Information Technology Reference
In-Depth Information
TABLE 4.3
Comparison of Category Parameters
Cat 3
Cat 5
TSB-95
Cat 5e
Cat 6
Cat 7
Max. operating
frequency, MHz
20
100
100
100
200
475
Test frequency,
MHz
20
100
100
100
250
600
Attenuation
Yes
NEXT
Yes
+3db
PS-NEXT
Yes
PS-ELFEXT
Yes
Propagation delay
Yes
Delay skew
Yes
Return loss
Yes
+2dB
added far-end crosstalk requirements (FEXT), added propagation delay and skew,
and added return loss to the more modest Category 5 parameters.
Category 6, AC6, and Category 7 increase working bandwidth to 200, 350,
and 450 MHz, respectively. You may have heard these numbers as 250, 500, and
600 MHz, but those are the required test limits. The attenuation-to-crosstalk ratio
(ACR) must be positive to the lower frequency limit, and that is the generally
accepted measure of the “useful bandwidth” of cables and connecting hardware.
Some Category 7 hardware actually exceeds even the 600 MHz specification (some
by more than double) and this may be subject to future standards making.
“Enhanced” Category X
The categories and classes of operation of the international cabling standards organ-
izations specify minimum performance parameters for cabling, components, and
links used in structured LAN wiring systems. It is the purpose of the standard to set
electrical characteristics of the wiring system, without regard to the particular type
of LAN network technology that is used with the cabling.
Each of the category specifications, in reality, has been targeted at the operat-
ing requirements of a current or anticipated LAN topology. Consequently,
Category 5 conveniently handles Fast Ethernet, Category 5e handles Gigabit
Ethernet (4-pair simultaneous transmit/receive), and Category 6 handles the 2-pair
transmit/2-pair receive version of Gigabit Ethernet, as well as ATM-622/1244
(OC-12 and OC-24 rates). AC6 can handle 10 Gb Ethernet and fiber channel (just
barely), and Category 7 can do 10 Gigs sitting down. With those technical guide-
