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Note: The following technical article was current at the time it was published. However, due to changing technologies and standards updates, some of the information contained in this article may no longer be accurate or up to date.


John Siemon on Category 6/Class E Cabling


The starting point for category 6 dates back to the Munich meeting of International Standards Committee ISO/IEC JTC 1/SC25/WG 3 in September of 1997. At this meeting, there was agreement to include two new performance classes for balanced cabling in the second edition of international cabling standard ISO/IEC 11801. One of these new cabling types, "class E" is targeted as being representative of the best performance achievable with unshielded and screened twisted-pair cabling.

Just as class D of ISO/IEC 11801 is representative of worst case 4-connector, 100-meter channel implementations using category 5 cable and connecting hardware, class E performance requirements are based on the same worst case cabling model using category 6 components. According to an ISO/IEC press release:

"The new channel specifications will allow manufacturers to start development of the required cabling components. Industry forums and applications standards groups will be able to base future developments on the performance specifications of these new balanced cabling classes…"

This decision spawned a flurry of activity on development of system and component specifications targeted to meet the goals set forth for class E and category 6. In Europe, CENELEC committee TC215, and in North America, TIA TR42.1 (formerly TR41.8.1) continue to drive these specifications forward in coordination with ISO/IEC with the goal of international harmonization. One difference between the TIA approach and other cabling standards is that TIA uses the "category" designation for both components and cabling. Other international standards organizations use "categories" to specify cables and connecting hardware, and "classes" to specify minimum requirements for cabling links and channels. Despite this difference in terminology, the goal is to align cabling and component requirements between TIA category 6 and ISO/IEC category 6/class E. This international involvement will make class E and category 6 the first set of comprehensive cabling requirements that are representative of cooperation between cabling experts throughout the world, from inception through standards approval.


In the mid-60's the future founder of Intel, Gordon Moore observed that the number of transistors on a memory chip doubles every 18 to 24 months. This observation still holds true today and is now known as Moore's Law. The implications of Moore's law on the pace of change in the computer industry are staggering. For example, from 1971 to 1997, the number of transistors on an Intel chip has increased by 190,000%. Although Moore's original observation was provided in the context of transistor counts, it is undisputed that computing power also increases exponentially with time. Does the same hold true for data rates over local area networks? History tells us that it does.

Figure 1 shows that, since the sixties, LAN transmission rates have increased by five orders of magnitude (105). Continued gains in LAN transmission speed are a natural byproduct of ongoing increases in transistor counts and computing power.

Figure 1

LAN Transmission Rates

As computer technology progresses, it creates opportunities in other related industries. A case in point is telecommunications cabling. The early nineties were marked by unprecedented advancement in the field of telecommunications cabling, going from a single set of UTP specifications in the first edition of TIA-568 to the first of several specifications for categories 3, 4 and 5 less than one year later. Incremental performance improvements in attenuation and crosstalk made the benefits of category 5 self-evident, even though there were no applications that called for this level of performance when it was first introduced. As category 5 became recognized as the best choice for IT cabling to the desk, unrelenting demand for greater information throughput prompted LAN applications to exploit its untapped bandwidth. New applications standards such as 100BASE-T and 155 Mb/s ATM followed, but it was not until 1000BASE-T that LAN technology tested the limits of category 5 cabling through the use of 4-pair bi-directional signal transmission.

Although it is not clear that 1000BASE-T is the end of the line for category 5, it is clear that the ability of LAN developers to continue adding zeros to the bit rate of future networking technologies will be severely handicapped without parallel advancements in cabling system performance. These factors have led to the realization that cabling system providers and standards bodies must look well beyond today's "killer" LAN application to prepare for those that will be introduced long after the cabling is installed. To do so, it is necessary to create new classifications of cabling that are specifically designed to support future networking technology. Enter category 6.


If the only consideration in selecting a cabling media were its ability to support high-speed transmission, the best choice would clearly be singlemode fiber. Even though it far surpasses other types of cabling in terms of bandwidth, the acceptance of singlemode fiber for a horizontal cabling is practically nil. Why? Because bandwidth is only one of many factors that drive an organization's decision to install a specific type of cabling.

Other important factors include its ability to:

  • provide a reliable and durable platform for information transfer;
  • accommodate ongoing infrastructure changes; and
  • support a wide array of telecommunications applications and legacy equipment.

In addition to these factors, there is cost. Cost of the cable and connectors, cost of installation/changes, and cost of the network equipment to which it connects are all-important factors to be considered before a decision is made.

Twisted-pair media owes its continued dominance in horizontal cabling to the fact that it has not yet been surpassed in terms of reliability, durability, adaptability, versatility or cost. Transmission performance, once thought to be its Achille's heel, has turned into one of its greatest assets. The fact that it can be used to access all of the generations of technology that both Bell and Moore envisioned, is the strongest argument for continued investment in twisted-pair cabling. Category 6 allows twisted-pair cabling to keep its promise to be there for future generations of networking applications.


Better attenuation, crosstalk, return loss and balance performance all add up to providing LAN equipment engineers with fewer constraints when developing new applications. This additional freedom can be used to develop more cost-effective implementations of established LAN technologies, and for achieving even higher bit rates for new applications. Improved performance makes it possible to develop new circuit designs that support existing transmission rates without complex encoding or signal processing technologies. This reduction in circuit complexity has the benefit of lowering the entry cost for Gigabit Ethernet and other advanced LAN technologies. Also, by using all of the tools at the disposal of LAN equipment designers, such as advanced encoding and signal processing, category 6 holds the promise of enabling LANs to surpass the gigabit barrier over unshielded and screened twisted-pair.

Gigabit Ethernet and other applications have taught us the importance of providing a fully specified and well-balanced suite of transmission requirements. Whereas category 5 was developed with two primary parameters in mind - attenuation and NEXT loss, category 6 includes new component and system requirements that refine all transmission parameters to the greatest extent possible. The result is a fully specified media that is specifically designed and modeled to enable simultaneous bi-directional transmission over all four pairs.


One risk associated with installing "category 6" cabling prior to standards approval is the possibility that the specified requirements will be more severe, or that new parameters will be added that are not accounted for in a specific supplier's "system" offering. To put this risk into perspective, it is important to note that since September 97, the target category 6 cut-off frequency of 200MHz for positive power sum ACR has not changed. Although the models used to provide linkage between component and system requirements continue to be refined by fractions of decibels, the underlying foundation for category 6 and class E requirements is extremely stable.

The longer these values exist, the more entrenched they become as design targets for cable and connecting hardware. For example, the proposed crosstalk requirement for category 6 connecting hardware has remained unchanged since 1997. New parameters such as balance and insertion loss deviation are under consideration by standards groups and are accounted for in many present day "category 6" component and system offerings.

Another risk is that different manufacturer's category 6 components will not be compatible with one another, or that the components will not be backward compatible with category 5/5e. It is well recognized within the standards community that backward compatibility and interoperability are interrelated and are essential to the success of category 6. Significant progress has been made in gaining consensus support for outlet and test plug requirements that specifically address these issues. Backward compatibility and interoperability cannot be assured without well-defined test methodologies and specifications for test plugs used to qualify category 6 outlets. By encompassing these new requirements within those used for qualification of category 5/5e outlets, the goal of backward compatibility and interoperability can be met.


Category 6 is a sound investment because it is built on the same foundation as category 5 and all of its predecessors. It provides all of the physical advantages of category 5, such as the same interface, installation practices and test methodologies, but with performance that was thought to be unachievable just a few years ago. One objective of category 6 and class E is to provide at least twice as much ACR bandwidth, and to do so using the same building blocks that led to global acceptance of category 5. Other benefits include significantly improved return loss, far-end crosstalk and balance.

As standards bodies build consensus for category 6 and class E requirements, increasing numbers of IT professionals will recognize that the risk of not installing cabling that offers category 6 performance on new installations far outweighs the risk of being constrained by older technology.

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