Information Technology Reference
In-Depth Information
Category 6 or AC6 cable will need special handling when used for 10 GigE.
Alien crosstalk is one of the major new parameters that affect traditional Cat 6
cable's ability to successfully provide a 10 Gb link. Alien crosstalk is that crosstalk
that comes from sources outside the cable jacket. Because most Category 6 cable is
unshielded, only the native interference-canceling properties of twisted-pair bal-
anced transmission can give immunity to alien NEXT (ANEXT) and alien FEXT.
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In addition to whatever natural interference reduction you may get from Cat 6 or
AC6, you can do a lot to avoid incidental interference by careful cable placement
and separation. The coupling of interfering signals from adjacent cables can dramat-
ically be reduced simply by not jamming the cables together. You should also take
additional care to avoid common interference sources, such as florescent lamps, bal-
lasts, and motors.
Shielded Cat 6 and AC6 cables are available, and are good alternatives for new
installations that might require 10 GigE at modest distances. The advantage to Cat
6/AC6, in this case, is total compatibility with lower-speed networking, and of
course, lower cost compared to Category 7.
Category 7 (Class F) Cabling.
Supershielded Category 7, Class F, cabling is clearly
best able to handle 10 Gb signaling. Cat 7 is a recent addition to the standards
efforts, but it has been preceded by an enormous amount of hype. The marketing
aside, Category 7 offers us a whole new range of performance to support applica-
tions that were never before feasible for structured cabling. Some of these applica-
tions include multiple technologies in the same cable: voice and data, two data
connections, video, CATV, and of course 10 GigE (and higher!).
The enormous amount of cabling infrastructure that uses the traditional 8-pin
modular RJ-style connector presents a special problem for Cat 7. As stated in other
chapters, the RJ-style connector is a terrible RF connector. Even when high-speed
data were defined as 10 Mbps, the RJ connector was one of the primary limiting
factors in extending cable runs. It is probably the reason that the horizontal link was
standardized at only 100 m. As you can imagine, problems with the RJ only increase
with higher speeds and categories of operation. At 100 MHz, its performance is
marginal, and at 600 MHz it is downright pathetic.
The answer for Category 7 is to authorize the use of two different connector
types. The first is a specially modified RJ-style shielded connector system (Fig. 12.7)
that is reverse-compatible with normal Cat 6 and lower cables. The common name
for the Cat 7 RJ-style connector is GG45. The second is a totally new connector that
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NEXT and FEXT are near-end crosstalk and far-end crosstalk, respectively. There is more informa-
tion on these and other parameters in Chapter 15.
