Cabling for Success with DXLink
Author: Curry Kinyon
Co-Author: Jeff Howes
Co-Author: Ann Yanecek
CABLING F O R SUCC E SS WI TH DX L I NK
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TM
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Table of Contents
EXECUTIVE SUMMARY .................................................................................................................... 3
INTRODUCTION ............................................................................................................................... 4
Overview ................................................................................................................................................... 4
DXLINK PERFORMANCE .................................................................................................................. 5
Basic Cable Information ............................................................................................................................ 5
Installed Cable Channel Performance ...................................................................................................... 6
Enova DGX Link Quality Reporting ........................................................................................................... 6
CABLE QUALITY ............................................................................................................................... 6
Cable Type ................................................................................................................................................ 6
Internal Channel Parameters .................................................................................................................... 6
External Channel Parameters ................................................................................................................... 7
Cable Shielding ......................................................................................................................................... 7
Cable End Termination ............................................................................................................................. 8
Bandwidth Performance ........................................................................................................................... 9
CABLE TOPOLOGY ........................................................................................................................... 9
Cable Length ............................................................................................................................................. 9
Cable Management ................................................................................................................................ 10
Patch Panels ............................................................................................................................................ 11
Patch Cables............................................................................................................................................ 11
ENVIRONMENT ............................................................................................................................. 12
Grounding ............................................................................................................................................... 12
Electrostatic Discharge (ESD) .................................................................................................................. 13
Electromagnetic Interference (EMI) ....................................................................................................... 14
Electrical Motors ..................................................................................................................................... 14
Proximity ESD Events .............................................................................................................................. 14
Ambient Operating Conditions ............................................................................................................... 15
CONCLUSION ................................................................................................................................. 15
Appendix A .................................................................................................................................... 16
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EXECUTIVE SUMMARY
Cabling For Success with DXLinkTM
After a full year of supporting deployments of DXLink solutions, it has become clear that using
unshielded cable is problematic. Installations with unshielded cable often have reliability issues with
the DXLink connection caused by changing environmental conditions. Therefore, our revised minimum
required cable type for DXLink systems is shielded CAT6 and that it’s installation follow the
recommended guidelines in this document.
DXLink™ delivers 10.2 Gb/s throughput over shielded category cable. It accomplishes this by leveraging
the transport layer of HDBaseT technology.
audio / video content at distances up to 100 meters when properly deployed and configured. The
following white paper provides detailed information on how cable quality, cable topology and the
environment affect the performance of DXLink systems. In summary, suffice it to say that looping, poor
cable end termination, using patch blocks, inadequate grounding of the cable/rack/building and
running cables near noisy devices will negatively affect the quality of the signal path and cause issues
such as offline events and blinking of video. Below are some helpful guidelines to follow when deploying
your DXLink system.
Best Practices
For best “it just works” results shielded Cat6A cable is recommended
If you have a cable deployment scheme running many cables in a bundled structure through
conduit or cable trays and have runs that traverse near large EMI or ESD generators you should
use shielded Cat6A cable to achieve reliable 100 meter performance
For optimal performance:
Keep the cable runs as short as possible
Follow cable shielding and termination techniques defined in this document
Follow Equipment and Building Ground requirements defined in this document
DXLink twisted pair cable runs for DXLink equipment shall only be run within a common building
Keep the DXLink cables as isolated as possible from noisy power cables
Avoid running cables in parallel with power runs, try to cross at 90 degree angles
Avoid running near noisy devices (motors) or inductive loads
Avoid tie wrapping and/or tightly bundling DXLink cables together
Avoid making sharp corners/bends in cable runs
Minimize “coiling” of the cables
Minimize patch panels & patch cables (every connection introduces losses)
Make sure connectors are properly terminated, higher quality shielded cables require
more intricate terminations
DXLink is state of the art technology capable of delivering
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INTRODUCTION
A multitude of aspects contribute to the overall system performance of DXLink products when installing
structured cabling solutions. The capabilities of this solution to pass Uncompressed HDMI Video,
Uncompressed HD Audio, Ethernet, Serial, IR and Power require a cable bandwidth of 250 MHz or
greater and cabling infrastructure performance that supports throughput of 10 Gb/s. Based on the
bandwidth required to transmit this amount of information we recommend following industry standard
practices designed for 10 Gigabit Ethernet. In order to perform at its best, the HDBaseT transport layer
utilized in DXLink requires specific rules which include management of not only to the cabling system
back-bone but also the patch locations and end-point runs. The primary focus of this paper is to review
the key challenges and solutions facing the structured copper cabling media required to properly
support the DXLink technology.
OVERVIEW
To achieve a high performing and reliable installation, several key factors need to be considered and
managed which all have a combined impact. When any one of these factors is not adhered to the
likelihood of inconsistent performance or sporadic video, audio and network drop-outs increase, to the
point where the products can fail to function at all if faced with several conditions not being met.
Three main areas need to be addressed in order to optimize the performance of DXLink installations.
They all have a direct impact on the performance of the overall DXLink system and also have relational
impact on each other, such that improving in one area can often provide ability to overcome
shortcomings in one of the other areas. A balancing of these three roles will allow for a successful and
robust DXLink system.
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Cat6A F/UTP (shielded and bonded)
Belden 10GX 10GX62F (Riser)
Belden 10GX 10GX63F (Plenum)
Cat6 F/UTP (shielded cable)
Belden 2412F DataTwist (Riser)
Belden 2413F DataTwist (Plenum)
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DXLINK PERFORMANCE
Depending on the link quality between DXLink devices over structured cabling, the product performance
can vary from a solid and reliable system to a system which may have intermittent problems or links
that fail to function altogether. The most common symptom of poor link quality due to deficiencies in
the structured cabling is intermittent momentary dropping of video and audio but can also degrade to
the point that end-points fall offline and can even cause a link not to function at all, incurring a failure to
link.
This section touches on specific guidelines which can be referenced to ensure success from the
beginning of the project all the way through installation providing validation of link quality after the job
has been completed.
BASIC CABLE INFORMATION
Pre-installation cable selection should be the first order of business when designing the overall
installation. The cable selection should be determined by the combination of these factors: the
environment, the length of DXLink cable runs and the planned cable topology. As shown in this
document they all play a role in overall system performance.
The primary goal is to negate any of the external environmental factors that can impact performance
while ensuring a quality transport path from end-point to end-point. The minimum required cable to
provide a successful system installation is a shielded Cat6 cable. To ensure robust performance in
installations with unmanaged environmental factors, stepping up to Cat6A STP or Cat7 is recommended.
STP is used in this document to cover the wide range of Shielded Twisted Pair implementations listed
below; the severity of environmental factors should be considered when selecting between them:
SF/FTP, S/FTP, F/FTP, SF/UTP, U/FTP and F/UTP
‘S’ represents Screened braid shielding (also sometimes referenced as ‘Sc’)
‘F’ represents Foil shielding
‘U’ represents Unshielded
‘TP’ represents Twisted Pair
And notations left of the ‘/’ defines outer cable shielding while right of the ‘/’ defines shielding of the
individual wire pairs. Some graphical examples are shown on page 8 of this document.
Note: Not all cable manufacturers use the same definitions regarding shielding nomenclature.
For best performance a shielded Cat6A cable is suggested, we recommend the following (or equivalent)
to provide a good price vs. performance point while minimizing environmental impact.
When using a Cat6 F/UTP cable we recommend the following (or equivalent).
A complete Belden shielded Cat6A cable and cable management solution is available here:
http://www.belden.com/docs/upload/CheatSheet_10GX_FT_Shielded_Systems.pdf
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INSTALLED CABLE CHANNEL PERFORMANCE
Once cable is installed there are generally several factors that can affect link quality such as cable
quality, cable termination, grounding techniques, building ground differences, cable length, cable
topology, service loops, patch panel quality and quantity, cable kinks, etc… In order to understand how
the overall cable paths perform from one end of DXLink to the other end of DXLink, you can utilize tools
such as the Fluke DTX 1800 to characterize a number of specifications defined by TIA-568-C.2. Any cable
type chosen should have its end-to-end performance meet the installed Channel Requirements specified
by TIA-568-C.2.
ENOVA DGX LINK QUALITY REPORTING
Another method for determining the link integrity for a given DXLink path is provided if it is connected
to an Enova DGX populated with DXLink Input/Output boards. The Enova DGX 64, 32, 16 and 8
Enclosures can report measured link integrity values which are useful in qualifying the overall system or
troubleshooting paths that are presenting problems. When connected to the Enova DGX Enclosure,
reporting of each DXLink Input/Output port can be captured which presents a decibel value for each of
the four twisted pairs on a given port. If any of these MSE values reports >= -15dB (i.e. -13dB) the link
quality is in a range that can affect performance. See Appendix A for instructions and examples of how
link quality reporting through the Enova DGX Enclosure can be acquired.
CABLE QUALITY
CABLE TYPE
AMX requires as a minimum using CAT6 shielded cable installed per the recommended guidelines in
this document.
As you might expect, the higher the quality of the category cable the more robust the DXLink system will
perform. The gains to be made in this area are improved bandwidth, improved internal channel
parameters, improved external channel parameters and reduced susceptibility to environmental EMI
and ESD events.
When using Cat6 STP, Cat6A STP and Cat7 which meet their correlating TIA-568-C.2 performance
requirements, the DXLink runs can fully reach the 100m specification when bundled in groups of 6+1
(TIA-568 Alien Crosstalk Bundle). Using the heavier shielded versions of them, such as S/FTP, provide
improved resistance to uncontrolled environmental EMI and ESD events.
The benefits of these increasing grades of cable type provide significant improvement in both internal
and external channel parameters. Specifically of note are:
INTERNAL CHANNEL PARAMETERS
Insertion Loss / Max Attenuation: The measure of signal loss that occurs from transmitter to
receiver.
o
Often referred to as the cable bandwidth, typical factors that affect insertion loss include
conductor size, insulation and jacket material type, frequency bandwidth, number of patch
connections and cable length.
Return Loss: The measure of how much signal gets reflected back to the source due to impedance
variations in the Channel.
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o
Typical factors that affect Return Loss include variations in twist rates and discontinuities in
impedance.
Near End Crosstalk (NEXT): The measure of unwanted signal coupling between pairs in the same
cable.
o
Power Sum NEXT (PSNEXT) is the sum of unwanted signal coupling between multiple pairs in
the same cable.
Equal Level Far End Crosstalk / Attenuation to Crosstalk Ratio, Far End (ELFEXT/ACRF): The
measurement of unwanted signal coupling between pairs in the same cable when a disturbing
signal is sent from one end and received by the transceiver on the opposite end, including
attenuation loss due to insertion loss.
o
Power Sum ELFEXT / Power Sum Attenuation to Crosstalk Ratio, Far End (PSELFEXT/PSACRF)
is the sum of unwanted signal coupling between multiple pairs in the same cable when the
disturbing signals are sent from one end and received by the transceiver on the opposite
end..
o
Typical factors in the severity of these internal crosstalk measurements are the cable
internal insulation and pair to pair separation.
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EXTERNAL CHANNEL PARAMETERS
Alien Crosstalk is the most significant external parameter that affects signal and channel
performance. Both near end and far end crosstalk can detract from robust functionality and
specifically include the Power Sum scenarios described above where multiple cables contribute
crosstalk to the channel under evaluation.
o
Power Sum Alien NEXT (PSANEXT) is the effect of multiple Alien/External cable channels
injecting NEXT on a given cable.
o
Power Sum Alien ELFEXT / Power Sum Alien ACRF (PSAELFEXT/PSAACRF) is the effect of
multiple Alien/External cable channels injecting ELFEXT/ACRF on a given cable.
Alien Crosstalk can significantly be reduced or mitigated by:
o
The use of higher grade cables such as Cat6A STP and Cat7 cabling, while some
improvements can still be achieved through the use of shielded or foiled Cat6 (F/UTP).
o
Separating the cables from each other for portions or the entire cable run.
CABLE SHIELDING
Properly managed STP cable will provide numerous benefits, with the double shielded version such as
S/FTP and F/FTP giving even greater protection against unmanaged environmental disturbances. When
utilizing shielded cable, the entire system and building ground should be managed to ensure end-to-end
common ground reference levels. Some specific benefits of STP include:
It will provide shielding from Alien forms of crosstalk, as covered in the cable type section, which
reduce or eliminate noise from adjacent or bundled cables.
It will provide a significant improvement in immunity to environmental EMI and ESD events that
might be occurring in the area of the DXLink TX, DXLink cable runs, DXLink Enclosure or DXLink RX.
o
This added immunity will generally eliminate possible video or network drops due to events
of this nature by the virtue of keeping the large area events that are radiated through the air
from coupling onto the high-speed DXLink signals and circuitry.
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F/UTP: Foil shielding that
encompasses the cable while
leaving individual pairs
unshielded.
S/FTP: Foil shielding or screened
braid that encompasses the cable
while including additional foil
shielding around each of the four
differential pairs.
U/FTP: No shielding or screening
around the cable, but including
individual foil shielded pairs
inside the cable.
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CABLE END TERMINATION
Termination techniques for using shielded cable need to be applied correctly for STP cable benefits to be
realized and keep from introducing negative effects. Not only do the cables include shielding
components which need to be terminated correctly, but the diameter of the cable itself will be larger
and in some cases require the use of shielded punch-down connectors to properly terminate.
Bonding to ground at both ends of the cable is required.
o
Bonding throughout the run, including patch panels and patch cables to achieve a true end
to end ground connection is necessary.
o
A full 360 degree shielding termination is required to ensure ground connection is robust
and will not make intermittent contact when stresses are applied to the cable once
installed. We recommend use of a copper tape to be wrapped around the cable end with
the grounded drain wire and possibly foil shielding placed underneath the copper tape as
shown below. The copper tape used here is a ¾” wide 3M 1181 brand, part number
80011181049. This will ensure a low impedance connection at each interconnect point. The
series of pictures below show the recommended termination process with the final picture
showing that even when the cable has stresses applied; the 360 degree shielding will ensure
contact between the cable shielding and the shielded RJ-45 plug.
o
A low impedance connection at the equipment rack ensuring a solid tie between equipment
and the rack itself as well as between rack and the buildings main ground buss bar is
needed.
Shielded or screened cable can reduce the effects of EMI and ESD on DXLink transmission, but
they require equal grounding of the screen at both ends of the cable. A difference in ground
potential between the termination points of the cable could cause the cable to act as an
antenna, virtually negating all benefits hoped to be gained. But with good grounding techniques
applied to all components of the DXLink system, including the cable drain wires, lost packets and
dropped video can be kept to a minimum.
Source: http://en.wikipedia.org/wiki/Twisted_pair
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BANDWIDTH PERFORMANCE
The published specification minimum requirement for supporting proper functionality is based on a
controlled environment with quality cable and meets the horizontal cable specifications for Cat6 defined
by TIA-568-C.2 at 250 MHz.
The indicator of a cable’s bandwidth performance is the Insertion Loss specification, also referred to as
Max Attenuation. We recommend a cable rating of no more than 32.8dB of attenuation at 250 MHz over
100m.
Source: www.belden.com/techdatas/english/2412F.pdf
Note: The bandwidth of the cable alone will not guarantee robust performance in any installation as the
overall performance is a factor of the three main categories referenced in this document as Cable
Quality, Cable Topology and Environmental Factors.
CABLE TOPOLOGY
CABLE LENGTH
DXLink maximum cable length is specified at 100m. Many contributing factors can impact the DXLink
signal performance over that length of category cable. Conduit density, loops, bends, kinks, patch panels
and patch cables are the areas addressed in the following section.
A standard 10G Base-T Ethernet cabling topology of 5m (patch) 90m (Horizontal cabling) 5m
(patch) is recommended. Better signal performance can be achieved if the DXLink system cabling does
not include patch cords, panels, or couplers which will degrade the signal.
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Shielded Cat6, Cat6A or Cat7
# of Cables bundled together
Total length of cable run
supported
>=1
100m
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Figure 1, in conjunction with its table depict the ability to achieve a full 100m distance run
when using Shielded Cat6, Cat6A and Cat7 cables. There are no restrictions on the number of
cables bundled together up to 100m.
Figure 1 - Bundling topology, shielded cabling
Figure 1 Table – Bundling lengths for shielded Cat6, Cat6A or Cat7 category cables.
CABLE MANAGEMENT
Cable management solutions
o There are several off-the-shelf cable management systems which provide a full offering
of compatible components to help ensure appropriate installation and management of
category cable infrastructures. These will provide solutions to cable routing, cable end
termination, punch down connectors, patch panels, patch cables and even preterminated horizontal back-bone cables among other items.
o One such offering that has been shown effective for both performance and installation
practices is offered here by Leviton:
http://www.leviton.com/OA_HTML/ibcGetAttachment.jsp?cItemId=80036&labe
l=IBE&appName=IBE&minisite=10251
Specifications for shielded category cables
Definition: Shield – A metallic layer placed around a conductor or group of conductors.
These specifications apply to F/UTP, U/FTP, S/FTP plus other shielded cable types in a bundle:
o Maximum conduit fill density will be no more than 60%.
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o At all termination points along the shielded cable’s path, the copper tape or foil must
make 360 degree contact with the shielded connector’s housing (e.g., RJ-45 conductive
housing).
o All patch cords, panels, and couplers must be shielded in the cable run.
o A low impedance connection must be maintained over the full length of the shielded
cable run.
o DXLink twisted pair cable runs for DXLink equipment shall only be run within a common
building.
Common building is defined as: Where the walls of the structure(s) are
physically connected and the structure(s) share a single ground reference.
o Additional care must be taken during installation not to kink the cable which can deform
the conductors, thereby degrading the cable’s performance.
o Avoid tie wraps. If tie wrap use is absolutely necessary, then they should only loosely
surround the cables. Cinching the tie wraps around a bundle will deform the cable
conductors and negatively affect performance.
o Use loose Velcro™ wraps to bundle cable, only if it is necessary.
o Use 10G Base-T horizontal wire management techniques.
o Service loops are sometimes required as a means to store excess cabling. We do not
recommend service loops as they increase the total length of the cable run, and the loop
will wrap the cable back on itself which will increase crosstalk. If you must store excess
DXLink system cabling do not use a loop, but instead use an “S” pattern.
o Bend radiuses tighter than the manufacturer’s recommendations and kinks (even
straightened out kinks) created during installation will have a negative impact on the
cable’s performance.
Excessive bends or kinks can deform the cable’s conductors, which will degrade
the cable’s performance.
Excessive bends or kinks can deform the cable, which can alter the cable’s pair
balance leading to noise immunity performance losses.
Kinked cable (even straightened out kinks) might perform adequately for
Ethernet applications, but will have a much larger effect on DXLink system
cabling.
It is our recommendation that any category cables with an excessive bend radius or kinks are
treated as a damage cable. Deformed category cables will limit the cable’s ability to properly
pass a 10 Gb/s signal.
PATCH PANELS
Recommended panel practices:
Utilize patch panel designed for the shielded cable class you are installing.
Ensure the patch panel itself is well grounded to the buildings ground bus.
Use proper strain relief to keep from damaging cable terminations.
o Cable management combs may be desirable.
Do not place patch panels near large EMI or ESD generators.
PATCH CABLES
Recommended Patch cable/cord practices:
As defined by the TIA standard, patch cables are intended to be relatively short cables.
Ensure the patch cable is the same cable type or better than the horizontal back-bone cabling.
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Do not install low quality patch cables as they will become the weakest link and negate the
integrity and quality of the rest of the installation and horizontal cabling infrastructure.
o Patch cables must also be shielded and properly terminated.
5 Meters is the maximum recommended length for the patch cables.
ENVIRONMENT
Environmental factors play an important role in determining the success of a DXLink installation,
especially when the cable runs are over 30 meters. Some factors could result in an installation suffering
intermittent failures or being inoperable if not carefully considered during the project development
phase. Factors could include:
Grounding
o Equipment Grounding
o Building Ground Integrity
Electrostatic discharge (ESD) of excess static in the category cable jacket or when excess static
electricity is discharged by a human hand through one of the DXLink components.
Electromagnetic interference (EMI) generated by proximity electrostatic discharges, or by
operating electrical motors.
Ambient operating conditions surrounding the system installation.
Note: EMI and ESD, can be greatly reduced through the use of well balanced, shielded cables with
grounded connectors, and keeping the cable runs as short as possible. Internal testing has shown that
unbalanced and improperly grounded or terminated cable runs and equipment will lead to erratic
behavior including network, audio and video losses.
GROUNDING
Transmission of DXLink data over twisted pair copper wire (differential mode) requires well balanced
cable and terminations at both ends of the twisted pair to minimize the effects of the common mode
hostile sources described in the EMI and ESD sections of this paper. Obtaining perfect balance becomes
increasingly difficult as the length of the cable increases, making the cable less immune to EMI and ESD
sources. Shielded or screened cable will reduce the effects of EMI and ESD on DXLink transmission, but
they require equal grounding of the screen at both ends of the cable. A difference in ground potential
between the termination points of the cable will cause the cable to act as an antenna, virtually negating
all benefits hoped to be gained. But with good grounding techniques applied to all components of the
DXLink system, including the cable drain wires, lost packets and dropped video can be overcome.
The following two sub-sections are discussed thoroughly and practically inside of the document link
provided below from Amp Netconnect and Tyco Electronics which when understood and followed will
provide a quality installation and robust DXLink performance. It incorporates practices defined in the
National Electric Code (NEC) NFPA 70 which defines grounding and bonding as well as providing
requirements of the grounding of a building’s electrical system. The linked document also incorporates
practices defined in the TIA J-STD-607 Commercial Building Grounding (Earthing) and Bonding
Requirements for Telecommunications.
http://www.ampnetconnect.com/documents/Grounding_and_Bonding_White_Paper_%5B0901%5D.pdf
Equipment Grounding
o Follow requirements defined in TIA STD-607.
The standard can be purchased through IHS here.
o The grounding of ALL equipment used in a DXLink installation is required.
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Examples of Static Generation
Typical Voltage Levels
Means of Generation
10-25% RH
65-90% RH
Walking across carpet
35,000V
1,500V
Walking across vinyl tile
12,000V
250V
Worker at bench
6,000V
100V
Poly bag picked up from bench
20,000V
1,200V
Chair with urethane foam
18,000V
1,500V
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o Grounding is recommended to be provided through a low impedance connection to
equipment racks which in-turn should be heavily tied into the buildings electrical ground
system.
Building Ground Integrity
o Follow requirements defined in NEC NFPA 70.
The standard can be accessed free through NFPA here.
o The entire building should have a common ground potential.
Siemon has provided an informative discussion of the benefits of shielded cable:
http://www.siemon.com/us/standards/Screened_and_Shielded_Guide_1_Overview_and_History.asp.
DXLink signals can be carried over long distances; equipment connected to AC power at one end of the
system may not be at the same ground potential as equipment at the other end of the system if
guidelines provided by NEC (National Electrical Code) and TIA-607 (Generic Telecommunications
Bonding and Grounding/Earthing for Customer Premises) are not followed.
ELECTROSTATIC DISCHARGE (ESD)
ESD is a type of EMI, but in this paper we are treating indirect ESD and direct ESD events separately.
Direct ESD events refer to any electrostatic discharge that takes place directly to the DXLink system,
where the system includes all components: DXLink receivers and transmitters, cables, and racks.
ESD is defined as the transfer of excess electrons (charge) from one surface at some electrical potential
to another surface at a different potential. The most common method of generating a charge is when
different materials are rubbed against each other, transferring electrons; this is known as triboelectric
generation. An example of triboelectric generation occurs when a person walks across a carpeted floor
wearing shoes with soles made of a different material than the carpet.
An example of the voltage potential created by various activities under two ranges of relative humidity is
provided in the following table by the Electrostatic Discharge Association, North Central Regional
Tutorial Program (http://www.esda.org/fundamentalsP1.html):
As this table indicates, the relative humidity of the air surrounding the activity can affect the amount of
potential; the drier the air the greater the potential. Note that the materials indicated in this table have
insulative properties, meaning they do not permit the flow of electrons. The potential on insulative
materials can exist for a long time if not placed in contact with a material having a different potential.
When a material with high potential created during these activities contacts a material that has very low
potential, such as when a person walking across a carpeted floor touches a metal door knob, the
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potential is rapidly dissipated causing an electromagnetic pulse and possibly the familiar spark (shock!).
This occurs regularly during the installation of a DXLink system:
Triboelectric generation of potential on cable outer jackets when they are installed may be
dissipated when the jacket comes in contact with a metal surface, such as a cable raceway.
Potential on the cable jackets may also be dissipated when the cable’s terminated ends are
connected to the DXLink receivers/transmitters.
An installer touches the metal frame of a DXLink system component, dissipating any charge built
up while walking across the floor.
When a potential is dissipated directly to the system, the path it takes varies so it is difficult to predict
exactly what effect it will have on the DXLink transmission. AMX has conducted experiments which show
static discharges with voltage potential of ±3.5kV and greater applied directly to system components
cause sufficient disruption to the transmission that result in momentary lost video. This is probably due
in part to EMI (discussed below) and to propagation of the voltage throughout the component being
discharged to.
Note: AMX equipment used in DXLink installations is protected against damage from ESD events.
ELECTROMAGNETIC INTERFERENCE (EMI)
Of the many forms of EMI, the greatest disruption to a DXLink installation is generated by
1) Electrical motors 2) Proximity ESD events and 3) Alien crosstalk from adjacent cables. The third form
is covered in another section of this paper and will not be discussed here.
ELECTRICAL MOTORS
The second form, EMI generated by electrical motors operating in proximity to a DXLink system cable
run, is greatly reduced by the use of twisted wire pairs provided the twisted pairs are well balanced.
However, EMI transients generated when cycling power to the motor could propagate quickly through
cable located nearby causing momentary loss of data, ultimately resulting in loss of video, audio or
network connection. The good news here is these EMI sources have fixed locations and their operation
is well understood; avoid placement of DXLink system cable runs close to large motors (e.g. heat pumps,
elevators, lifts) and keep the runs perpendicular to power line cables.
PROXIMITY ESD EVENTS
Proximity ESD events are severe EMI occurrences produced when static electricity is discharged close to
a DXLink system cable run – no direct contact with the cable is made, but the resulting electrostatic field
can induce voltages in the category cable and cause momentary interference with transmission of the
DXLink stream. In a typical Ethernet installation lost packets are simply retransmitted, but in an DXLink
installation the lost packets are perceived by the user as dropped video, audio or network connection. In
the real world, certain DXLink installations can be prone to the effects of proximity ESD events;
examples are casinos where electrostatic air cleaners are used, and carpeted conference centers.
AMX has conducted testing to empirically quantify the effect of real-world ESD events on transmission
of DXLink data: the test configuration is shown in Figure 2. In this testing a Schaffner ESD generator was
used to apply controlled static discharges to various locations around the DXLink switcher, and to
locations connected to ground along the length of the cable run. Various cable types (shielded,
unshielded, Cat5e, Cat6) and cable configurations (straight one-way run, straight two-way run, loosely
coiled, with and without patch cables) were tested using discharge voltages between +/-2kV and +/-8kV.
Page 14 AMX White Paper | Cabling for Success with DXLinkTM | V 3.1 6.2013
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Results from this testing showed that discharge voltages as low as 4kV at a distance of ~4 meters from
the cable run were responsible for causing video to drop.
Figure 2 - Proximity ESD Event Test Diagram
Conclusions from this testing are that DXLink system susceptibility to EMI generated by proximity ESD
events is related to the length of the cable run (shorter runs are less susceptible), the distance from the
event to the cable, and the type of cable (properly terminated and bonded shielded cable is least
susceptible).
AMBIENT OPERATING CONDITIONS
Temperature - Cable manufacturers specify their cables in different ways, but most will provide
specifications for both installation temperature and operating temperature. To minimize damage to the
cables, these specifications should be well understood before attempting to install a DXLink system
cable run.
Humidity - As was demonstrated above, relative humidity has a distinct effect on the voltage generated
during an ESD event which in turn can have an effect on the quality of the transmitted DXLink signal
when the event occurs in proximity to an unshielded cable.
CONCLUSION
DXLink products can provide a wealth of features and benefits for your installation. Ensuring a properly
shielded and terminated transmission medium plus a well-grounded system for distribution of signals
will allow for a successful and robust solution.
For more information on DXLink products, contact your AMX Representative or visit www.amx.com.
Page 15 AMX White Paper | Cabling for Success with DXLinkTM | V 3.1 6.2013
MSE Value
Cable Quality
Unlinked
No cable connected
0dB to -8dB
Unusable – Likely no link made
-9dB to -11dB
Bad – Likely no video
-12dB to -14dB
Poor – Frequent video drops
-15dB to -17dB
OK – Rare video drops
-18dB to -20dB
Good – Stable
-21dB to -23dB
Ideal – Very robust
CAB LING F O R SUCC E SS WI TH DX L I NK
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APPENDIX A
Enova DGX Link Quality Reporting
Link quality measurements can be reported by the Enova DGX DXLink Input and Output boards to help
determine the quality of the link established between a DXLink Input board and connected TX or a
DXLink Output board and connected RX. The reporting information can potentially identify cable runs
that will cause performance issues due to items such as poor cable quality, excessive length or patch
cables discussed in this White Paper.
Link Quality Reporting over Enova DGX Serial or USB Port
If your system has DXLink Input with FW v1.0.3.1 or higher and DXLink Output with FW v1.0.4.1 or
higher, which are included in the Enova DGX FW KIT upgrade v 1.2.5.1 or higher (released on 8/21/2012)
you will have access to the individual input & output port statistical reporting from the CPU’s Serial or
USB port. With this capability you will be able to view the link quality of a given cable run and determine
if there are potential cabling issues which could cause performance issues. Another metric which can be
viewed in this reporting is the cable length which has a +/-10% tolerance and is reliable at 25 meters and
above.
The reporting is gathered and presented by the Enova DGX’s CPU and accessed using the SHELL
command mode over the DB-9 serial port or mini-USB port using a terminal program.
To gain access to the SHELL you should follow the instructions in the Enova DGX product manual under
the Installation and Setup Chapter – Attaching an External Serial Controller section to establish
communication with the CPU. Once in communication, the commands shown below with values
reported will guide you into the SHELL and show examples of how to get the MSE Link Quality reporting.
1. After establishing CPU communication with a terminal program:
a. Press “CTL+C” (Control and C) to enter the command SHELL, you should see a prompt of
‘DGX_SHELL>’.
i. Note: The SHELL interface will time-out after a brief period and return to the
BCS interface so if you don’t enter the commands before the time-out you’ll
need to re-enter the SHELL with the “CTL+C” key combination.
b. Type “show stats” followed by <Enter>, you should get a statistic report for all DXLink
Input and Output boards in the enclosure.
c. The MSE (Mean Square Error) value is included in this information and BOLDED below.
The data for all 4 twisted pairs of each cable/port are displayed with the dB values
below. The BER and DSP Reset reporting that is presented with the MSE is not currently
meaningful for diagnostic purposes.
d. The following table shows the -dB value ranges and their typical performance levels.
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DGX_SHELL>show stats
MCPU:
i2c failure count: 2
reboot count: 10
BCPU1:
Ch1-[DxLink In] BER Video:10^(-0), Audio:10^(-0), Blank:10^(-0), Ctrl:10^(-10)
Ch1-[TX] Cable Length: 90 (Meters), 295 (Feet)
Ch1-[DxLink In] MSE Chan A:-19db, Chan B:-18db, Chan C:-18db, Chan D:-20db
Ch1-[DxLink In] DSP Reset Count: 0
Ch2-[DxLink In] BER Video:10^(-0), Audio:10^(-0), Blank:10^(-0), Ctrl:10^(-10)
Ch2-[TX] Cable Length: 80 (Meters), 262 (Feet)
Ch2-[DxLink In] MSE Chan A:-20db, Chan B:-20db, Chan C:-20db, Chan D:-21db
Ch2-[DxLink In] DSP Reset Count: 0
Ch3-[DxLink In] BER Video:10^(-0), Audio:10^(-0), Blank:10^(-0), Ctrl:10^(-10)
Ch3-[TX] Cable Length: 33 (Meters), 108 (Feet)
Ch3-[DxLink In] MSE Chan A:-21db, Chan B:-21db, Chan C:-22db, Chan D:-22db
Ch3-[DxLink In] DSP Reset Count: 0
Ch4-Unlinked.
Ch4-Unlinked.
Ch4-Unlinked.
Ch4-Unlinked.
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