Paul Kish,
nordx/cdt Inc.
Anumber of recent magazine articles and misinformation in the cabling industry have spread fear, uncertainty, and giga-confusion regarding the category or level of cabling required to support gigabit data rates over copper wire. The key objective of the 802.3 committee of the Institute of Electrical and Electronics Engineers (ieee--New York City), which is responsible for the 1000Base-T Gigabit Ethernet standard, is to make the protocol work over the vast majority of installed Category 5 cabling. That will be accomplished by implementing sophisticated digital signal-processing technology while using all four wire pairs in the cable for parallel bidirectional transmission. The data rate for each pair is 250 megabits per second for a total effective rate of 1000 Mbits/sec, or 1 Gbit/sec. The ieee standard for Gigabit Ethernet over copper should be finalized by March 1999.
The ieee 802.3 committee has requested the Telecommunications Industry Association (tia--Arlington, VA) TR-41.8.1 working group to characterize existing cabling for two new transmission parameters, namely far-end crosstalk (fext) and return loss. tia TR-41.8.1 has completed this work and has prepared two documents as a supplement to the tia/eia-568a cabling standard. The first document provides field-test procedures and guidelines for the installed base of Category 5 cabling and will be published as a telecommunications systems bulletin. The second document covers Enhanced Category 5 (Category 5E) cabling for new installations and will be published as an addendum to the tia/eia-568a cabling standard.
The fly in the ointment is that not all existing Category 5 installations can meet the new transmission parameters for a worst-case channel, which can include as many as four connectors. In such cases, the channel may need to be reconfigured with fewer connectors, or the connectors may need to be upgraded to enhanced-connectivity hardware. To ensure compliance with the Gigabit Ethernet specification for worst-case channels, Category 5E components will need to be specified.
To add to the confusion, both the iso/iec SC25 WG3 group of the International Organization for Standardization/International Electrotechnical Commission (iso/iec--Geneva) and the tia`s TR-41.8.1 are working on a new standard for Category 6 cabling, which provides a usable bandwidth of 200 megahertz--twice the bandwidth of Category 5. Please note, however, that bandwidth should not be confused with some manufacturers` claims of testing or specifying cables to 350 or more MHz. These testing claims add another dimension to the overall confusion. Bandwidth of cabling is defined as the frequency range in which the signal output at the end of a 100-meter channel exceeds the power-sum crosstalk noise level. Today, Category 6 is in the early stages of development, with several proposals on the table. Category 6 will probably not be specified before the year 2000 and is intended for future applications. Category 6 cabling is not required for 1000Base-T transmission.
To add yet another level to the confusion, other specifications are being used within the industry for procurement purposes. These specifications are being used to differentiate products based on levels of performance. They are proprietary in nature and are not industry standards. There is no assurance that components meeting these higher-level specifications will meet the future Category 6 standard. When eventually finalized, the Category 6 standard may specify a lower- attenuation cable, a higher frequency range, or a plug specification for patch cords that is not defined today. A standard is developed by consensus among many manufacturers. Today, it is still too early to tell when consensus for Category 6 component requirements will be reached.
This explanation is intended to clear up some confusion. It is important for users to be informed of the latest developments in standards because a standard provides a performance benchmark on which users can base their decisions when specifying products. Also, beware of manufacturers claiming Category 6 compliance. Category 6 is very much a moving target and is subject to change.
Paul Kish is senior product manager of ibdn systems and standards with nordx/cdt Inc. (Pointe-Claire, QC, Canada), a subsidiary of Cable Design Technologies. He chairs the tia`s TR-41.8 subcommittee.
