0m <= Bundled cabling
length <= 50m
2.5GBASE-T
5GBASE-T Assured Assured
Category 5e Category 6 Category 6A
Assured
Category 6 Category 6A
Assured
75m <= Bundled cabling
length <= 100m
2.5GBASE-T
5GBASE-T Assured Assured
Category 5e Category 6 Category 6A
Assured
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 streaming
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 performance
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
50m <= Bundled cabling
length <= 75m
2.5GBASE-T
5GBASE-T Assured
Category 5e
High Medium Low
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 performance
specifications were introduced
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. Therefore,
an assessment should be
made to determine which channels
might be at risk.
The NBASE-T Alliance provides
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 frequencies.
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).