Cim 20070701 jul_2007

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Installation 7Maintenance
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Exceptional optical performance comes naturally.
Nothing is more treasured in field termination than exceptional optical performance. The secret to UniCam® Pretium™-
Performance Connectors is inside – a laser-cleaved, factory-polished fiber stub that ensures outstanding connectivity in
a no-epoxy/no-polish (NENP) connector. UniCam Pretium-Performance Multimode Connectors offer 0.1 dB insertion loss.
And UniCam Pretium-Performance Single-Mode Connectors enable 0.2 dB insertion loss. That’s exceptional optical
performance in less than a minute per fiber, from the most widely deployed NENP connector on the market. Naturally ...
Customer-focused innovation is second nature at Corning.
www.corning.com/cablesystems/cimls

© 2007 Corning Cable Systems LLC / LS-02413

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Contents Zoom In Zoom Out Front Cover Search Issue Next Page EMaGS
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Turn your cable tester into an OTDR
and watch the transformation begin.

See how the DTX Compact OTDR Module
can turn your cable tester into an OTDR
and your staff into fiber experts – to
completely transform your fiber business.
Imagine. A cable tester that becomes a
compact, easy-to-use, full-featured OTDR.
Better yet, imagine what that means for your
business. A single tool to test copper and
fiber. An OTDR your current technicians can
easily use. Fiber jobs you couldn’t do before.
Just snap the DTX Compact OTDR module onto
a DTX mainframe – the industry’s benchmark
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tion. Perform powerful single-ended trouble-
shooting. Deliver professional documentation.
Win jobs that require OTDR
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Go to www.flukenetworks.com/seehow
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N E T W O R K S U P E R V I S I O N ©2007 Fluke Corporation. All rights reserved. 02152

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Our U.S. area of expertise.

No matter where you’re located, our fiber optic cable products are there. Optical Cable Corporation
has built a network of reliable stocking distributors and a dedicated sales team committed to
getting you the best fiber optic cables for your requirements when you need them...where you
need them. For over 20 years, we have been manufacturing the broadest range of top-performing
tight-buffered fiber optic cables for most applications in the government, military, and commercial
markets. Your order is our top priority. Contact Optical Cable Corporation for a stocking
distributor nearest you. We are where you are.

1-800-622-7711
5290 Concourse Drive • Roanoke, Virginia 24019 • Phone 540-265-0690 • www.occfiber.com

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COVER IMAGES SUPPLIED BY ANIXTER.

JULY 2007 VOL. 15, NO. 7

ABOUT THE COVER
Using vendor-neutral
testing, Anixter’s features
15
Infrastructure Solutions
Lab is demonstrating real- The myths and realities of
world IP convergence of shielded, screened cabling
security and networking Potential users must separate fact from fiction concerning noise
infrastructure products so
immunity, grounding, and the antenna effect. VALERIE RYBINSKI
that customers can know

25
what will work best for their
installation before investing. Abandoned cable removal
TO LEARN MORE,
SEE PAGE 49.
a dogged challenge for all
Unfortunately, for everyone, ignoring the issue won’t
make it go away. PATRICK McLAUGHLIN

29 Twisted pair options for 10-Gigabit Ethernet
Conducting appropriate tests will help ensure your medium of choice
is ready for high-frequency, high-speed transmission. HUGO DRAYE

37 Products and technologies
meeting myriad challenges
Latest innovations aim to alleviate problems associated with cable
management, power consumption, security and, oh-by-the-way,
signal transmission. PATRICK McLAUGHLIN & STEVE SMITH

40 WLAN goes fat to thin and back again
When the industry moved to centralized wireless
solutions with switch-based controllers, many thought
the war between “fat” and “thin” was over. But now it
appears the battle is still on. BETSY ZIOBRON
departments
6 Editorial
Your network’s health is everything
49 INDUSTRY SPOTLIGHT
■ Anixter lab integrates networking, security
9 Ask Donna
‘Abandoned’ headaches
■ Big Blue digging deep for data center purge begin early
■ Cat 6A solution undergoes 10-GbE traffic test 54 New Products
■ Flexible racks meet military media center specs 56 Product Focus:
■ Wireless Gigabit Ethernet on-the-fly FIBER-OPTIC POLISHING
EQUIPMENT

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www.cable-install.com Cabling Installation & Maintenance ■ July 2007 ■ 3

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Chief Editor / Patrick McLaughlin
(603) 891-9222 • patrick@pennwell.com

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Are you ready to feel the speed?
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_____________________
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_________________________ engineers by calling our 800 #s.

© Agilent Technologies, Inc. 2006

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Your network’s health is everything
R
ecently, I had occasion to A doctor had ordered radiologi- department will.
spend time in a special-care cal tests on a patient and required But even more striking was the
unit at a hospital—not as a the results “stat.” Now, I have seen doctor’s exasperation at being put
patient, but visiting for many hours enough episodes of ER (I’ll never on infinite hold twice, not by some
with a loved one who was a patient in admit to watching Grey’s Anatomy) automated answering system, but
the unit. Because all medical matters to know that “stat” means right away. by a real person. Then it dawned on
were resolved positively and this Two hours later, the doctor could me that the doctor, along with all her
member of my family came home find no results in the hospital’s data colleagues, relies first and foremost
healthy, I was able to reflect on my network. So, she called the radiology on the data network for the infor-
time in that hospital with some department desk, demanding to mation she needs. And there’s good
practicality rather than completely know why so much time had elapsed reason for this doctor to look for in-
emotionally. with no answers. The individual who formation in a database long before
And one or two answered the phone in the radiology looking for it from an individual.
of my observations department put the doctor on hold— We live in a fully connected world
made me think and kept her there. Frustrated, the whose human element is almost
about networking doctor called the desk again and always disconnected. We’ve had cell
and cabling. made the same demand. Unbeliev- phones forever and through Black-
But fi rst things ably, the same thing happened: on berries have been able to get our
first. While a visi- hold forever. e-mail from just about anywhere.
tor at the hospital, I So, the situation got escalated to the But how many phone messages go
was the beneficiary top-ranking member of the radiology unreturned? How many e-mails
of many comforts and accommoda- department. At that time, the doctor unanswered? The digital signals do
tions, one of which was the opportu- learned the results were, in fact, avail- their jobs by getting information
nity to spend time at my loved one’s able; the head of radiology read the from one point to another; it’s the
bedside any time of the day or night. results to the doctor over the phone, people who have become the black
As such, I witnessed more inner and the doctor went about caring for hole. I have been a frustrated mes-
workings of that environment than her patient based on the information sage-sender at times. I have also been
I ever imagined I would. That means she had just received. In an environ- a guilty non-returner of correspon-
I saw patients in various stages ment of such immediacy, the doctor dence. So, if I’m going to point a finger
of distress, and observed the quick quickly moved on to the next order anywhere, it will point to me first.
(and I don’t mind saying heroic) of business. She did not have the lux- The experience made me realize
actions of doctors and nurses who ury of stopping to either ponder or that many of the information sys-
literally saved at least one life in complain about the communication tems you build and use today have
front of my eyes. breakdown that had just taken place. become more relied-upon than
So, here are these health-care pro- I eavesdropped on this event with people. Scary. But not nearly as scary
viders working around the clock to interest because, after all, my loved as sitting by a loved one’s hospital
maintain the health of the patients in one could have been the next one for bed for a few days.
their care, or to restore their patients’ whom radiological test results were
health. They don’t need, and won’t needed stat. One thing that occurred
tolerate, something like a network to me was the information that was
interruption getting in their way. But supposed to be in the hospital’s da-
they almost did while I was watching. ta network and available to the doc-
While I’m sure there’s much more to tor, was not. A network problem? PATRICK McLAUGHLIN
Mc
the story than I saw and heard, I’ll Could be. Cabling-related? I’ll never Chief Editor
retell it from my vantage point. know, but hopefully the hospital’s IT patrick@pennwell.com

6 ■ July 2007 ■ Cabling Installation & Maintenance www.cable-install.com

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How many tools do you use to
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____________________________

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‘Abandoned’ headaches begin early
Editor’s note: This month, we bring you a slice of “Best of Ask Donna” from tion Systems, Section 820.2 defines
years past. This column originally ran all the way back in February 2003, “Abandoned Coaxial Cable” as
so why did we take it out of mothballs now? The first question-and-answer “Installed coaxial cable that is not ter-
volley provides complementary information to another article running in minated at equipment other than a
this issue (see pages 25 and 26). When reading, please note that the portions coaxial connector and not identified
of the NEC discussed herein look essentially the same in the 2005 edition as for future use with a tag.”
they do in the 2002 edition. Article 830 Network-Powered
Then Donna finishes up with a question about the potential danger of lay- Broadband Communications Sys-
ing unshielded twisted-pair cables too neatly. It struck me as an eerie fore- tems, Section 830.2 defines “Aban-
shadowing of what the industry has been dealing with for the past couple doned Network-Powered Broadband
years. I hope you enjoy this month’s “Best of Ask Donna” and, even more Communications
importantly, find it useful.—Ed. Cable” as “Installed
network-powered
Q: I have a quick question. Could and Power-Limited Circuits, Sec- broadband com-
I get the exact wording of what tion 725.2 defines “Abandoned Class munications cable
the National Electrical Code 2002 2, Class 3, and PLTC Cable” as “in- that is not termi-
states concerning abandoned stalled Class 2, Class 3, and PLTC nated at equip-
cables in the plenum? cable that is not terminated at equipment other than a
Brent Clements ment and not identified for future connector and not
Rice University use with a tag.” identified for future
Houston, TX Article 760 Fire Alarm Systems, use with a tag.”
Section 760.2 defines “Abandoned So, what is this telling us? No-
A: The question may be quick, but Fire Alarm Cable” as “Installed fire tice the common thread, “and not
the answer certainly is not. Let’s alarm cable that is not terminated identified for future use with a tag.”
begin with the definitions of aban- at equipment other than a connec- Any cable addressed in these specific
doned cable. In NEC 2002, there tor and not identified for future use articles that is “tagged for future use”
are seven definitions for abandoned with a tag.” is not abandoned cable.
cable. Ironically, none are in Article Article 770 Optical Fiber Cables In some cases, having a connec-
100, the section on definitions (yet). and Raceways, Section 770.2 defines tor terminated at one end (audio dis-
Article 640 Audio Signal Pro- “Abandoned Optical Fiber Cable” as tribution cable; Class 2, Class 3, and
cessing, Amplification, and Repro- “Installed optical fiber cable that is PLTC Cable) or both ends (commu-
duction Equipment, Section 640.2 not terminated at equipment other nications cable) of the cable means
defines “Abandoned Audio Distri- than a connector and not identified that it is not abandoned cable.
bution Cable” as “installed audio for future use with a tag.” While in other cases, having the
distribution cable that is not termi- Article 800 Communications Cir- cable connected to equipment that
nated at equipment and not identi- cuits, Section 800.2 defines “Aban- is not a connector (fire alarm ca-
fied for future use with a tag.” doned Communications Cable” as ble; optical fiber cable; coaxial ca-
Article 725 Class 1, Class 2, and “Installed communications cable that ble; network-powered broadband
Class 3 Remote-Control, Signaling, is not terminated at both ends at a communications cable) means that
connector or other equipment and it is not an abandoned cable. In NEC
DONNA BALLAST is BICSI’s standards
s standards
not identified for future use with speak, a “connector” is “equipment,”
representative, and a BICSI registered
and a BICSI registered
communications distribution designer (RCDD).
distribution designer a tag.” and that is why the “equipment other
(RCDD). Send your question tovia e-mail:
Send your questions to Donna Donna at: Article 820 Community Anten- than a connector” verbiage is used.
dballast@swbell.net na Television and Radio Distribu- Most Sections [640.3(A); ➤


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725.3(B); 760.3(A); 770.3(A); 800.52(B); You asked specifically about ple- Q: I was reviewing the discussion on the
820.3; 830(A)] only address the “acces- num spaces, but the same text applies BICSI Public Forum about laying cables
sible portion” of an abandoned cable to plenum, riser, and hollow spaces in parallel to each other in a fi xed physical
as “not be permitted to remain.” Arti- the building. If it is “abandoned” and relationship. I noticed that one comment
cle 100 defines “Accessible (as applied to “accessible,” take it out. said that the European norm addresses
wiring methods)” as “Capable of being Seven definitions for almost the same it to some degree. Do you know if any
removed or exposed without damag- term is a lot, even for the NFPA. So, for of the U.S. standards have intentions to
ing the building structure or finish or NEC 2005 the International Brother- address it? I have a client in New Jersey,
not permanently closed in by the struc- hood of Electrical Workers Codes and with a large data center, that is asking
ture or fi nish of the building.” … So, Standards Committee is proposing to me for input. At present they are laying
this is not a surgical removal in a fin- delete the current seven to add a new large bundles of cables into cable trays
ished space. But if the entire area of the definition to Article 100, which would and they want the cables combed as they
building is undergoing demolition for read: “Abandoned Cable. Installed are installed. I told them I would check
remodeling, then all of the cable should cable that is not terminated at both and let them know.
be accessible and removed. ends at equipment and not identified for Bobby Ashton, Jr.,
And then there is Article 645—the future use with a tag.” But so far the RCDD/LAN Specialist
one that did not bother to uniquely other “stakeholders,” who carefully South Windsor, CT
define “abandoned cable,” which is crafted the various definitions in their
only concerned with abandoned cable respective Articles, are not supportive A: Intentions, yes. At the TIA TR-42.1
that is not contained in metal raceway. of this “one-size-fits-all” approach. February 2002 meeting, a presentation
So, metal raceways full of dead cable It is going to be an interesting couple (TR 42.1-2002-013) was made, which ref-
under raised floors in data centers are of years. erenced a list of contributions, previously
not a concern? submitted to either the TR-42.7 Tele-

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communications Copper Cabling Sub- and the pathway is not overfilled, then have seen use seven cables—six disturb-
committee or the Cable Working Group, “alien crosstalk” should be one less net- ers and one victim cable. That would
dating from 1997 through 2002. Each of work anomaly you have to address. mean seven sets of field test instruments
these contributions had addressed some And what about testing? While your in use at the same time to test one cable
negative effect on the transmission per- network can certainly suffer from the link. And there are currently no pass/fail
formance of category UTP cabling effects, measuring alien crosstalk is not limits proposed or set.
caused by bundling or other similar something you want to attempt in the My advice: loosen up and avoid the
cabling installation practices. field. Most measurement models that I problem.
TR-42.1-2002-013 suggested that,
based on these contributions, a Study
Group be formed to develop informa-
tion on the expected variance in trans-
mission performance of cables that are
installed in close proximity.
TR-42.1-2002-013 further proposed
that once the work was completed and
validated, it would be drafted as a matrix,
and published as an informative Annex
to TIA/EIA-568B.1. The matrix would
include alien NEXT and FEXT for Cat-
egory 5e and Category 6 cables that are
tie-wrapped at specified intervals, cables
installed in a tray with 50% fi ll, cables
installed in a conduit with 40% fill, and
cables suspended on J-hooks.
Meanwhile, we will have to contin-
ue to scare our clients suffering from
“overneatness tendencies” using threats
of the dreaded “alien crosstalk.” You
are welcome to use the following. It has
worked for me in the past.
Cabling systems and network hard-
ware are designed to handle predict-
What’s at the core of your fiber?
able noise, like NEXT and FEXT, which
comes from within the same cable. This
is why when you remove the sheath from
a twisted-pair cable, each of the pairs is
twisted at a different rate.
But when UTP cables of the same con-
struction are neatly dressed and packed,
Chances are you don’t know. Some fiber manufacturers
you are inviting trouble. You are creating don’t specify bandwidth in the critical center region of
a quasi field-manufactured hybrid cable, the fiber. But when you select OFS’ LaserWave® OM3
because the twists are the same in each of fiber, you get outstanding performance right down to
the neighboring cables. This creates un- the core. LaserWave fiber delivers DMD specified in the
predictable noise between neighboring 0 – 5 micron range and up to twice the bandwidth for
lasers that launch power in the fiber’s center. Enjoy fast,
cables; the noise is called alien crosstalk.
reliable transmission and easier connectivity. To learn more,
And the neater the cables are laid, and the ask your cabler about OFS or visit ofsoptics.com/fiber.
closer you pack them together, the more
likely you are to experience the problem.
If the UTP cables are randomly laid


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Chrysler Financial is a business unit of DaimlerChrysler Financial Services.

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Mohawk’s pre-terminated fiber optic Plug’n Play
solutions combine ease of installation with the
flexibility to work with any corresponding fiber
cassette.
Whether long runs or short runs, Mohawk’s Plug’n Play
fiber solutions complement data center performance with
its compact cable size and maximum flexibility.
Features and Benefits:
• Pre-terminated cables for premium performance.
• Small diameter and bend radius for installation in
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• The MPO terminations allow the cables to plug
into any corresponding fiber cassette.
• Compliant to TIA-568-C.3.

MOHAWK
For more information or a copy of our Application Note
visit www.mohawk-cable or call 800-422-9961.

Cabling Excellence for
Open Architecture

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www.cable-install.com design

The myths and realities
of shielded, screened cabling

A global standard since the 1980s,
screened and shielded twisted-pair cop-
per cabling varieties are still a mainstay
Potential users must separate fact
from fiction concerning noise immunity,
grounding, and the antenna effect.
in some markets. While many other mar-
kets have migrated largely to unshielded twisted-pair not yet be realized by early-generation twisted-pair design
(UTP) cables, the recent ratification of the 10GBase- and manufacturing capability. It is not surprising that this
T standard for 10-Gbit/sec Ethernet over copper has robust cabling type still supports some buildings today.
re-established the commercial viability of screened and By 1990, however, LAN industry experts began to recog-
shielded systems, and has fueled greater adoption of nize Ethernet’s performance and reliability advantages over
these systems in markets that
previously were UTP-centric. LAN noise sources
In this competitive landscape, H
many confusing and often con- Ve
E
tradictory messages are finding l
their way to the marketplace.
This article addresses common
questions, issues, and miscon-
ceptions regarding screened and h Vd

shielded cabling.

From Token Ring to Ethernet Vg
When LAN cabling emerged in Equipment Interconnect Work area outlet End-user device
the 1980s to support the first Source: Siemon

computer networks in commer-
cial building space, the networks typically deployed IBM This setup shows the three sources of noise for LAN cabling sys-
Token Ring transmission, which was standardized as tems. Differential noise (Vd) is induced from an adjacent twisted-
IEEE 802.5 in 1985. Cabling for Token Ring networks pair or balanced cable; environmental noise (Ve) is induced by
was IBM Type 1 cable—consisting of two loosely twist- an external electromagnetic ﬁeld; and ground loop noise (Vg) is
ed, foil-shielded, 150-Ω pairs surrounded by an overall induced by a difference in potential between conductor ends.
braid—mated to unique hermaphroditic connectors.
This cabling was an optimum choice for support of first- Token Ring. Concurrently, twisted-pair design and man-
generation LAN topologies. Its design took advantage of ufacturing capabilities had progressed to the point where
the twisted-pair transmission protocol’s ability to individual foils were no longer required to provide inter-
maximize distance (Token Ring served distances up to nal crosstalk isolation, and overall shields were not neces-
100 meters) and data rates using cost-effective transceivers. sary to provide immunity against outside noise sources in
The foils and braid improved crosstalk and electromagnet- the 10Base-T and 100Base-T bands of operation.
ic compatibility (EMC) performance to levels that could Publication of the 10Base-T application in 1990, and
the first edition TIA/EIA-568 cabling standard the fol-
VALERIE RYBINSKI is global sales engineer with Siemon (www.siemon.com). lowing year, in conjunction with the lower cost as- ➤


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sociated with UTP cabling, firmly established UTP as the While this bandwidth provides more than sufficient noise
medium of choice for new LAN networks. immunity for such applications as 100Base-T and 1000Base-T,
Shannon Capacity modeling demonstrates that this level pro-
Balancing act vides no headroom to the minimum 10GBase-T noise immu-
The benefit of specifying balanced twisted-pair cabling for nity requirements. The use of shielding, however,
data transmission is clearly demonstrated by examining the significantly improves noise immunity, doubles the available
types of signals present in building environments. Electrical Shannon Capacity, and substantially increases practical oper-
signals can propagate in either common mode or differential ating bandwidths for future applications.
(i.e., “balanced”) mode.
Common mode describes a signal scheme between two con- Noise and immunity
ductors in which the voltage propagates in phase and is ref- Modal conversion is an effect of degraded twisted-pair signal bal-
erenced to ground. Examples of common mode transmission ance above 30 MHz, which occurs when differential mode signals
include DC circuits, building power, cable TV, heating/venti- convert to common mode signals, and vice versa. The conversion
lation/air-conditioning (HVAC) circuits, and security devices. can adversely impact noise immunity from the environment
Electromagnetic noise induced from disturbers, such as as well as contribute to crosstalk between pairs and balanced
motors, transformers, fluorescent lights, and radio-frequency cables, and must be minimized whenever possible. Shielding
(RF) sources, also propagates in common mode. Virtually can decrease the potential for modal conversion by limiting
every signal and disturber type in the building environment noise coupled onto the twisted-pair from the environment.
propagates in common mode, with one notable exception— All applications require positive signal-to-noise ratio (SNR)
twisted-pair cabling, which is optimized for balanced, or dif- margins to transmit within allocated bit error rate (BER)
ferential mode, transmission. levels. This means that the data signal being transmitted must
Differential mode transmission refers to two signals that have be of greater magnitude than all of the combined noise dis-
equal magnitudes, but are 180° out of phase, and that propa- turbers coupled onto the transmission line—i.e., the struc-
gate over two conductors of a twisted pair. In a balanced cir- tured cabling.
cuit, two signals are referenced to each other rather than one Noise can be coupled onto twisted-pair cabling in any or
signal being referenced to ground. There is no ground con- all of three ways.
nection in a balanced circuit and, as a result, these types of • Differential noise: Noise induced from an adjacent twist-
circuits are inherently immune to interference from most com- ed-pair or balanced cable;
mon mode noise disturbers. • Environmental noise: Noise induced by an external elec-
In theory, common mode noise couples equally onto each tromagnetic field;
conductor of a perfectly balanced twisted-pair. Differen- • Ground loop noise: Noise induced by a difference in poten-
tial mode transceivers detect the difference in peak-to-peak tial between conductor ends.
magnitude between the two signals on a twisted pair by per- Different applications have varying sensitivity to interfer-
forming a subtraction operation. In a perfectly balanced ence from these three noise sources, depending upon their
cabling system, the induced common mode signal would capabilities. For example, the 10GBase-T application is com-
appear as two equal voltages that are simply subtracted out by monly recognized to be extremely sensitive to alien crosstalk
the transceiver, thereby resulting in perfect noise immunity. (differential mode cable-to-cable coupling) because its digi-
In the real world, however, twisted-pair cables are not per- tal signal processing (DSP) capability electronically cancels
fectly balanced, and their limitations must be understood by internal pair-to-pair crosstalk within each channel. Unlike
application developers and system specifiers. pair-to-pair crosstalk, alien crosstalk cannot be cancelled by
TIA and ISO/IEC committees take extreme care in speci- DSP. Conversely, because the magnitude of alien crosstalk is
fying balance parameters, such as transverse conversion loss very small compared to pair-to-pair crosstalk, the presence of
(TCL), transverse converse transfer loss (TCTL), and equal- alien crosstalk minimally impacts the performance of other
level transverse converse transfer loss (ELTCTL) in their applications, such as 100Base-T and 1000Base-T, that employ
standards for higher-grade (Category 6 and above) struc- partial or no crosstalk-cancelling algorithms.
tured cabling. By examining the performance limits for these EMC describes both a system’s susceptibility to interfer-
parameters and noting when they start to approach the noise ence from, and potential to disturb, outside sources. It is an
isolation tolerance required by various Ethernet applica- important indicator of a system’s ability to co-exist with other
tions, it becomes clear that the practical operating bandwidth electronic/electrical devices. Noise immunity and emissions per-
(defined by acceptable levels of common mode noise immu- formance is reciprocal, meaning that the cabling system’s abil-
nity due to balance) is approximately 30 MHz. ity to maintain immunity to interference is proportional ➤


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to the system’s potential to radiate. Interestingly, while the outermost conductive element of the cabling—the conduc-
unnecessary emphasis is placed on immunity considerations, tors themselves in a UTP environment, and the overall screen/
it is understood that structured cabling systems do not radi- shield in a screened/fully shielded environment.
ate or interfere with other equipment or systems in the tele- Again, through the means of calculations, what becomes
communications environment. readily apparent is that the common mode impedance is not
Here’s a more detailed look at the various noise disturbers: very well controlled in UTP environments. This impedance
Differential noise disturbers. Alien crosstalk and internal depends on factors such as distance from metallic raceways,
pair-to-pair crosstalk are examples, and must be minimized metallic structures surrounding the pairs, use of non-metallic
through proper cabling-system design. Susceptibility to inter- raceways, and termination location. Conversely, this common
ference from differential mode sources is dependent upon sys- mode impedance is well defined and controlled in screened/
tem balance and can be improved by isolating or separating shielded cabling environments.
conductors that are interfering with each other. Cabling with Importantly, the overall susceptibility of twisted-pair
improved balance—Category 6 and above—exhibits better cables to electric field disturbance depends on both the bal-
internal crosstalk and alien crosstalk performance. Because no ance performance of the cabling and the presence of a screen
cable is perfectly balanced, strategies such as using dielectric or shield. Well-balanced cables (Category 6 and above) should
material to separate conductors or using metal foil to isolate be immune to electromagnetic interference up to 30 MHz. The
conductors are employed to further improve crosstalk perfor- presence of a shield or screen is necessary to avoid electromag-
mance. For example, Category 6A F/UTP cabling is proven to netic interference at higher frequencies, which is an especially
have substantially superior alien crosstalk performance than critical consideration for next-generation applications.
Category 6A UTP cabling because its overall foil construction For example, it is reasonable to model that an emerging
reduces alien crosstalk to virtually zero. Category 7 S/FTP is application using DSP techniques will require a minimum
proven to have substantially superior pair-to-pair and alien SNR of 20 dB at 100 MHz. Because the minimum isolation
crosstalk performance than any Category 6A cabling design yielded by balance alone is also 20 dB at 100 MHz, the addition
because its individual foiled twisted-pair construction reduc- of a screen or shield is necessary to ensure this application has
es pair-to-pair and alien crosstalk coupling to virtually zero. sufficient noise immunity headroom for operation.
These superior crosstalk levels could not be achieved solely Ground loops. These develop when there is more than one
through compliant balance performance. ground connection, and the difference in common mode volt-
Environmental noise disturbers. Environmental noise age potential at these ground connections induces noise on the
is electromagnetic noise made up of magnetic fields gener- cabling. It is a misconception that common mode noise from
ated by inductive coupling, and electric fields generated by ground loops can only appear on screens and shields; this noise
capacitive coupling. Magnetic field coupling occurs at low regularly appears on the twisted pairs as well. A key point about
frequencies, such as 50 or 60 Hz, where the balance of the the voltage generated by ground loops is that its waveform is
cabling system is more than sufficient to ensure immunity. Its directly related to the profi le of the building’s alternating
impact can be ignored for all types of balanced cabling. Elec- current (AC) power. In the United States, the primary noise
tric fields, however, can produce common mode voltages on frequency is 60 Hz and its related harmonic, which is often
balanced cables depending on their frequency. The magni- referred to as AC “hum.” In other regions of the world, the pri-
tude of the voltage induced can be modeled, assuming that the mary noise frequency is 50 Hz and its related harmonic.
cabling system is susceptible to interference in the same Because each twisted pair is connected to a balun transformer
manner as a loop antenna. and common mode noise rejection circuitry at both ends of
Mathematical formulas demonstrate that a 60-Hz signal the circuit—the network interface card (NIC) and the network
results in an electric field disturbance that can only be mea- equipment—differences in the turn ratios and common mode
sured in the thousands-of-mV (millivolt) range, while sources ground impedances can result in common mode noise. The
operating in the MHz range can generate a fairly large electric magnitude of the induced noise on the twisted pairs can be
field disturbance. For reference, 3 Volts/meter (V/m) is consid- reduced, but not eliminated, through the use of common mode
ered to be a reasonable approximation of the average electric terminations, chokes, and filters within the equipment.
field present in a light industrial/commercial environment, and Ground loops induced on the screen/shield typically
10 V/m is considered to be a reasonable approximation of the occur because of a difference in potential between the ground
average electric field present in an industrial environment. connection at the telecommunications grounding busbar
The loop area is the one variable that impacts the magnitude (TGB) and the building ground connection provided through
of the voltage coupled by the electric field. Common mode cur- the network equipment chassis at the work-area end of the
rents generated by an electric field induce unwanted signals on cabling. Note that it is not mandatory for equipment ➤


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1990s
1970s Shielded
“Vampire” Modular
Tap Jack

1980s
4 Position
Data
Connector

Follow The Leader In Shielded Technology

The new AMP-TWIST Jack is our latest
shielded product evolution. It can be
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Tyco Electronics has always been forward, have been the leading Proceed With Confidence
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and manufacturing quality shielded brand that knows shielded best! Visit
communications products for more Tyco Electronics has always believed www.ampnetconnect.com to see why
than three decades. In fact, we what the industry is just now a high performance 10 G Shielded
introduced our first fully shielded realizing, that a Shielded System is Cabling System from Tyco Electronics
twisted pair cabling products in the by far the best choice for today’s is the best choice for your structured
early ‘80s – and from that point 10 G performance requirements. cabling needs.

Tyco Electronics, TE Logo, AMP AMP NETCONNECT, NETCONNECT, and AMP-TWIST are trademarks.
,
Other products, logos, and company names mentioned herein may be trademarks of their respective owners.

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