Issue link: https://www.e-digitaleditions.com/i/1156106
October/November/December 2019 I 39 An AXT problem is not like NEXT or far-end cross- talk (FEXT) because it is the interference coming from another cable that is disturbing adjacent cables. Therefore, the issue now is how to support the higher bandwidth 802.11ac Wi-Fi devices required to handle video stream- ing apps over a large installed base of Cat 5e and Cat 6 cabling infrastructure. 2.5GBASE-T and 5GBASE-T cir- cuits were introduced by the NBase-T Alliance to help reap the benefits of faster Wi-Fi without having to do an expensive cabling upgrade. The NBASE-T Alliance published a spec which is compatible with the IEEE 802.3bz standard that specifies 2.5Gb/s should work over 100 meters of Cat 5e cabling and 5Gb/s should work over FIGURE 7: Shielded Cat 6A cable (STP). 6 100 meters of Cat 6 cabling. A technical article, NBase-T Performance and Cabling Guidelines, published a few weeks before IEEE 802.3bz's official completion in September 2016 introduced the cabling perfor- mance parameter alien limited signal-to-noise ratio (ALSNR). The ALSNR provides a single numerical value for cabling performance to indicate support for 2.5GBase-T and 5GBase-T. 4 Assured Assured 0m <= Bundled cabling length <= 50m 2.5GBASE-T 5GBASE-T Assured Assured Assured Category 5e Category 6 Category 6A 50m <= Bundled cabling length <= 75m 2.5GBASE-T 5GBASE-T Assured Category 5e High Medium Low Category 6 Category 6A 75m <= Bundled cabling length <= 100m 2.5GBASE-T 5GBASE-T Assured Assured Assured Category 5e Category 6 Category 6A ALSNR Risk FIGURE 6: NBASE-T Alliance chart to determine ALSNR risk. ALSNR is a limiting factor in both 2.5GBASE-T and 5GBASE-T applications, but Cat 5e and Cat 6 cabling do not include ALSNR specifications! Consequently, the Telecommunications Industry Association (TIA) TSB-5021 and ISO/IEC TR 11801-9904 perfor- mance specifications were intro- duced to address the evaluation of existing Category 5e and 6 cabling to support these applications. 5 ALSNR combines calculations for insertion loss, alien NEXT, and alien FEXT. It is well known that longer, tighter cable bundles, such as those shown in Figure 5, ex- hibit more alien crosstalk. There- fore, an assessment should be made to determine which chan- nels might be at risk. The NBASE-T Alliance pro- vides a good guide for determining risk (Figure 6). The longer the length of bundled cabling, the higher the ALSNR risk. IS SHIELDED CABLE SUPPOSED TO BE THE SOLUTION FOR EMI? Shielded twisted pair (STP), shown in Figure 7, can be a solution for EMI in LANs but only at higher frequen- cies. Higher frequencies usually start in the voice frequency range (3 kHz), but shielding effectiveness increases dramatically in the radio frequency interference (RFI) range (100 kHz and above) and impulse noise range (10 MHz and above).