"With 250 Mbps being shot down each of the four copper pairs, you're carrying a lot of energy," says Bruce Tolley, marketing manager in Cisco's workgroup business unit and VP of the 10 Gigabit Ethernet Alliance. "Users should be testing for crosstalk at the far end, as well as echoes at the transmission end."

The Gigabit Ethernet Alliance also recommends that potential users of 1000Base-T test their Category 5 cabling for return loss and equal level far-end crosstalk (ELFEXT). Return loss is a measure of reflected energy from impedances in the cabling, while ELFEXT measures the noise from signal leakage at the receiving end of a connection.

The alliance warns that these two dynamics may have little effect at the 10Base-T threshold of operation, but that higher speeds, 100-and 1000Base-T, are prone to performance degradation.

Most enterprises shouldn't have to worry or overstate the potential for problems. The 1000Base-T Task Force and the cabling companies estimate that less than 10% of the installed base of Category 5 cable was improperly installedÐthat is, not installed in accordance to the standards, the alliance says in its testing white paper. If there are substandard links, it's possible they aren't "a product of the Category 5 cable itself, but rather a product of the connectors in the link," the alliance says.

Test suites are available from a number of vendors, including Datacom/Textron, Fluke, Hewlett-Packard, Microtest, and Wavetek Wandel Goltermann.

If after testing, IT managers find that the Category 5 links fail, the alliance recommends three kinds of corrective measures: switching to high-performance patch cables; reducing the number of connectors in the link; and reconfiguring some or all the connectors.

For more information about Gigabit Ethernet over copper, visit www.gigabit-ethernet.org/technology/whitepapers.