Category 6A Cables, Shielded or Unshielded?

You have decided upon a Category 6A infrastructure to support you network needs.  You realize that 10 gigabit Ethernet is your application of choice or you grasp that at the rate that throughput demand is growing, not preparing for 10 gigabit Ethernet will significantly hinder future network upgrades.  But now, another decision is waiting to be made.  Should you go with an unshielded Category 6A solution or a shielded solution?  What are the main advantages and disadvantages of each?  The purpose of this paper is to identify the strengths and weaknesses of each solution so that the appropriate decision can be made. 

Category 6A is the latest infrastructure performance level to be widely accepted.  Accommodating network speeds that are 10 times that of the previous application (1 gigabit Ethernet), 10 gigabit Ethernet over a Category 6A infrastructure offers the throughput that many users now demand.  This increase in the data burden of that application, however, requires a higher level of performance from the infrastructure than previous solutions were capable of providing.

Category 6A cable, in accordance to the TIA/EIA 568-C.2 standard, is tested from 1 to 500MHz. This wide range of frequency is required to handle the frequencies at with 10GBase-T (10 gigabit Ethernet) operates.   As a result of the higher frequencies utilized by 10GBase-T, alien crosstalk performance parameters are incorporated into the TIA/EIA standard for Category 6A cable.  Alien crosstalk occurs when signal from a cable jumps to an adjacent cable.  Alien crosstalk, like crosstalk that occurs between the pairs within a cable, will have a detrimental impact on cable’s ability to send and receive data packets.  Category 6A is the first cable category standard to include alien crosstalk performance parameters.

Alien crosstalk can be mitigated by a couple approaches.  It can be overcome by creating space between the cores of adjacent cables, usually accomplished by means of adding internal space under the jacket in the case of UTP (unshielded twisted pair) cable, which helps create space between adjacent cable cores, or by using some type of physical barrier to block alien crosstalk.  This barrier is typically some type of metallic tape.  (It is worth noting that if you are researching UTP cables for your Category 6A solution, it is highly recommended to obtain physical samples or any candidate cables.  The use of the term “nominal” to describe cable diameter has increased and sample testing of cable on the market has shown discrepancies between many cables’ actual outside diameter and that which is represented in the company’s marketing literature.)

The ANSI/TIA-568-C.2 standard, which governs the electrical and physical characteristics for category cable states that the cable must be smaller than 0.354 inches in outside diameter, regardless of whether the cable is shielded or unshielded.  Due to the use of space (air) as a barrier against alien crosstalk, UTP cables tend to be larger in diameter than shielded cables. In fact many UTP cable designs fall close to the maximum diameter permitted.  As a result of the larger outside diameters of the UTP cables, larger conduit and hanging devises must be used to support them.  This can add cost to a project as well as necessitate more pathway space for the cables.  UTP cables, however, are an established cable design that is simple to terminate since they do not possess shields and their associated drain wires.  The connective hardware in a UTP solution (jacks and patch panels) can be terminated faster than that for a shielded solution and they cost less.  Unshielded cable also tends to cost less than its shielded counterparts.  These factors, and the belief that bonding and grounding of rack equipment also add cost to the project, lend one to believe that there is a substantial cost savings when choosing a UTP solution over a shielded one.

However, the overall smaller diameter that shielded cables offer, which also require smaller pathways and support hardware, does help offset some cost difference.  Additionally, there are also benefits provided by a shielded solution that may have a significant impact on the performance of the network. 

The UTP designs tend to have larger diameters than their shielded counterparts due to the use of an air gap as a barrier to alien crosstalk versus a shield.

In addition to choosing between shielded or unshielded cables, there are multiple types of shielded cable designs to choose from.   Some manufacturers offer a shielded cable with foil around each of the four individual pairs.  This cable, known as U/FTP (overall unshielded, but foil over twisted-pairs), offers excellent shielding performance, but is more challenging to terminate than other constructions since each pair is individually wrapped in foil.  F/UTP (foil shield over unshielded twisted pairs) cable, like that of HCA’s Category 6A shielded cable, requires a more technologically advanced manufacturing process to build, but is significantly easier to terminate and has a smaller outside diameter than the U/FTP cable. F/UTP cable utilizes a single foil shield wrapped around the cable core and includes a drain wire.  In addition to helping with alien crosstalk mitigation, the shield offers immunity from signal generated by nearby electrical wiring and equipment. Known as EMI (electromagnetic interference) and RFI (radio frequency interference), this interference is generated by motors, light fixtures, electrical wiring and other electronic devises.  As more and more devices become networked, data cabling is finding itself in physical locations that are detrimental to its performance.  Though shielded cables require proper bonding and grounding to ensure performance, this is not an issue since good-practice installation methods (TIA-607-B standard) recommend bonding and grounding of all rack equipment regardless of whether the cable is shielded or unshielded.  And, using shielded jacks and patch panels has never been easier since every leading connectivity manufacturer now has smartly engineered shielded components. 

In summary, you should carefully evaluate your current and future throughput needs before selecting the appropriate network infrastructure.  The infrastructure is the most complicated and costly to replace if upgrading is necessary.  Don’t let it become the bottleneck for network traffic. Basically, if you are installing a cable infrastructure, install the most advanced solution possible.  You may not need it today, but the likelihood that you will absolutely need it down the road is virtually guaranteed.

Some manufacturers provide a third design that offers shield-like protection in an unshielded cable.  These designs are limited to a couple manufacturers and their presence on the market has been relatively short in comparison to standard shielded and unshielded cables. It would appear, based on the limited information available about these designs that thorough vetting by the market itself, versus unilateral conclusions provided in marketing materials from those manufacturers, is still in progress.