Published In September 2000
The expansion of high-speed copper data cabling options—from Category 5 into Enhanced Category 5e, Category 6, and a multitude of proprietary classification schemes—has left customers and contractors confused about what they need, and even about what they’ve got once they’ve bought it. Manufacturers have been marketing Category 5e and Category 6 products for a couple of years, but until standards are finalized, requirements may change. Category 6 is still a moving target, but the Category 5e standard has been finalized and published in January 2000 as TIA/EIA-568-A-5, “Additional Transmission Performance Specifications for 4-Pair 100 Ohm Category 5e Cabling.” Most recent developments in unshielded twisted pair (UTP) cabling have been driven by the Institute of Electrical and Electronic Engineers’ (IEEE) work to implement Gigabit Ethernet on Category 5 cable. 1000Base-T is radically different from preceding networks, because it is transmitted over the cable. Because of that, the IEEE asked the Telecommunications Industry Association (TIA) to quantify additional parameters for those Category 5 components and systems that were not originally specified. Previous local area network (LAN) technology (up to 155 Mbps asynchronous transfer mode (ATM)) uses two cable pairs for operation: one to transmit and one to receive. Gigabit Ethernet uses all four pairs to transmit four simultaneous bi-directional data streams. The original Category 5 specification was defined primarily by attenuation and near-end crosstalk (NEXT). 1000Base-T technology requires the definition of additional performance parameters, such as return loss, propagation delay skew, and equal level far-end crosstalk (ELFEXT). The TIA has provided the IEEE with a “best guess” about how a Cat 5 system might perform in TSB95, “Additional Transmission Performance Guidelines for 4-Pair 100 Category 5 Cabling.” However, only additional testing of installed Cat 5 systems is needed to determine their suitability for 1000Base-T. Gigabit Ethernet will push the limits: it may even exceed some installed Category 5 cabling systems’ performance capabilities. In fact, it may be impossible to exercise all of the allowed options for cabling architectures and still support 1000Base-T on Category 5 cabling. This is where Category 5e comes in. The TIA has defined performance criteria and established a standard for Category 5e that meets or exceeds 1000Base-T system requirements while addressing four-pair networking application needs. Category 5e provides the extra performance headroom required to support Gigabit Ethernet while still taking advantage of all TIA-defined standard cabling system architectures (such as four-connector channels). Category 5e even provides additional performance headroom to make 10Base-T and 100Base-T networks more robust and reliable. Although 1000Base-T represents leading-edge data communications technology, the differences between Category 5 and Category 5e are actually small. Both categories are specified through 100 MHz. The primary difference is that the NEXT requirements for Category 5e have been raised so that Category 5e power sum NEXT (PS NEXT) is equivalent to Category 5 NEXT. This means that Category 5e offers Category 5 performance—even when all four pairs are transmitting. The above table shows the 100 MHz channel performance requirements for original Category 5, TSB95 Category 5, and Category 5e. The bottom line is Category 5e is essentially what Category 5 would have been if we’d considered four-pair applications like 1000Base-T back in 1990. Although small, the difference between Category 5 and Category 5e is significant. Using Category 5e is the only way to ensure that a cabling system can provide the flexibility offered by TIA architectural options while performing as required to support 1000Base-T. Because of this, the TIA will be raising the minimum performance requirements of data-grade cabling to Category 5e in the upcoming revision of ANSI/TIA/EIA-568-B and will not be standardized on TSB95. To ensure the cabling systems you install will comply with upcoming standards and offer your customers the flexibility and life-span they expect, make the move to Category 5e now. BEAM is director of systems marketing at AMP NETCONNECT Systems. He can be reached at (336) 727-5784 or firstname.lastname@example.org.