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De-Mystifying Cabling Specifications From 5e to 7A

By Valerie Maguire (Updated June 2009)

About the Author

Valerie Maguire

Valerie Maguire, BSEE holds the position of Director of Standards & Technology at Siemon. Her expertise is focused on balanced twisted-pair and optical fiber telecommunications cabling and transmission theory. She is Vice Chair of the TIA TR-42 Telecommunications Cabling Systems Engineering Committee, Vice Chair of the TIA TR-42.7 Copper Cabling Subcommittee, TIA TR-42 appointed liaison to IEEE 802.3, Treasurer of the IEEE 802.3 Ethernet Working Group, Secretary of the IEEE 802.3 Maintenance Task Force, and clause 1 editor of IEEE Std 802.3-2012. In addition, Valerie has authored over 45 technical articles and engineering papers, holds one U.S. Patent, received the 2008 Harry J. Pfister Award for Excellence in Telecommunications, and was named one of CI&M's Top 20 Positive Contributors to the Cabling and Networking Industry.

Structured cabling standards specify generic installation and design topologies that are characterised by a "category" or "class" of transmission performance. These cabling standards are subsequently referenced in applications standards, developed by committees such as IEEE and ATM, as a minimum level of performance necessary to ensure application operation. There are many advantages to be realised by specifying standards-compliant structured cabling. These include the assurance of applications operation, the flexibility of cable and connectivity choices that are backward compatible and interoperable, and a structured cabling design and topology that is universally recognised by cabling professionals responsible for managing cabling additions, upgrades, and changes.

The Telecommunications Industry Association (TIA) and International Organization for Standardization (ISO) committees are the leaders in the development of structured cabling standards. Committee members work hand-in-hand with applications development groups to ensure that new grades of cabling will support the latest innovations in signal transmission technology. TIA Standards are often specified by North American end users, while ISO Standards are more commonly referred to in the global marketplace. In addition to TIA and ISO, there are often regional cabling standards groups such as JSA/JSI (Japanese Standards Association), CSA (Canadian Standards Association), and CENELEC (European Committee for Electrotechnical Standardization) developing local specifications. These regional cabling standards groups contribute actively to their country's ISO technical advisory committees and the contents of their Standards are usually very much in harmony with TIA and ISO requirements.

While the technical requirements of TIA and ISO are very similar for various grades of cabling, the terminology for the level of performance within each committee's Standards can cause confusion. In TIA Standards, cabling components (e.g. cables, connecting hardware, and patch cords) are characterised by a performance "category" and are mated to form a permanent link or channel that is also described by a performance "category". In ISO, components are characterised by a performance "category" and permanent links and channels are described by a performance "class". TIA and ISO equivalent grades of performance are characterised by their frequency bandwidth and are shown in table 1.

Table 1: TIA and ISO Equivalent Classifications
Frequency Bandwidth TIA (Components) TIA (Cabling) ISO (Components) ISO (Cabling)
1 - 100 MHz Category 5e Category 5e Category 5e Class D
1 - 250 MHz Category 6 Category 6 Category 6 Class E
1 - 500 MHz Category 6A Category 6A Category 6A Class EA
1 - 600 MHz n/s n/s Category 7 Class F
1 - 1,000 MHz n/s n/s Category 7A Class FA

When faced with the daunting task of upgrading an existing network or designing a new building facility, cabling experts are encouraged to look to the Standards for guidance on performance and lifecycle considerations. Also consider cabling lifecycles and total cost of ownership. Both TIA and ISO state that the cabling systems specified in their Standards are intended to have a useful life in excess of 10 years. Since applications, such as Ethernet, typically have a useful life of 5 years, it is recommended practice to specify cabling systems that will support two generations of network applications. For most commercial building end-users, this means specifying a cabling plant that is capable of supporting 1000BASE-T (Gigabit Ethernet) today and a planned upgrade to 10GBASE-T in 5 years.

TIA categories and ISO classes of structured cabling that are recognised for the support of data-speed applications are specified in the Standards listed in Table 2.

Table 2: TIA and ISO Standards References

TIA Cabling Standards
Category 5e ANSI/TIA/EIA-568-B.2, Commercial Building Telecommunications Standard
Part 2: Balanced Twisted pair Cabling Components, 2001
Category 6 ANSI/TIA/EIA-568-B.2-1, Commercial Building Telecommunications Standard, Part 2.
Addendum 1: Transmission Performance Specifications for 4 Pair 100 Ohm category 6 cabling, 2002
Category 6A ANSI/TIA-568-B.2-10, Commercial Building Telecommunications Standard Part 2:
Addendum 10: Transmission Performance Specifications for 4 Pair 100 Ohm Augmented Category 6 Cabling, 2008
ISO Cabling Standards
Class D ISO/IEC 11801, 2nd Ed., Information technology - Generic Cabling for Customer Premises, 2002
Class E ISO/IEC 11801, 2nd Ed., Information technology - Generic Cabling for Customer Premises, 2002
Class EA Amendment 1 to ISO/IEC 11801, 2nd Ed., Information technology - Generic Cabling for Customer Premises, 2008
Class F ISO/IEC 11801, 2nd Ed., Information technology - Generic Cabling for Customer Premises, 2002
Class FA Amendment 1 to ISO/IEC 11801, 2nd Ed., Information technology - Generic Cabling for Customer Premises, 2008

It is important to remember that TIA and ISO Standards are copyright protected and are not available in the public domain. Copies of these Standards can be purchased online through IHS Global Engineering Documents.

Category 5e/Class D

Category 5e/class D cabling requirements were first published in 2000 in order to address the additional transmission performance characterisation required by applications such as 1000BASE-T that utilise bi-directional and full four-pair transmission schemes. The Standard added headroom to category 5 performance limits and characterised several new transmission criteria that were required for support of Gigabit Ethernet over a worst case four-connector channel (the 1000BASE-T application was originally targeted for operation over category 5 channels having just two connectors). To ensure that additional performance margins were satisfied, category 5e/class D specifications added headroom to the parameters of NEXT loss, ELFEXT, and return loss and introduced the characterisation of crosstalk using power summation, which approximates the total crosstalk present when all pairs are energized as in a four-pair transmission scheme.

Although no longer recognised by the Standards for new installations, a substantial number of installed category 5 channels are likely to support the 1000BASE-T application. Information on the qualification of legacy category 5 installations for this application can be found in annex D of ANSI/TIA/EIA-568-B.2.

Category 6/Class E

The majority of structured cabling specified for new buildings in the past 5 years has been category 6/class E rated because it provided the maximum performance headroom and return-on-investment. Category 6/class E cabling delivered double the signal-to-noise margin (attenuation-to-crosstalk margin is positive to 200 MHz) of category 5e/class D cabling and provided the performance headroom desired by end-users to ensure that their cabling plant could withstand the rigors of the cabling environment and still support 1000BASE-T when it was time for an application upgrade. The category 6/class E cabling specification development process also brought to light the need to limit the conversion of differential mode signals to common mode signals and vice versa through the characterisation of component balance, resulting in cabling systems with improved electromagnetic compatibility (EMC) performance.

Although, category 6/class E cabling was primarily targeted to support 100BASE-T and 1000BASE-T applications, the good news is that some of the installed base of category 6/class E cabling can support the 10GBASE-T application. The TIA TSB-155 and ISO/IEC 24750 technical bulletins identify the additional performance headroom, as well as applicable field qualification test requirements and procedures, which must be satisfied by the installed base of category 6/class E cabling in order to support the 10GBASE-T application.

Since the digital signal processing (DSP) capabilities of the 10GBASE-T application result in full internal pair-to-pair crosstalk cancellation, this application is particularly sensitive to undesired signal coupling between adjacent components and cabling. This coupling is called alien crosstalk and the characterisation of alien crosstalk in the installed category 6/class E cabling plant is the main focus of the TIA TSB-155 and ISO/IEC 24750 technical bulletins. Because the alien crosstalk in category 6/class E UTP cabling is extremely dependent upon installation practices (e.g. bundling, the use of tie-wraps, and pathway fill), performance values were developed based upon a "typical" worst case environment. The result is that 10GBASE-T should operate over category 6/class E UTP channel lengths of up to 37 meters and may operate over channel lengths of 37 to 55 meters of category 6/class E UTP cabling depending upon the actual alien crosstalk levels present. Since the overall foil in category 6/class E F/UTP cabling designs significantly reduces alien crosstalk, these length limitations are not applicable to F/UTP cabling.

TIA TSB-155 and ISO/IEC 24750 also specify recommended mitigation practices in the event that an installed category 6/class E channel does not satisfy the minimum alien crosstalk levels. Mitigation techniques include using non-adjacent patch panel ports to support the 10GBASE-T application, separating or using improved equipment cords, using F/UTP equipment cords, unbundling cables, reconfiguring cross-connects as interconnects, and replacing category 6/class E components with category 6A/class EA components.

Category 6/class E cabling is not recommended for new installations targeted for support of the 10GBASE-T application. The reason for this is that, while field test devices for determining compliance to the new PSANEXT loss and PSAACRF (previously known as PSAELFEXT loss) parameters are just now being introduced to the market, the test methodology remains extremely time-consuming, overly onerous to implement, and may not be fully conclusive. Furthermore, in a majority of installations, alien crosstalk mitigation will be required. Often, the recognised mitigation methods cannot be easily implemented due to existing pathway fill restrictions and the potential need to replace components. In addition, there is no guidance on qualification procedures for large installations or future MAC work.

Since the category 6/class E Standard was published in 2002, it is at the halfway point of its targeted 10-year lifecycle. Today's cabling specifiers are looking to even higher performing grades of cabling to ensure maximum performance and return-on-investment.

Category 6A/Class EA

Video: Category 6A Termination Process (for Z-MAX outlets)

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Representative products: Category 6A Shielded Outlets and Category 6A UTP Outlets

Category 6A/class EA cabling requirements address the extended frequency bandwidth and alien crosstalk headroom required to support 10GBASE-T over 100 meters of cabling containing up to four-connectors. Category 6A/class EA cabling delivers positive signal-to-alien crosstalk margin up to 500 MHz and is recommended as the minimum grade of cabling capable of withstanding the rigors the cabling environment and supporting 10GBASE-T when it is time for an application upgrade. Balance requirements for channels and permanent links are also specified for the first time, thereby ensuring better electromagnetic compatibility (EMC) performance than any previous generation of cabling.

Performance headroom has been incorporated into all transmission parameters, including power sum alien crosstalk, and both laboratory and field test qualification methods are specified for category 6A/class EA cabling. Average power sum alien crosstalk across all four-pairs is specified for use by the IEEE committee in their channel capacity modeling. It is interesting to note that the term "equal level far-end crosstalk loss" (or ELFEXT loss) previously used in TIA specifications has been replaced by "attenuation to crosstalk ratio, far-end" (or ACRF). The intent of this change is for TIA to harmonize with the ISO terminology and more accurately describe the actual test measurement configuration.

Category 6A/class EA cabling provides the maximum return-on-investment when the calculations are performed using a 10-year lifecycle.

Class F

Class F requirements were published in 2002 and describe performance criteria for a fully shielded media type (i.e. cabling with an overall shield and individually shielded pairs). Category F cabling delivers positive attenuation-to-crosstalk margin up to 600 MHz and offers unsurpassed electromagnetic capability (EMC) performance because of its shielded construction.

Due to its ease of use, performance headroom, ability to support multiple applications under one sheath, and its specification as the recommended category 7 interface in the ISO 15018 Standard, the non-RJ style plug and socket interface specified in IEC 61076-3-104:2002 is the most commonly specified category 7 connector. This interface is commercially available from multiple manufacturers whose products are interoperable. There is significant evidence that the cabling industry and applications developers are ready to adopt fullyshielded cabling. For example, class F cabling was identified as the copper media of choice in one IEEE new application call-for-interest and the published ISO/IEC 14165-114 application Standard, entitled, "A Full Duplex Ethernet Physical Layer Specification for 1000 Mbit/s operating over balanced channels Class F (Category 7 twisted pair cabling)", specifies operation over a minimally rated class F channel.

It is interesting to note that, although TIA is not actively developing a standard for category 7 at this time, it is acceptable to specify class F cabling in North American and other markets. The rationale for this is that, in addition to being recognised by BICSI, NEMA, IEEE, and other standards organisations, class F is simply a superset of TIA category 6A requirements. Field test requirements and adapters for class F cabling qualification have been commercially available since 2002.

The advantage that class F has over other grades of cabling is that it is targeted for support of next generation applications beyond 10GBASE-T. Class F cabling is the only media to have a 15-year lifecycle and class F cabling provides the maximum return-on-investment when calculations are performed using a 15-year lifecycle.

Category 7/Class F Interface Implementation Case Studies

Class FA

Class FA requirements are based upon the existing class F cabling requirements and category 7 non-RJ style plug and socket interface. The significant enhancement in class FA specifications is the extension of the frequency bandwidth of characterization from 600 MHz to 1,000 MHz. This enhancement allows class FA cabling to be uniquely capable of supporting all channels of broadband video (e.g. CATV) that operate up to 862 MHz. It is likely that all fully-shielded cabling solutions specified in the near future will be class FA.

Applications Support

Table 3 summarizes cabling types capable of supporting commonly specified applications over 100-meter, four-connector topologies.

Table 3: Applications Chart
  Category 5e Class D Category 6 Class E Category 6A Class EA Class F Class FA
4/16 MBPS Token Ring x x x x x
10BASE-T x x x x x
100BASE-T4 x x x x x
155 MBPS ATM x x x x x
1000BASE-T x x x x x
TIA/EIA-854   x x x x
10GBASE-T     x x x
ISO/IEC 14165-144       x x
Broadband CATV         x

Performance Comparison Chart:

Table 4 provides comparative channel performance data at 100 MHz for category 5e/class D, category 6/classE, category 6A/class EA, class F, and class FA channels. Where there is a slight difference between TIA and ISO performance limits, ISO performance limits are indicated in parenthesis.

TABLE 4: Industry Standards Performance Comparison at 100 MHz for Channels
  Category 5e Class D Category 6 Class E Category 6A Class EA Class F Class FA4)
Frequency Range (MHz) 1 - 100 1 - 250 1 - 500 1 - 600 1 - 1,000
Insertion Loss (dB) 24.0 21.3/21.7 20.9 20.8 20.3
NEXT Loss (dB) 30.1 39.9 39.9 62.9 65.0
PSNEXT Loss (dB) 27.1 37.1 37.1 59.9 62.0
ACR (dB) 6.1 18.6 18.6 42.1 46.1
PSACR (dB) 3.1 15.8 15.8 39.1 41.7
ACRF1) (dB) 17.4 23.3 23.3/25.5 44.4 47.4
PSACRF2) (dB) 14.4 20.3 20.3/22.5 41.4 44.4
Return Loss (dB) 10.0 12.0 12.0 12.0 12.0
PSANEXT Loss (dB) n/s n/s 60.0 n/s 67.0
PSAACRF (dB) n/s n/s 37.0 n/s 52.0
TCL (dB) n/s n/s 20.3 20.3 20.3
ELTCTL (dB) n/s n/s 0.5/0 3) 0 0
Propagation Delay (ns) 548 548 548 548 548
Delay Skew (ns) 50 50 50 30 30
  1. Specified as ELFEXT for category 5e/class D and category 6/class E.
  2. Specified as PSELFEXT for category 5e/class D and category 6/class E.
  3. ELTCTL is specified at 30 MHz.
  4. Industry specifications for category 6A/class EA and class FA cabling are not published yet.


When designing and installing structured cabling systems, choose the strongest foundation to support your present and future network applications needs. To ensure support of emerging technologies that utilise the latest advances in signaling schemes, it is critical to be as informed as possible. Trust the TIA and ISO standards developmental groups to specify complete cabling criteria capable of providing applications assurance for tomorrow's technologies today.

Important Definitions

Alien Crosstalk

Unwanted signal coupling from one component, channel, or permanent link to another is defined as alien crosstalk. Since alien crosstalk is an indicator of differential (or balanced) signal coupling, alien crosstalk cannot be adversely impacted by common mode noise (e.g. noise from motors or florescent lights) that is present in the environment. Alien crosstalk is only specified by the Standards as a power sum parameter for components and cabling to approximate the energy present when all pairs are energized. Power sum alien crosstalk measured at the near-end is called power sum alien near-end crosstalk loss (PSANEXT loss) and power sum alien crosstalk measured at the far-end is called power sum alien attenuation to crosstalk ratio, far-end (PSAACRF). High power sum alien crosstalk levels can compromise the operation of the 10GBASE-T application.

Attenuation to Crosstalk Ratio, Far-End (ACRF) (previously know as ELFEXT)

Pair-to-pair far-end crosstalk (FEXT) loss quantifies undesired signal coupling between adjacent pairs at the far-end (the opposite end of the transmit-end) of cabling or a component. ACRF is calculated by subtracting the measured insertion loss from the measured far-end crosstalk loss and yields a normalized value that can be used to compare cable and cabling performance independent of length. Poor ACRF levels can result in increased bit error rates and/or undeliverable signal packets. Note that NEXT loss margin alone is not sufficient to ensure proper ACRF performance.

Attenuation to Crosstalk Ratio (ACR)

A critical consideration in determining the capability of a cabling system is the difference between insertion loss and near-end crosstalk (NEXT) loss. This difference is known as the attenuation to crosstalk ratio (ACR). Positive ACR calculations mean that transmitted signal strength is stronger than that of near-end crosstalk. ACR can be used to define a signal bandwidth (i.e. 200 MHz for category 6) where signal to noise ratios are sufficient to support certain applications. It is interesting to note that digital signal processing (DSP) technology can perform crosstalk cancellation allowing some applications to expand useable bandwidth up to and beyond the point at which calculated ACR equals zero. Even so, the maximum frequency for which positive ACR is assured provides a benchmark to assess the useable bandwidth of twisted-pair cabling systems.


Twisted-pair transmission relies on signal symmetry or "balance" between the two conductors in a pair. Maintaining proper balance ensures that cabling systems and components do not emit unwanted electromagnetic radiation and are not susceptible to electrical noise. Component balance requirements are specified for category 6/class E cabling. Component and cabling balance requirements are specified for category 6A/class EA and higher grades of cabling. Balance may be characterized by longitudinal conversion loss (LCL), longitudinal conversion transfer loss (LCTL), transverse conversion loss (TCL), or equal level transverse converse transfer loss (ELTCTL).

Equal Level Far-End Crosstalk (ELFEXT)

See definition for Attenuation to Crosstalk Ratio, Far-End.

Insertion Loss (Attenuation)

Insertion loss is a measure of the decrease in signal strength along the length of a transmission line. Ensuring minimal signal attenuation is critical because digital signal processing (DSP) technology can not compensate for excessive signal loss.

Near-End Crosstalk (NEXT) Loss

Pair-to-pair near-end crosstalk (NEXT) loss quantifies undesired signal coupling between adjacent pairs at the near-end (the same end as the transmit-end) of cabling or a component. Excessive NEXT loss can be especially detrimental to applications that do not employ crosstalk cancellation digital signal processing (DSP) technology.

Power Sum

All pair-to-pair crosstalk parameters can be expressed as a power summation, which approximates the level of undesired internal signal coupling present when all pairs are energized. Power sum NEXT loss, ACRF, ANEXT loss, and AACRF characterisation confirms that the cabling is significantly robust to minimize crosstalk from multiple disturbers. This type of characterisation is necessary to ensure cabling compatibility with applications that utilize all four pairs for transmitting and receiving signals simultaneously such as 1000BASE-T and applications that are sensitive to alien crosstalk such as 10GBASE-T.

Propagation Delay & Delay Skew

Propagation delay is the amount of time that passes between when a signal is transmitted and when it is received at the opposite end of a cabling channel. The effect is akin to the delay in time between when lightning strikes and thunder is heard - except that electrical signals travel much faster than sound. Delay skew is the difference between the arrival times of the pair with the least delay and the pair with the most delay. Transmission errors that are associated with excessive delay and delay skew include increased jitter and bit error rates.

Return Loss

Return loss is a measure of the signal reflections occurring along a transmission line and is related to impedance mismatches that are present throughout a cabling channel. Because emerging applications such as 1000BASE-T and 10GBASE-T rely on full duplex transmission encoding schemes (transmit and receive signals are superimposed over the same conductor pair), they are sensitive to errors that may result from marginal return loss performance.

Transfer Impedance

Shield effectiveness characterises the ability of screened (F/UTP) and fully-shielded (S/FTP) cables and connecting hardware to maximize immunity from outside noise sources and minimize radiated emissions. Transfer impedance is a measure of shield effectiveness; lower transfer impedance values correlate to better shield effectiveness

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