 results if both
ends are tested
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Alien Crosstalk Margin Computation
� The alien crosstalk margin computation is used if the
PSANEXT or the PSAACRF limits are not met on Class
E or Category 6 links
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� The alien crosstalk margin computation ensures that the
total combined PSAFEXT and PSANEXT that couples
into a channel is limited in order to maintain the
10GBASE-T minimum signal to noise ratio
� The alien crosstalk margin calculation is a sufficient
qualification for suitability of Class E or Category 6
channels to support 10GBASE-T operation
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Link Certification
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Certifying Class EA/F/FA & Category 6A
� Certify the channel or link performance of every link saving
the Autotest result and graphical data
� Using the test plan criteria and result data, identify the
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disturbed links deemed most prone to alien crosstalk
interference and their associated disturbing links
� Per the test plan criteria, select from the identified links
those disturbed and disturbing links that require alien
crosstalk certification
� Certify the alien crosstalk of the selected disturbed links per
the test plan
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Re-certifying Class E & Category 6
� Re-certify the channel or link performance of every link
designated to support 10BASE-T saving the Autotest
result and graphical data
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� Using the test plan criteria and result data, identify the
disturbed links deemed most prone to alien crosstalk
interference and their associated disturbing links
� Re-test the channel or link performance of all identified
disturbing links saving the Autotest result and graphical
data*
� Certify the alien crosstalk of the selected disturbed links
per the test plan
*Links designated only as a disturber do not have to pass channel or link certification
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Typical PSANEXT Test Setup
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Typical PSAACRF Test Setup
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Alien Crosstalk Testing
� Testing is conducted from
the PC result manager alien
crosstalk (AXT) application
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� The AXT application
provides the tools needed to
certify alien crosstalk
� The AXT application
displays alien crosstalk
certification results and link
statistics in real time
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Conclusion
� Alien crosstalk is a unwanted disturbing signal coupling
from one balanced twisted-pair component, channel or
permanent link to another
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� Alien crosstalk is extremely dependent upon installation
practices and occurs where links come into close proximity
such as in cable bundles and patch panels
� ISO/IEC 11801 Ed 2.0 Amendment 1 and BS EN 50173-
1 A1 provide channel and alien crosstalk performance
requirements for Class EA/F/FA links
� ANSI/TIA-568-C.2 provides channel or link and alien
crosstalk performance requirements for Category 6A links
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Conclusion (cont)
� ISO/IEC TR 24750 & CLC/TR 50173-99-1:2007 provide
guidance for supporting 10GBASE-T on Class E channels
� TIA TSB-155 provides guidance for supporting
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10GBASE-T on Category 6 channels and links
� Create a quality plan addressing the unique requirements for
installation, certification and alien crosstalk mitigation prior
to starting
� A good quality plan will reduce installation and certification
time while increasing confidence in installation’s ability to
meet alien crosstalk requirements
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Thank you
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