Shielded Systems versus Unshielded Systems

Now that copper 10-Gigabit active devices are becoming readily available system designers and
IT managers are being tasked with implementation of 10G-Gigabit Ethernet networks. Industry
standards for 10G Ethernet have been defined for some time now. The IEEE 802.3an 10GBASE-T standard
was published in 2006 and the Telecommunications Industry Association (TIA) ratified
theTIA-568-B.2-10 standard in April of 2008. The ISO group also ratified a Category 6A channel for
10GBASE-T in its ISO 11801:2002 Amendment 1 for Class EA. It’s important to point out that these
standards apply to both unshielded and shielded cabling systems.

CAT 6A shielded systems are becoming the ideal choice for the transmission of 10GBASE-T over copper
cabling. This article focuses on the well know advantages of shielded CAT 6A cabling systems over
unshielded CAT 6A cabling systems.

The main advantage of a CAT 6A shielded system is the suppression of alien crosstalk (AXT). AXT is
defined as unwanted signal coupling from one balanced twisted-pair component, channel, or permanent
link to another. AXT is not a problem for applications designed to operate over lower frequency
ranges specified for CAT 5e (100MHz) or CAT 6 (250Mz), but AXT becomes an issue at higher
frequencies required for Cat 6A (500MHz). The standard committees all agree that AXT is the single
most significant performance barrier for the transmission of 10GBASE-T over copper cabling.

There are two known methods to mitigate AXT. The first method is obtained by adding space between
cables and port outlets. Cable manufactures typically increase the cable’s outer jacket diameter to
create space between adjacent cables. The other and more effective mitigation method is obtained by
wrapping a metal foil around the inner twisted pairs (shielded cable). Shielded jacks are typically
achieved by manufacturing jacks from die cast zinc, stamped metal or plated plastic.

Furthermore, CAT 6A UTP cabling systems require AXT field testing to insure 10G performance. Most
experts agree that it’s practically impossible to100% field verify a CAT 6A UTP system. AXT testing
is a costly and time consuming process. As such, several cabling and connectivity manufac- tures do
not require AXT testing as part of their CAT 6A UTP warranty, however, bypassing this step would be
a bad decision on such a large investment. As long as proper installation procedures are followed
CAT 6A shielded systems do not require AXT testing because the shielding virtually elimi- nates
AXT. Lab and field testing has verified that shielded CAT 6A systems pass AXT requirements with
significant headroom under worst configurations whereas CAT 6A UTP systems provide only marginal
passes under normal configurations. Therefore, it’s safe to conclude that a CAT 6A shielded system
can be installed with confidence that AXT will not be an issue.

CAT 6A shielded systems offer the added benefit of providing excellent protection against electro-
magnetic and radio magnetic frequencies (EMI/RFI). This protection is essential for eliminating EMI/RFI noise from sources such as machinery, generators, or medical imaging equipment, making
shielded systems an ideal choice for industrial environments and healthcare facilities. EMI protec-
tion also leads to improved security. The electromagnetic fields emitted by unshielded cables can
be
detected by equipment used to eavesdrop and monitor network traffic. Even when risk is minimal,
IT managers choose shielded systems for high security networks to eliminate any risk of external
eavesdropping. Shielded systems are by far the best choice for military networks.

Another advantage of a CAT 6A shielded cable is its smaller diameter as compared to CAT 6A
UTP cable. The typical diameter of a CAT 6A shielded cable is .29” (7.2mm), whereas the typical
diameter of a CAT 6A UTP cable is .35” (9mm). Cable diameters can have a major impact when
planning for 10G Ethernet networks. System designers must pay careful attention when designing
containment systems for CAT 6A cabling systems. Pathways must be designed to accommodate the
larger cable diameters, heavier cable weight and the cable’s minimum bend radius. Cable pathways
and cable managers designed for CAT 5e or CAT 6 cable may not be suitable for CAT 6A UTP cables.
Some cable manufactures will argue that the diameter difference between CAT 6A UTP and CAT 6A
shielded cable is insignificant. However, cable diameters do have a significant impact on perimeter
raceways, cable trays, furniture systems, and pathways. System designers should refer to the latest
ANSI/TIA/EIEA-569-B, Commercial Building Standard for Telecommunications Pathways and Spaces
or the ISO/IEC 18010, Information Technology – Pathways and Spaces for Customer Premises
Cabling.

A drawback that designers must plan for with CAT 6A UTP cable containment is that it’s not recom-
mended to mix CAT 6 UTP, CAT 5e UTP, or even multiple manufacturer’s CAT 6A UTP cables due to
potential AXT issues. There are basically two options here: either clear existing containment or
build a new containment system. Mixing CAT 6A shielded cable with CAT 6 UTP or CAT 5e UTP cables
isn’t an issue.

Misconceptions such as shielding systems being costly and difficult to install have prevailed for
decades. The truth is that installing CAT 6A UTP systems can be more tedious and troublesome due to
more rigid and larger cables diameters. CAT 6A shielded cable typically does cost more than CAT
6A UTP and shielded jacks typically do require a few more steps to terminate than unshielded jacks.
However, when the cost of AXT testing, reduced cable tray fill, and reduced cabinet densities due
to larger cable diameters are considered, the benefits of a CAT 6A UTP cabling system quickly fade
away.

Proper bonding and grounding is another important aspect for all shielded cabling systems. This
article does not cover the critical aspects or benefits of a properly bonded and grounded structured cabling system. System designers should refer to the ANSI /EIA/TIA 607: Commercial Building Grounding and Bonding Requirements for Telecommunications or the IEC 61000-5-2: Electromag-
netic capability (EMC) – Part 5: Installation and mitigation guidelines – Section 2: Earthing and
bonding, industry standards for proper guidance and recommendations.

In conclusion, in most parts of the world unshielded copper cabling systems have been the predomi-
nate choice for Ethernet networks due to lower material cost and ease of termination. However,
with the emergence of 10GBASE-T, these cabling systems are no longer the best choice due to
issues such as AXT field testing, reduced cable tray capacities, and reduced cabinet densities due
to
larger cable diameters. Shielded systems eliminate these issues and they also provide EMI/RFI and
security benefits that unshielded systems do not. Many structured cabling manufactures who once
only offered unshielded systems now offer shielded systems to address market demands required
for 10G Ethernet networks.