This new standard was developed in order to support the more rigorous demands of Gigabit Ethernet but because of its improved signal-to-noise ratio all networks perform better because of the maximized throughput it provides. The current standard, 568-B.2, requires the use of Category 5e cabling and for good reason too. It meets the extra performance requirements that not only double its usable bandwidth but also reduce the noise level, making the data signal more easily detected at the receiving end. TIA / EIA has relegated Category 5 cabling to "legacy" status and no longer supports its use in horizontal applications.

The requirements for Enhanced Category 5e cables were clearly defined by the TIA with the publication last November of the 5^th addendum to TIA 569A, known as ANSI/TIA/EIA – 568-A-5. This specification was driven by the need to support higher performance / higher speed LAN systems, specifically Gigabit Ethernet.

TIA 568-A-5 adjusts an existing characteristic, Near-End Crosstalk (NEXT) so that it is 3 dB more stringent than before. This increases the attenuation to crosstalk ratio (ACR) of cable, effectively reducing the noise level and making the data signal easily detected at the receiving end.

The addendum also adds several other characteristics. These are Equal Level Far End Crosstalk (ELFEXT), Power Sum ElFEXT )PSELFEXT), Power Sum NEXT (PSNEXT), and Return Loss.

While all of the aforementioned characteristics have a role in defining the performance of the cable, it’s Headroom, (or ACR/PSACR margin over spec.) that defines how high the signal level is relative to the noise level and thus provides the simplest measure of how well the cable will provide a strong signal profile.

With good Return Loss values, the cable is reducing signal reflections that result in a attenuation of the signal and cause echoes that become noise. As with ACR, good RL values mean a very robust signal compared to noise.