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Alien Crosstalk for the
Inexperienced User
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Agenda
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What is alien crosstalk
Where does alien crosstalk occur in the link
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
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 Alien crosstalk (AXT) is a unwanted disturbing signal coupling
from one balanced twisted-pair component, channel or
permanent link to another
 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
Component
AXT
Cable
AXT
Component
AXT
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History - Alien Crosstalk
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 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
 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
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 Near end alien crosstalk is a reflected mode that is
sourced and received at the same ends of the
disturbing and disturbed links
Signal on
Disturbing
Link
Component AXT
Cable AXT
Noise on
Disturbed
Link
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Transmitted Mode of Alien Crosstalk
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 Far end alien crosstalk is a transmitted mode that
is sourced and received at opposite ends of the
disturbing and disturbed links
Signal on
Disturbing
Link
Component
AXT
Cable
AXT
Component
AXT
Noise on
Disturbed
Link
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Where Does Alien Crosstalk
Occur in the Link
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Where Does Alien Crosstalk Occur
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 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
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
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 Alien crosstalk occurs when
different cables run in parallel for
an extended distance in close
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
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 Alien crosstalk occurs when
different equipment and patch
cords are routed together in
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
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 Alien crosstalk occurs where
components of different links
come into close proximity
 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
Defining Alien Crosstalk
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Standards Defining Alien Crosstalk
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 ISO/IEC 11801 Ed 2.0 Amendment 1 provides channel
and alien crosstalk requirements for Class EA, Class F and
Class FA
 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
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 Guidelines provide methods for re-characterizing installed
Class E and Category 6 cabling to ensure 10GBASE-T
operation
 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
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 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
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
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 UTP Class EA and Category 6A equipment and patch
cords typically have a larger outside wall thickness to
reduce alien crosstalk
 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
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 Minimize the number of cables in a bundle, reducing the
number of possible disturbers
 Un-bundle the horizontal link in the first 15 metres
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)
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 Separate equipment and patch cords and eliminate cable
ties to reduces the alien crosstalk coupling in the first few
metres of the link
 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
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 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 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)
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 Alien crosstalk testing consumes significantly more time
than channel or link testing
 Worst case instrument test time for a single disturbed link
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
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 Seek guidance from cable and component manufacturers
for installing and certifying Class EA/F/FA or Category 6A
links
 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
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 Create a quality plan that considers how the selection and
installation of cable and components affects the alien
crosstalk environment
 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)
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A good quality plan that
considers and incorporates the
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
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 Wiremap
 Delay/Delay Skew/Length*
 Resistance**
 Pair to pair performance
extended to 500MHz
 Insertion Loss
 Return Loss
 NEXT & PSNEXT
 ACR-N & PSACR-N**
 ACR-F & PSACR-F
 Alien crosstalk added
1-500MHz
 PSANEXT
 Average PSANEXT
 PSAACRF
 Average PSAACRF
 Marginal Computation
* Not a recognized Class E measurement
** Not a recognized Category 6 measurement
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Performance Class EA & Category 6A
 Pair measurements
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 Wiremap
 Delay/Delay Skew/Length*
 Resistance**
 Pair to pair performance
1-500MHz
 Insertion Loss
 Return Loss
 NEXT & PSNEXT
 ACR-N & PSACR-N**
 ACR-F & PSACR-F
 Alien crosstalk 1-500MHz
 PSANEXT
 Average PSANEXT
 PSAACRF
 Average PSAACRF
* Not a recognized Class EA measurement
** Not a recognized Category 6A measurement
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Performance Class F
 Pair measurements
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 Wiremap
 Delay/Delay Skew
 Resistance
 Pair to pair performance
1-600MHz
 Alien crosstalk added
1-600MHz
 PSANEXT
 Average PSANEXT
 PSAACRF
 Average PSAACRF
 Insertion Loss
 Return Loss
 NEXT & PSNEXT
 ACR-N & PSACR-N
 ACR-F & PSACR-F
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Performance Class FA
 Pair measurements
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 Wiremap
 Delay/Delay Skew
 Resistance
 Pair to pair performance
1-1000MHz
 Alien crosstalk 1-1000MHz
 PSANEXT
 Average PSANEXT
 PSAACRF
 Average PSAACRF
 Insertion Loss
 Return Loss
 NEXT & PSNEXT
 ACR-N & PSACR-N
 ACR-F & PSACR-F
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Power Sum Alien NEXT (PSANEXT)
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 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 a total of 8 results if both ends are tested
Signal on
Disturbing
Link
Component AXT
Cable AXT
Noise on
Disturbed
Link
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Power Sum Alien ACRF (PSAACRF)
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 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
total of 8 results if both ends are tested
Signal on
Disturbing
Link
Component
AXT
Cable
AXT
Component
AXT
Noise on
Disturbed
Link
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Average PSANEXT & PSAACRF
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 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
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
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 The alien crosstalk margin computation is used if the
PSANEXT or the PSAACRF limits are not met on Class
E or Category 6 links
 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
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 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
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
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 Re-certify the channel or link performance of every link
designated to support 10BASE-T saving the Autotest
result and graphical data
 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
User Patch or
CAT6A Test Cord
User Patch or
CAT6A Test Cord
Disturber Link
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Disturbed (Victim) Link
100 Ohm
Terminators
Patch Cord Connecting
Sycronization Ports
USB Cord
Far End Device
PC Running
Result Manager
Near End Device
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Typical PSAACRF Test Setup
User Patch or
CAT6A Test Cord
User Patch or
CAT6A Test Cord
Disturbed (Victim) Link
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Disturber Link
100 Ohm
Terminator
100 Ohm
Terminator
Patch Cords and 3rd Link Connecting
Synchronization Ports
USB Cord
Near End Device
PC Running
Result Manager
Far End Device
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Alien Crosstalk Testing
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 Testing is conducted from
the PC result manager alien
crosstalk (AXT) application
 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
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 Alien crosstalk is a unwanted disturbing signal coupling
from one balanced twisted-pair component, channel or
permanent link to another
 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 501731 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)
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 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
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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