Information Technology Reference
In-Depth Information
TABLE 12.6
Comparison of Category 5, Category 5e, Category 6, and Category 7 Channel Performance Limits
Category 5
Category 5e
Category 6
Category 7
Parameter
Class D
Class D
Class E
Class F
Frequency
1-100
1-100
1-250
1-750
range, MHz
Positive ACR
100
100
200
600
frequency, min.,
MHz
Attenuation,
†
24.0
24.0
21.7
20.8
dB
Return loss,
†
8.0
10.0
12.0
14.1
dB
NEXT,
†
dB
27.1
30.1
39.9
62.1
PSNEXT, dB
‡
27.1
37.1
59.1
ACR,
†
dB
3.1
6.1
18.2
41.3
ELFEXT,
†
dB
17.0
‡
17.4
23.2
f/s
548
‡
Propagation
548
548
504
delay, ns
Delay skew, ns
50
‡
50
50
20
†Specified at 100 MHz for installed link.
‡Requirement for Cat 5 added by TSB-95 to certify installed cable for gigabit operation.
Backward Compatibility of Categories 5e, 6, and 7.
The new performance cate-
gories present a more serious problem. You will recall that the major performance
hit in a Category 5 link turns out to be the crosstalk, due to the connectors. The
8P8C, RJ-45 style, terminations have a relatively poor score for NEXT and FEXT,
which always show up as the major contributors to return loss and impedance mis-
matches. The Category 6 designs adjust the conductor geometry within the RJ form
factor to bring these degrading performance parameters an absolute minimum. This
allows a positive ACR out to 200 MHz, rather than the 100 MHz range of Cat 5.
This performance holds true as long as you are using all Category 6 hardware,
which is designed to compensate for reactance differences between the plug and
jack. Unfortunately, preliminary testing revealed that Cat 6 hardware does not
always give sterling performance when mated with legacy Cat 5 components. In
some cases, the link performance may be degraded
below
even Category 5. Needless
to say, this is a shocking result.
We have depended on being able to use a compatible jack, plug, or patch cord
of a higher category with no penalty. However, Category 5/5e and Category 6 may
not necessarily mix, although the connections may give mechanical compatibility
and have DC electrical continuity.
