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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.

Connecting Hardware Backward Compatibility and Interoperability With Emphasis on De-embedded Plug Qualification Criteria

Background:

As development progresses in the specification of category 5e and category 6 component requirements, standards groups have found that compatibility with existing categories is no longer assured. As a result, the issue of backward compatibility and product interoperability between manufacturers has gained prominence as a primary consideration for next generation twisted-pair connecting hardware.

Backward compatibility implies that next generation cabling is not only superior to, but is also a superset of existing specifications. An electrical superset encompasses the total number of pairs supported and transmission performance. For example, four-pair category 5e and 6 cabling and components must meet or exceed all of the category 5 reliability and transmission requirements. Just as category 5 requirements are a superset of categories 3 and 4, category 5e and 6 cabling systems and components must at least be electrical supersets of category 5 to ensure that new cabling standards will support all applications designed to operate over existing categories.

In particular, the concept of backward compatibility poses a unique dilemma for the specification of next generation connecting hardware. Currently, the performance of a category 5 modular plug is specified in Annex B.5.2 of ANSI/TIA/EIA-568-A and in Annex A.3.1 of ISO/IEC 11801 by a terminated-open-circuit or "TOC" measurement. These requirements anchor test plug NEXT performance for the worst case pair combination between a lower range of 40 dB and an upper range simply specified to be "greater than 41.5 dB". Because the same test plug criteria is applied o category 3, 4, and 5 connecting hardware, category 5 connectors are inherently compatible with lower category cabling. Shortcomings known to be associated with the TOC method include the inability to characterize both inductive and capacitive coupling effects of the test plugs and poor correlation to mated performance. Although these limitations were acceptable for testing category 3, 4, and 5 outlets, a more accurate plug specification is necessary for the qualification of category 5e and 6 connecting hardware due to the complex electrical interaction between the plug and outlet.

Although the TOC method is adequate for the qualification of category 5 outlets, standards groups agree that the inherent deficiencies of the TOC method make it inadequate for the qualification testing of category 5e and 6 outlets.

The latest TIA research led to agreement that a "de-embedded" plug characterization is the preferred test method for fully specifying test plugs used to qualify telecommunications outlets to category 5e and 6 performance requirements. This method specifies the construction of a reference jack that is characterized by its real and imaginary NEXT loss contributions. The measured reference jack NEXT loss values are then subtracted or "de-embedded" from a mated test plug/reference jack measurement. The result is a plug NEXT characterization that can be used to qualify (or disqualify) any plug for use in determining if specific outlet designs meet category 5e or 6 performance requirements.

The de-embedded plug technique has been proven to yield more complete component characterization and to enable improved accuracy and repeatability between test facilities. As a result, the de-embedded test method provides complete plug qualification criteria to ensure backward compatibility and product interoperability for next generation components.

The concepts of backward compatibility and product interoperability are inherent to the spirit of generic cabling standards. The adoption of de-embedded qualification criteria for test plugs results in accurate and complete characterization of next generation outlet designs. This new test methodology will result in full backward compatibility and product interoperability for future cabling standards. To complete this initiative, standards groups must:

  1. Adopt a formal position on next generation backward compatibility and product interoperability.
  2. Impose an upper limit for the specification of TOC performance for the pair combination terminated on pins 4,5 and 3,6 and adopt a corresponding de-embedded test plug range.
  3. Specify a de-embedded test plug performance range for the qualification of all other pair combinations of category 5e and 6 outlets. The test plug requirements for category 5 outlet qualification must encompass the test plug requirements for category 5e and 6 outlet qualification.
  4. Require category 5e and 6 outlets to be qualified over the entire range of de-embedded qualification plugs to ensure backward compatibility.

TIA and ISO/IEC standards groups continue to make progress on category 5e and 6 requirements for cables, connecting hardware, links, and channels.

Progress Report: Objective 1 - Formalizing a Position Statement

TIA formulating group TR42.1 recently finalized a position statement on next generation backward compatibility and product interoperability. The position text details the following points:

Backward Compatibility and Interoperability Statement

When developing next-generation cabling requirements, TIA shall specify performance criteria necessary to ensure that systems and components are backward compatible with existing categories. Backward compatibility means that next-generation cabling, components, and mated connections shall satisfy all requirements of their category in addition to all existing lower category specifications.

See Table 1 for a matrix of mated modular connector performance that is representative of backward compatible connectivity. To ensure generic cabling system performance, connector requirements shall be specified to support interoperability between mated modular products from different manufacturers.

Table 1: Matrix of Backward Compatible Mated Connector Performance

 

Category of Modular Connector Performanceiii

Category 3

Category 5

Category 5ei

Category 6ii

Modular Plug and Cord Performance

Category 3

Category 3

Category 3

Category 3

Category 3

Category 5

Category 3

Category 5

Category 5

Category 5

Category 5ei

Category 3

Category 5

Category 5ei

Category 5ei

Category 6ii

Category 3

Category 5

Category 5ei

Category 6ii

i - Category 5e plug performance requirements are under study.
ii - Category 6 plug and mated performance requirements are under study.
iii - Category 7 connector uses the same physical interface as lower performing categories, then it is the intent that these components will be backward compatible and interoperable.

Progress Report: Objective 2 - Fully Characterize Reference Test Plug Criteria for Outlet Qualification to Category 5 Requirements

The TIA TR42.7.1 (previously PN-2948) connecting hardware working group has rigorously studied a wide range of commercially available modular plugs and patch cords (including special plug constructions such as those containing a "load-bar"). Based on this research, the working group concluded that a large percentage of commercially available modular plugs have worst case TOC performance of greater than 42 dB. Moreover, the group found that there is no evidence indicating that installing these plugs leads to problems when qualifying category 5 links and channels. Data plots, such as the one shown in Figure 1, were used to correlate plug TOC NEXT loss versus mated category 5 connecting hardware performance for a variety of cable designs.

Figure 1

Figure 1

As a result of this analysis, the working group has agreed to adopt an upper limit of 44 dB for the specification of plug TOC performance for the pairs terminated on pins 4,5 and 3,6.

In order to support the specification of a reference de-embedded plug range for the pairs terminated on pins 4,5 and 3,6, the TR42.7.1 working group evaluated comprehensive correlation plots of de-embedded NEXT loss versus TOC NEXT loss plug data similar to that shown in Figure 2.

As a result of de-embedded plug analysis, TIA has adopted a range of 34 - 38 dB, which correlates to the TOC plug values for the pairs terminated on pins 4,5 and 3,6.

Progress Report: Objective 3 - Specify De-embedded Plug Verification

Figure 2

There is consensus agreement that plug requirements for category 6 outlet qualification shall be encompassed by the existing and additional plug requirements for category 5 and 5e outlet qualification. Without this condition, there can be no assurance that category 6 plugs and outlets will be backward compatible with category 5 and 5e components. Due to the additional electrical design constraints required to achieve 250 MHz performance, it is logical that the plug qualification range for category 6 outlets be narrower than that of the plug qualification range for category 5 and 5e outlets.

The TR42.7.1 working group has tentatively adopted the ranges of de-embedded plug qualification values for category 5e and 6 outlet qualification as shown in Table 2. Note that the category 5e and 6 qualification values are encompassed by the requirements for category 5. These values may still be subject to revision after additional review.

Table 2 De-embedded Test Plug Values

De-embedded Test Plug Values for Category 5e Outlet Qualification

Pin/Pair Combination

Low Range (dB)

High Range (dB)

Total Range (dB)

Phase (degrees)

Pins 3-6, 4-5

34 - 34.2

37.7 - 38

34 - 38

-90 +/- 20

Pins 3-6, 1-2

42 - 42.5

49.5 - 50

42 - 50

-90 +/- 20

Pins 3-6, 7-8

42 - 42.5

49.5 - 50

42 - 50

-90 +/- 20

Pins 3-6, 1-2

50 - 52

N/R

=/>50

-90 +/- 20 or 90 +/- 20

Pins 3-6, 7-8

50 - 52

N/R

=/>50

-90 +/- 20 or 90 +/- 20

Pins 3-6, 7-8

60 - 70

N/R

=/>50

-90 +/- 20 or 90 +/- 20

N/R: Not Required

Proposed De-embedded Test Plug Values for Category 6 Outlet Qualification

Pin/Pair Combination

Low Range (dB)

High Range (dB)

Total Range (dB)

Phase (degrees)

Pins 3-6, 4-5

36 - 36.2

37.7 - 38

36 - 38

-90 +/- 20

Pins 3-6, 1-2

46 - 46.5

49.5 - 50

46 - 50

-90 +/- 20

Pins 3-6, 7-8

46 - 46.5

49.5 - 50

46 - 50

-90 +/- 20

Pins 4-5, 1-2

57 - 60
57 - 60

=/>70

=/>57

-90 +/- 20
90 +/- 20
no phase requirement

Pins 4-5, 7-8

57 - 60
57 - 60

=/>70

=/>57

-90 +/- 20
90 +/- 20
no phase requirement

Pins 1-2, 7-8

60 - 70
60 - 70

N/R
N/R

=/>60

-90 +/- 20
90 +/- 20

N/R: Not Required

Progress Report: Objective 4 - Category 5e and 6 Backward Compatibility

The backward compatibility and interoperability position mandates that category 5e and 6 outlets be qualified over the entire de-embedded range of category 5/5e qualification plugs. To support this position, the connecting hardware working group has specified the following proposed category 6 and 5e backward compatibility tests:

Category 5e Backward Compatibility Test:

Test category 5e outlet mated to the full range of worst case de-embedded test plugs (i.e. 34 to 38 dB for pins 4,5 and 3,6).

Mated performance shall exceed minimum category 5e requirements over the full de-embedded plug range.

To demonstrate the category 5e backward compatibility test, three of The Siemon Company's category 5e telecommunications outlet product lines were evaluated against the proposed methodology as shown in Figure 3. The data demonstrates that The Siemon Company MC6™ modular plugs are backward compatible with these category 5e telecommunications outlet product lines. Similar tests have been performed to demonstrate backward compatibility with other parameters such as far-end crosstalk. Reference Siemon ITR-981124-906.

Figure 3

Category 6 Backward Compatibility Test:

Test category 6 outlet mated to the full range of worst case de-embedded test plugs for all pair combinations.

For example, mated performance shall exceed minimum category 6 requirements for the pairs terminated on pins 3, 6 and 4,5 over the de-embedded plug range of 36 to 38 dB. Mated performance shall exceed minimum category 5e requirements over the de-embedded plug range of 34 to 36 dB.

To demonstrate the category 6 backward compatibility test, The Siemon Company MAX® 6 telecommunications outlet was evaluated against the proposed methodology as shown in Figure 4. This data demonstrates that The Siemon Company MAX® 6 module is backward compatible with components and systems of lower performing categories. Similar tests have been performed to demonstrate MAX® 6 backward compatibility with other parameters such as far-end crosstalk. Reference Siemon ITR-981124-888 for additional information.

Figure 4

Standards Update:

The TIA and ISO standards groups have made significant progress on the characterization and specification of next generation cabling and components. At this time, the proposed industry performance requirements for components and cabling are unlikely to be revised further. The ongoing emphasis will be to specify laboratory and field qualification procedures that are suitable for extended bandwidth testing. Achieving consensus on a plug qualification methodology that can support backward compatibility and product interoperability represents a significant milestone towards industry acceptance of a complete category 6 connecting hardware specification.


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