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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.

Standards Update

The TIA and ISO Standards development bodies have spent the last months finalizing details on new generic requirements for high bandwidth cabling in preparation for their technical review by the industry. This is no small feat considering the fact that category 6 and 7 cabling offers two and six times the bandwidth capacity of category 5e, respectively. Couple these twisted-pair cabling advances with the revolutionary improvements that have been realized in fiber connectivity and it's clear to see that the Standards have armed the end-user with cabling solutions that will support even the most extreme network demands.

Couple the advances of twisted-pair cabling with the revolutionary improvements that have been realized in fiber connectivity and it's clear to see that the Standards have armed the end-user with cabling solutions that will support even the most extreme network demands.

Category 6 & Category 7

Historically, information transmission rates double every 18 to 24 months. To support this growth, in September of 1997, ISO began formalizing per-formance criteria for cabling systems designed to support positive power sum attenuation-to-crosstalk (PSACR) values to 200 MHz (category 6/class E) and 600 MHz (category 7/class F). At that time, TIA also recognized the urgent demand for a high bandwidth unshielded twisted-pair cabling solution and began concurrent development on category 6. Although TIA has not initiated development of a category 7 solution, there is significant harmonization between the status of the TIA category 6 and ISO class E draft Standards. The latest revisions of the working documents are shown in Table 1.

Table 1

Latest Industry Category 6/Class E and Category 7/Class F Draft Standards

TIA Draft Standards

ISO Draft Standards

Category 6
Transmission Performance
Specifications for 4-Pair 100 ohm Category 6 Cabling

Class E & Class F
ISO/IEC 11801 2nd Edition
Customer Premise Cabling

Draft 6 - April, 2000

N598 - May, 2000

Prepared by:
TR-42.7.1 Copper Cabling Systems
Working Group

Prepared by:
ISO/IEC JTC 1/SC 25/WG 3

Category 7
Not under developement at this time.

 

It is interesting to note that, although the positive PSACR frequency for category 6/class E cabling systems is 200 MHz, due to considerations such as equipment crosstalk cancellation capability, both TIA and ISO will be characterizing these cabling systems to 250 MHz. At this time, ISO class F is characterized to an upper frequency value of 600 MHz.

In conjunction with the cabling objectives outlined in 1997, TIA and ISO have implemented provisions into their draft Standards to ensure that category6/class E and category 7/class F cabling systems will work in harmony with existing generic infrastructures. The achieve this, systems and components are required to be backward compatible with existing categories and classes, as well as be interoperable with components of like categories from different manufacturers. TIA has since devised a test method that provides a benchmark against which active equipment and systems manufacturers can qualify their category 6 plugs and sockets. Compliance to these provisions ensures component interoperability and backward compatibility. Work on a category 7 plug and socket requirement is still pending the final outcome of the ISO/IEC category 7 connecting hardware interface selection process.

The significant differentiator between category 6/class E and category 7/class F is the cabling media. Category 6/class E is generally considered to represent the highest bandwidth capable of being supported by unshielded twisted-pair (UTP) and screened twisted-pair (ScTP) cables; to achieve even greater performance, category 7 cables must utilize a more robust, fully shielded construction which virtually eliminates crosstalk between all pairs up to 600 MHz (see Figure 2). A typical category 7 cable design consists of four 23 AWG (0.55mm) twisted-pairs, each enveloped within a foil wrap. An overall braided sheath typically surrounds the four foil-wrapped pairs. A drain wire may be provided to facilitate grounding. Category 7 fully shielded cable types are sometimes referred to as SSTP ("double shielded twisted-pair") or PiMF ("pairs in metal foil").

Figure 1 - Category 6 Channel PSACR

Although any compliant connecting hardware design may be used at the cross-connect and consolidation/ transition point connections, the connecting hardware interface at the work area has been traditionally defined as an 8-position modular or "RJ-style" interface. This has been done to ensure that the end-user is not subjected to interface designs with uncontrolled fit and dimension. The TIA and ISO communities have agreed that the standard 8 position modular plug/outlet connection will still be specified to support proposed category 6/class E cabling at the telecommunications outlet. Ideally, the ISO Standards development committee would prefer to maintain this interface in their specification of category 7/class F cabling systems as well. However, due to backward compatibility and interoperability concerns, some industry experts considered a category 7 "RJ-style" interface unachievable in a practical operating environment.

Category 6/class E is generally considered to represent the highest bandwidth capable of being supported by unshielded twisted-pair (UTP) and screened twisted-pair (ScTP) cables; to achieve even greater performance, category 7 cables must utilize a more robust, fully shielded construction which virtually eliminates crosstalk between all pairs up to 600 MHz.

As a result, the ISO/IEC/ SC 48/WG 3 technical committee began investigating the capabilities of both an "RJ-style" and a "non RJ-style" connector for use at the work area. In June of 1999, the technical committee selected an "RJ-style" category 7 connector design and The Siemon Company's TERA™ (as the fallback "non RJ-style" category 7 connector design (see Figure 3).

Figure 2 - Cable Media

Category 6 cable is similar in construction to category 5e cable. The exception is that most category 6 cables have a center filler that separates each pair within the jacket.

Category 7 cable is of a different construction than category 5e or 6 cable. Not only is there an overall braid and/or foil around all four pairs, but each pair is individually wrapped in foil.

In the event that the performance feasibility of the "RJ-style" design is not validated, the technical committee will select the Siemon TERA™ as the category 7 Standard's specified work area interface. Regardless of which design is chosen, the committee is chartered to specify complete category 7 work area interface criteria addressing dimensional, transmission, electrical, mechanical, and reliability characteristics by the first quarter of 2001.

The construction of the category 7/ class F media offers some significant performance advantages, particularly with respect to crosstalk, over category 6/ class E cabling. Table 2 provides the latest draft channel requirements provided by TIA and ISO for their next generation of cabling. The third column in the table provides an indication of the signal performance improvement, in volts, realized by category 7/class F cabling over category 6/class E cabling.

At this time, the channel and permanent link performance values for category 6/class E and category 7/class F are firm and unlikely to undergo significant revisions The released TIA and ISO Standards are also expected to specify laboratory test and field verification methods, installation practices, and other considerations such as reliability and durability in addition to transmission performance. The few remaining items that need to be addressed prior to standard publication are generally related to these topics. Table 3 provides a list of items that are still under study by these groups.

The short list of remaining items under study means that the task of developing the category 6/class E and category 7/class F Standards is drawing to a close. At this time, the ISO committee has already processed comments on two drafts of the ISO/IEC 11801 2nd edition and TIA is gearing up to present their draft category 6 Standard for industry ballot review in September of 2000. Barring any unforeseen technical issues, it is likely that TIA and ISO approved category 6/ class E and category 7/class F Standards will be available to the industry in 2001.

Figure 3 - "Non RJ-Style" and "RJ-Style" Category 7 Connectors

Siemon's TERA™ connector has been accepted as the "non RJ-style" category 7 interface. The "RJ-style" category 7 interface is in development and uses four additional pins in the outlet and plug as seen above.

Small Form Factor (SFF) Fiber Connectors

In March of 2000, the TIA TR-42 Engineering Committee unanimously approved the publication of the ANSI/TIA/EIA-568-B.3 Optical Fiber Cabling Components Standard. This document is part three in a series of telecommunications Standards being developed to supersede the TIA/EIA-568-A (‘568-A) Commercial Building Cabling Standard. When complete, the third edition of TIA's Commercial Building Telecommunications Cabling Standard will include:

  • TIA/EIA-568-B.1 (‘568-B.1), General Requirements
  • TIA/EIA-568-B.2 (‘568-B.2), 100 ohm Balanced Twisted- Pair Cabling
  • TIA/EIA-568-B.3 (‘568-B.3), Optical Fiber Cabling Components

Table 2

Latest Industry Draft Category 6/Class E and Category 7/Class F Channel Transmission Parameters

Parameter

Category 6/Class E VALUE AT 100 MHZ (250 MHZ)

Category 7/Class F VALUE AT 100 MHZ (600 MHZ)

PERCENT VOLTAGE IMPROVEMENT OVER CATEGORY 6/CLASS E

Insertion Loss (Attenuation)

21.3 dB (36.0 dB)

20.8 dB (54.6 dB)

10% less attenuation

NEXT Loss

39.9 dB (33.1 dB)

62.9 dB (51.2 dB)

93% less NEXT

Return Loss

12 dB (8 dB)

12 dB (4 dB)

-

ELFEXT

23.2 dB (15.3 dB)

29 dB (ffs)

15% less ELFEXT

ACR

18.6 dB (-2.9 dB)

42.1 dB (-3.4 dB)

n/a

PSACR

15.8 dB (-5.8 dB)

39.1 dB (-6.4 dB)

n/a

The content of 568-B.3 addresses the mechanical and transmission performance requirements of optical fiber cable, connecting hardware, and patch cords. The two most significant enhancements over '568-A include the recognition of 50/125 µm multimode fiber and the use of small form factor (SFF) fiber connectors in addition to the 568SC at the work area connection. It is interesting to note that, even though the ISO committees recognize the use of 50/125 µm multimode fiber in their Standards, they intend to maintain the duplex SC-connector as the only fiber optic connector recognized for use at the work area. Both TIA and ISO recognize the use of any compliant fiber optic connector at all locations other than the work area.

Table 3

Items Under Study by the TIA and ISO Standards Groups

Category 6/Class E

  • Permanent link models
  • Insertion loss deviation (ILD), balance specification
  • Test plug characteristics (i.e., de-embedded NEXT and FEXT loss)
  • Patch cord test method

Category 7/Class E

  • Conformation of work area interface
  • Field test methods
  • High frequency laboratory test methods
  • Patch cord test method

Barring any unforeseen technical issues, it is likely that TIA and ISO approved category 7/class F Standards will be available to the industry in 2001.

When high density is an important consideration for the Campus Distributor (CD), Building Distributor (BD), Floor Distributor (FD), or Consolidation Point (CP), then SFF connector designs that accommodate at least two fibers within the footprint of an IEC 60603-7 connector are recommended. When used, SFF connectors shall be covered by an approved IEC interface Standard.

As part of the ‘568-B.3 Standard, TIA recognizes SFF connector designs that are physically specified to satisfy the requirements of a corresponding TIA Fiber Optic Connector Intermateability Standard (FOCIS) document or IEC Standard. Compliance to a FOCIS or IEC Standard ensures that the mechanical interface is described in sufficient detail to ensure intermateability between different manufacturers of the same SFF connector style. In addition, in conjunction with IEC and ANSI policy, any patents related to a given SFF interface must be fairly licensed to all manufacturers wishing to produce the interface.

Figure 4 - 568SC Duplex Connector

Engineers developing connecting hardware found that they could easily provide connectivity for two optical fibers in the same amount of space presently occupied by the copper-based 8-position modular (RJ-45) footprint.

In the previous TIA/EIA-568-A document, only the 568SC duplex adapter and connector (see Figure 4) was recognized for use in the work area for new fiber optic installations. The allowance of the SFF connector offers several potential benefits to the end-user over the 568SC. For example, the 568SC connector, although universally recognized, is larger and does not support the industry trend towards high-density solutions at the equipment interfaces. Engineers developing connecting hardware found that they could easily provide connectivity for two optical fibers in the same amount of space presently occupied by the copper-based 8-position modular (RJ-45) footprint. Since the advent of TIA's recognition of SFF connectors, fiber optic equipment manufacturers such as Cisco Systems, 3Com, and IBM have already incorporated these interface designs into their products.

Figure 5 - MT-RJ and LC Fiber Optic Connectors

To address the industry's need for SFF fiber optic connecting hardware, The Siemon Company offers a full line of MT-RJ and LC small form factor interconnect products (see Figure 5).


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