Cabletron Systems 100BASE-FX, Руководство по кабельной продукции

Страница: 83 / 192

100BASE-TX 8-3
Full-Duplex Fast Ethernet Network Requirements
25-Pair Cable
The acceptable amount of NEXT between pairs in a 25-pair cable is at least 60 dB
for a 10 MHz link.
Four-Pair Cable
The acceptable amount of NEXT between pairs in a four-pair cable is not less than
60 dB for a 10 MHz link.
Noise
As “noise” is not a readily quantified and tested aspect of installed cables, there
are no hard and fast rules for the amount of acceptable cable noise on a
100BASE-TX segment. If a cable that meets all other requirements for
100BASE-TX operation is experiencing an unusual number of errors, the
introduction of noise may be a problem.
If you suspect that noise is causing signal degradation, examine the cable or
cables in question. If they are near possible sources of outside noise, such as
lighting fixtures, electric motors, or transformers, reroute the cable.
Other Considerations
Due to the small gauge of the wires in UTP cabling, it is susceptible to changes in
attenuation due to heat. In an installation that exceeds the control temperature of
20
°
C (68
°
F), the attenuation of PVC jacketed UTP cabling that is within the 11.5
dB limitations may fall outside the acceptable range. In installations where UTP
cables are expected to be subjected to temperatures of 40
°
C (104
°
F) or greater, the
use of plenum-jacketed cabling is recommended. The thicker insulating jacket of a
plenum-rated cable reduces the susceptibility of that cable to heat-induced
changes in attenuation characteristics.
The IEEE 802.3 100BASE-TX specification requires that all 100BASE-TX devices
support UTP cables of not less than 100 m (328 ft) in length. This requirement
does not factor in losses due to connectors, patch panels, punchdown blocks, or
other cable management hardware, which introduce additional loss.
For each connector or other intrusive cable management device in the total link,
subtract 12 m (39.4 ft) from the total allowable link length.
NOTE
Due to the construction of the connectors and organization of
wires, the 25-pair RJ21 connector is not Category 5 compliant.