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The Cat. 7 A cable has to be newly specified with better alien crosstalk characteristics in order to improve this parameter.
To illustrate this difference, this newly specified cable is referred to here as Cat. 7 B. That designation is not
based on any standard, however.
The key to future proof the cabling therefore lies in the specification of a new Cat. 7 B cable and not necessarily in
the use of a Cat. 7 A connector system.
Summary
• 10GBase-T up to 100 m appears to be the limit of what is feasible for unscreened cabling.
• 40GBase-T up to 100 m is technically feasible but appears to be too challenging for field use. Presumably
it will be defined with reduced cable length (e.g. with 45 m PL).
• 100GBase-T up to 100 m appears to be technically unfeasible.
• Today's Class F A standardization does not support 40GBase-T because the specification for alien
crosstalk is not stringent enough >>> a new Class F B will be needed.
• It has not yet been shown that a Cat. 7 A connector system is necessary to achieve 40GBase-T.
Given the uncertainties about connector system requirements, one should wait for clarification in the standardization
before using Cat. 7 A connecting hardware. Cat. 7 A cables with improved alien crosstalk (Cat. 7 B) can be
used to be 40GBase-T ready.
3.10.6 EMC Behavior in Shielded and Unshielded Cabling Systems
The motivation to once again investigate the topic of the EMC behavior of shielded and unshielded cabling, which
has been examined a number of times already, is the introduction of the new application 10GBase-T.
The use of ever higher order of modulation may well reduce the necessary bandwidth, but it makes the new protocols
more and more susceptible to external interference. Here it is worth noting, that the separation between
symbols with 10GBase-T is approximately 100x smaller than with 1000Base-T (see Figure below).
Comparison of the signal strength of various Ethernet protocols at the receiver
The figure shows the relative levels of signal strength at the receiver for various protocols after the signal has
been transmitted through 100 m of Class E A cabling. As a general principle, the higher the signal’s frequency or
bandwidth, the larger the attenuation through the cabling is. For reasons concerning EMC, the level of the output
signal is not increased above +/- 1V. Of this 2V range, depending on the frequency and attenuation in the cabling,
an ever smaller part reaches the receiver. In addition, the voltage differences from one symbol to the next get
increasingly smaller as a result of higher modulations. While in the past the separation between symbols at the
receiver has decreased by roughly a factor of three for each step from 10M to 100M to 1G, in the final step in
development from 1G to 10G it has decreased by a factor of 100.
Page 148 of 156 © 08/2011 Reichle & De-Massari AG R&M Data Center Handbook V2.0