Cabletron Systems 100BASE-FX, Руководство по кабельной продукции

Страница: 37 / 192

Cabling Types 4-13
Ethernet Media
UTP Cable Quality
UTP cabling is produced in a number of overall quality levels, called Categories.
The requirements of networking limit UTP cabling for Ethernet to Categories 3, 4,
and 5. Any of these cable Categories can be used in an Ethernet installation,
provided that the requisite IEEE 802.3 specifications regarding the cables are met.
Category 3
UTP cabling that is built to the Category 3 specification consists of two or more
pairs of solid 24 AWG copper strands. Each strand, approximately 0.02 inch thick,
is surrounded by a layer of insulation. The characteristics of the insulation are
determined by the fire resistant construction of the cable (plenum cable is thicker
and made with slightly different material than normal PVC cabling).
The individual wires are twisted into pairs. The twisted pairs of cable are laid
together within an outer jacket, that may be low-smoke PVC plastic or a
plenum-rated insulating material. The outer jacket surrounds, but does not
adhere to, the wire pairs that make up the cable.
Category 3 UTP cabling must not produce an attenuation of a 10 MHz signal
greater than 98 dB/km at the control temperature of 20
°
C.
Category 4
Category 4 UTP cabling is constructed in the same manner as the Category 3
cabling discussed previously. Category 4 UTP is constructed using copper center
strands of 24 or 22 AWG. The resulting wire pairs are then covered by a second
layer of insulating jacketing. Higher-quality materials and a closer association of
the twisted pairs of wire improve the transmission characteristics of the cable in
comparison to Category 3 cabling.
Category 4 UTP cabling must not produce an attenuation of a 10 MHz signal
greater than 72 dB/km at the control temperature of 20
°
C.
Category 5
Category 5 UTP cabling is manufactured in the same fashion as Category 3 cable,
but the materials used are of higher quality and the wires that make up the pairs
are more tightly wound than those in lower Category classes. This closer
association helps to reduce the likelihood that any one member of a pair may be
affected by external noise sources without the other member of the pair
experiencing the same event. Only Category 5 cable may be used in 100BASE-TX
networks.