John A. Siemon, The Siemon Co.
Now that the Telecommunications Industry Association TR41.8.l working group on telecommunications cabling has successfully published standard TIA/EIA-568-A, numerous issues that have surfaced as a result of its ongoing efforts should be addressed. Last October, a special planning meeting was held to discuss these open issues and to formulate recommendations on a strategic plan to address them. During this meeting, each pending technical issue was assigned to one of three classifications. These classifications relate to their importance and the manner with which resulting specifications will be conveyed to the industry:
Critical technical issues
The following topics are pending investigation by members or task groups of TR41.8.1. Because of their critical technical nature, the approved technical resolutions for many of these issues will likely be released in the form of an addendum to TIA/EIA-568-A.
Short link resonance. Investigations of field transmission measurements on twisted-pair links has resulted in the discovery of a new phenomenon known as Oshort link resonance.O This resonance effect is characterized by peaks in near-end crosstalk performance at periodic intervals throughout the frequency range of testing. In links of short lengths, these peaks have been found to result in failure of the basic-link crosstalk requirements specified in TIA/EIA Technical Systems Bulletin 67, or TSB. The TR41.8.1 working group?s top priority is explaining and resolving this phenomenon.
Hybrid-cable transmission requirements. Open office cabling and the need to support multiple telecommunications applications in a shared sheath have resulted in increased demand for hybrid cables. As a result, the hybrid-cable requirements that appear in both the 1991 and the 1995 editions of TIA/EIA-568 have come under increased scrutiny.
Unshielded twisted-pair cable and connecting hardware issues. Among the topics under investigation are test methods and requirements for balance and various harmonization issues with the International Standards Organization/International Electrotechnical Commission 11801 standard. Revision of the low-frequency limit for cable attenuation, clarification for temperature testing and restrictions on reversals/pair transpositions are also pending.
STP-A cable and connecting hardware issues. Among the topics under investigation are characteristic impedance, attenuation and near-end crosstalk temperature range for STP-A, or shielded twisted-pair, cables. Connector resistance and link performance requirements for the cabling type are also open.
Ongoing standards development
The following issues require development of new technical matter that will likely be released in the form of Interim Standards or TSBs. (Note that a TSB is an informative bulletin and not a standard.)
Y Technical specifications for 100-ohm patch cords. This draft TSB is being developed by the PN-2948 task group and will specify test methods and requirements for patch cord assemblies.
Y Technical specifications for 100-ohm STP cabling. This draft TSB is being developed by the PN-3193 task group. It will build on TIA/EIA-568-A by specifying additional technical requirements on shield effectiveness, installation practices and link performance relative to cabling with an overall shield.
Y Additional practices for open-office cabling. This draft TSB was developed by the PN-3398 task group. It specifies horizontal cabling methodologies in open-office environments by means of multiuser telecommunications outlets and consolidation points. Ballot is pending.
Y Additional cable requirements. Items under consideration are far-end crosstalk, balance and velocity of propagation. Specifications for testing channels and links that cover component characteristics, test methods, modeling, verification and link characteristics will also be addressed.
The third classification includes issues to be addressed in the third edition of the Commercial Building Telecommunications Cabling Standard, TIA/EIA-568-B, which will be covered in the TIA update next month.
John A. Siemon is vice president, engineering, at The Siemon Co. (Watertown, CT) and has been active in TIA?s engineering committee, TR-41.8, and its working groups since 1986. He is on the steering committee for the development of Revision B of TIA/EIA-568-A and also serves as the vice chair of the U.S. advisory group for international cabling standards.