De-Mystifying Category 5, 5e, 6, and 7 Performance Specifications

Even though the IEEE 802.3ab Gigabit Ethernet specification has released and applications group's are turning their attention towards next generation solutions, there is still a great degree of uncertainty as to the capability of today's telecommunications cabling systems to support tomorrow's high bit-rate applications. Fortunately, the Telecommunications Industry Association (TIA) and International Organization for Standardization (ISO) have made great strides in the specification and clarification of the minimum cabling performance criteria necessary to support these next generation applications.

Additional requirements and recommendations for category 5 and class D cabling that are intended to supplement the existing TIA/EIA-568-A and category ISO/IEC 11801 class specifications have recently been published. These specifications address additional transmission performance characterization required by systems developers to support bi-directional and full four-pair transmission schemes (such as those utilized by Gigabit Ethernet). Table 1 identifies these new cabling documents developed by the TIA and ISO technical committees:

Table 1: Additional Category 5/Class D Specifications
Document Name	Title
TIA/EIA/TSB95	"Additional Transmission Performance Guidelines for 4-pair 100 W Category 5 Cabling", September 1999
TIA/EIA-568-A-5	Addendum 5 to TIA/EIA-568-A entitled, "Additional Transmission Performance Specifications for 4-pair 100 W Enhanced Category 5 Cabling", November 1999
ISO/IEC 11801:1995 FDAM 2	Amendment 2 to ISO/IEC 11801 entitled, "Information Technology - Generic Cabling for Customer Premises Amendment 2", September, 1999

TIA and ISO working groups are also actively developing category 6, category 7, class E, and class F requirements capable of supporting greater frequency bandwidths and higher performance than previously achievable. It is anticipated that these specifications will soon be presented to the industry for technical comment and review.

TSB95

TSB95 provides recommendations for the new category 5 channel parameters of return loss and equal level far-end crosstalk (ELFEXT) loss. These recommendations are specified to verify the performance of installed or "legacy" category 5 cabling in order to ensure Gigabit Ethernet application support. The TSB95 return loss and ELFEXT loss recommendations were derived from the worst case transmission performance of channels with only two connection points. The two connector channel topology is consistent with the IEEE committee's assumption that cabling used to support Gigabit Ethernet systems will most likely utilize an interconnect instead of a cross-connect field and will not include a consolidation or transition point connection.

Existing installed category 5 cabling should be verified to ensure that performance meets the minimum recommendations of TSB95 prior to attempting to support the Gigabit Ethernet protocol. It is important to note that existing channel configurations with three or four connectors that satisfy the TSB95 ELFEXT loss and return loss requirements will also support Gigabit Ethernet. Because the recommendations of TSB95 are applicable for the qualification of existing, installed cabling only, they are not recommended to be used as the minimum performance criteria for new category 5 cabling.

Originally balloted as an addendum to '568-A, these recommendations have been published in the form of a Telecommunications Systems Bulletin (TSB). TSB95 is informative in nature and does not contain mandatory or "shall" requirements.

TIA/EIA-568-A-5 ('568-A-5)

Addendum 5 to ANSI/TIA/EIA-568-A specifies enhanced category 5 (category 5e) performance requirements. It is strongly recommended that new category 5 cabling installations be specified to satisfy the minimum requirements of this document and it is expected that '568-A-5 will emerge as the new de facto minimum standard for category 5 cabling. '568-A-5 specifies the minimum equal level far-end crosstalk (ELFEXT) loss and return loss requirements necessary to support developments in applications technology and defines the minimum performance that is required for a worst case four-connector channel to support applications that utilize full-duplex transmission schemes (such as Gigabit Ethernet). To ensure additional crosstalk headroom for robust applications support, '568-A-5 also specifies power sum NEXT and ELFEXT loss performance for category 5e cables, links and channels.

Addendum 5 to TIA/EIA-568-A is a normative document and, unlike TSB95, it provides mandatory requirements, not recommendations.

ISO/IEC 11801:1995 FDAM 2

The performance specifications in ISO FDAM 2 provide new requirements for return loss and ELFEXT loss to compliment the existing ISO class D requirements. The FDAM 2 specified return loss and ELFEXT loss requirements are in harmony with the values in '568-A-5, however, FDAM 2 does not specify additional NEXT loss margin over and above the existing class D requirements. FDAM 2 also includes propagation delay and delay skew requirements for channels and permanent links that are in harmony with the requirements of TIA/EIA-568-A-1.

The requirements of amendment 2 to ISO/IEC 11801 are normative and this document is expected to become the de facto standard for new Class D cabling installations.

Category 6/Class E

The proposed category 6/class E work area connector shall be an 8-position modular jack interface.

The proposed category 6/class E standards that are currently under development by TIA and ISO working groups describe a new performance range for unshielded and screened twisted-pair cabling. The charter of the working group developing category 6/class E requirements is to specify the best performance that UTP and ScTP cabling solutions can be designed to deliver. It is anticipated that the category 6/class E requirements will be specified in the frequency band of at least 1-250 MHz and be capable of supporting a positive power sum attenuation to crosstalk ratio (ACR) up to 200 MHz.

For category 6/class E cabling topologies, it has been agreed that the 8-position modular jack interface shall be the mandatory work area interface to be consistent with existing category/class requirements. Category 6/class E specifications will be backward compatible meaning that applications running on lower categories/classes will be supported by the category 6/class E infrastructure. If different category/class components are to be mixed with category 6/class E components, then the combination shall meet the transmission requirements of the lowest performing category/class component.

TIA, ISO, CENELEC, and others are collaborating closely on the development of category 6 and class E standards and their proposed requirements are very much in harmony. It is expected that category 6/class E requirements will soon become available for industry review. If TIA and ISO do not encounter unexpected technical issues, it is possible that the industry could have access to published category 6/class E requirements within twelve months.

<== попередня сторінка	\|	наступна сторінка ==>
Table 3	\|	Category 7/Class F

Не знайшли потрібну інформацію? Скористайтесь пошуком google:

Генерація сторінки за: 0.004 сек.